In this paper

sudden tripping of 4 sets of 35 kV capacitor bank at certain 220 kV substation during operation period is introduced.Throughout analysis of protection action information and fault recorder chart of the capacitor together with the inspection result of the capacitors after disassembly

it is conducted that the tripping of capacitor bank is due to following reasons: A large number of third harmonics caused by no load charging during switching of main transformer of up power grid is transmitted into circuit of capacitor bank and partial resonance with system is happened

causing significant amplification of harmonic current

finally leading to such consequences such breakdown of partial elements

fusing of external fuse and tripping of capacitor bank.