NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA. Code for Earthing Design of AC Electrical Installations

Transcription

1 NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA r=fl$a~~fo~~%t~it Code for Earthing Design of AC Electrical Installations X~TI Et!~ ~I: 8{] ~±-fu ~it tjli m GB/T Chief Development Department: China Electricity Council Approval Department: Ministry of Housing and Urban-Rural Development of the People's Republic of China Implementation Date: June 1, 2012 Beijing 2011

2 NOTICE This code is written in Chinese and English. The Chinese text shall be taken as the ruling one in the event of any inconsistency between the Chinese text and the English text.

3 Announcement of Ministry of Housing and Urban-Rural Development of the People's Republic of China No Announcement on Publishing the National Standard of"code for Earthing Design of AC Electrical Installations" "Code for Earthing Design of AC Electrical Installations" is approved as the national standard with the serial number of GB/T and implemented on June 1, The standard "Code for the Design of Earthing (Earthing) of Industrial and Civil Electric System" GBJ shall be abolished simultaneously. Authorized by the Standard Rating Research Institute of the Ministry of Housing and Urban Rural Development of the People's Republic of China, this code is published and distributed by China Planning Press. Ministry of Housing and Urban-Rural Development of the People's Republic of China, December 5, 2011

4

5 Foreword This code is formulated on the basis of revision of the original national standard "Code for the Design of Earthing of Industrial and Civil Electric System (Trial)" GBJ by the China Academy of Building Research with relevant organizations, according to the requirements of Document Jian Biao [2004] No. 67 issued by the Ministry of Construction-"Notice on Printing the Development and Revision Plan of National Engineering Construction Standards in In the revision of the code, the revision group added many new details based on the base of the original standard by the collection of the recent new requirements, relevant scientific achievements and practical experience in engineering required by the electric installation earthing in electrical engineering with the development of the electric power system after investigation. The draft for examination shall be approved after feedback to carefully dealt draft for comments and the draft will be finalized after examination. The code is classified into 8 chapters and 9 appendixes, and the main technical details include: General Provisions, Terms, Earthing of high voltage electrical installations, Earthing grid of power plant and transformer substation, Earthing of high voltage overhead lines and cable lines, Earthing of high voltage electrical installations in distribution network, earthing method types of low voltage system, earthing of overhead line, earthing resistance and protective equipotenial bonding system of electrical installations, earthing installations and protective conductor of low voltage electrical installations. The main details for the revision of this code are: 1. Revision is made in the application scope of this code, the application at and below 35kV shall be extended to the voltage class at and below 750kV. Meanwhile, due to the differences in earthing requirements, the AC electrical installations shall be divided into high-voltage (above 1Kv~750kV) and low-voltage (lkv or below) electrical installations according to differences in the nominal voltage of system. 2. Some terms are added properly according to the revision of the article details. 3. Earthing categories are specified. With the enlargement of the application scope of this code, the range of high-voltage electrical installation and protective earthing are enlarged. 4. General requirements of 11 OkV and above substation earthing net design are proposed. The earthing potential rise limit and voltage balance requirements are proposed on the effective earthing system substation earthing grid. Copper and copper coating steel material are required to be introduced according to earthing installation anti-corrosion. Gas-insulated metal-enclosed switchgear (GIS) substation's earthing, the earthing requirements of the power plant and substation lighting protection shall be supplemented. 5. Requirements are made for high-voltage overhead line and cable line earthing. 6. Requirements are made for the earthing of electrical installations with high-voltage distribution. 7. The requirements of low voltage system earthing type, overhead lines earthing, earthing resistance of low-voltage electrical installations and protective main equipotential bonding are proposed according to IEC relevant standard and current national standards. 8. The requirements of the earthing installations and protective conductors of the low-voltage

6 electrical installation are proposed by reference to IEC relevant standards and current national standards. The Ministry of Housing and Urban-Rural Development is responsible for the management of this code, standardization management center of China Electricity Council is responsible for the specific management and China Electric Power Research Institute is responsible for the explanation of specific technical contents. During the process of implementing this code, all organizations are kindly requested to combine the engineering practice, to sum up experience carefully, and send comments or recommendations (if any) to China Electric Power Research Institute (Address: Xiaoying East Road No. 15, Haidian District, Beijing; postcode: ) for the reference in future revision. Chief Development Organizations, Participating Development Organizations, Chief Drafting Staffs and Chief Examiners of this code: Chief Development Organization: China Electric Power Research Institute Participating Development Organization: Tsinghua University Chief Drafting Staff: Du Shuchun, Lu Jiayu, He Jinliang, Ju Yong, Guo Jian, Ge Dong, Zeng Rong Chief Examiners: Fang Jing, Wang Zhuo, Chen Junzhang, Li Hui, Dong Xiagohui, Liang Xueyu, Zeng Xiaochao, Chen Hongming, Peng Yong, Huang Baoying, Dingjie, Ma Jingbo, Zhang Huihuan, Ba Tao, Han jingjun, Liu Qingshi, Wang Rongliang, Lu Chonghui, Liu Wenjian, Chen Guanghua, Wang Biyun, Wang Houyu, Huagn Miaoqing and Liu Ji

7 Contents General Provisions Tenns High-voltage Electrical Installtion Earthing General Requirements... ; Range of the Protective Earthing Earthing Grid of Power Plant and Transformer Substation General Priovisions of Earthing Grid Design of Power Plant and Transformer Substation at 110kV or Above Requirements for earthing resistanceand Average Voltage The design of Horizontal Earthing Network Earthing of Gas Insulated Substation (GIS) Earthing of Lightning Protection and Static Protection High-voltage Overhead and Cable Line Earthing Earthing of High-voltage Overhead Line kV.--220kV Cable Line Earthing Earthing of High-voltage Electrical Distribution Devices Earthing Resistance of High Voltage Electrical Distribution Devices Earthing Installation of High-voltage Power Distribution Electrical Devices Low Voltage System Earthing Type, Overhead Line Earthing, Earthing Resistance of the Electrical Installation and Protective Equipotential Bonding System (PEBS) Low Voltage System Earthing Type Earthing of Low-voltage Overhead Line, Earthing Resistance of the Electrical Installation and Protective Equipotential Bonding System (PEBS) Earthing Installation and Protective Conductor of Low-voltage Electrical Installation Earthing installation Protective Conductor Protective Bonding Conductor Appendix A Appendix B Calculation Method of Power-Frequency Earthing Resistance of Artificial Earthing Electrode in Soil Calculation Method of Earthing Fault Current and Earth Potential Rise Through Power Plant and Substation Earthing Grid... 45

8 Appendix C Surface Layer Decrement Factor Appendix D Appendix E Calculation Method of Touch Potential Difference and Step Potential Difference of Earthing Grid in Uniform Soil... ' Thermal Stability Check of Earthing Conductor of High Voltage Electrical Installations58 Appendix F Calculation Method of Earthing Resistance of Pole Tower of Overhead Lines Appendix G Calculation Method of Coefficient k Appendix H Specification of Low Voltage Earthing Configuration, Protective Conductor and Protective Bonding Conductor Appendix J Resistivity Reference Value of Soil and Water Explanation of Wording in This Code List of Quoted Standards... 69

9 1 General Provisions This code was formulated especially to make the earthing design of AC electrical installations be able to guarantee the safety of electrical installations and human beings during the operation and fault of power system as well as make the earthing design be with advanced technology and be economical and rational This code applies the earthing design of the electrical installations for power generation, transformation, transmission and distribution in the high voltage high-voltage electrical installation with nominal AC voltage above lkv to below 750kV and the earthing design of low-voltage electrical installation at and below lkv The earthing design of AC electrical installations shall follow certain design procedures. The determination of the design scheme and the adoption of the materials of earthing conductor and earthing electrode shall be in accordance with local conditions. For the relatively important power plants and transformer substations in the region with complex soil regime, the earthing design of the earthing grid should be determined through scheme comparison by numerical calculation with computer dependent program The earthing design of AC electrical installations shall not only comply with this code, but also shall comply with those specified in the relevant current national standards.

10 2 Terms Earthing It means connecting given points and partial parts of the power system, installation or equipment through electrical connectors System earthing It means functional earthing at one point or multiple points of the electrical system Protective earthing It means the earthing connected to one point or multiple points of the system, installation or equipment for the electrical safety Lightning protective earthing It means the earthing set for discharging the lightning current from the lightning protection installation (lightning rod, lightning conductor and lightning arrester, etc.) to the ground Static protective earthing It means the earthing set for preventing the static electricity from endangering the storage tanks and pipelines of combustible oil and natural gas Earthing electrode The conductive parts embedded into the soil or specific conducting medias (such as the concrete or coke) in electric contact with the earth Earthing conductor The conductors of the conductive path or partial conductive paths between given points of the system, installations or equipments and the earthing electrode or earthing grid Earthing system All the electrical connectors and appliances included in the earthing of the system, installation or equipment Earthing installation Sum of the earthing conductors and earthing electrodes Earthing grid The composition of earthing system, only including earthing electrode and interconnected parts Concentrated earthing installation; con-centrated earthing installation The additional earthing installation installed to strengthening the distribution function of lightning current and to reduce the potential to ground. Generally, 3,..,5 perpendicular earthing electrodes shall be laid. In regions with high soil electrical resistivity, 3,..,5 actinoid horizontal earthing electrodes shall be laid. 2

11 Erthing resistance At given frequency, the resistive component of impedance between the given points of the system, installation or equipment, and the reference ground Pwer frequency earthing resistance The resistance obtained according to the power frequency AC current into the ground by means of earthing electrode Impulse earthing resistance The earthing resistance obtained according to the shock current into the ground through the earth electrode (the ratio between peak value of the earthed voltage and that of the current on the earthing electrode) Earth potential rise The potential difference between the earthing divice and reference ground where the current flows to the ground through the earthing electrode of the earthing installation Touch potential difference The potential difference between the point of l.om of the horizontal distance from the ground to the equipment and the point of 2.0m of vertical distance from the equipment enclosure, framework or walls to the ground as the distributed potential is formed on the ground surface where the earthing fault (short circuit) circuit flows through earthing installation Maximal touch potential difference The maximum potential difference between the aperture centre of the earthing grid and the earthing electrode of the earthing grid Step potential difference The potential difference between the two points at l.om of horizontal distance on the ground where the earthing fault (short circuit) current flows through the earthing installation Maximal step potential difference The maximum potential difference between l.om of the horizontal distance on the ground outside earthing grid network and the edge earthing electrode of the earthing grid Diverting potential Where the current flowing through the earthing installation due to the short circuit (fault) of grounding, the potential to reference ground of earthing installation transited through the metallic conductor that is connected to the earthing installation at one end Exposed conductive part The touchable conductive part of the electrical installation that is not with voltage usually but may be with voltage where the basic insulation is damaged Extraneous conductive part The conductive part not belonging to the components of electrical installation but easy to 3