A Flux Matching Method for Mitigating the Inrush Current of Single-Phase Transformers

Inrush current refers to the high-magnitude current drawn by a power transformer upon energization. The severity of inrush current is a function of the instantaneous value of voltage at the energization instant and the transformer's residual flux density. This paper proposes an effective energization method for mitigating the inrush current of single-phase power transformers. The method does not rely on the knowledge of transformer design specifications, but the magnitude of the transformer's excitation current. The reference residual flux density is determined with respect to the limitations of the closing operation of the circuit breaker. The method then adjusts the residual flux density of the core to a value deemed appropriate by injecting controlled current into the transformer's winding. This is followed by identifying an appropriate instant for transformer energization that matches the instantaneous value of the steady-state flux density with the adjusted flux density. To validate the efficiency of the proposed method, over 8,000 simulations are conducted in PSCAD/EMTDC. The method is also implemented on a laboratory-scale testbed and extensively tested to demonstrate its effectiveness and superiority over most recent methods under a wide variety of realistic conditions.