Spurious Current-Induced Breaker Failure Protection in the 220kV DMT Bus Switching Scheme– A Case Study from Indian Power Sector

The Double Main & Transfer (DMT) bus switching scheme, commonly employed at the 220kV voltage level within POWERGRID India, is the focus of this paper. During routine transmission line maintenance, the standard practice involves opening the circuit breakers at both ends of the transmission line and subsequently closing the line earth switches after disconnectors are opened at both ends. The key concern lies in the positioning of the current transformer (CT) within the DMT scheme, situated on the line side and sandwiched between the earth points at both ends of the transmission line. This arrangement significantly heightens the probability of spurious current generation during line shutdowns. This paper presents a case study from the Indian power sector in which spurious current, as detected by the CT, inadvertently triggered the operation of the breaker failure protection (BFP) during line maintenance. However, the correct isolation procedures and the precise implementation of protective functions prevented a widespread outage. The research contributes to an enhanced understanding of how CT and earth switch placement in the DMT scheme can lead to BFP activations during line shutdowns. It also underscores the critical role of human factors within the protection system, ultimately serving to bolster the reliability and stability of the power transmission network.