In the process of transformer no-load closing

overvoltage appeared due to electromagnetic oscillation

if there are high voltage cables in the system

internal overvoltage can couple to the cable sheath which results in sheath’s high voltage

and this voltage is related to cable arrangement and sheath grounding method.This article aim at the abnormal discharge phenomena in cable ends of Bailianhe Pumped Storage Station when transformer closes in no-load situation

transformer no-load closing overvoltage is measured

discharge phenomena is observed

and ATP/EMTP software is adopted to calculate cable sheath overvoltage coupled by no-load closing overvoltage.Measurement results show that the no-load closing overvoltage of main transformer is not high

then calculation results show that cable sheath overvoltage in the discharge place is 21.49 kV

with the maximum frequency 600 kHz

which is greater than the arrester operation voltage

this high frequency current flowing into the ground results in ground potential rising at cable bracket

which cause the air gap between the cable sheath insulation and cable bracket breaking down.