Efficient resonant-type transformer inrush current limiter

This study presents a new structure of a solid-state inrush current limiter (SSICL) to mitigate the inrush current of transformers. The proposed SSICL has a series-parallel resonant structure that is formed by two resonant circuits tuned at the supply frequency. During the energisation of transformers, the SSICL offers very high impedance by the parallel resonant circuit; therefore inrush current is dramatically reduced. Under normal conditions, an SSICL exhibits very low impedance through the series resonant circuit. By energising the transformer, an auto-triggered silicon-controlled rectifier (SCR) circuit inserts the parallel resonance circuit in the transformer input terminals. In addition to the self-controlling capability, the proposed SSICL can be triggered by an external command. This effective remedy assures the proper operation of the transformer protection system. Therefore with a very simple structure, it has a fast and reliable performance as well as full control capability. A prototype single-phase SSICL is simulated by electro-magnetic transient program (EMTP) and tested. The simulation and experimental results show that the proposed SSICL considerably reduces the inrush current during the energisation process of the transformer.