Bidirectional impedance-type transformer inrush current limiter

Transformer inrush current is harmful to the transformer's windings and may bring about inadvertent tripping of the protective relays. In order to reduce the magnitude of inrush current, a bidirectional impedance-type inrush current limiter (BIT-ICL) is proposed in this paper. When a power transformer is energized, the BIT-ICL immediately and automatically inserts into the circuit to suppress the inrush current without any control or detection circuit. After completing transformer inrush suppression, the BIT-ICL is bypassed automatically, and the transformer appears to connect directly to the voltage source. Thus, when the transformer is loaded, there is almost no distortion in the steady-state load voltage and current waveforms due to the voltage-compensation effect in the limiter. The feasibility and performance of the proposed BIT-ICL are verified by a low-voltage single-phase power transformer under different residual flux and load conditions. Moreover, as long as the power loss that results from the related components in the BIT-ICL can be greatly reduced, this limiter can be applied to high-voltage and large-capacity distribution transformers.