Transient current limiter for suppressing transformer inrush, motor starting and fault currents in power system

TTransient currents (TCs) including transformer inrush, motor starting and fault currents cause mechanical, thermal and electrical stresses to the transformer windings and the power utility equipments. Of these, the inrush current suppression is crucial due to high second harmonic level, causing inadvertent operation of the protective relays. In this study, a TC limiter (TCL) comprising of two diodes and two reactors in each phase is proposed. The number of diodes in the proposed TCL is the half of those employed in the single-phase diode-bridge type inrush current limiter (ICL); thus, the proposed TCL topology offers much more reliability and lower cost in addition to lower current ripple. Comparing with the three-phase diode-bridge type ICL, the proposed topology is independent of the transformer primary winding connection type. The analysis and design procedure is provided and the performance is verified through simulation and an experimental scaled down prototype for transformer energising, motor starting and fault event.