Analysis on a Transformer Lightning Accident
Bao Yu-shu · Electric Power · 2012
In order to investigate the causes for generator outage after a high-voltage auxiliary power transformer of a power plant experienced a lightning,the fault wave record was analyzed and tests were conducted on the oil chromatogram,insulation resistance,DC resistance,DC leakage,dielectric loss,low voltage short circuit impedance and AC voltage endurance.It was judged from the test results that the transformer worked normally after experiencing a large short-circuit current and the fault was caused by two-phase short-circuit and subsequent three-phase short-circuit.Based on the investigation of lightning protection grounding layout,with consideration of the condition of soil and thunder arc,the fault process is calculated and inferred that the lightning overvoltage firstly caused insulation flashover,and then continuous arc-discharge occurred under power frequency voltage,which in turn caused the two-phase and three phase short-circuit of the transformer's low voltage side bus.Analysis indicates that the cause for the fault is that the layout of lightning arrester's grounding wiring on the transformer's wall area failed to meet the standard provisions.In the end,several countermeasures are put forward,which can provide an important reference for similar lightning fault analysis.