Abstract: Abstract:In the 6kV ungrounded system of the water source area of Huadian International Zouxian Power Plant project phase III, when the power supply was switched on after protection overhaul, the voltage transformer gave out a zero sequence over voltage alarm signal, and the each phasetoground capacitors of the 6kV ungrounded system were not balanced. The reasons of the fault were analyzed. The effective measures were adopted, and the problem was solved.

Key words: Key words:ungrounded system, compensation capacitor, ground protection, reason analysis