Shunt capacitor zero sequence voltage protection can judge whether the outage of internal capacitor elements in banks by detecting zero sequence voltage to send a warning signal or a trip signal for the banks′ breaker to remove the bank from the system.Zero sequence voltage protection fails to identify the faulted phase and to wipe out the influence of three phase unbalance voltage.In order to overcome its disadvantages

a study of mended zero sequence voltage protection scheme for shunt capacitor is made.This paper analyses the internal over voltage and changes of the phase current

and gives corresponding equations.At the same time

it gives a developed method about eliminating the three phase unbalance voltage and identifying the fault phase.