In this paper

an explosion of 35 kV capacitor voltage transformer (CVT) at a 110 kV substation is introduced

which caused various damage to a number of outgoing porcelain insulators and metering boxes. Based on the fault information and the results of field inspection and test

the ferromagnetic resonance fault is initially determined

and the damper does not effectively suppress the resonance. It is found after its return to the factory

disassembly and testing that the insulation oil of electromagnetic unit is deteriorated seriously

and the secondary winding insulation to the ground is low. It is further determined that the cause of the accident is the oscillation due to the short-circuit grounding on the primary side of the system

which leads to the continuous increase of the excitation current under the continuous influence of the resonant overvoltage

and the accumulation of heat inside the capacitor to the limit value

eventually causing explosion. The ATP-EMTP software is used to construct a simulation model and restore the accident process

simulating the voltage distortion and excitation current variation on the secondary side under the excitation condition that the ground short circuit fault occurred on the 35 kV bus side and is quickly eliminated. The calculation results are consistent with the test analysis results

which improving the accident cause analysis and giving relevant suggestions for the safe operation in the future.