A Brief Talk on AC withstand Voltage Test of 110kV GIS

Kong Tao, Zeng Pu
HIMALAYAL - SHANGHAI - CHINA

Abstract: Through GIS AC withstand voltage test of 110kV substation, the paper discusses the principle, procedure and precautions of GIS AC withstand voltage test and analyzes test phenomenon and results.    

Key words: quality factor, serial resonant, AC withstand voltage, frequency modulation

Some 110kV substation has been completely constructed in Sichuan province. Routine high voltage test of electric device and debugging work of relay protection have been over as well. According to the schedule of contractor organization, it is going to conduct AC voltage after getting the authorization from the supervision organization.

At present, the AC voltage test of high-voltage GIS equipment with large capacity adopts variable-frequency voltage resonant method. First, the voltage resonant occurs in the circuit through adjusting output frequency of variable-frequency power supply; then adjusting output voltage to make test voltage reach the test voltage value. The test frequency can be adjusted within a certain range; quality factor is high and there is no "dead band"; test equipment has perfect protection function and can effectively protect the test object.

1.Test Preparation
(1)Determination of test parameter When conducting GIS field test, weather condition imposes a significant impact on quality factor Q. Quality factor Q = (L/C)1/2/R. However, as test voltage rises slowly, the corona occurs in the test circuit and active loss R will also increase, resulting in the reduction of quality factor. In the overcast day or the air humidity is large, Q will reduce by 30% or so, which causes the input voltage of exciting transformer to increase. Hence, GIS voltage test must be conducted in a sunny day or the air is dry.

As for 110kV GIS, the capacitance between each interval is 600~800pF. Because this project has seven intervals, the capacitance is 5000pF or so.

Selection of inductance L of high voltage reactor. In the actual application, high voltage reactor matches with variable-frequency voltage resonant test equipment under the guide of test equipment manufacturer and the inductance L is fixed. As for test equipment with different capacity, the inductance of matched high voltage reactor is also different. How to connect high voltage reactor depends on test voltage and test current. If test voltage is greater than rated voltage of high voltage reactor, then the high voltage reactor adopts the method of serial voltage dividing; if test current is greater than rated current of high voltage reactor, shunt current dividing should be utilized. This project adopts the mode of serial voltage dividing.