In this paper

one fault of 35 kV capacitor bank at 500 kV substation is analyzed.Firstly

the factors possibly causing damage of capacitor such as harmonics amplification is eliminated through the test of background harmonics.Then

it is found that imbalance current protection settings at neutral point of capacitor bank are too high in accordance with the mechanism and requirement set by the internal fuse.The settings of replaying protection is adjusted

thus assuring relaying protection operation in case of small scope of damage to the internal elements of capacitor unit and preventing occurrence of similar serious faults.For the capacitor banks with internal fuse

installation of external fuse is in general unnecessary

and

therefore

the external fuse of capacitor bank is removed.