The case of serious damage of multiple units of three-phase capacitors occurred during normal operation of shunt capacitor installation at a newly established 220 kV substation.It is thought

throughout analysis of possible faults capacitors from the aspects of quality

operating over voltage

rise of system voltage

switching inrush current

harmonics and fault of capacitor protection device

that the cause of the fault is due to the 4th harmonic resonance generated between the device and the system and is verified by the harmonic test

and the fault development is mainly caused by the big imbalance current protection settings at the neutral point.Finally

corresponding suggestions are raised with hope of providing a definite reference for the safe operation of capacitors.