This chapter develops a circuit model of the transformer that can be used to analyze impulse and other transient electrical shocks to a transformer. The inductive elements include mutual inductances between elements in the same winding and between different windings and the effects of the iron core. The high-voltage (HV) or series winding consists of two coils in parallel with two ends joined at the center where the impulse is applied. The other two ends are joined at the autopoint with the low voltage (LV) or common and X-line tap windings. The HV and LV windings are disk windings. The tap winding is a multi-start winding and is grounded for the impulse test. The tertiary voltage (TV) winding is a helical winding and is grounded at both ends for the impulse test. The chapter outlines a method for obtaining a set of generator parameters, if they exist, which will produce an impulse waveform closely approximating the ideal one.