Transformer Inrush and Rectifier Transient Currents

Formulas are developed and curves given for the magnetizing inrush current for a single-phase transformer. Series system inductance and resistance are included. The transformer is assumed to have no exciting current below saturation and constant saturated inductance above saturation. The formulas apply to circuits with either low or high resistance. The curves permit calculation of peak, average, or rms current, and show how these currents decay with time. The theory can also be used for certain cases where there is direct current in a transformer winding and also for certain types of phase controlled rectifiers supplying a series resistance and inductance load.