GB/T 50064-2014 in English

1 General Provisions

1.0.1 This code is formulated with a view to ensuring safe, reliable, technology-advanced, economical and reasonable overvoltage protection and insulation coordination design for AC electrical installations.
1.0.2 This code is applicable to the design of overvoltage protection and insulation coordination for power generation, transmission, transformation and distribution electrical installations and rotating electrical machines in AC power system with nominal voltage of 6kV~750kV.
1.0.3 Differentiated design shall be conducted for the overvoltage protection and insulation coordination for AC electrical installations through calculation, analysis and technical and economical comparison by combining the power network structure, lightning characteristics in the region, ground flash density and operating experience.
1.0.4 The design of overvoltage protection and insulation coordination for AC electrical installations shall not only comply with the requirements specified in this code, but also meet those specified in the current relevant standards of the nation.

2 Terminologies

2.0.1 High-resistance neutral grounding method
At least one conductor or one point of the system is grounded through high-resistance. The system equivalent zero-sequence resistance is not greater than single-phase capacitive reactance of system distributed to the ground and the system grounding fault current is less than 10A.
2.0.2 Low-resistance neutral grounding method
At least one conductor or one point of the system is grounded through low-resistance. The system equivalent zero-sequence resistance is not less than 2 times system equivalent zero-sequence inductive reactance.
2.0.3 Resonant neutral grounding method
At least one conductor or one point of the system is grounded through inductance to compensate the capacitive component of the single-phase fault current of system to ground.
2.0.4 Very fast transient overvoltage (VFTO)
The high-frequency oscillation overvoltage with frequency up to hundreds of thousands of hertz to several megahertz generated by the disconnecting switch of gas-insulated metal-enclosed switchgear (GIS) and HGIS (namely Hybrid-GIS) under certain operation mode is referred to as very fast transient overvoltage.
2.0.5 Ground flash density (GFD)
The annual lightning times on ground per square kilometer.
2.0.6 Less thunderstorm region
The region where the average annual thunderstorm days do not exceed 15d or the ground flash density does not exceed 0.78 times /(km2·a).
2.0.7 Middle thunderstorm region
The region where the average annual thunderstorm days are between 15d~40d or the ground flash density is between 0.78 times /(km2·a)~2.78 times/(km2·a).
2.0.8 More thunderstorm region
The region where the average annual thunderstorm days are between 40d~90d or the ground flash density is between 2.78 times /(km2·a)~7.98 times/(km2·a).
2.0.9 Strong thunderstorm region
The region where the average annual thunderstorm days exceed 90d or the ground flash density exceeds 7.98 times/(km2·a) and regions with particular serious thunderstorm damage according to the operating experience.
2.0.10 Shielding angle
The shielding angle of ground wire to conductor refers to the included angle of the perpendicular line of ground wire to the horizontal plane at the pole tower position (irrespective of wind deflection) and the connecting line between the ground wire and the conductor of the sub-conductor at the outermost side of bundled conductor.

Contents
1 General Provisions
2 Terminologies
3 System Neutral Grounding Method and Voltage on Insulation of Electrical Installations
3.1 System Neutral Grounding Method
3.2 Voltage on Insulation of Electrical Installations
4 Temporary Overvoltage, Switching Overvoltage and Mitigation
4.1 Temporary Overvoltage and Mitigation
4.2 Switching Overvoltage and Mitigation
4.3 VFTO and Mitigation
4.4 Basic Requirements of MOA to Suppress Switching Overvoltage
5 Lightning Overvoltage and Protection
5.1 General Requirements
5.2 Protection Scope of Lightning Rods and Shield Wires
5.3 Lightning Overvoltage Protection of High-voltage Overhead Transmission Lines
5.4 Lightning Overvoltage Protection of Power Plants and Substations
5.5 Lightning Overvoltage Protection of Power Distribution Systems
5.6 Lightning Overvoltage Protection of Rotating Electrical Machine
6 Insulation Coordination
6.1 Principles of Insulation Coordination
6.2 Insulation Coordination of Overhead Transmission Lines
6.3 Insulation Coordination of Insulator String and Air Clearance in Substations
6.4 Insulation Coordination of Electrical Equipment in Substations
Appendix A Altitude Correction of Discharge Voltage for External Insulation
Appendix B Uneven Factor of Wind Speed for Calculation on Angle of Wind Deflection of Suspension Insulator String on Overhead Lines
Appendix C Calculation Methods of Insulation Flashover Rate of Line Under Switching Overvoltage
Appendix D Analysis and Calculation Methods of Lightning Performance of Overhead Lines and Substations
Appendix E Requirements on Duration of Temporary Overvoltage for Electrical Equipment
Appendix F Discharge Voltage Data for Air Clearance of Ultra-high Voltage Overhead Lines and Substations
Explanation of Wording in This Code
List of Quoted Standards