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KINGDOM OF CAMBODIA 

NATION KING RELIGION 

Ministry of Industry, Mines and Energy 

            No. 701                                                                                                                                                                                                                                      July 17, 2007 

PROKAS 

ON ESTABLISHMENT OF SPECIFIC REQUIREMENT 

OF ELECTRIC POWER TECHNICAL STANDARDS 

OF THE KINGDOM OF CAMBODIA 

MINISTER OF INDUSTRY, MINES AND ENERGY 

-   Seen the Constitution of the Kingdom of Cambodia; 

-   Seen the Royal KRET No. NS/RKT/0704/124 Dated July 15, 2004 on the appointment of the Royal Government;

-   Seen the Royal KRAM No. NS/RKM/0196/05 Dated January 24, 1996 promulgating the law on establishment of the Ministry of Industry, Mines and Energy; 

-   Seen the Royal KRAM No. NS/RKM/0201/ 03 Dated February 02, 2001 promulgating the Electricity Law of the Kingdom of Cambodia; 

-   Seen the Prokas No. 470, dated July 16, 2004 on the establishment of Electric Power Technical Standards of The Kingdom of Cambodia;

-   Seen the urgent need and real situation at present;

DECIDES 

Article 1 

To establish the Specific Requirement of Electric Power Technical Standards of the Kingdom of Cambodia, for implementation, in 2 main parts as below: 

1-  Specific Requirement of Electric Power Technical Standards for Thermal Generating 

Facilities. 

2-  Specific Requirement of Electric Power Technical Standards for Transmission and 

Distribution Facilities. 

Article 2 

To issue the Specific Requirement of Electric Power Technical Standards in above 2 parts full contents of which are attached here with. 

Article 3 

All electric suppliers and consumers shall fully follow this specific requirement of the Standards. 

Article 4 

The electric suppliers are allowed to use their existing electric system for 2 years or any extension as decided by Electricity Authority of Cambodia from the date of signing of this Prokas, during which they are to improve their facilities to be in accordance with the electric power technical Standard. When the system is improved or changed or new installed, this standard shall be followed.  

Article 5 

Prokas or any decision in contradition to this Prokas shall be null and void. 

Article 6 

This Prokas shall come into force from the date of signing. 

Minister of Industry Mines and Energy 

                                                                                                                Sign and Seal 

                                                                                                                   SUY SEM 

Specific Requirements for 

Transmission and Distribution 

Facilities 

CONTENTS 

CHAPTER 1 

INTRODUCTION 

Article 1: Definitions 

Article 2: Purpose 

Article 3:  Area of Application 

Article 4 :  Applicable Standards 

Article 5: Types of Power Transmission and Distribution Facilities 

Article 6: Voltage 

CHAPTER 2 

GENERALS FOR TRANSMISSION AND DISTRIBUTION  

PART 1  

General Provisions 

Article 7:   Prevention of Electric Power Disasters 

Article 8:  Prevention of Accidents Caused by Electric Power Facilities 

Article 9:   Safety of Third Persons 

Article 10:  Prevention of Failures of Electric Power Facilities from Natural Disasters 

Article 11:  Prevention of Electric Power Outage 

Article 12:  Protection against Over-current 

Article 13:  Protection against Ground Faults 

Article 14:  Environmental Protection 

Article 15:  Life of Electric Power Facilities  

Article 16:  Requirements related to the Design of Electric Power Facilities 

Article 17:  Technical Documents of Electric Power Facilities 

Article 18:  Communication System 

Article 19:  Accuracy of Power Meters 

PART 2  

Grounding 

Article 20:  General Requirements for Grounding 

Article 21:  Classification of Grounding  

Article 22:  Grounding for Electrical Lines 

Article 23:  Grounding for Power Stations, Substations, Switching Stations and High-voltage and Medium-

voltage Users’ Sites 

Article 24:  Grounding for Distribution Lines and Low-Voltage Users’ Sites 

PART 3  

Conductor 

Article 25:  Conductors for Transmission and Distribution Facilities 

Article 26:  Connection of Conductors  

Article 27:  Safety Factor of Bare Conductors and Ground Wires of Overhead Electrical Lines 

Article 28:  Side-by-Side Use and Joint Use of Electrical Lines or Communication Lines Article 29:  Underground Lines 

CHAPTER 3 

HIGH-VOLTAGE TRANSMISSION FACILITIES 

Article 30:  Protective Devices for Electrical Equipment 

Article 31:  Design of Supporting Structures of Overhead High-voltage Lines 

Article 32:  Design of Fittings for Conductors and/or Ground Wires of Overhead High-voltage Lines 

Article 33:  Protection against Lightning for Overhead High-voltage Lines 

Article 34:  Bare Conductors of Overhead High-voltage Lines  

Article 35:  Clearance between Bare Conductors and Supporting Structures of Overhead High-voltage Lines 

Article 36:  Height of Overhead High-voltage Lines 

Article 37:  Clearance between Overhead High-voltage Lines and Other Facilities or Trees 

Article 38:  Prevention of Danger and Interference due to Electrostatic Induction and Electromagnetic Induction 

Article 39:  Surge Arresters 

CHAPTER 4 

MEDIUM AND LOW-VOLTAGE DISTRIBUTION FACILITIES  

Article 40:  Supporting Structures

Article 41:  Overhead Medium-voltage and Low-voltage Lines 

Article 42: Mechanical Strength of Insulators 

Article 43:  Medium-voltage/Low-voltage (MV/LV) Transformers 

Article 44:  Installation of Distribution Transformers for Single Wire Earth Return (SWER) Systems  

Article 45:  Protective Devices 

Article 46:  Height of Overhead Medium-voltage and Low-voltage Lines 

Article 47:  Clearance between Overhead Medium-voltage and Low-voltage Lines and Other Objects 

Article 48:  Proximity and Crossing of Overhead Medium-voltage and Low voltage Lines 

CHAPTER 1 INTRODUCTION 

Article 1:  Definitions 

In this Specific Requirements of Electric Power Technical Standards, unless the context otherwise requires, the terms below shall have the following meanings assigned to them: 

1. EAC           

                    “EAC” is the acronym for the Electricity Authority of Cambodia. 

1. Electrical Line 

       “Electrical Line” means the part of electric power facilities used to transmit or supply electricity. “Electrical Line” connects power stations, substations, switching stations and user’s sites. The "Electrical Line " also includes lines in associated protective devices and switchgears. 

1. Electric Power Facility 

    “Electric Power Facility” means all facilities for generation, transmission and supply of electric power such as power stations, substations, switching stations, electrical lines, dispatching centers etc... in this also including equipment, buildings, dams, waterways, fuel storage yards, ash disposal areas, etc.  

1. Electrical Equipment 

         “Electrical Equipment” means electrically-charged facilities. 

1. GREPTS 

“GREPTS” is the acronym for the General Requirements of Electric Power Technical Standards of the Kingdom of Cambodia. 

1. Guy 

“Guy” means a wire to reinforce the foundation of a supporting structure. It is usually installed between the ground and the upper part of the supporting structure. 

1. High-voltage Line 

       “High-voltage Line” means an electrical line of voltage higher than 35kV. 

1. IEC 

       “IEC” is the acronym for the International Electro technical Commission. 

1. Insulated Conductor

        “Insulated Conductor” means a cross-linked polyethylene (XLPE) insulated conductor for the mediumvoltage lines and a XLPE insulated conductor or a polyvinyl chloride (PVC) insulated conductor for the low-voltage line.

1. ISO 

      “ISO” is the acronym for the International Organization for Standardization.

1. Joint Use 

       “Joint Use” means a condition that electrical lines and/or communication lines belonging to two or more owners are installed on the same supporting structure.

1. Low-Voltage Line 

       “Low-voltage Line” means an electrical line having voltage of not more than 600V. 

1. Medium-Voltage Line 

        “Medium-voltage Line” means an electrical line having voltage of between 600V and 35kV. 

1. National Grid 

       “National Grid” is the high voltage backbone system of interconnected transmission lines, substations and related facilities for the purpose of conveying bulk power.  

1. Reversed phase-formation 

“Reversed   phase-formation” means a formation of double-

circuit overhead-lines where three phase order of one side circuit is different from that of the other circuit as given in the right drawing. 

1. RTU 

“RTU” is the acronym for “Remote Terminal unit” for the SCADA system, installed at electric power facilities for monitoring and controlling those facilities.  

1. SCADA 

“SCADA” is the acronym for “Supervisory, Control, and Data Acquisition” and refers to the equipment used for monitoring and receiving data. 

1. Side by Side Use 

       “Side by Side Use” means a condition that electrical lines and/or communication lines of one owner are installed on the same supporting structure. 

1. SREPTS 

“SREPTS” is the acronym for the Specific Requirements of Electric Power Technical Standards of the Kingdom of Cambodia. 

1. Substation 

  “Substation” means the electric power facilities where voltage of electrical power is transformed and including transformers, lightning arresters, circuit breakers, disconnecting switches, voltage transformers, current transformers, bus bars, protective relay systems, RTU for SCADA system, telecommunication facilities, etc.

1. Supporting Structure 

“Supporting structure” means a structure that supports electrical lines, such as wooden poles, iron poles, reinforced concrete poles and steel towers. 

1. SWER 

“SWER” is the acronym for the Single Wire Earth Return system. “SWER” is an electricity distribution method using one conductor with the return path through the earth. 

1. Switching Station  

        “Switching Station” means the electric power facilities used to change-over the electrical lines, which include disconnecting switches, circuit breakers, bus-bars, protective relay system, the RTU for the SCADA system, etc.

1. The Technical Standards 

“The Technical Standards” means the Electric Power Technical Standards in the Kingdom of Cambodia. 

1. User’s Site 

       “User’s Site” means any place at which machines, apparatus and devices for using electricity are installed. 

Article 2:  Purpose 

This Specific Requirements of Electric Power Technical Standards for Transmission and Distribution Facilities prescribes the basic requirements necessary to regulate the existing and the planned transmission and distribution facilities in the Kingdom of Cambodia. The requirements in this standard document are mainly for facility security and safety operation of the most important parts for facilities. 

Article 3:  Area of Application 

All transmission and distribution facilities in the Kingdom of Cambodia shall be in accordance with the requirements prescribed in this Technical Standard. 

All persons including licensees, consultants, contractors and consumers who are related to the study, design, construction and operation of transmission and distribution facilities shall follow these Specific Requirements of electric Power Technical Transmission and Distribution Standards. 

Article 4:  Applicable Standards 

Power transmission and distribution facilities planned to construct and operate in the Kingdom of Cambodia shall be as per the provision of this Technical Standards. In case a matter is not stipulated in the Technical Standards, IEC Standards shall be applied.  If it is not covered in the IEC standards, ISO Standards shall be applied. If it is not covered in the ISO Standards, internationally recognized standards shall be applied, subject to the approval by MIME. 

Article 5:  Types of Power Transmission and Distribution Facilities 

Power transmission and distribution facilities regulated in this Specific Requirements of Electric Power Technical Standards has been divided into 2 types: 

- High Voltage Facilities 

- Medium and Low Voltage Facilities. 

Article 6:  Voltage 

1. Standard Voltage 

AC voltage shall be as follows below: 

Table 1    Voltage Classification 

If in the interest of development of the power sector in the Kingdom of Cambodia it becomes necessary to use a nominal voltage other than that given in the table above, the Ministry of Industry, Mines and Energy may allow the use of such nominal voltage as a standard voltage through issuing Prokas. 

6.2 Variation of voltage 

The AC voltage at low voltage power supply points shall be maintained to the value according to the nominal system voltage in accordance with the following table: 

Table 2    Voltage Variation 

Notwithstanding the table above, variation of voltages can be extended only in the following cases: 

-  The licensee owns only low-voltage distribution line(s); 

-  The supply point where the voltage is out of the range of the table above is almost at the end of the feeder; 

-  The voltage does not affect the consumer’s appliances; - The licensee has obtained the consumer’s consent. 

CHAPTER 2 GENERALS FOR TRANSMISSION AND DISTRIBUTION  

PART 1  General Provisions 

Article 7:  Prevention of Electric Power Disasters 

The electrical equipment shall be installed in such a manner that does not cause electric shock, fire and other accidents. 

Article 8:  Prevention of Accidents Caused by Electric Power Facilities 

The electric power facilities shall be installed with proper measures for operators not to touch their moving parts, hot parts and other dangerous parts, and to prevent them from falling accidentally. 

Article 9:  Safety of Third Persons 

1. Safety of Third Persons at Power Stations, Substations and Switching Stations 

Appropriate measures shall be taken to prevent third persons from entering compounds containing power stations, substations and switching stations. These measures shall include: 

a.   External fences or walls to separate outside from inside compound. The height of external fences or walls shall not be lower than 1,800 mm. Boundary Clearance from these fences or walls to electrical equipment shall not be less than the values described in the following table:  

Table 3    Boundary Clearance from Walls or Fences to Electrical Equipment 

1. Signs to alert third persons to danger shall be installed at the entrances/exits. Moreover, where necessary, signs shall also be displayed on walls and fences. 
2. Locking devices or other appropriate devices shall be installed at the entrances/exits.

2.  Safety of Third Persons at Electric Supporting Structures 

Appropriate measures shall be taken to prevent third persons from climbing supporting structures of overhead electrical lines. To prevent danger to third persons related the supporting structures of electrical lines the following measures shall be taken: 

-   Any metal steps on supporting structures shall be installed more than 1.8m from the ground. 

-   Warning signs to alert the third persons to danger shall be installed at each supporting structure. 

-   As for high-voltage lines, appropriate devices shall be installed at all legs of supporting structures to prevent third persons from climbing the supporting structures. However, in case the supporting structures are located at places where third persons seldom approach such as in the mountains or where the supporting structures are surrounded by fences or walls with of an appropriate height, this article shall not be applicable. 

Article 10:  Prevention of Failures of Electric Power Facilities from Natural Disasters 

Proper measures shall be taken to prevent failures of electric power facilities from anticipated natural disasters such as floods, lightning, earthquakes and strong winds 

Article 11:  Prevention of Electric Power Outage 

-   When any generating facilities have a serious fault, these facilities shall be disconnected from the power system so that the effect of the fault on the system can be minimized and the system could be operated continuously. 

-   When a power system fault occurs in a system connected to a generating facility, the generating facility shall immediately be disconnected from the system, so that the generator runs continuously with no-load while waiting for the recovery of the system from fault.  

-   When a power system fault affecting electrical lines occurs, the power cut areas shall be minimized as much as possible by disconnecting the faulty section or by other appropriate methods. 

Article 12:  Protection against Over-current 

1. General provision  

Protection equipment against over-current shall be installed at the appropriate places of electrical circuits to prevent electrical equipment from over-heating due to excessive current and not to cause fire.  

1. Properties of Over-current Protection Equipment for High-Voltage Lines and Medium Voltage 

Lines 

1. Properties of fuses used for protection of over-current on a medium-voltage electrical circuit shall conform to related IEC 60282 (2002-01) [High-voltage fuses]. 
2. Properties of circuit breakers used for protection against over-current on a medium-voltage electrical circuit shall conform to related IEC 62271[High-voltage switchgear and control gear]. 
3. An over-current breaker shall have a device to indicate its switching status according to its operation. However, if its switching status can be easily confirmed, it need not have such a device. 

Article 13:  Protection against Ground Faults 

Protection equipment against ground faults or other appropriate measures shall be provided to prevent damage of electrical equipment, electrical shock and fire. 

Article 14:  Environmental Protection 

1. Compliance with Environmental Standards

To prevent environmental pollution, the electric power facilities shall be constructed in accordance with the environmental laws and regulations of the Kingdom of Cambodia.

1. Prohibition of Installation of Electrical Machines or Equipment Containing Polychlorinated Biphenyls (PCBs) 

1. The installation of new electrical equipment using insulating oil that contains greater than 0.005 percent (50ppm) polychlorinated biphenyls (PCBs) shall be prohibited. 
2. The use of existing electrical equipment using material containing PCBs, if it was installed before the Specific Requirements of Electric Power Technical Standards came into force, and effective and sufficient measures shall be taken in order to prevent the material containing PCBs from escaping from the oil container, shall be permitted. 
3. Once removed from the electrical equipment, the material containing PCBs greater than 0.005 percent (50ppm) PCBs shall not be reinstalled in another electrical facility and shall be safely scrapped as noxious industrial wastes. 

Article 15:  Life of Electrical Power Facilities  

 Electrical power facilities shall be durable for long term usage with efficient and stable operation.  

Article 16:  Requirements related to the Design of Electrical Power Facilities 

With regard to the design of electrical power facilities, selection of the materials, assembling and installation of the equipment, suitable safety factors against foreseeable stresses, such as insulation strength, thermal stress and mechanical stress shall be considered. 

1.  Insulation Co-ordination  

Taking everything into consideration technically, economically and operationally, the insulation strength of electrical equipment and facilities of an electric power system, including power stations, substations, switching stations, transmission lines and distribution lines, shall be coordinated so that it may be in the most rational conditions. In co-ordination of insulation the following important items shall be considered: 

a.   Standard Withstand Voltage of Insulation  

In selection of electrical equipment, its insulation shall be suitable with the “Standard lightning impulse withstand voltage” and “Standard short-duration power-frequency withstand voltage” given in the table of standard withstand voltage of insulation below.  

Table 4    Standard Withstand Voltage of Insulation 

1. Installation of Surge Arresters  

“Lightning impulse” and “Switching impulse” shall be controlled by installing surge arresters to coordinate them correctly. 

1. Insulation Co-ordination of Power Stations, Substations, Switching Stations and Transmission Lines  In order to prevent the lightning impulse invasion to power stations, substations and switching stations from transmission lines as much as possible, the arcing horn gaps of the steel tower near the power stations, substations and switching stations shall coordinate with the standard withstand voltage of electrical equipment in the power stations, substations and switching stations. 

1. Dielectric Strength of Electrical Circuits 

The dielectric strength of electrical circuits shall be examined by dielectric strength test, insulation resistance measurement and so on, to ensure that their performance corresponds to their nominal voltage.  

Moreover, before starting operation, the dielectric strength shall be confirmed by charging nominalvoltage to the circuit continuously for 10 minutes. 

However, if the nominal voltage of the electrical circuit is low-voltage, it can be tested by insulation resistance measurement or leakage current measurement. In case of the leakage measurement, it is sufficient to keep 1mA or less. 

1. Thermal Strength of Electrical Equipment 

Electrical equipment to be installed in the substations, switching stations and high-voltage and mediumvoltage users’ sites shall be able to withstand the heat generated by electrical equipment in normal operations. 

1. Mechanical Strength of Electrical Equipment against Short-circuit Current 

Generators, transformers, reactive power compensators, switching devices, bus bars and insulators for supporting bus bars to be installed in the substations and high-voltage and medium-voltage users’ sites shall be able to withstand the mechanical shock caused by short-circuit current. 

1. Prevention of Damage of Pressure Tanks 

Gas insulated equipment installed in the substations, switching stations and high-voltage and mediumvoltage users’ sites shall be designed as the following in order to avoid any risk of damage: 

1. Materials and structure of the parts receiving pressure shall be able to withstand the maximum operating pressure and shall also be safe. 
2. Parts receiving pressure shall be corrosion-resistant. 
3. Insulation gas shall not be inflammable, corrosive or hazardous. 
4. Tanks shall withstand the gas pressure rising during fault continuous time at internal failure of gas insulated equipment. 

Article 17:  Technical Documents of Electrical Power Facilities 

To secure long term power supply, each facility shall have its drawings, installation records, technical manuals, instruction manuals and operation records necessary for its proper maintenance works. These documents shall be safekept well.

Article 18:  Communication System 

To secure the power supply, suitable communication facilities consisted of SCADA systems and voice communication systems shall be provided. 

1. SCADA System 

SCADA systems are used to monitor and control electric power facilities and consist of RTUs, telecommunication lines and a master station. 

1. The RTU for the SCADA System shall be installed in electric power facilities so that the state of the National Grid can be monitored and the power facilities can be controlled at the Dispatching Center.
2. Necessary SCADA system shall be installed between the Dispatching Center and electric power facilities. 

1. Telecommunication Line 

Necessary telecommunication lines for SCADA systems and voice communication systems shall be installed as follows. 

2.1  Installation Sites 

1. Between the NCC and the Load Dispatching Center;
2. Between the Load Dispatching Center and the power facilities that compose the National Grid. 
3. Between the NCC and neighboring countries’ NCCs when the power system is connected to a neighboring country. If there are any agreements on these systems with neighboring countries, this may not be applicable. 

 Figure 1: Installation Sites 

2.2  Kinds of Lines and Condition of Lines for Domestic Telecommunication line 

- At least two different telecommunication lines shall be required for the National Grid. 

- Lines for domestic telecommunication systems for the power system shall be provided in accordance with Table 5. 

Table 5: Type of Lines for Facilities Connected to the National Grid 

3. Securing means of communication in an emergency 

Communication facilities, which are essential to recover the power system when unexpected disasters occur, shall be sufficiently reliable to be secure in an emergency. 

Article 19:  Accuracy of Power Meters 

Power meters shall be accurate, fair and equitable. The accuracy of a meter shall be generally as follows: 

Table 6: Accuracy of Electro-magnetic Mechanical Power Meters and Electric 

Power Meters 

                      * In accordance with the IEC 

PART 2  Grounding 

Article 20:  General Requirements for Grounding 

Grounding or other appropriate measures shall be provided for electrical equipment to prevent electric shock, danger to human beings, fire, and other trouble to objects. 

Grounding for electrical equipment shall be installed to ensure that current can safely and securely flow to the ground. 

Article 21:  Classification of Grounding 

Grounding for electrical equipment of all electric power facilities can be classified in 4 classes as shown in the following table: 

*1 - I is Single-line ground fault current (A) 

Article 22:  Grounding for Electrical Lines

The types of grounding, the places to be applied, installation conditions, and the resistance value to earth of electrical lines shall be as given in the following table. 

Table 8: Kinds of Groundings for Electrical Lines 

Remarks: 

(*1) “Exposed conductive parts” refers to parts such as steel stands, metal case or similar, of apparatus installed in the electrical circuit. 

(*2) Groundings for high-voltage substations and switching stations shall be individually designed, depending on the short-circuit capacity. 

Article 23: Grounding for Power Stations, Substations, Switching Stations and High-voltage and Medium-voltage Users’ Sites 

1. Grounding for Electrical Facilities 

1.1 Safety Grounding 

Electrical equipment to be installed in power stations, substations, switching stations and high-voltage and medium-voltage users’ sites shall be equipped with the protective groundings listed below so that there is no risk of rise of potential under abnormal conditions, no harm to human bodies and no damage to other objects due to electric shocks and fires caused by high voltage invasion. 

1.1.1   Grounding for Exposed Conductive Parts of Electrical Equipment 

Exposed conductive parts of electrical equipment such as metal stands and metal case shall be connected with the ground by grounding. Grounding for exposed conductive parts of electrical equipment of different voltage is provided in the table below: 

Table 9: Grounding for Exposed Conductive Parts of Electrical Equipment 

1.1.2   Grounding for other facilities 

Other facilities such as outdoor metal structures, external metal fences, protective metal fences and metal stands for operation shall be provided also with grounding work according to the voltage of the electrical facilities or equipment listed in table above.  

1.1.3   Grounding for Conductive Parts in Electrical Equipment 

At necessary points in electrical circuits, the grounding listed below shall be provided: 

1. Grounding of Instrument Transformers (Current or Voltage Transformers)  

                                            Class A grounding work shall be provided at an arbitrarily chosen point in the electrical 

circuit on the secondary side of a high-voltage or medium-voltage instrument transformer.  

In case where grounding work is provided for the electrical circuit on the primary side of a high-voltage or medium-voltage instrument transformer, Class A grounding work shall be provided.       

1. Grounding for Station Service Transformers 

In case where grounding is provided for the electrical circuit on the secondary side of transformers connecting a medium-voltage electrical circuit and a low-voltage electrical circuit, Class B grounding work shall be provided.   

A “low-voltage electrical circuit” means an electrical circuit that supplies electricity to automatic control circuits, remote control circuits, signal circuits for remote monitoring devices, and the like. 

1. Grounding for the Stabilizing Windings in Transformers 

In case where the star-star winding high-voltage and medium-voltage transformers have a stabilizing winding for reducing the zero phase impedance which is not connected with outgoing electrical circuit, this winding shall be grounded with Class A grounding. 

1.2  Grounding for Neutral Points in High-voltage and Medium-voltage Electrical Circuits 

In case where grounding is provided for the neutral point of high-voltage and medium-voltage electrical circuits in power stations, substations, switching stations and high-voltage and mediumvoltage users’ sites in order to secure reliable operation, to suppress abnormal voltage and to reduce the voltage to ground for protective devices of electrical circuits, the grounding electrode shall be installed to prevent risks of danger to people, domestic animals and other facilities due to the potential difference generated between the pole and the nearby ground when any failure occurs.

1.3  Grounding for Electrical Equipment for SWER 

In case where electrical equipment for SWER are installed in power stations and substations, grounding for electrical equipment for SWER shall be provided to prevent risks of danger to people, domestic animals and other facilities due to the potential difference between the electrical equipment and the nearby ground caused by load current and when any failure occurs. 

1.4  Grounding for Lightning Guards 

The grounding resistance provided for lightning guards such as overhead ground wires and lightning rods to be installed in power stations, substations, switching stations and high-voltage and mediumvoltage users’ sites shall be not greater than 10 Ω. 

However, in case where overhead ground wires are used as SWER, the grounding work shall apply as grounding on earth-return side of SWER provided above. 

1.5  Grounding for Surge Arresters 

The grounding resistance provided for surge arresters for high-voltage and medium-voltage electrical circuits in power stations, substations, switching stations and high-voltage and mediumvoltage users’ sites shall be less than 10 Ω as much as possible to prevent hindrance to the functions of the surge arrester

1. Particularities of Grounding Arrangement 

2.1 Properties of Grounding Conductors  

Grounding conductors to be installed in electrical circuits in power stations, substations, switching stations and high-voltage and medium-voltage users’ sites shall be constructed of corrosion-resistant metallic wire and shall be able to carry the current safely during failures.  

a.   Mechanical Strength of Grounding Conductors 

In order to secure necessary mechanical strength, the grounding conductors listed in Table 9 shall be used, depending on the kind of grounding work for which the grounding conductor is used. 

Table 10: Grounding Conductors to be used for Grounding Work 

b.   Thermal Strength of Grounding Conductors 

Grounding conductors in which grounding current flows when any abnormality occurs, such as those for neutral points of electrical equipment and high-voltage and medium-voltage electrical circuits, shall have also enough thermal strength against the heat from grounding current during the occurrence of such abnormality or failures in addition to mechanical strength.  

2.2   Installation of Grounding Conductors 

Grounding conductors for instrument transformers, neutral points, surge arresters and SWER to be installed in power stations, substations, switching stations and high-voltage and medium-voltage users’ sites shall be grounded directly to the ground without being connected to stands of equipment. Bare live parts of grounding conductors shall be installed so that there is no risk of operators easily coming into contact with them.

2.3   Neutral Grounding Devices 

Resistors and reactors to be connected to grounding conductors in power stations, substations, switching stations and high-voltage and medium-voltage users’ sites shall be suitable and safe for the flows of electric current when any failure occurs. 

Bare live parts of resistors, reactors and other neutral grounding devices shall be installed so that there is no risk of operators easily coming into contact with them. 

2.4 Prohibition against Installation of Switching Devices on Grounding Conductors for Neutral 

No switching device and power fuse, excluding switching devices to be installed to switch neutral resistors and neutral reactors, shall be installed on grounding conductors for neutral in power stations, substations, switching stations and high-voltage and medium-voltage users’ sites. 

2.5   Connection between Grounding Conductors 

Grounding conductors of earth-return side of SWER to be installed in power stations and substations shall not be connected to the grounding conductors of other electrical equipment.  

Article 24:   Grounding for Distribution Lines and Low-Voltage Users’ Sites 

1. Particularities of Grounding Arrangement 

Grounding for distribution lines and low-voltage users’ sites shall be installed according to the following.  

1.1    Grounding Electrodes 

1.1.1     Materials and dimensions of the grounding electrodes shall be selected for corrosion resistance and adequate mechanical strength. 

1.1.2     The following are examples of grounding electrodes which may be used: a.   Metal plates 

1. Metal rods or pipes 
2. Metal tapes or wires 
3. Underground structural networks embedded in foundations (foundation grounding) 
4. Other suitable underground metalwork approved by MIME 

1.2    Grounding Conductors and Protective Conductors 

Protective conductors in this provision mean the conductors used for connecting electrical equipment to the grounding system. 

1. Grounding conductors and protective conductors shall be constructed of corrosion-resistant metallic wire and shall be able to carry the current safely at failures. 

1. Grounding conductors shall comply with paragraph c and, where buried in the soil, their crosssectional areas shall be in accordance with Table 11A. 

Table 11A: Minimum Cross-sectional Areas of Grounding Conductors Buried in the Soil 

c. The cross-sectional area of protective conductors shall be selected in accordance with Table 11B or paragraph d. 

Table 11B: Minimum Cross-sectional Area of Protective Conductors 

*k is selected from Table 11C. 

Table 11C: Factor k, for Table 11B 

*Note: Factor k provided here is used only for insulated protective conductors not incorporated in cables and not bunched with other cables. In case of other protective conductors, the factor shall follow IEC60364-5-54.

d. The cross-sectional area of every protective conductor which does not form part of the cable or which is not in a common enclosure with the line conductor shall be not less than the size given in Table 11D. 

Table 11D: Cross-sectional Area of Protective Conductors (IEC60364-5-54）

                    1.3   Installation of Grounding Electrodes and Conductors 

In case there is any danger of persons touching grounding conductors, electrodes and conductors for Class A and Class B shall be installed as described below: 

1. Grounding electrodes shall be installed at depths of not less than 75cm underground. 
2. Grounding conductors shall be covered in the section from 75cm underground to 2.0 m above ground by a synthetic resin pipe or another shield of equivalent or higher insulating effect and strength. 
3. If the grounding electrode is installed along iron poles or other metallic objects, insulated conductor or cable shall be used for the full length of the grounding conductor. 
4. If the grounding electrode is installed along iron poles or other metallic objects, the grounding electrode shall be buried with a clearance of not less than 1m from those metallic objects. 

 In case where the grounding electrode is installed along iron poles or other metallic objects, the clearance between the top of the electrode and the bottom of iron poles or other metallic objects shall be not less than 30 cm. 

1. Class B Grounding Resistance 

Single-line ground fault current (I) of an electrical circuit in the medium-voltage side used for calculation of resistance of Class B grounding provided in Article 21 of these SREPTS shall conform to an actual value, or the following: 

                    2.1   Medium-voltage Electrical Circuit of Isolated Neutral System 

Class B grounding resistance for isolated neutral systems shall be determined by the following: 

1. Electrical circuits using an electric conductor other than a cable 

 For electrical circuits using an electric conductor other than a cable, Class B grounding resistance shall be not more than ten 10 Ω. 

1. Electrical circuits using a cable for an electrical conductor 

 For electrical circuits using a cable for an electrical conductor, Class B grounding resistance shall be determined by Table 11E and Table 11F according to the total length of mediumvoltage circuit (limited to that using a cable for an electrical conductor) connected to the same bus. 

Table 11E: In Case Class B is Decided by 230/I 

Table 11F: In Case Class B is Decided by 600/I* 

* In case of an earth leakage breaker that cuts off the electrical circuit within 1 second 

 Where: 

L:  the total length of medium-voltage circuit (limited to that using a cable for an electrical conductor) connected to the same bus. 

c.    Electrical circuits using an electrical conductor other than cable and also a cable for an electrical conductor 

 In this case, Class B grounding resistance shall be determined by Table 11E and Table 11F according to the total length of medium-voltage feeders (limited to that using a cable for an electrical conductor) connected to the same bus.  

2.2 Medium-voltage Electrical Circuit of Solidly Grounded Neutral System 

Single-line ground fault current (I₂) of an electrical circuit in the medium-voltage side used for calculation of grounding resistance in Class B grounding provided in Article 21 of these SREPTS  shall conform to an actual value, or the following formula. 

2

                                                       10

 I2 = I1 +3VR22 × 6

* Any fraction less than the decimal point shall be rounded up. 

Where: 

I₂: Single-line ground fault current (A); 

I₁: Single-line ground fault current of the electrical circuit in case of no solidly system grounding which is calculated by a theoretical formula (A); 

V: Nominal system voltage of the electrical circuit (kV); 

R: Electric resistance value of the resistance used in the neutral point (including the resistance to ground value of the neutral point) (Ω); 

3.   Grounding Systems for Low-voltage Lines 

Grounding systems for low-voltage lines have 2 types: TT and TN. These grounding works shall comply with IEC 60364-1. 

1. The TT system has one point directly grounded and the exposed-conductive parts of the installation are connected to ground that are electrodes electrically independent of the ground electrodes of the power system. 

1. The TN system has one point directly grounded and the exposed-conductive parts are connected to the point by protective conductors. Two types of TN system are considered according to the arrangement of neutral and protective conductors, as follows: 

- TN–S system: in which, throughout the system, a separate protective conductor is used; - TN-C system: in which neutral and protective functions are combined.

1. Low-voltage electrical equipment to be installed at users’ sites shall be installed according to the IEC 60364 series. If it is directly connected to a power supplier, the grounding system shall be the same as that of the supplier’s equipment involved in the supply of low-voltage electricity. 

 Low-voltage electrical equipment shall not be installed in such a manner that the grounding systems are different from those used at the same user’s site. 

 (LEGEND) 

                                              Neutral Conductor (N) 

                                              Protective Conductor (PE) 

              Combined Protective and Neutral Conductor (PEN)   

                                   System Grounding 

Figure 2: TT System

                                          System Grounding 

Figure 3: TN-S System 

Figure 4: TN-C System 

PART 3  Conductor 

Article 25:  Conductors for Transmission and Distribution Facilities  

1. Generals 

The conductors for transmission and distribution facilities shall be cables, insulated conductors or bare conductors. Bare conductors shall not be used for low-voltage lines.  

Cables and insulated conductors shall have sufficient insulation capacity appropriate for the conditions of the applied voltage.  

1. Property of Conductors

2.1   The conductors shall withstand temperatures under ordinary use. 

2.2   The structure of the conductors 

1. Insulated Conductors 

                            The structure shall be an electric conductor covered with insulating material. 

1. Cables used in Low-voltage Line 

      The structure shall be such that an electric conductor is covered with insulating material that is protected with armor. 

1. Cables used in Medium-voltage Line  

     The structure shall be such that an electric conductor is covered with insulating material that is protected with armor, and that has a metal electric shielding layer made of metal provided on the cable core in a single-core cable, and on the cable cores bundled together, or on each cable core in a multi-core cable. 

2.3   The conductors, the completed product to be used in a transmission line, or in a distribution line shall pass an appropriate AC withstand voltage test. 

2.4   The tensile strength per unit area (MPa) of hard-drawn aluminum wires used for single conductors in an overhead line shall be not less the value given in Table 12 conforming to the related IEC standards. 

Table 12: Tensile Strength of Hard-drawn Aluminum Wires (IEC 60889) 

Article 26:  Connection of Conductors  

Conductors shall be connected as per following methods:  

1. Conductors shall be connected firmly and the resistance of conductors shall not increase more than the resistance of conductors without connection. 

1. Conductors shall be connected so that the insulating capacity of cables and insulated conductors shall not decrease less than the insulating capacity without connection. 

1. With regard to connecting conductors of different kind of materials, electrochemical corrosion shall be prevented. 

Article 27:   Safety Factor of Bare Conductors and Ground Wires of Overhead Electrical Lines 

1. Generals 

As for tensile strength of conductors and ground wires for overhead electrical lines except for cables, the safety factor shall be 2.5 or more. 

1. Loads on Conductors for Overhead Transmission Lines 

2.1    Assumed Load and Safety Factor 

Overhead transmission conductors and overhead ground wires (excluding cables, the same applies hereafter in this clause) shall be installed with the tension to allow a safety factor specified in the following Item 2.1.2 when they are subject to the assumed load specified in the following Item 2.1.1 below at the average temperature in the area. 

2.1.1    Assumed Load 

The assumed load for the calculation of tension of overhead transmission conductors and overhead ground wires shall be the composite load of the vertical loads specified in the following item a and the horizontal loads specified in the following item b. 

1. The vertical load shall be the weight of the electrical conductor. 
2. The horizontal load shall be the horizontal maximum wind pressure load of the electrical conductor’s vertical projected area. 

2.1.2    Safety Factor 

A safety factor of 2.5 or more shall be applied to the tensile strength (ultimate tensile strength; breaking strength) of overhead transmission conductors and overhead ground wires. 

2.1.3    Reference Wind Velocity 

 Reference wind velocity to design overhead lines shall be as given in Table 13. 

Table 13: Reference Wind Velocity 

In the following circumstances, the above reference wind velocity can be changed. 

1. When sufficient observed data have been accumulated. 
2. When greater reliability is especially needed. 
3. When the design is needed to cooperate with the designs of neighboring countries. 

Figure 5:  Assumed Load 

2.2   Every Day Stress of conductors 

EDS* (Every Day Stress) of conductors shall be considered to avoid conductor’s fatigue in overhead lines due to aeolian vibration. 

* EDS is expressed as the percentage of ultimate tensile strength (UTS) under windless condition. 

Article 28:   Side-by-Side Use and Joint Use of Electrical Lines or Communication Lines 

1. High-Voltage Lines, Medium-Voltage Lines and Low-Voltage Lines  

Side-by-side use and joint use of electrical lines shall be done by the following methods. 

1.1 High-voltage Lines and Medium-voltage Lines 

1. When a high-voltage line and a medium-voltage line are installed at the same supporting structure, the medium-voltage line shall be installed under the high-voltage line and on separate crossarms. 

1. The clearance between any overhead high-voltage line conductors and any overhead mediumvoltage line conductors shall under no circumstances be less than the values specified in Article 37 of these SREPTS at any point in the span. 

1. The overhead high-voltage line conductor shall be stranded wire with a tensile strength of at least 30kN, unless they are cables. 

1. The nominal voltage of the high-voltage electrical lines in side-by-side use or joint use shall be not more than 115kV.

1.2 Medium-voltage Lines and Low-voltage Lines 

1.2.1        When a medium-voltage line and a low-voltage line are installed at the same supporting structure, the low-voltage line shall be installed under the medium-voltage line and on separate cross arms. 

1.2.2        The conductor of the low-voltage line shall be conformed with following provisions, except in cases where cables are used: 

a- In case the span of the low-voltage line is shorter than 50m, the tensile strength shall be not less than 5kN.  b- In case the span of the low-voltage line is 50m or over, the tensile strength shall be not less than 8kN. 

1.2.3        The low-voltage line in a part installed on the same supporting structure of an overhead medium-voltage line shall be grounded with class B grounding and its resistance shall be not more than 10Ω. 

1.2.4        The clearance between any overhead medium-voltage line conductors and any overhead lowvoltage line conductors shall under no circumstances be less than the values specified in Article 48 of the SREPTS at any point in the span. 

1.3 High-voltage Lines and Low-voltage Lines 

1.3.1        No low-voltage line shall be installed at the same supporting structure where a high-voltage 

line is installed. 

1.3.2        Exception of Side-by-side Use of High-voltage Lines and Low-voltage Lines 

Side-by-side use of high-voltage lines and low-voltage lines is permitted only if all following measures are taken to intensify the facilities. 

(1) The conductor of the low-voltage line shall be conformed with following provisions, except in cases where cables are used: 

1. In case the span of the low-voltage line is shorter than 50m, the tensile strength shall be not less than 5kN.  
2. In case the span of the low-voltage line is longer than 50m, the tensile strength shall be not less than 8kN. 

(2)       The low-voltage line in a part installed on the same supporting structure of an overhead high-voltage line shall be grounded with Class B grounding and its resistance shall be not more than 10Ω. 

(3)       The clearance between any overhead high-voltage line conductors and any overhead lowvoltage line conductors shall under no circumstance be less than 4.5m at any point in the span. 

(4)       The overhead high-voltage line conductor shall be stranded wire with a tensile strength of at least 30kN unless they are cables. 

(5)       The nominal voltage of the high-voltage line shall be not more than 115kV. In case the high-voltage line has double circuits, reversed phase-formation shall be adopted. 

(6)       The distance of side-by-side use of high-voltage lines and low-voltage lines shall be decided taking the assumed induction voltage into consideration. 

(7)       Exception can be allowed in the following unavoidable circumstances: 

1. There is no suitable space to install a low-voltage line in urban areas, because houses stand close together and the only appropriate low-voltage line route is along a road but a high-voltage transmission line has been already installed there. 
2. Other special circumstances approved by the EAC. 

1. Electrical Lines and Communication Lines 

Side-by-side use and joint use of electrical lines and communication lines shall be done by the following methods. If communication lines consist of optical fibers and they are tied to electrical lines or ground wires, this may not be applicable. 

1. When a medium-voltage or a low-voltage line and a communication line are installed on the same supporting structure, the medium-voltage or the low-voltage line shall be installed above the communication line and on separate cross arms. 
2. No communication line shall be installed at the same supporting structure where a high-voltage line is installed. 

Article 29:  Underground Lines 

1. Conductors of Underground Lines 

Cables shall be used for underground electrical lines. 

1. Draw-in Conduit System and Culvert System 

1. In case underground lines are installed with a draw-in conduit system, tubes of the draw-in conduit system shall have sufficient strength to withstand the pressure of vehicles and other heavy objects. 
2. In case the strength of the tubes cannot be verified, they shall be installed not less than 1.2 m in depth to prevent a danger due to the pressure from vehicles and other heavy objects. 
3. In case underground lines are installed with a draw-in culvert system as shown in Figure 6 B, culverts shall be capable of withstanding the pressure of vehicles and other heavy objects. 

                                 Steel, plastic, or polyvinyl chloride tube                      Concrete 

Figure 6A: Example of Draw-in Conduit System 

Figure 6B: Example of Draw-in Culvert System 

1. Direct Burial System 

3.1       In case underground lines are installed with a direct burial system, they shall be installed in accordance with the following methods. 

1. Installation of proper plates above the underground lines or other proper measures shall be taken to protect the underground lines against mechanical shocks. 

1. The installed position of underground facilities shall be not less than 1.2 m in depth at a place where there is a danger of receiving pressure from vehicles or other objects, and not less than 

0.6 m at any other place. 

3.2       The depth of underground facilities described in 3.1.b above signifies the depth of such facility measured from the plate to protect cables. 

3.3       The following places shall be included among the ‘any other place’ of 3.1.b above. 

1. The sidewalk of a road. 
2. A road where no cars pass. 

Figure 6C: Explanation of the Depth of the Direct Burial System 

Table 14A: Depth in case of Direct Burial System 

1. Clearance between Multiple Underground Lines  

4.1 Minimum clearance between a new underground line and other electrical lines shall be as shown in the following table: 

Table 14B: Clearance between Multiple Underground Lines 

(Unit: m) 

4.2 In case one of two electrical lines is installed in an incombustible stout tube, the minimum clearance shall not be required. 

5. Clearance between Underground Lines and Other Facilities 

a. Minimum clearance between a new underground line and other facilities shall be as shown in the following table:

Table 14C: Clearance between Underground Lines and Other Facilities 

(Unit: m) 

* The approval of the owner of the communication line shall be required. 

1. In case the electrical line is installed in an incombustible stout tube and the tube does not come into direct contact with other facilities, the minimum clearance shall not be required. 

1. In case communication lines are united with electrical lines, the minimum clearance shall not be required. 

1. Connection of Underground Cables 

The connection of underground cables shall be implemented with the following methods, in addition to Article 26 of these SREPTS. 

1. The connecting device shall be able to withstand the external forces that will be extended under the expected conditions. 
2. The connected cables shall be in good order for the permissive current of the original cables. 
3. The connected cables shall have same waterproof performance. 

1. Structure of Underground Boxes 

In case underground boxes are installed, their structure shall be as follows: 

1. The underground boxes shall be able to withstand the pressure of vehicles and other heavy objects. 
2. When there is some possibility that explosive gases or combustible gases are filled in the box and the capacity of the box is 1m³ or more, a device such as a ventilator to exhaust the gases shall be installed. 
3. The lids of underground boxes shall be so installed that third persons are unable to open them easily. 

1. Grounding for Underground Facilities 

Safety grounding of Class D shall be installed at the metallic part of such facilities as the tube, culvert and joint box, and the metallic shield tape of a cable.  

CHAPTER 3 

HIGH-VOLTAGE TRANSMISSION 

FACILITIES  

Article 30:   Protective Devices for Electrical Equipment 

1. Measures for protecting Conductors and Electrical Equipment against Over-current 

 At necessary points in electrical circuits, over-current circuit breakers that protect against heating damage by over-current and prevent outbreaks of a fire shall be installed.  

1. Protection and Alarm Devices for Transformers and Reactive Power Compensators 

Transformers and reactive power compensators to be installed in stations and high-voltage and mediumvoltage users’ sites shall be equipped with devices to automatically cut off the transformer and the reactive power compensator from the electrical circuit when any abnormality that might cause significant damage and serious trouble to the supply of electric power occurs, in addition to other appropriate protection systems, as shown in Table 15. 

Table 15: Protection Systems for Transformers and Reactive Power Compensators 

               Notes- ○      : Equips 

                          --     : No need 

Article 31:   Design of Supporting Structures of Overhead High-voltage Lines 

1.   Basic Conditions 

a.   Supporting structures of overhead lines shall be designed, taking into account the following loads. 

Table 16A: Type of Loads 

1. Supporting structures and foundations of overhead high-voltage lines shall be designed, taking the value of wide pressure based on the reference wind velocity prescribed in Article 27 of these SREPTS into consideration. 

1. Supporting structures and foundations of overhead high-voltage lines shall be designed to withstand the maximum loads, taking appropriate safety factors into consideration. 

1. In case overhead high-voltage lines are installed at places with the worst conditions, such as inside river areas, windy areas, and so on, the supporting structures and the foundations shall be designed to withstand such severe conditions. 

1. Components of Supporting Structures 

Components of supporting structures shall satisfy the following or shall have an equivalent strength to these items. 

2.1       Fundamental Properties of Components of Supporting Structures 

Flat steel, shaped steel, steel pipes, steel plates, steel bars and bolts which compose a steel tower or an iron pole used for overhead transmission lines shall be appropriate ones as specified in the ISO (International Organization for Standardization) standards or other standards equivalent to these standards. 

2.2       Thickness of Steel Members etc. 

Shaped steel, steel pipes and steel plates to be used for a steel tower or an iron pole for overhead transmission lines shall have the thickness and other dimensions specified below. 

2.2.1    Minimum Thickness of Shaped Steel 

1. Those to be used as a main post member of an iron pole (in which a main member of a cross arm is included. The same shall apply hereafter in this article) shall have a thickness of 4 mm. 
2. Those to be used as a main post member of a steel tower shall have a thickness of 5 mm. 
3. Those to be used as other structural members shall have a thickness of 3 mm. 

2.2.2    Minimum Thickness of Steel Pipes 

1. Those to be used as a main post member of an iron pole shall have a thickness of 2 mm. 
2. Those to be used as a main post member of a steel tower shall have a thickness of 2.4 mm. 
3. Those to be used as other structural members shall have a thickness of 1.6 mm.

2.2.3    Slenderness Ratio of Steel Members 

The slenderness ratio of a steel member is an indicator showing the state of tallness of its form. Slenderness Ratio of steel member is a division of its length to its section turning radius. More slenderness ratio means longer length or smaller section, so the form of steel member is more slim and weaker. Lesser slenderness ratio means shorter length or bigger section, so the form of steel member is more rotund and stronger.  

The slenderness ratio of a compression member shall be not more than 200 for those to be used as the main post members, not more than 220 for compression members other than main post members (excluding those used as auxiliary members) and not more than 250 for those used as auxiliary members. 

2.2.4    Minimum Thickness of Steel Plates 

 The thickness shall be not less than 1 mm. 

2.3       Strength of Steel Members and Bolts 

Steel members and bolts to be used for a steel tower or an iron pole of overhead transmission lines shall have the strength as specified in Table 16B. 

Where: 

σY: Yield point strength of steel members and bolts σB: Tensile strength of steel members and bolts λ_k:  Effective slenderness ratio ( = L_k / r ) L_k:  Effective buckling length of steel members r:  Turning radius of a steel member cross section 

E:  Elastic modulus (20.6 × 10² N/m²)

                        Λ:  π (1.5E   2.2K Yσ )

K, K₀, K₁, K₂: Refer to Table 16C. 

 Table 16C    K, K₀, K₁, K₂, for Table 16B 

(*) Note that the buckling strength shall be not more than 0.6σY for structural members with significant decentering. 

2.4   Strength of Foundation Components used for Steel Poles or Steel Towers 

Foundation components of a steel pole or steel tower for overhead transmission lines shall have the strength specified below: 

a.   Strength of Concrete  

The strength of concrete at yield point shall be based on the design standard strength (4-week strength; Fc) of concrete and conform to Table 16D. 

Table 16D: Strength of Concrete              

b.   Bond Strength of Concrete  

The bond strength of concrete at yield point shall be based on the design standard strength    (4week strength; Fc) and conform to Table 16E. 

Table 16E: Bond Strength of Concrete 

c.   Strength of Shaped Steel, Flat Steel and Steel Bars 

The strength of shaped steel, flat steel and steel bars at yield point shall conform to Table 16F. 

Table 16F: Strength of Shaped Steel, Flat Steel and Steel Bars 

σY: Strength of material at yield point σB: Tensile strength of material 

d.   Strength of Bolts 

                         The strength of bolts shall conform to Table 16B. 

1. Wind Pressure Load 

3.1   Wind Pressure Values 

The wind pressure load shall be the value obtained by calculation based on the wind pressure specified in the following Table 16G. 

 This shall not apply when calculation is made based on values obtained by a wind pressure (wind duct) test using a wind at a velocity of not less than 32 m/s. 

The wind receiving area shall be the vertical projected area of the structural member.  For crossarms of a concrete pole, an iron pole except a columnar pole, and a steel tower, the wind receiving area shall be the vertical projected area of the front structures that receive the wind. 

Table 16G:  Wind Pressure to calculate the Wind Pressure Load 

* This value shall be applied to 115kV high-voltage towers which are less than 40m high. 

3.2   Wind Pressure Load at an Oblique Wind 

When the wind blows to the electrical line at an angle of 60°, the wind pressure load in an assumed normal load of a common type steel tower shall be that calculated by the wind pressure load multiplier (in case of a square tower) in Table 16H. 

Table 16H: Multiplier to Wind Pressure Load 

1. Loads on Supporting Structures and Safety Factors 

Loads on supporting structures and safety factors shall satisfy the following items or shall have an equivalent performance to these items. 

4.1   Types and Combinations of Assumed Loads 

The types and combinations of assumed loads to be used for calculating the strength of supporting structures for overhead transmission lines shall conform to the following provisions. 

The assumed loads on supporting structures shall be classified as the loads specified in Table 16I. The combination of these loads on the supporting structures shall be in accordance with Table 16J depending on the classification and type of supporting structures. 

Table 16I: Classification of Assumed Loads on Supporting Structures 

Table 16J: Combination of Loads on the Supporting Structures 

Where: 

           Dead-end type:                     Supporting structure with a large unbalanced load in the horizontally 

longitudinal direction, e.g. the first tower from a substation. 

            Abnormal Condition:           An assumption for tower design where any one or two of conductors and 

ground wires will be broken down 

           Notes:                                Circles "{" indicate the assumed loads to be considered at the same time that 

can combine together. 

The wind direction that brings the bigger assumed load should be selected. 

Where strung wires are arranged asymmetrically on the supporting structure, the assumed vertical eccentric load shall be added to the load in Table 16J and the load by normal torsional load shall also be added for the dead-end type. 

4.2   Unbalanced Maximum Tension and so on 

Unbalanced maximum tension and so on used in 4.1 shall conform to the following requirements: 

4.2.1   The unbalanced maximum tension and torsional force shall conform to Table 16K. 

Table 16K: Unbalanced Tension and Torsional Force 

4.2.2   For steel towers, the strung wires shall be cut according to the following requirements, depending on the total number of phases of electrical conductors (which mean phases for each circuit. The same shall apply hereafter). 

1. The overhead ground wire shall not be cut at the same time as the electrical conductors and only one wire shall be cut; 

1. Where the total number of phases of electrical conductors is not more than twelve (12), one phase that maximizes the stress generated in each structural member (two electrical conductors from one phase in case of multiple conductors for steel towers other than deadend type); 

1. Where the total number of phases of electrical conductors is over twelve (12) (excluding the case specified in the following Item d.), two phases in different circuits that maximize the stress generated in each structural member (two electrical conductors from one phase in case of multiple conductors for steel towers other than dead-end type); 

1. Where electrical conductors are arranged so that nine or more phases are in a longitudinal row and two phases are in a transverse row, one of the top six phases in the longitudinal row (two electrical conductors from one phase in case of multiple conductors for steel towers other than dead-end type) and one phase from the other phases (two electrical conductors from one phase in case of multiple conductors for steel towers other than dead-end type) that maximize the stress generated in each structural member. 

4.2.3   The unbalanced tension generated by cutting the strung wire shall be equal to the assumed maximum tension. 

Provided，however, that the unbalanced tension may be 0.6 times the assumed maximum tension if, depending on the mounting method of the strung wire, the supporting point of the strung wire shifts when the wire is cut or the strung wire slides at the supporting point. 

            4.3     Safety Factor of Supporting Structure 

The yield strength of the structural members of reinforced concrete poles, iron poles and steel towers used for overhead transmission lines shall satisfy the safety factor listed in Table 16L for the assumed loads specified in 4.1 to 4.2. 

Table 16L: Safely Factors of Supporting Structures 

5    Loads on Foundations of Supporting Structures and Safety Factors 

5.1    Loads on the Foundation of a Supporting Structure 

The loads applied to the foundation of a supporting structure for overhead transmission lines shall be calculated from combinations of the assumed loads of the supporting structure specified in paragraph 4 and the resulting maximum values shall be the assumed normal and abnormal loads for the foundation. 

5.2    Safety Factor of the Foundation 

The safety factor of the foundation of a supporting structure for overhead transmission lines shall satisfy the value listed in Table 16M for its yield strength. 

Table 16M: Safety Factors of the Foundations 

5.3   Treatment of the Weight of the Foundation 

The weight of the foundation used for calculating the safety factor shall be treated in accordance with the following provisions: 

1. For a foundation that is subject to a lifting load, not more than two-thirds of the weight of the foundation (or the weight of the foundation of a steel tower to an abnormal load) may be included in the lift bearing power. 

1. For a foundation that is subject to a compressive load, the weight of the foundation shall be included in the compressive load. 

Article 32:  Design of Fittings for Conductors and/or Ground Wires of Overhead High-voltage Lines 

1. Safety Factor of Fittings for Conductors and/or Ground Wires of Overhead High-voltage Lines  

1.1    The safety factor for the tensile strength (the maximum tensile strength or breaking strength) of fittings of conductors and ground wires for overhead high-voltage lines shall be 2.5 or more. 

1.2    The safety factor mentioned in 1.1 shall be obtained as follows: 

1. Tension insulator device (insulator device that anchors electrical conductors) 

[Safety factor] = [Tensile break strength] / [Assumed maximum tension at a support point]; 

1. Suspension insulator device (Insulator device from which electrical conductors are hung) 

[Safety factor] = [Tensile break strength] / [Composite load of vertical load and horizontal 

transverse load]; 

1. Supporting insulator device 

[Safety factor] = [Bending break strength] / [Horizontal transverse load or vertical load applied 

perpendicular to the axis of the insulator device]. 

2    Mechanical Strength of Insulators for Overhead Transmission Lines 

2.1   Assumed Load 

The assumed loads to be used for calculating the strength of insulator devices for overhead transmission lines shall conform to the following requirements. 

1. Vertical Load 

The vertical load shall be the sum of the weight of electrical conductors, the weight of insulator devices and the vertical component of the force generated by the assumed maximum tension of the electrical conductors. 

1. Horizontal Transverse Load 

The horizontal transverse load shall be the sum of the wind pressure loads of electrical conductors and insulator devices and the horizontal component of load generated by the assumed maximum tension of the electrical conductors.  The wind pressure loads shall be calculated based on the values listed in Table 16G. 

1. Assumed Maximum Tension of Conductors 

The assumed maximum tension of conductors shall be the tension of the transmission conductor under the composite load of the vertical load generated by the weight of the electrical conductor, and the horizontal load generated by the horizontal wind pressure stipulated in Table 16G at the average temperature in the area. 

Article 33:   Protection against Lightning for Overhead High-voltage Lines  

The following measures shall be taken for overhead high-voltage lines to decrease the number of electrical faults and to protect equipment from damage caused by the faults. 

1. Installation of ground wires for overhead high-voltage lines; 
2. Installation of arcing horns for both ends of insulator assemblies of overhead high-voltage lines; 
3. Installation of armor rods to wrap conductors in a clamp of suspension insulator assemblies of overhead high-voltage lines. 

Article 34:  Bare Conductors of Overhead High-voltage Lines 

1. Vibration Dampers 

An appropriate type and number of dampers shall be installed to prevent fatigue of bare conductors and ground wires for overhead high-voltage lines due to their aeolian vibration. 

1. Connection 

In case bare conductors and ground wires are jointed with each other or with insulated conductors or cables, the connection shall conform to the following requirements in addition to Article 26 of these SREPTS. 

1. Bare conductors and ground wires shall be connected with compression type sleeves or compression type devices. 

1. The tensile strength of connection of bare conductors and ground wires shall be not less than 95 % of the tensile strength of the connected bare conductors and ground wires. This requirement, however, shall not be applied to cases where the maximum tension to be designed is substantially less than the ultimate strength of the bare conductors and ground wires such as jumper conductors, the end span to substations and others. 

Article 35:  Clearance between Bare Conductors and Supporting Structures of Overhead High-voltage Lines 

Clearance between bare conductors and supporting structures, arms, guy wires and/or pole braces of overhead high-voltage lines shall be as follows. The clearances shall be secured, in any cases where the maximum swing of conductors under the maximum wind velocity to be designed. 

Table 17: Clearance between Bare Conductors and Supporting Structures 

Clearance between ground wires and the nearest conductor in the same span shall be larger at any point in the span than the clearance of the supporting point at both sides of the span. 

Article 36:   Height of Overhead High-voltage Lines 

        The height of conductors of overhead high-voltage lines shall be as follows: 

1.   Height in Urban Areas 

Height of conductors of overhead high-voltage lines in urban areas shall be not less than the value     calculating by adding 0.060 m to a base height 6.5m for every 10kV over 35kV. 

        Table 18A: Height in Urban Areas

1. Height in Areas Where Third Persons Hardly Approach 

The height of conductors of overhead high-voltage lines in areas where third persons hardly approach shall be not less than the value calculated by adding 0.06 m to a base height of 5.5m for every 10kV over 35kV. 

Table 18B:  Height in Areas Where Third Persons Hardly Approach 

1. Height over Roads and/or Railways 

The height of conductors of overhead high-voltage lines crossing over roads and/or railways shall be not less than the value calculated by adding 0.060 m to a base height of 13m for every 10kV over 35kV. 

Table 18C:  Height over Roads and/or Railways 

4.   Height over Rivers and/or Seas 

The height of conductors of overhead high-voltage lines crossing rivers and/or seas shall be as follows: 

Table 18D: Height over Rivers and/or Seas 

(*1)  The highest point of vessels shall be decided taking into account any future possible changes. 

5.   Note 

All the heights described above shall be secured in any cases of the maximum sagging of conductors in the maximum temperature to be designed.

Article 37:   Clearance between Overhead High-voltage Lines and Other Facilities or Trees 

1   Generals 

The clearance between each conductor of overhead high-voltage lines and other facilities or trees shall be as follows: 

a.   Clearance to Other Facilities 

 The clearance between each conductor of overhead high-voltage lines and other facilities shall be not less than the value calculated by adding 0.06 to a base height of 3m for every 10kV over 35kV. 

Table 19A: Clearance to Other Facilities 

b.   Clearance to Trees 

 The clearance between each conductor of overhead high-voltage lines and trees shall be not less than the value calculated by adding 0.06 m to a base height of 2m for every 10kV over 35kV. 

Table 19B: Clearance to Trees 

                  c.      Note 

 The clearances described above shall be secured in any cases of the maximum sagging of conductors in the maximum temperature and/or the maximum swing of conductors under the maximum wind velocity to be designed. 

                                                               Support <-At the maximum temperature Condition of Conductors>  

Figure 7: Direct Proximity 

2    Proximity to and Crossing with Buildings 

2.1   230kV Overhead High-voltage Line 

Overhead transmission conductors with a nominal voltage 230kV shall be installed not less than 3 meters away in a horizontal distance above or to the side of buildings. 

Figure 8: Proximity to Buildings (230kV) 

2.2   115kV Overhead High-voltage Line 

Overhead transmission conductors with a nominal voltage of 115kV shall be installed not less than 6 meters from the top of buildings when the 115kV overhead high-voltage line is adjacent laterally within 3m or crossing with buildings. 

Figure 9: Crossing with Buildings (115kV) 

3.   Proximity to and Crossing with Medium-voltage Lines and High-voltage Lines 

The clearance between each conductor of overhead high-voltage lines and other medium-voltage lines or high-voltage lines shall be not less than the value calculated by adding 0.06m to a base height of 2m for every 10kV over 35kV. 

Table 20: Clearance between Conductors 

* Refer to Figure 10. 

Support

Figure 10: Proximity and Crossing with Medium-voltage Lines and High-voltage Lines

Article 38: Prevention of Danger and Interference due to Electrostatic Induction and Electromagnetic Induction 

1. Electrostatic Induction 

High-voltage lines shall be installed to prevent danger to persons and/or interference on communication lines installed near the high-voltage lines caused by electrostatic induction, taking appropriate measures including the following items a, b and Article 28 of these SREPTS into consideration. 

1. The electrical field caused by overhead high-voltage lines shall be 3kV/m or less at 1 m above the ground surface, except for overhead high-voltage lines in places where third persons hardly approach, such as in mountains, on farming land and so on. 

1. Conductive materials on the surface of the buildings under overhead high-voltage lines shall be grounded with the Class D grounding in accordance with Article 22 of these SREPTS. 

1. Electromagnetic Induction 

High-voltage lines shall be installed to prevent danger to persons and/or interference on communication lines caused by electromagnetic induction on the low voltage lines and/or communication lines installed near the high-voltage lines, taking appropriate measures including Article 28 of these SREPTS. 

Article 39:   Surge Arresters 

1. Generals 

Surge arresters shall be installed at the appropriate places on electrical lines.

1. Installation of surge arresters 

2.1   Installation Points for Surge Arresters 

In high-voltage and medium-voltage electrical circuits surge arresters shall be installed at the points listed below or at locations close to such points, in order to prevent damage to be electrical equipment installed in electrical circuits in the power stations, substations and switching stations and high-voltage and medium-voltage users’ sites, by over-voltage. 

However, the same shall not apply in cases where there is no risk of damage to such electrical equipment. 

1. Receiving and outgoing points on overhead electrical lines in the power stations, substations and switching stations; 

1. Receiving points on the high-voltage and medium-voltage users’ sites to which power is supplied from high-voltage and medium voltage overhead electrical lines; 
2. Locations where there is a risk that the protective effects of surge arresters installed in accordance with the above provisions may not be achieved. 

                 Power station, 

                                                                                                                                               Surge       

User arrester 

Figure 11: Installation Points for Surge Arresters 

2.2   Grounding of Surge Arresters 

       Grounding of surge arresters shall be installed in accordance with Article 22 and 23 of these SREPTS. 

 The grounding resistance provided for surge arresters in high-voltage and medium-voltage electrical circuits in power stations, substations, switching stations and high-voltage and mediumvoltage users’ sites shall be as much lower than 10 Ω as possible in order to prevent hinder to the functions of the surge arrester. 

CHAPTER 4 

MEDIUM AND LOW-VOLTAGE DISTRIBUTION FACILITIES  

Article 40:   Supporting Structures 

            1.    Loads on Overhead Distribution Lines 

Supporting structures of overhead medium-voltage and low-voltage lines shall be designed taking into account the loads shown in Table 21A. 

Table 21A: Kinds of Loads 

By calculating, firstly, the load when wind pressure is applied in a horizontal transverse direction to the distribution line, and secondly, the load when wind pressure is applied in the horizontal longitudinal direction of the distribution line, the one of these two loads which generates greater stress on the structural member shall be adopted for the assumed normal load.    

            2.   Safety Factor of Foundations of Supporting Structures 

-     The safety factor of the foundations of supporting structures for low-voltage lines shall be 2 or more to the wind pressure. 

-     The safety factor of the foundations of supporting structures for medium-voltage lines shall be 2 or more to the load prescribed in Table 21A. 

-     If wooden poles, iron-poles and iron-reinforced concrete poles are installed at other than soft ground in accordance with Table 21B, this article may not be applicable. 

Table 21B    

1. Strength of Iron-reinforced Concrete Pole 

-     Iron-reinforced concrete poles for low-voltage lines shall have the strength to withstand wind pressure. 

-     Iron-reinforced concrete pole for medium-voltage lines shall have the strength to withstand the load prescribed in Article 31 of these SREPTS. 

-     Iron-reinforced concrete pole shall have the strength to withstand two times of the design load. 

1. Safety Factor of conductors and supporting structures 

4.1    Conductor

A safety factor of 2.5 or more shall be applied to the tensile strength (ultimate tensile strength; breaking strength) of overhead distribution conductors and overhead ground wires. 

4.2    Supporting Structure 

(1)          Supporting structures for overhead low-voltage lines shall have the strength to withstand a load of 1.2 times the wind pressure for wooden poles, and a load equal to the wind pressure for others. 

(2)          Wooden poles to be used as the supporting structures for overhead medium-voltage lines shall be installed in accordance with the following items: 

1. The safety factor against a wind pressure shall be 1.5 or more; and 
2. The thickness shall be not less than 12 cm in diameter at the top end. 

(3) Iron-reinforced concrete poles and iron poles to be used as supporting structures for overhead medium-voltage lines shall have the strength to withstand the assumed normal load.  

1. Reference Wind Velocity  

Reference wind velocity used in the calculation of wind loads on overhead distribution lines shall be as follows: 

Table 21C: Reference Wind Velocity 

In the following circumstances, the above reference wind velocity shall be changed: 

1. When sufficient observed wind velocity data have been accumulated. 
2. When greater reliability is particularly needed. 
3. When a terrain has the effect to decrease the wind velocity. 

1. Reinforcement for Supporting Structures by Guys 

Supporting structures shall be guyed to share strength with the guys according to Table 21D.  In such case, the strength of the supporting structure itself shall be such that it bears at least half of the wind load. 

6.1   Installation and Safety Factor of Guys 

a.   Installation of Guys 

Guys shall be installed in order to reinforce the foundation of a supporting structure if the calculated result of the safety factor of supporting structure’s foundation is less than 2.0 under the following conditions. 

Table 21D: Conditions of Installation of Guys 

1. Section near the Ground of the Guy 

For the section near the ground, that is, from the underground portion of the guy to 30cm above the ground, a galvanized iron rod or similar rod equal or superior to it in strength and corrosion resistance shall be used. 

1. Foundation of the Guy 

The guy anchor shall be installed firmly so that it can adequately bear the tensile load from the guy. A guy anchor installed with a supporting structure shall be of such a material that it hardly corrodes. 

1. Globe Insulator 

If a guy is installed on an overhead distribution line that is in danger of touching an electrical conductor, a globe insulator shall be inserted in the upper part of the guy. 

A globe insulator, however, need not be inserted if the guy is installed on a low-voltage overhead distribution line in a place other than a rice field or other swamp area. 

e.   Height of Guy 

A guy crossing a road shall have a height of not less than 6.5 m from the road surface. If this is impossible for technical reasons, a height of not less than 4.5m (not less than 2.5m, if a sidewalk) is allowed if there is no danger of interfering with traffic. 

f.   Strut 

   A strut that has equivalent or higher effect than a guy can be substituted for a guy. 

Article 41:   Overhead Medium-voltage and Low-voltage Lines

1. Cables for Overhead Lines  

1. When cables are used for overhead lines, the cables shall be installed using messenger wires or other appropriate measures so that they bear no tensile strength. The messenger wires shall be installed in accordance with the provision of Article 32 of these SREPTS. 

1. When cables are installed along a building or another object, the cables shall be supported so that they are not damaged by contacting the building or the object. 

1. Connecting Methods of Overhead Conductors 

The tensile strength of the conductors shall not be reduced by 20% or more, when electric conductors are connected. If the tension on the conductors is distinctly less than the general tensile strength of conductors, this may not apply. 

1. Branching of Overhead Lines 

Branching of overhead lines shall be made at the supporting point of the lines. If branching can be done in a way that does not to inflict tension on the conductor at the branch point, this may not be applicable. 

Article 42:   Mechanical Strength of Insulators 

1. Generals of Mechanical Strength of Insulators 

The insulator to support medium-voltage lines shall be installed in such a manner that it has sufficient strength to attain the safety factor of at least 2.5 based on the assumption that the following loads are exerted on the insulators. 

1. For the insulators to anchor lines, the load is the assumed maximum tension of the lines. 
2. For the insulators to support lines, the load is the horizontal lateral load or vertical load exerted perpendicular to the axis of the insulators. 
3. Safety factor of Insulators 

The safety factor of insulators for medium-voltage lines shall be calculated using the following equations. 

1. Tension insulator (Insulator that anchors electrical conductors) 

[Tensile break strength] [Safety factor] = 

[Assumed maximum tension of the lines] 

1. Supporting insulator 

[Tensile break strength] 

                            [Safety factor]  =        

[Horizontal transverse load or vertical load applied perpendicular to the 

axis of the insulator device] 

1. Assumed Load 

The assumed loads to be used for calculating the strength of insulator for medium-voltage lines shall conform to the following requirements. 

1. Vertical load 

The vertical load shall be the sum of the weight of electrical conductors and the weight of insulator devices. 

1. Horizontal transverse load 

The horizontal transverse load shall be the sum of the wind pressure loads of electrical conductors and insulator devices and the horizontal component of a load generated by the assumed maximum tension of the electrical conductors.  The wind pressure loads shall be calculated based on the values listed in Table 22. 

Table 22: Wind Pressure Loads 

*The wind pressures are obtained from 32m/s wind velocity as same as Table 21C. 

4.  Assumed Maximum Tension of the Lines 

The assumed maximum tension of the lines shall be the tension of the medium-voltage line conductor under the composite load of: 

1. The load generated by the weight of the electrical conductor, and 
2. The horizontal load generated by the horizontal wind pressure stipulated in Table 22. 

Article 43:   Medium-voltage/Low-voltage (MV/LV) Transformers 

MV/LV transformers, including medium-voltage conductors other than cables, shall be installed so that they are not in danger of electrical shock using either of the following methods. 

1. MV/LV transformers shall be installed in an exclusive cabin that is locked. 

1. MV/LV transformers shall be installed at a height of not less than 5.0m above the ground in order that persons can not touch them easily. 

1. Appropriate fences shall be installed around the MV/LV transformers in order that persons can not touch them easily and warning signs to indicate the danger shall be displayed. Otherwise MV/LV transformers, the charged parts of which are not exposed shall be installed so that persons can not touch them easily. 

Article 44:   Installation of Distribution Transformers for Single Wire Earth Return (SWER) Systems  

1. Grounding Arrangement for SWER  

Grounding on the primary side of distribution transformers for SWER shall be installed by the following methods, in order to avoid risk of danger to persons, domestic animals and other facilities due to the potential difference between the grounding conductor and the ground caused by load current, when any failure occurs. 

1. The grounding resistance shall be not more than 5ohms. 
2. The cross-sectional areas of grounding conductors   shall be not less than 16mm². 
3. The grounding conductors placed up to a depth of 75cm underground or up to a height of 2.0 m above ground shall be covered by a synthetic resin pipe or another shield of equivalent or higher insulating effect and strength. 
4. The grounding for SWER installed on the primary side of a distribution transformer and the Class B grounding for it shall be completely separated to keep the safety of low voltage line system. 

1. Load Current of Distribution Transformers  

The load current in any earth-return circuits shall be not more than 8 amperes.

1. Isolating Transformer 

SWER circuits shall be supplied from double-wound transformers (isolating transformers). 

1. Safety of Third Persons 

Warning signs to alert third persons’ attention shall be installed near the grounding point. 

Article 45:   Protective Devices 

1. Installation of Medium-Voltage Over-current Circuit Breakers 

1. On medium-voltage lines, an over current circuit breaker shall be installed at the outgoing point of a substation or similar location and on the primary side of a transformer.  
2. Over current breakers for short circuit protection shall have the ability to break the short circuit current that passes the breakers. 

1. Installation of Medium-Voltage Ground Fault Circuit Breakers  

A ground fault breaker that breaks circuit automatically when an earth fault happens in the lines shall be installed at an outgoing point of substation or similar locations. 

1. Installation of Surge Arresters 

To prevent electrical equipment from being damaged by lightning, surge arresters shall be installed at the places of lines stated below or their surrounding areas. If electric power facilities are not damaged by lightning, this may not be applicable. 

1. A lead-out of overhead line from power station, substation, and equivalent places. 
2. The connecting point of overhead medium-voltage lines with a main transformer. 

1. Exceptions to Installation of an Over Current Breaker for Medium-voltage and Low-voltage Lines 

No over current circuit breaker shall be installed at the following places: 

1. Grounding conductor of grounding work. 
2. Neutral conductor of an electrical conductor. An over-current circuit breaker, however, may be installed if all the poles are shut off simultaneously. 
3. Grounding conductor of a low-voltage overhead electrical conductor whose circuit is provided with class B grounding work in part. 

Article 46:   Height of Overhead Medium-voltage and Low-voltage Lines 

1.  Regulations for Medium and Low-voltage Overhead Distribution Conductors 

The height of medium and low-voltage overhead lines shall be no less than the values in the following table: 

Table 23: Height of Medium and Low-Voltage Overhead Lines 

                                                                    (Unit: meter) 

1. Urban Areas to be Included 

The following areas shall be included in the urban area. 

1. Area

-  Phnom Penh city and other cities 

-  Provincial towns 

1. Road

-The National Road 

-  The Provincial Roads  

1. Exclusions for Road Crossings 

The conductor is not regarded as crossing a road in the followings: 

-     The road is so narrow that cars can not pass through it. 

-     The road is on private land. 

1. Mitigation of Height for Low-voltage Conductors 

The minimum height of the low-voltage conductor is mitigated up to 4.0 m on the place other than a road. Furthermore, the minimum height of the low-voltage conductor is mitigated up to 3.0 m on the following conditions: 

-       The licensee owning the distribution line is a small licensee in the area other than urban areas; 

-       The insulation of the conductor(s) must be always kept in good condition; -      Vehicles including carts never pass under the line. 

Article 47:  Clearance between Overhead Medium-voltage and Low-voltage Lines and Other Objects 

1.  Clearance between Overhead Lines and Buildings/Plants 

The minimum clearance between a line and another object shall be the values shown in the Table 24A. 

Table 24A: Clearance between Overhead Lines and Other Objects 

                                             (Unit: meter) 

Low-voltage cable including ABC (Aerial Bundle Conductor) type cable may be installed directly on a wall of a building by using a clip and clamp in such a way that in normal circumstances a person cannot reach the cable. 

2.   Clearance between Overhead Distribution Lines and a Road 

When a supporting structure is installed below a road, the minimum clearance between a line and a road shall be the values shown in Tables 24B and 24C. 

Table 24B: Clearance between a Line and a Road on a Bank 

(Unit: m) 

*  If the lateral proximity is equal to the direct proximity, the lateral proximity required the same value as the direct adjacency. 

*  If the lateral proximity is equal to the direct proximity, the lateral proximity required the same value as the direct proximity. 

Figure 12: Explanation of Direct Proximity and Lateral Proximity (Road on a Bank) 

Table 24C: Minimum Clearance between a Line and an Overpass 

(Unit: m) 

proximity 

Figure 13: Explanation of Direct Proximity and Lateral Proximity (Overpass) 

Article 48:   Proximity and Crossing of Overhead Medium-voltage and Low-voltage Lines 

1. Multiple Medium-voltage Line 

When a medium-voltage line is installed adjoining or crossing other medium-voltage lines, the clearance between the two medium-voltage lines shall be not less than 2.0m. If one is a cable and the other is a cable or an insulated conductor, the clearance shall be not less than 0.5m. 

Above requirements shall be also applied, when two or more medium-voltage lines are installed at the same supporting structure. 

1. Medium-voltage Lines and Low-Voltage Lines 

When a medium-voltage line and a low-voltage line are installed so that they adjoin or cross each other, they shall be installed in the following manners. 

-          The medium-voltage line shall not be installed under the low-voltage lines. If the medium-voltage line maintains a horizontal clearance of not less than 3.0m from the low-voltage line, and the low-voltage line does not come in contact with the medium-voltage line when the support structure of the lowvoltage line collapses, this may not be applicable. 

-          The clearance between the medium-voltage line and the low-voltage line shall be not less than 0.5m when the medium-voltage line is a cable, not less than 1.0m when it is an insulated conductor, and not less than 2.0m when it is a bare conductor. 

-          The medium-voltage line shall not cross under the low-voltage line. If the medium-voltage line is a cable and the clearance between the medium-voltage line and the low-voltage line is not less than 0.5m, this may not be applicable. 

1. Multiple Low voltage Lines  

When a low-voltage line is installed adjoining or crossing other low-voltage lines, the clearance between the two low-voltage lines shall be not less than 0.6m. When one is a cable and the other is a cable or an insulated conductor, the clearance shall be not less than 0.3m. 

Above requirements shall be also applied, when two or more low-voltage lines are installed at the same supporting structure. 

1. Medium-voltage Lines and Communication Lines 

When a medium-voltage line is installed adjoining or crossing a communication line, the medium-voltage line shall be installed in the following manners. 

-          The medium-voltage line shall not be installed under the communication line. If the medium-voltage line maintains a horizontal clearance of not less than 3.0m from the communication line, and the communication line does not come in contact with the medium-voltage line when the support structure of the communication line collapses, this may not be applicable. 

-          The clearance between the medium-voltage line and the communication line shall be not less than 0.5m when the medium-voltage is a cable, not less than 1.0m when it is an insulated conductor, and not less than 2.0m when it is a bare conductor. 

-          The medium-voltage line shall not cross under the communication line. If the medium-voltage line is a cable and the clearance between the medium-voltage line and the communication line is not less than 0.5m, this may not be applicable. 

1. Low-voltage Lines and Communication Lines 

When a low-voltage line is installed adjoining or crossing a communication line, the low-voltage line shall be installed in the following manners. 

-          The low-voltage line shall not cross under the communication line. If other methods are not technically realistic, this may not be applicable. 

-          The clearance between the low-voltage line and the communication line shall be not less than 0.3m when the low-voltage line is a cable, and not less than 0.6m when conductor is insulated. 

Specific Requirements for Thermal Power Generating Facilities

Specific Requirements for  

Thermal Power Generating Facilities

CONTENTS

CHAPTER 1  

Introduction 

Article 1:  Definitions 

Article 2:  Purpose 

Article 3:  Area of Application 

Article 4:  Applicable Standards 

Article 5:  Facilities regulated in this Specific Requirements 

CHAPTER 2  

Requirements for all types of Thermal Generating Facility 

            Article 6:  Prevention of Electric Power Disasters from the Facility      

Article 7:  Safety of Third Persons

Article 8: Requirements related to the Fuel 

Article 9:  Requirements related to the Handling of Chemical Materials

Article 10:  Requirements related to the Natural Disasters

Article 11:   Requirements related to the Operation of Generating Facility with Power System 

Article 12:  Requirements related to the Environment 

Article 13:  The Life of Electric Power Facilities 

Article 14:  Requirements related to the design of Electric Power Facilities 

Article 15:  Requirements related to the Technical Document of Electric Power Facilities Article 16:  Requirements related to the Grounding 

CHAPTER 3 

Requirements for Steam Turbine Generating Facility 

Article 17:  Steam Turbine Generating Facility  

PART 1 Boiler 

Article 18:  Requirements for Materials of Boiler and its Accessories 

Article 19:  Requirements for Structure of Boiler and its Accessories 

Article 20:  Safety Valve for Vessels and Tubes of the Boiler 

Article 21:  Feed Water System of Boiler 

Article 22:  Water Feeding and Steam Outpouring of Boiler 

            Article 23:     Monitoring the Running Condition of Boiler and Safety and Alarm System 

PART 2 Steam Turbine 

Article 24:  Requirements for Materials of Steam Turbine and its Accessories 

Article 25: Mechanical Strength of Structure of Steam Turbine and its Accessories  

Article 26: Bearings of Steam Turbine 

Article 27: Governance of Turbine Speed 

Article 28: Requirements to Alarm and to Stop the Turbine in Emergency Case 

Article 29: Monitoring the Condition of Turbine Operation 

Article 30: Reviewing the Safety of Steam Turbine and its Accessories 

CHAPTER 4 

Requirements for Gas Turbine Generating Facility 

Article 31: Gas Turbine Generating Facility  

Article 32: Requirements for Materials of Gas Turbine and its Accessories 

Article 33:       Mechanical Strength of Structure of Gas Turbine and its Accessories 

Article 34: Bearings of Gas Turbine 

Article 35: Governance of Turbine Speed  

Article 36: Emergency Alarm and Stop Devices 

Article 37: Monitoring and Alarm Systems 

Article 38: Reviewing the Safety of Gas Turbine  

Article 39: Requirements for Gas-Turbine Combined Cycle and its Accessories 

CHAPTER 5 

Requirements for Internal Combustion Engine 

Article 40: Internal Combustion Engine  

Article 41: Requirements for Materials of Internal Combustion Engine 

Article 42: Mechanical Strength of Structure of Internal Combustion Engine 

Article 43: Bearings of Internal Combustion Engine 

Article 44: Governance of Internal Combustion Engine Speed 

Article 45: Emergency Stop and Alarm Devices

Article 46: Overpressure Protection Devices 

Article 47:  Monitoring and Alarm Systems 

CHAPTER 6 

Requirements for Generators 

Article 48:  Protection of Generators 

Article 49:  Electrical Equipment 

Article 50:  Cables in Thermal Power Plants 

Article 51:  Installation of Hydrogen Cooling Type Generators 

Article 52:  Control Systems 

CHAPTER 7  

Transitional Provisions 

Article 53:  Transitional Provisions for Small and Medium Licensees 

Article 54:  Prevention of Electric Power Disasters 

Article 55:  Safety of Third Persons

Article 56:  Safety Measures for Fuel and Chemical Materials 

Article 57:  Environmental Protection 

Article 58: Requirements for Operation 

Article 59:  Safety and Technical Training  

CHAPTER 1 

Introduction

CHAPTER 1 

Introduction 

Article 1:  Definitions 

In this Specific Requirements of Electric Power Technical Standards, unless the context otherwise requires, the following terms shall have the meanings assigned to each term:

1. EAC      

                        “EAC” is the acronym for the Electricity Authority of Cambodia. 

1. Electrical Line 

“Electrical Line” means the part of electric power facilities used to transmit or supply electricity, which connects power stations, substations, switching stations and user’s sites, and includes lines and associated protective devices and switchgears. 

1. Electric Power Facility 

“Electric Power Facility” means generating facilities, substations, switching stations, electrical lines, and dispatching centers, including equipment, buildings, dam, waterways, fuel storage yards, ash disposal areas, etc.  

1. Electrical Equipment 

                        “Electrical Equipment” means electrically-charged facilities. 

1. GREPTS

“GREPTS” is the acronym for the General Requirements of Electric Power Technical Standards of the Kingdom of Cambodia. 

1. IEC 

                        “IEC” is the acronym for the International Electrotechnical Commission. 

1. ISO

                        “ISO” is acronym of International Organization for Standardization. 

1. Licensee

 “Licensee” means an electric power service provider who has been issued a license by the EAC. 

1. SREPTS

“SREPTS” is the acronym for the Specific Requirements of Electric Power Technical Standards of the Kingdom of Cambodia. 

1. The Technical Standards 

“The Technical Standards” means The Electric Power Technical Standards in the Kingdom of Cambodia. 

Article 2:  Purpose 

This Specific Requirements of Electric Power Technical Standards for Thermal Power Generating Facilities prescribes the basic requirements necessary to regulate the existing and the planned thermal power generating facilities in the Kingdom of Cambodia. The requirements in this standard document are mainly for facility security and safety operation of the most important parts for thermal generating facilities. 

Article 3:  Area of Application 

All thermal power generating facilities in the Kingdom of Cambodia shall be in accordance with the requirements prescribed in this Technical Standard. 

All persons including licensees, consultants, contractors and consumers who are related to the study, design, construction and operation of thermal power generating facilities shall follow this Specific Requirements of Electric Power Technical Standards for Thermal Power Generating Facilities. 

Article 4:  Applicable Standards 

Thermal Power Generating Facilities planned to construct and operate in the Kingdom of Cambodia shall be as per the provision of this Technical Standards. In case a matter is not stipulated in the Technical Standards, IEC Standards shall be applied.  If it is not covered in the IEC standards, ISO Standards shall be applied. If it is not covered in the ISO Standards, internationally recognized standards shall be applied, subject to the approval by MIME. 

Article 5:  Facilities regulated in this Specific Requirements 

A thermal power plant consists of three main components, a turbine/engine, a generator and a substation. This Specific Requirements provides the requirements to regulate the generating facilities such as turbine/engine and its accessories, and the generator including control systems, except the substation. 

The requirements for the substation shall be in accordance with the Specific Requirements of Electric Power Technical Standards for Transmission and Distribution. 

Thermal power generating facilities regulated in this Specific Requirements of Electric Power Technical Standards for Thermal Power Generating Facilities are following: 

1- Steam Turbine Generating Facility 

2- Gas Turbine Generating Facility 

3- Internal Combustion Engine 

4-Generator 

CHAPTER 2 

Requirements for all types of Thermal 

Generating Facility 

CHAPTER 2 

Requirements for all types of Thermal Generating Facility 

            Article 6:  Prevention of Electric Power Disasters from the Facility      

The facilities shall be installed in such a manner that does not cause electrical shock, fire and other accidents. 

The power facilities shall be installed with proper measures to protect operators from touching their moving parts, hot parts and other dangerous parts, and to prevent them from falling accidentally. 

Article 7:  Safety of Third Persons

Appropriate measures shall be taken to prevent third persons from entering compounds containing a power plant. These measures shall include: 

a.  External fences or walls separated outside from inside compound. The height of external fences or walls shall not be lower than 1,800 mm. Boundary clearance from the fences or the walls to the electrical equipment shall not be less than the values described in the following table: 

Table 1: Boundary Clearance from Walls or Fences to Electrical Equipment 

1. Signs to alert third persons to danger to be installed at the entrances/exits. Moreover, where necessary, signs shall also be displayed on walls and fences. 

1. Locking devices or other appropriate devices to be installed at the entrances / exits. 

Article 8:  Requirements related to the Fuel 

1. Requirements related to Fuel Handling 

1. Fuel handling shall be in accordance with the related laws. 
2. Maintenance and safety checks of fuel facilities shall be implemented every day. 
3. A responsible person for fuel facilities shall be designated. 
4. The responsible person shall receive education and training regarding fuel handling every year. 
5. Requirements related to Fuel Storage 

1. Fuel storage tanks and fuel storage yards shall be in accordance with the related laws. 
2. An appropriate vessel shall be used for the storage tank. 
3. The storage yard shall be kept clean and appropriate signs shall be indicated in front of the storage tank. 
4. Necessary fire extinguishers or fire fighting systems shall be installed around the fuel storage area. 

1. Requirements related to Fuel Transportation

1. Specifications of fuel transportation facilities or vehicles shall be in accordance with the related laws. 
2. Working areas for fuel unloading shall be kept clean and appropriate lighting systems shall be installed around the working area. 
3. Working procedures for fuel transportation shall be prepared and be followed by the persons concerned. 

Article 9:  Requirements related to the Handling of Chemical Materials

Handling of chemical materials at power plants shall follow the provisions of environment law and regulations of the Kingdom of Cambodia. 

Taking the characteristics of chemical materials to be used into consideration, appropriate measures against those chemical materials shall be implemented and tools to protect against potential danger shall be installed. 

Article 10:  Requirements related to the Natural Disasters

Proper measures shall be taken to prevent failures of electric power facilities from anticipated natural disasters such as floods, lightning, earthquakes and strong winds 

Article 11:  Requirements related to the Operation of Generating Facilities with Power System 

When any generating facility has a serious fault, this facility shall be disconnected from the power system so that the effect of the fault on the system can be minimized and the system could be operated continuously. 

When a power system fault occurs in a system connected to a generating facility, the generating facility shall be immediately disconnected from the system, so that the generator runs continuously with no-load while waiting for the recovery of the system from fault. The next action shall be in accordance with procedures of Grid Code and/or Distribution Code of the system. 

Article 12 :  Requirements related to the Environment 

1. Compliance with Environmental Standards

To prevent environmental pollution, the electric power facilities shall be constructed in accordance with the environmental laws and regulations of the Kingdom of Cambodia.

1. Prohibition of Installation of Electrical Machines or Equipment Containing Polychlorinated Biphenyls (PCBs) 

1. The installation of new electrical equipment using insulating oil that contains greater than 0.005 percent (50ppm) polychlorinated biphenyls (PCBs) shall be prohibited. 

1. The use of existing electrical equipment using material containing PCBs, if it was installed before the Specific Requirements of Electric Power Technical Standards came into force, and effective and sufficient measures shall be taken in order to prevent the material containing PCBs from escaping from the oil container, shall be permitted. 

1. Once removed from the electrical equipment, the material containing PCBs greater than 0.005 percent (50ppm) PCBs shall not be reinstalled in another electrical facility and shall be safely scrapped as noxious industrial wastes. 

Article 13:  The Life of Electric Power Facilities 

Electric power facilities shall be durable for long term usage with efficient and stable operation.  

Article 14:  Requirements related to the Design of Electric Power Facilities 

With regard to the design of electric power facilities, selection of the materials, assembling and installation of the equipment, suitable safety factors against foreseeable stresses, such as thermal stress, mechanical stress and insulation strength shall be considered. 

1. Insulation Co-ordination  

Taking everything into consideration technically, economically and operationally, the insulation strength of electrical equipment in the power plant shall be coordinated with the insulation of electrical equipment in substations, transmission lines and distribution lines so that it may be in the most rational conditions.  

1. Dielectric Strength of Electrical Circuits 

The dielectric strength of electrical circuits in the power plant shall be examined by dielectric strength test, insulation resistance measurement and so on, to ensure that their performance corresponds to their nominal voltage.  

Moreover, before starting operation, the dielectric strength shall be confirmed by charging nominalvoltage to the circuit continuously for 10 minutes. 

However, if the nominal voltage of the electrical circuit is low-voltage, it can be tested by insulation resistance measurement or leakage current measurement. In case of the leakage measurement, it is sufficient to keep 1mA or less. 

1. Mechanical Strength of Electrical Equipment against Short-circuit Current 

All electrical equipment to be installed in the power plant shall be able to withstand the mechanical shock caused by short-circuit current. 

1. Thermal Strength of Electrical Equipment 

Electrical equipment to be installed in the power plant shall be able to withstand the heat generated by electrical equipment in normal operations. 

1. Prevention of Damage of Pressure Tanks 

Gas insulated equipment placed in the power plant shall be designed as following in order to avoid any risk of damage: 

1. Materials and structure of the parts receiving pressure shall be able to withstand the maximum operating pressure and shall also be safe. 
2. Parts receiving pressure shall be corrosion-resistant. 
3. Insulation gas shall not be inflammable, corrosive or hazardous. 
4. Tanks shall withstand the gas pressure rising during fault continuous time at internal failure of gas insulated equipment. 

Article 15:  Requirements related to the Technical Document of Electric Power Facilities 

To secure long term operation, each facility shall have its drawings, installation records, technical manuals, instruction manuals and operation records necessary for its proper maintenance works. These documents shall be safekept well. 

Article 16:  Requirements related to the Grounding 

Grounding or other appropriate measures shall be provided for electrical equipment of thermal generating facilities to prevent electrical shock, danger to human beings, fire, and other trouble to objects. 

Grounding for electrical equipment shall be installed to ensure that current can safely and securely flow to the ground. This grounding shall be in accordance with the types, the method and the resistance value of grounding of each equipment provided in the Specific Requirements of Technical Standard for Transmission and Distribution. 

CHAPTER 3 

Requirements for Steam Turbine Generating 

Facility 

CHAPTER 3 

Requirements for Steam Turbine Generating Facility 

Article 17:  Steam Turbine Generating Facility  

A steam turbine generating facility is a facility which generates electric power from the rotation of steam turbine which rotates by the power of pressurized steam spoutted out from the boiler. Two main components of the steam turbine generating facilty are the boiler and the steam turbine. 

A boiler is a closed vessel in which water is heated under pressure. Then the steam from the boiler is used for turbine rotation and preheating feed water. 

A steam turbine is a mechanical device that can extract thermal energy from pressurized steam, which is supplied from a boiler, and converts it into useful mechanical work to rotate the turbine. The steam turbine consists of a rotor supported on bearings and enclosed in a cylindrical casing. The rotor is turned by steam, which expands through nozzles and spouts out at a high speed against the moving blades to turn the impellers. 

PART 1 

Boiler 

Article 18:  Requirements for Materials of Boiler and its Accessories 

Vessels and tubes of the boiler, independent superheater and steam storage vessel and its accessories, and the parts which are subject to an internal pressure higher than 0MPa (hereinafter, referred to as pressure parts) shall be made of materials having sufficient mechanical strength and chemical stability under the maximum working pressure and temperature.  

“Sufficient mechanical strength” shall mean having good weldability, tensile strength, ductility, toughness, hardness and other mechanical properties. 

“Sufficient chemical stability” shall mean having character like good corrosion resistance, good heating resistance and other chemical properties. 

Article 19:  Requirements for Structure of Boiler and its Accessories 

1. Safety margins against the maximum stress 

Structure of pressure parts of the vessels and tubes of the boiler shall have adequate safety margins against the maximum stress under maximum working pressure or temperature condition. In this case, to prevent the danger the stress shall keep the level not exceeding the allowable stress of the material. The allowable tensile stress for each material shall be determined in accordance with its material temperature condition. 

To ensure adequate safety margins against the maximum stress, the structure of pressure parts of the boiler and its accessories shall be able to withstand a water pressure test with a water pressure 1.5 times as high as their respective maximum allowable working pressures without the occurrence of leakage. 

The design pressure of economizers shall be not less than the maximum working pressure of the economizer determined based on the maximum working pressure of the feed pump. 

1. Prevention against Overheat 

                  To prevent overheat of the water tubes in the furnace the following conditions shall be provided: 

1. Boiler water shall be sufficiently circulated to the water tubes. 
2. Boiler water shall be sufficiently purified. For this, proper measures such as a water softener, a demineralizer, etc. shall be provided. 

1. Protections against Flame 

In case part of the boiler drum and tube heater are so constructed that they are exposed to flames or high temperature gas, proper thermal protection, such as installation of a heat resisting tube material and/or installation of a heat protection, or other suitable means shall be provided. 

1. Considerations for Structural Strength 

Where the effects of additional stresses such as spot concentration stress, repeated loads and thermal stress are significant, suitable measurements such as increasing thickness shall be taken if necessary.

Article 20:  Safety Valve for Vessels and Tubes of the Boiler 

Vessels and tubes of the boiler which may be subjected to overpressure shall be equipped with safety valves in order to release the pressure. In case of overpressure such as when the steam pressure of the boiler goes up beyond regulation limits, safety valves shall be operated to release the pressure in order to prevent danger. 

The safety valves for the boiler and its accessories shall have the following conditions: 

1. The safety valves shall be installed in position that can be easily inspected. 
2. At least, one safety valve shall be installed on the drum and one on the super-heater outlet. 
3. The total capacity of the safety valves shall be not smaller than the maximum designed steam capacity of the boiler. 
4. At least one set pressure of the safety valves shall be not higher than the maximum allowable pressure of any parts of the boiler (including superheaters and reheaters). 
5. The safety valves shall be spring loaded safety valves or safety valves with a spring loaded pilot valve. 

Article 21:  Feed Water System of Boiler 

A feed water system is the system of equipment for feeding water to a boiler. The requirements for the feed water system for boiler are the following: 

-        The feed water system shall be able to prevent thermal damage to the boiler during the maximum evaporating condition. 

-        In order to prevent the thermal damage to the boiler caused by the feed water system's trouble, the feed water system of the boiler shall be equipped with two or more means of water supply equipment. 

-        The feed water system shall be able to independently supply a quantity of water not less than the maximum designed steaming capacity of the boiler at any time and independently. 

Article 22:  Water Feeding and Steam Outpouring of Boiler 

Water feeding and steam outpouring of boiler shall be required as follows: 

-        The steam outlet of the boiler shall be able to shut off the steam; 

-        The feed water inlet of the boiler shall be able to automatically and firmly shut off; 

-        A circulation boiler shall be equipped with a drain-off device which protects deposit and regulates the water level. 

Article 23:  Monitoring the Running Condition of Boiler and Safety and Alarm System 

The boiler and its accessories shall be equipped with the systems to monitor the running condition and the alarm systems to prevent from the damage to the boiler and its accessories. The monitoring and alarm systems as described above shall be equipped with devices as defining below: 

1. For monitoring Circulation Boilers 

1. Water level indicator in the boiler drum  
2. Pressure indicator in the boiler drum 
3. Temperature indicator at superheater and reheater outlet steam 

1. For monitoring Once-through Boilers  

1. Pressure indicator at superheater outlet steam 
2. Temperature indicator at superheater and reheater outlet steam 

1. For Safety and Alarm 

The boiler shall be fitted with safety devices, which are capable of shutting off automatically the fuel supply to all burners, and alarm devices which are capable to alarm when: 

1. The flame vanishes 
2. The water level falls (for circulation boiler drums) 
3. The combustion air supply stops 

1. For monitoring Boiler Water 

The boilers shall be provided with means such as a water analyzer or other suitable devices to supervise and control the quality of the feed water and boiler water. 

* All above monitoring devices shall be installed in position that allows easy observation. 

PART 2 

 Steam Turbine 

Article 24:  Requirements for Materials of Steam Turbine and its Accessories 

Cylinders, vessels and tubes of the steam turbine and its accessories, and the pressure parts shall be made of materials having sufficient mechanical strength such as good weldability, tensile strength, ductility, toughness, hardness, and other mechanical properties and chemical stability such as having character like corrosion resistance, abrasion resistance and other chemical properties under the maximum working pressure and temperature. 

Article 25: Mechanical Strength of Structure of Steam Turbine and its Accessories  

Structure of steam turbines shall have sufficient mechanical strength such as having good weldability, tensile strength, ductility, toughness, hardness and other mechanical properties, even when they are operated at the speed, that the steam turbine reaches when the emergency governor is actuated. “Speed that the steam turbine reaches when the emergency governor is actuated” shall include not only the actuated point of the emergency governor but also the accelerated speed from the actuated point. 

Structure of steam turbines shall have sufficient mechanical strength against the maximum amplitude value of vibration produced on the major bearings and shafts. “Maximum amplitude value of vibration” shall mean the maximum vibration reached during turbine operation including turbine start and stop operation. 

The pressure parts and its accessories of the steam turbine shall have a sufficient safety margin against the maximum stress under the maximum working pressure and shall not exceed the allowable stress of the material. 

 A steam turbine and its accessories which are likely to be subjected to overpressure shall be equipped with an overpressure protection device in order to release the pressure. 

Article 26:  Bearings of Steam Turbine 

Bearings of steam turbines shall be constructed to be able to stably support the load during operation and without the occurrence of abnormal wear and deformation and overheat. To prevent the bearings from “its abnormal wear and deformation and overheat” the following measures shall be provided:  

1. Steam turbines shall be equipped with main lubricating oil feed pumps, auxiliary oil pumps and an emergency oil pump.  
2. Quantity of lubricating oil for steam turbines shall be sufficient in all times. 
3. Auxiliary oil pumps shall start automatically when the main oil pump out-put pressure becomes abnormally low 
4. An emergency oil pump or manual operation auxiliary oil pumps, which are installed for safety stop of the main turbine when the main and/or auxiliary oil pumps have broken down. 
5. The lubricating oil tank shall have necessary lubricating oil for the turbine. 
6. Devices to clean lubricating oil shall be equipped 
7. Device to control temperature of lubricating oil shall be equipped. 

Article 27:  Governance of Turbine Speed 

1.  Speed Governor 

A steam turbine shall be equipped with a system capable to adjust automatically the steam entering the steam turbine in accordance with the actual speed of the turbine in order to prevent its speed and output from fluctuating continuously even in case of a change in load condition. This system is called speed governor. The speed governor consists of a speed monitoring device used for monitoring the actual speed of steam turbine and then providing the order to a steam adjusting valve to adjust the quantity of steam flow entering the steam turbine for the purpose to maintain speed of the turbine at the constant level. This speed governor shall regulate the turbine speed not to reach the tripping speed even if the rated turbine output is shut down instantaneously. 

1. Emergency Speed Governor 

In addition to a speed governor, a main turbine shall be equipped with an independent emergency speed governor in order to prevent the speed from being increased abnormally. The emergency speed governor shall be activated to interrupt the flow of steam to the turbine when the speed of turbine reaches the tripping speed. The tripping speed of the turbine shall be at 110% (±1%) of the rated speed.  

1. Normal Speed, Over Speed and Critical Speed of Turbine 

Normal Speed of a steam turbine is the operational speed of the turbine when it normally loaded and when the governor is in normal operation. The turbine shall be capable to operate at normal speed without any restrictions upon the time and output. This normal speed shall be in between 98 to 101% of the rated speed of the turbine. The normal speed of the turbine shall not be the speed remarkably less or more than the rated speed.  

Over-speed is the speed over than the normal speed which could do harm to the turbine.  

Critical speed of a turbine is the speed which creates the resonance on the turbine. To avoid the damage of the turbine caused by this resonance, the critical speed of the turbine combined with the generator on the same shaft shall not be in the speed between the minimum speed controlled by the governor and the maximum available speed of emergency stop device. However, it will be exempted if it will be arranged to have enough countermeasure against the vibration at critical speed during operation of the turbine.  “Speed between the minimum speed controlled by the governor and the maximum available speed of the emergency governor” is the speed can be operated by the steam turbine. 

1. Limits of Turbine Speed 

A turbine shall be capable to maintain the speed within the following limits: 

1. Momentary variations shall be not more than 10% of the maximum rated speed when the rated output of the generator is suddenly thrown off; 
2. At all loads in a range between no load and the rated load, the permanent speed variation shall be within ±5% of the maximum rated speed. 

5.  Protection against Over-speed 

1. All main and auxiliary turbines (in case of turbine-driven boiler feed pumps) shall be equipped with over-speed protective devices to prevent the turbine speed from being exceeded by more than 10% of the normal speed of turbine.  
2. In addition to the over-speed protective device, the main steam turbine shall be equipped with a device capable to control the speed of the unloaded turbine without activating the over-speed protective device into action. 

Article 28: Requirements to Alarm and to Stop the Turbine in Emergency Case 

In order to avoid the occurrence of damage from abnormal conditions (emergency case) during steam turbine operation, the steam turbine shall be equipped with two systems: 1-protection system and 2-alarm system. 

1. Emergency Protection System or Tripping System 

In order to avoid the occurrence of damage from abnormal conditions, a main turbine shall be equipped with a protection system which is capable to automatically shut off the steam supply to the turbine (automatic emergency stop device) in the following cases: 

1. Low lubricating oil pressure 
2. High exhaust steam pressure 
3. Low condenser vacuum 
4. Over-speed
5. Emergency stop button is locally or remotely operated. 

In addition to the automatic emergency stop device, the protection system shall have also a manual emergency stop device.  

When the above emergency stop device is actuated, the emergency stop alarm shall be energized. 

1. Emergency Alarm System 

The steam turbine shall be provided with alarm systems which give visual and audible alarm in the event of abnormal conditions before steam shut off devices are activated. The abnormal conditions of steam turbine operation can be indicated by the level of vibrations of the steam turbine. 

When the maximum double amplitude value of vibrations of the major bearings or the shaft close to it is detected to be beyond the allowable level during the turbine operation, the steam turbine operation is considered as in abnormal condition. 

The steam turbine shall be equipped with an alarm system, which gives an alarm when the maximum double amplitude of vibrations of the major bearing or the shaft close to it exceeds the value shown in the table below: 

Table2: Allowable Level of Maximum Double Amplitude of Vibrations 

3.   Reviewing of Emergency Protection and Alarm System   

For insuring the safety of steam turbine operation, before commercial operation of steam turbines, Licensee shall submit to EAC for reviewing the following documents related to emergency protection and alarm system: 

1. Turbine protection system diagram  
2. Explanation sheet for alarming and tripping set-points figure 

Article 29:  Monitoring the Condition of Turbine Operation

A steam turbine and its accessories shall be equipped with systems necessary to monitor the operating condition and necessary alarm system to prevent any damages to the steam turbine and its accessories during the operation. 

Monitoring and alarm systems of steam turbines shall be capable to monitor the following data: 

1. Rotational speed of the turbine 
2. Main steam temperature and pressure (before main stop valve position)  
3. Reheated steam temperature and pressure (before reheat stop valve position) 
4. Steam turbine exhaust steam pressure 
5. Lubricating oil inlet pressure of steam turbine bearings 
6. Lubricating oil outlet temperature of steam turbine bearings or bearing metal temperature 
7. Steam flow control valve position 
8. Steam turbine vibration amplitude (with automatic recorder - media record is acceptable.) 

Article 30:  Reviewing the Safety of Steam Turbine and its Accessories 

To ensure the safety of steam turbine operation, Licensees who plan to install a steam turbine in the Kingdom of Cambodia shall submit the drawings and data related to the steam turbine on the items as follows to EAC for reviewing the adoption of the requirements in this standard:

1. Turbine casings 
2. Turbine rotors 
3. Critical speed of turbine rotor 
4. Technical data for strength calculations specified above 
5. Material specifications of principal components 
6. Assembly drawings 
7. Control system diagram 
8. Drawings and data which are deemed necessary by the Government  

CHAPTER 4 

Requirements for Gas Turbine Generating 

Facility 

CHAPTER 4 

Requirements for Gas Turbine Generating Facility 

Article 31:  Gas Turbine Generating Facility  

A gas turbine generating facility is a facility which generates electric power from the rotation of the gas turbine which rotates by the power of the flow of combustion gas spoutted out from the combustor. In the combustor, fuel is mixed with air and ignited, this combustion increases the temperature, velocity and volume of the gas which expands through nozzles and spouts out at a high speed against the moving blades to turn the impellers.  

Main components of the gas turbine which are regulated by the requirements in this chapter are the following: 

-      Turbine itself 

-      Bearings

-      Governor

-      Emergency stop and alarm device 

-      Overpressure protection device 

-      Monitoring and alarm system 

Article 32:  Requirements for Materials of Gas Turbine and its Accessories 

Principal components of gas turbines which are subject to an internal pressure higher than 0MPa shall be made of materials having enough mechanical strength such as having good weldability, tensile strength, ductility, toughness, hardness and other mechanical properties and chemical stability such as good corrosion resistance, good heating resistance and other chemical properties under the maximum working pressure and temperature.  

These principal components of gas turbines are following: 

1. Rotors, stationary blades and moving blades of turbines 
2. Rotors, stationary blades and moving blades of compressors 
3. Turbines and compressor casings 
4. Combustion chambers 
5. Turbine output shafts 
6. Connecting bolts for main components of turbines 
7. Shaft coupling and bolts 
8. Pipes, valves and fittings attached to turbines 

The principal components of gas turbines excluding bolts, pipes, valves and fittings shall have been subjected to the non-destructive tests. 

The materials used in high temperature parts shall possess properties suitable for the design performance and service life against corrosions, thermal stresses, creeps and relaxations. 

 In case where the base material coated with corrosion-resistant surfacing, the coating material shall be firmly attached to the base material and shall not impair the strength of the base material.  

The mechanical strength of all materials of gas turbines shall be confirmed to be sufficient through strength calculation or other methods. 

Article 33:  Mechanical Strength of Structure of Gas Turbine and its Accessories 

Structure of gas turbines shall have sufficient mechanical strength such as having good weldability, tensile strength, ductility, toughness, hardness and other mechanical properties even when it is operated at the speed that the gas turbine reaches when the emergency speed governor is actuated. Even if the rotational speed of the gas turbine exceeds the rated rotational speed for any reasons and an emergency speed governor is actuated, the turbine shall not be damaged. 

Structure of gas turbines shall have sufficient mechanical strength against the maximum amplitude value of vibration produced on the major bearings and shaft. “Maximum amplitude value of vibration” shall mean the maximum vibration reached during turbine operation including turbine start and stop operation. 

The pressure parts and their accessories of the steam turbine shall have a sufficient safety margin against the maximum stress under maximum working pressure and temperature. In this case, the stress shall not exceed the allowable stress of the material. To ensure the sufficient safety margin again the maximum stress, the structure of pressure parts of the gas turbine and its accessories shall be able to withstand a water pressure test with a water pressure 1.5 times as high as their respective maximum allowable working pressures without leakage. 

Gas turbine and its accessories which are likely to be subjected to overpressure shall be equipped with an overpressure protection device in order to release the pressure. 

Article 34:  Bearings of Gas Turbine 

Bearings of gas turbines shall be constructed to be able to stably support the load during operation and without the occurrence of abnormal wear and deformation, and overheat. To prevent the “abnormal wear and deformation and overheat” of bearings, the gas turbine shall be equipped with the following lubricating oil feed pumps to provide the satisfactory lubricating oil to the bearings: 

1. Main lubricating oil feed pumps   

 While the turbine is operating, the main lubricating oil feed pumps shall be operated to provide a satisfactory lubricating oil to the bearing of the gas turbine. 

1. Auxiliary oil pumps  

 Auxiliary oil pumps shall automatically start when the main oil pump out-put pressure becomes abnormally low  

 However, if a gas turbine is equipped with a device to automatically shut off the inflow of fuel and safety stop when the outlet pressure of a main oil pump decreases, it is not required to equip an auxiliary oil pump. 

1. Emergency oil pump 

 An emergency oil pump or manual operation auxiliary oil pumps shall be installed for safety stop of the main turbine when main and/or auxiliary oil pumps have broken down. 

Article 35:  Governance of Turbine Speed  

1.  Speed Governor

A gas turbine shall be equipped with a device capable to automatically adjust the flow of fuel entering the gas turbine in order to prevent its speed and output from fluctuating continuously even in case of a change in load condition. The device to automatically adjust the flow of fuel entering into the gas turbine automatically is called Speed Governor. This Speed Governor shall have an ability to hold the turbine speed after the interruption of the rated load below the speed at which the emergency governor is actuated. 

Even the gas turbines without direct fuel burning shall be equipped with a device to control the maximum rotational speed.  

2.  Normal Speed, Over-Speed and Critial Speed of Gas Turbine

Normal Speed of a gas turbine is the operational speed of the turbine when it normally loaded and when the governor is in normal operation. The turbine shall be capable to operate at normal speed without any restrictions upon the time and output. This Normal Speed shall be in between 98 to 101% of the rated speed of the turbine. The normal speed of the turbine shall not be the speed remarkably less or more than the rated speed.  

Over-speed is the speed over than the normal speed which could do harm to the turbine.  

Critical speed of a turbine is the speed which creates the resonance on the turbine. To avoid the damage of the turbine caused by this resonance, the critical speed of the turbine combined with the generator on the same shaft shall not be in the speed between the minimum speed of governor and the maximum available speed of emergency stop device. However, it will be exempted if it will be arranged to have enough countermeasure against the vibration at critical speed during operation of the turbine. 

“Speed between the minimum speed of governor and the maximum available speed of emergency stop device” is the speed can be operated by the steam turbine. 

“The minimum speed of governor” shall mean the following; 

1. The minimum speed in speed variation when the turbine is not combined with a generator or a rotor. 
2. The minimum speed of grid frequency when the turbine is combined with a generator or a rotor. 

Article 36:  Emergency Alarm and Stop Devices 

In order to avoid the occurrence of damage from over-speed and abnormal conditions (emergency case) during operation, the gas turbine shall be equipped with two devices: 1-Emergency Stop Device and 2- Emergency Alarm Device. 

1. Emergency Stop Device 

In order to avoid the occurrence of damage from over-speed or other abnormal conditions during gas turbine operation, the gas turbine shall be equipped with a device which automatically interrupts the inflow of fuel or gas called Automatic Emergency Stop Device. In addition to the Automatic Emergency Stop Device, the gas turbine shall be also equipped with a manual emergency stop device. When the above emergency stop device is actuated, the emergency stop alarm shall be activated. 

In case of over-speeds or speeds exceeded the rated speed of the gas turbine, the automatic emergency stop device shall be actuated to stop the turbine when the speed reaches the tripping speed. The tripping speed of the turbine shall be at 110% (±1%) of the rated speed. 

“Other abnormal conditions” are the following cases: 

1. The case where an internal failure occurs in a generator. 
2. The case where the gas temperature significantly increases. 
3. The case where the lubricating oil temperature significantly increases. 
4. The case where the lubricating oil pressure significantly decreases. 

1. Emergency Alarm Device 

A gas turbine shall be equipped with a device that functions to provide an alarm when the amplitude value of vibrations is detected to be beyond the allowable level during the gas turbine operation. 

Article 37: Monitoring and Alarm Systems 

A gas turbine and its accessories shall be equipped with systems necessary to monitor the operating condition and alarm system to prevent any damages of the gas turbine and its accessories during the operation.  

Monitoring systems of gas turbines shall be capable to monitor the following data: 

1. Rotational speed of the turbine (Gas turbine tachometer) 
2. Outlet pressure of an air compressor of gas turbine 
3. Gas temperature at the inlet of a gas turbine (The calculation method to determine the inlet temperature of gas based on the measured outlet temperature of the gas is applicable.) 
4. Lubricating oil inlet pressure of gas turbine bearings 
5. Lubricating oil outlet temperature of gas turbine bearings or bearing metal temperature 

Alarm systems of gas turbines shall provide an alarm when the following situations occur: 

1. Temperature of inlet or outlet gas of gas turbine is high 
2. Lubricating oil pressure is low (shall alarm before the function of the emergency stopping device.) 
3. Fuel oil supply pressure is low. 

Article 38:  Reviewing the Safety of Gas Turbine  

To ensure the safety of gas turbine operation, Licensees who plans to install gas turbine in The Kingdom of Cambodia shall submit the drawings and data related to the gas turbine on the items as follows to EAC for reviewing the adoption of safety requirements in this standard: 

1. Combustion chambers 
2. Piping arrangements fitted to turbines (including fuel, lubricating oil and cooling water system) 
3. Particulars (type of turbine, power and rotation speed of turbine, gas pressure and temperatures at turbine inlet and outlet, ambient condition, service fuel and lubricating oil) 
4. Material specifications of principal components 
5. General arrangement 
6. Control system diagram 
7. Calculation sheets for vibration of turbine blades   

Article 39: Requirements for Gas-Turbine Combined Cycle and its Accessories 

Gas turbine combined cycle plants and their accessories shall be designed, manufactured, constructed and operated in accordance with the requirements in this chapter and chapter 3. 

CHAPTER 4 

Requirements for Gas Turbine Generating 

Facility 

CHAPTER 5 

Requirements for Internal Combustion Engine 

Article 40:  Internal Combustion Engine  

A generating facility by an internal combustion engine is a facility where the generator is rotated by the internal combustion engine to generate the electric power. The internal combustion engine is a engine in which the fuel is mixed with air and burnt in confined space called a combustion chamber. The combustion of mixed fuel and air in the combustion chamber creates gases of high temperature and pressure which moves the moving parts of the engine such as pistons, rotors. 

Main components of the internal combustion engine which are regulated by the requirements in this chapter are the following: 

-      Engine itself 

-      Bearings

-      Governor

-      Emergency stop and alarm device 

-      Overpressure protection device 

-      Monitoring and alarm system 

Article 41:  Requirements for Materials of Internal Combustion Engine 

 Cylinders, vessels and tubes of the internal combustion engine and its accessories and the pressure parts shall be made of the materials which have sufficient mechanical strength such as having good weldability, tensile strength, ductility, toughness, hardness and other mechanical properties and chemical stability such as good corrosion resistance, good heating resistance, and other chemical properties under the maximum working pressure and temperature. 

The scope of properties of materials shall be chosen according to the specific conditions of use. 

Article 42:  Mechanical Strength of Structure of Internal Combustion Engine 

Structure of an internal combustion engine shall have sufficient mechanical strength such as having good weldability, tensile strength, ductility, toughness, hardness and other mechanical properties even when it is operated at the speed that the engine reaches when the emergency speed governor is actuated. Even if the rotational speed of the engine exceeds the rated rotational speed for any reasons and the emergency speed governor is activated, the machine shall not be damaged. 

Pressure parts and their accessories of the internal combustion shall have a sufficient safety margin against the maximum stress under the maximum working pressure and temperature. In this case, the stress shall not exceed the allowable stress of the material.  

To provide “sufficient safety margins” to the pressure parts and their accessories, the following conditions shall be fulfilled: 

1. Combustion chamber and pipes of the ancillary equipment for internal combustion engines shall meet the requirement of good weldability, tensile strength, ductility, toughness, hardness and other properties. 
2. Internal combustion engines and ancillary equipment shall meet the requirement of corrosion resistance and abrasion resistance, if it’s necessary. 
3. The pressure parts of internal combustion engines and their accessories shall be able to withstand a water pressure test using a water pressure 1.5 times their respective maximum allowable working pressures without leakage. 
4. However, the water pressure test is not required for; 

(i)      Internal combustion engine’s casing which has the result of a water pressure test that was conducted under the same structure and same material conditions.  

(ii)     Internal combustion engines, the strength of which has been proven theoretically by calculation to have the mechanical strength to resist a water-pressure of 1.5 times of the maximum allowable pressure. 

Article 43:  Bearings of Internal Combustion Engine 

Bearings of the internal combustion engine shall be structurally able to stably support the load during operation and without the occurrence of abnormal wear, deformation and overheat. 

For the bearings with lubricating oil system to prevent the abnormal wear and deformation and overheat of bearings the following conditions shall be provided: 

1. The main lubricating oil pump shall be capable to feed sufficient lubricating oil to the engine during normal conditions 
2. The lubricating oil tank shall be capable to store the quantity of lubricating oil required for the engine.  
3. Devices capable to clean the lubricating oil (An oil filter which has the capacity to clean the lubricating oil can be one of them.) shall be equipped. 
4. Devices capable to regulate the temperature of the lubricating oil (An oil cooler for controlling the oil temperature, which may be automatic or manual, can be one of them.) shall be equipped. 

Bearings without lubricating oil system shall also be regarded as satisfactory if their technical mechanism is proved to be sufficient for the required level of safety. 

Article 44:  Governance of Internal Combustion Engine Speed 

An internal combustion engine shall be equipped with a device to automatically adjust the fuel entering the engine in order to prevent its speed and output from fluctuating continuously even in case of a change in load condition. This device is called a speed governor. Speed governors shall be capable of preventing the rotational speed and output of the engine from hunting in case of any changes. The maximum rotational speed shall be controlled in the range lower than the speed at which the emergency speed governor is actuated, even when the rated load is cut off. 

Article 45:  Emergency Stop and Alarm Devices

In order to avoid the occurrence of damage from over-speed or other abnormal conditions during the engine operation, the internal combustion engine shall be equipped with an automatic emergency stop device, a manual emergency stop device and emergency alarm device. Emergency stop device automatically interrupts the inflow of fuel. When the above emergency stop device is actuated, the emergency stop alarm shall be activated. “Over-speed” in this article is the state which an internal combustion engine speed exceeds its rated rotational speed. “Other abnormal conditions” in this article is the state with an excessive rise of the cooling water temperature, the accidental stoppage of the cooling water feed and so on. 

All internal combustion engines except those with a rated output less than 3000kW shall be equipped with an emergency governor which is actuated to stop the engine at a speed higher than engine rated speed but not higher than 1.16 times of this rated speed.  

All internal combustion engines except those with a rated output less than 3000kW shall be equipped with a device which stops the fuel flow automatically in case the cooling water temperature rises abnormally or the cooling water feeding stops. 

Article 46: Overpressure Protection Devices 

An engine and its accessories which are likely to be subjected to overpressure shall be equipped with an overpressure protection device in order to release the pressure such as relief valve which shall have a sufficient capacity for preventing overpressure, and shall activate at a pressure lower than the maximum pressure. 

“An engine and its accessories are likely to be subjected to overpressure” means the following parts: 

1. Cylinders with a diameter of more than 230mm and the maximum allowable pressure of more than 3.4 MPa (excluding gas fuel engines). 
2. Sealed crankcases in the cylinders with a diameter of more than 250mm. 

Article 47:  Monitoring and Alarm Systems 

An engine shall be equipped with systems necessary to monitor the operating condition and systems necessary to provide an alarm to prevent damages to the engine and its accessories during the operation. 

Monitoring systems of internal combustion engines shall be capable to monitor the following data: 

1. The rotation speed of the internal combustion engine 
2. The temperature of the cooling water at the outlet of the internal combustion engine 
3. The pressure of the lubricating oil at the inlet of the internal combustion engine 
4. The temperature of the lubricating oil at the outlet of the internal combustion engine 

CHAPTER 6 

Requirements for Generators 

CHAPTER 6 

Requirements for Generators 

Article 48:  Protection of Generators 

Thermal power generators shall be equipped with a protection device against any over-current accident.  The thermal power generators shall be also equipped with devices to automatically cut off the generator from the electrical line when: 

1. Over-current occurs. 
2. Internal failures, such as grounding or short-circuit of stator windings, of the generator with a capacity of 3000kVA or more occurs. 
3. The thrust bearings of the turbine with a rated capacity of 3000kW or more are significantly worn down and there is a significant rise in the temperature of the bearings. 

Article 49:  Electrical Equipment 

Electrical equipment installed in thermal power plants shall be designed and constructed so that it structurally allows easy operation, inspection, overhauls and repairs. 

Article 50:  Cables in Thermal Power Plants 

Cables used in thermal power plants shall be installed so that the original properties of non-flammability are not impaired. 

In case cables are installed in such hazardous areas that there is a risk of fire or explosion in the event of an electrical fault, proper protections against such risks shall be provided. 

Cables and wires shall be installed and supported so that they will not be damaged by any mechanical stress.  

Article 51:  Installation of Hydrogen Cooling Type Generators 

The hydrogen cooling system is usually adopted in a large capacity generator. Such generators are filled with hydrogen to cool all windings of generator. Because hydrogen explodes if it is mixed with air, the following measures against the explosion shall be taken for the generator with the hydrogen cooling system: 

1. The generator shall be structurally constructed so that the hydrogen will not leak to the outside and the air will not go into the inside.  

1. The structure of the generator shall have sufficient mechanical strength (explosion-proof construction) to withstand pressure generated by hydrogen explosion.  
2. The generator shall be equipped with an alarm device to be activated when purity of hydrogen decreases to 85% or less. Moreover, the device shall raise an alarm when pressure and/or temperature of the hydrogen change remarkably. 
3. Tubes and valves filled with hydrogen shall have the structure to prevent hydrogen leakage. The tubes shall be a copper pipe or a seamless steel pipe. 
4. When the hydrogen leaks from the shaft seal part of the generator, the gas leakage shall be stopped and the gas shall be safely discharged outside.  

Article 52:  Control Systems 

The control system for generators shall have the integrated interlocking system to properly and safely control the generator. 

Annunciators shall be provided for detection of abnormal operating conditions and shall be equipped with emergency trip functions necessary to assure equipment integrity and overall plant safety. The annunciator and trip functions shall be implemented through each independent device. 

The control system shall have a function to start up and shut down the generator. The thermal power plant including the generator shall be started up and shut down manually from the control panel and automatically through the individual sequence programs. 

CHAPTER 7 

Transitional Provisions 

CHAPTER 7 

Transitional Provisions 

Article 53:  Transitional Provisions for Small and Medium Licensees 

Requirements in this chapter are the minimum requirements and temporarily applicable to generation facilities of small and medium licensees when their generation facilities are in the transitional stage taking into consideration present level of existing generation facilities in Cambodia. Therefore these requirements will be cancelled in the future by Ministry of Industry, Mines and Energy when the generation facilities of Licensees in Cambodia passed the transitional stage. 

“Small licensee” means the licensees with an installed capacity of less than 500 kW. 

“Medium licensee” means the licensees with an installed capacity from 500kW up to 3000kW. 

                   The minimum requirements to temporary apply to generation facilities of small and medium licensees are 

described in the following articles in this chapter.  

Article 54:  Prevention of Electric Power Disasters 

For prevention of electric power disasters, all power generating facilities of small and medium licensees which are in the transitional stage at present shall be at least in accordance with the following minimum requirements: 

-     A generator circuit breaker shall be equipped to each generator. 

-     A bare conductor is allowed only when it is installed inside of the panel or box.

-     A naked knife-switch is allowed only when it is installed inside of the panel or box. 

-     Each cable shall have the cable number attached. 

-     Electrical facilities shall be grounded appropriately. 

-     All power cables and control cables shall be installed inside the cable tray or conduit pipe in the facility area. 

Article 55:  Safety of Third Persons

For prevention of danger to third persons, all power generating facilities of small and medium licensees which are in the transitional stage at present shall be at least in accordance with the following minimum requirements: 

-     Fences and/or walls shall be installed around the generating facilities to prevent third persons’ accidents. 

-     The entrances/exits of above fences or walls needs appropriate key lock systems. 

-     “Keep out” signs shall be indicated at the entrance of generating facilities. 

-     Generating facility area shall be kept clean. 

-     All rotating and working parts shall be covered and protected from workers’ accidents. 

-     Any belt drive power transmission systems shall be not approvable. 

Article 56:  Safety Measures for Fuel and Chemical Materials 

For safety in using fuel and chemical materials, all power generating facilities of small and medium licensees which are in the transitional stage at present shall be provided with the following measures: 

-     Fire fighting systems and/or extinguishers shall be equipped near the fuel storage area. 

-     Fuel tanks shall be equipped at least 1 (one) meter away from electrical facilities.

-     Fuel tanks shall be equipped solidly and combustible materials shall not be left within 1 (one) meter. 

-     Exhaust gas shall be discharged at least 2(two) meters high outside of the building. 

-     Exhaust pipes and/or hot parts of engines shall be protected. 

Article 57:  Environmental Protection 

-     Noise of generating facilities shall be prevented in residential areas. (Refer to related laws). 

Table 3: Countermeasures for Preventing Noise of Generating Facilities

- Waste oil shall not be discharged directly to the ground in order to prevent soil pollution and protecting well water. 

Article 58:  Requirements for Operation 

1. Monitoring Devices 

Generators and generating facilities shall be equipped with the following monitoring devices:  

1. Generator volt meter 
2. Generator ammeter 
3. Generator frequency meter 
4. Energy meter (kWh) 
5. Generator out put (kW) meter 
6. Fuel tank level (or fuel flow meter) 
7. Engine oil pressure meter 
8. Engine oil temperature meter (if any) 
9. Cooling water temperature (if any) 

1. Record Requirements and Maintenance of Generating Facilities   

-      Daily operational data, such as generated energy (kWh), Voltage, frequency, operation time and all instrument data, shall be recorded.  

-      Considering the operational period, overhaul of the engines shall be scheduled and implemented. 

-      Maintenance records including replacement parts and checking points shall be established. 

1. Report Requirement 

The following reports shall be submitted to EAC and copied to MIME every year: 

1. Operation records  
2. Maintenance records 
3. Trouble records 

If any trouble or accidents in relation to the generating facilities occurs, the licensee shall report to EAC without delay. 

Article 59: Safety and Technical Training  

“Small and Medium Licensee” and/or technical staff who operate and maintain their facilities shall pass a training school program or course recognized by MIME or EAC. The technical training shall be provided to refresh their memory within three years or less.