Volt-second Balance Method for Mitigation of Inrush Current in Single Phase Transformers

During the transient period at the start of transformer energization, it experiences a flux linkage that is up to twice its nominal steady state value and saturates the core. This causes a large inrush current to flow which affects the power system stability and power quality especially when the source is weak. Sequential phase energization technique and addition of neutral resistor are the major methods for minimization of inrush current. This paper proposes a simple technique to limit the flux linkage during the time of transformer energization and prevents the flux saturation there by reducing the inrush current. This is based on a volt-second balance which injects a transient voltage to the primary of the transformer during inrush currents. The effectiveness of the proposed scheme is verified by simulation.