In the field

the oscillatory surge voltage is usually used to evaluate the insulation performance of GIS equipment. Based on a 750 kV substation

the voltage waveform of a 800 kV UHV GIS equipment under oscillatorylightning shock wave and the parameters of surge voltage generator were calculated by the numerical simulation soft-ware ATP-EMTP. According to on the simulation results

on-site impulse withstand voltage test was carried out on acertain interval of the 800 kV GIS equipment to evaluate the insulation performance of the equipment. Impulse testsunder 50%

75%

and 100% of the rated voltage of positive and negative polarities（corresponding to ±840

±1 260 and ±1 680 kV）were conducted

respectively

and the waveforms were adjusted according to the requirements. Theresults show that the simulating calculation plays an important guiding role in the field test. The waveforms of the on-site withstand test with the calculated parameters of surge voltage generator are in accordance with the simulationwaveforms. Under the action of 50%

75% or 100% rated voltage

no discharge or breakdown happened in the equipment

and the insulation performance of the equipment is good.