CEMIG experience in the analysis of transient recovery voltages associated with Transformer-fed faults

摘要

This paper presents the transient studies carried out by CEMIG (Companhia Energetica de Minas Gerais - Brazil) to determine the transient recovery voltage (TRV) parameters of 230 kV circuit-breakers regarding the clearing of transformer-fed faults. As the frequency transformer response is the dominant feature in the determination of these parameters, it is clear that the transformer modeling is a very important factor in this type of analysis. So, the main focus of the study was to represent the transformers associated with the circuit-breakers under analysis as accurate as possible. TRT results considering different transformer models will be presented, compared and discussed, emphasizing the parameters more sensitive to the transformer model. It is shown that the transformer response is of multi-frequency form and can affect the results in different ways. The circuit-breakers in analysis will be part of a new link that interconnects a very long and weak 138 kV sub transmission system to CEMIG main extra - high voltage grid. The necessary steps to upgrade the usual CEMIG circuit-breaker specification will be shown to ensure a reliable operation as far as the TRT parameters are concerned.