Analysis of a generator step-up transformer failure following faulty synchronization

An analysis was carried out to investigate an out-of-phase synchronizing condition which resulted in the failure of a 725 MVA GSU (generator step-up) transformer. Using a technique described, the circuit breaker closing angle was estimated from oscillograph traces. This information was used with the Electromagnetic Transients Program (EMTP) to simulate the disturbance events and thereby produce a complete set of probable synchronizing currents and generator electrical torques experienced during the disturbance. The analysis of the simulation results, and the analysis of the failure of the GSU transformer have been viewed in light of the large number of prior system faults in the vicinity of the transformer. A review of the ANSI/IEEE standards on transformer fault withstand capabilities as related to this type of analysis is presented