Transient Recovery Voltages with Steep Front which Appear at Interrupting Inrush Current of Transformer

Abstract

In the underground sub-stations connected with transmission cables, lightning high overvoltages don't appear. So, it is very important to investigate well switching overvoltages to achieve the rational insulation coordination for apparatus installed in such underground substations. This paper discusses occurrence of steep front at the transient recovery voltages (TRV) which appear at circuit breakers when the inrush current of the transformers are interrupted. Caused by the steep front at the TRV, reignitions should occur at the circuit breakers resulting in generation of high overvoltages of high frequency. The overvoltages would be one of the highest switching overvoltages which would appear at the terminal of the transformers.
The authors clarified the mechanism of the generation of the steep front of the TRV by conducting EMTP analysis as well as by carrying out testing at high power laboratory.