The paper describes a digital simulation of a 3-phase model of a synchronous generator, directly in phase quantities. It is shown how, on the assumption that saturation arises principally from the resultant direct-axis current, the corresponding nonlinearities may be included in the equations of the model. The equations are developed in a form suitable for the study of both symmetrical and asymmetrical operating conditions of an isolated machine, and a digital-computer program using predictor-corrector techniques is described for their solution. Predictions of the transient conditions following a variety of switching operations are shown to compare closely with experimentally obtained results on a 15 kV A machine.