Recently, the Transmission and Transformation Technology Center of the State Grid Anhui Electric Power Research Institute has completed several high-quality GIS (Geographic Information System) expansion projects in the province with the same frequency and phase withstand voltage testing. Through the risk assessment of the same frequency and phase withstand voltage testing under different operation modes, various safety prevention and control measures, such as installing damping resistors and increasing joint trip circuit breakers, have been developed to effectively reduce the risk after test failure. The achievement will be used to support the rapid development of power grid construction in the province.

"GIS expansion or maintenance projects in substations of 220 kilovolts or below using traditional voltage withstand methods may require full shutdown of double bus lines, resulting in increased risk levels in some areas of the power grid. The same frequency and phase voltage test technology uses the secondary voltage of the bus or the voltage transformer of the adjacent line as the reference voltage, and dynamically tracks the frequency and phase of the test voltage through the phase-locked loop technology, which can ensure that at least one bus is in the running state. Such efforts can greatly reduce the network risk caused by the total shutdown of the double buses and reduce the overall maintenance period," said Zhang Guobao, director of the Transmission and Transformation Technology Center.

However, at the same time, the same frequency and phase voltage testing technology will also inflate the consequences that arise from the defects of GIS equipment itself. In the test, part of the isolation switch is between the test voltage and the operating voltage. Once a grounding fault occurs in a certain part of the circuit during the test, the isolation switch may break down, causing the ground fault of the bus in service, thus expanding the power outage range and causing more serious regional load loss.

In order to solve the above problems, the State Grid Anhui Electric Power Research Institute and the High Voltage Teaching and Research Office of the School of Electrical Engineering at Xi'an Jiaotong University carried out the risk assessment of the same frequency and phase withstand voltage testing. They established the ATP-EMTP simulation model of the same frequency and phase withstand voltage test under different operating modes and developed different prevention and control measures for different fault locations in the test loop, such as installing damping resistors and adding double-trip circuit breakers. The solution effectively reduced the network risk caused by GIS equipment defects in the testing process.

In the next step, the State Grid Anhui Electric Power Research Institute will continue to contribute to the development of differentiated control measures for GIS same-frequency and same-phase withstand voltage testing by accumulating work experience in the test work, and comprehensively improving the reliability of GIS expansion and maintenance engineering handover testing in the province.