Analysis of flashover fault for a 500 kV circuit breaker of a generator-transformer unit and its countermeasures

In the synchronization process of a large-scale generator-transformer unit and the power system,the circuit breaker fracture may be flashover.Due to the voltage angle(δ) changes between the generator and power system,the flashover current varied in the circuit breaker fracture.In order to operate reliably for the flashover protection and circuit breaker failure protection,the current setting values of flashover protection and circuit breaker failure protection should be within a certain level.According to the practical recorder waveform of the fault,the principle of setting calculation for negative sequence current and zero-sequence current units of flashover protection and circuit breaker failure protection was analyzed,which provides a reference for engineers.