The paper describes the application of an analogue computer to the study of the transient stability of a synchronous generator when subjected to an unsymmetrical fault. The system is analysed by the method of symmetrical components and reduced to a form in which it is readily represented in a direct- and quadrature-axis reference frame, which is most convenient for simulation on an analogue computer.Results are given of a specimen study on a machine connected to an infinite system. Saliency and flux decay are taken into account, and the effect on stability of the negative-sequence torque in the machine is shown. The simulation of the machine is based on the operational form of Park's equations.