Impact of installing FSFCL on the neutral point of the medium-voltage side of a 220kV transformer on the reliable response of protection systems

With the development of power grids, the issue of short-circuit current has become increasingly severe. Installing Fast Switching Fault Current Limiter (FSFCL) at the neutral point of transformers is an effective current-limiting measure, but its impact on the relay protection system still needs to be evaluated. This paper uses Simulink simulations to analyze the impact of installing FSFCL at the neutral point of the medium-voltage side of a 220kV transformer on relay protection. The results show that after the installation of FSFCL, the transformer’s zero-sequence equivalent impedance increases, which reduces the magnitude of zero-sequence current during asymmetric short-circuit faults. This can affect the sensitivity of the protection devices, requiring recalibration and adjustment of some protection settings. In addition, the rapid response of FSFCL and the reliable operation of the current-limiting reactor are crucial for the protection system. If FSFCL fails to disconnect, it may lead to excessive fault current impact; if it fails to reconnect, it may damage the current-limiting reactor.