Investigation of Internal Fault Modeling of Powerformer Part I: The Machine Model

This paper discusses the set-up of a mathematical model of powerformer, a new type of salient pole synchronous machine, for analyzing internal phase and ground faults in stator windings. The method employs a direct phase representation considering the cable capacitance. To effectively implement the internal fault simulation, the magnetic axis locations of fault parts are arranged appropriately. Besides, all machine windings supposed to be sinusoidally distributed in space and the system is magnetically linear. With above-mentioned assumptions, the current equivalent equations, voltage equivalent equations and the rotor motion equations are formed and combined to implement the fault simulations. Simulation results showing the fault currents, during a single phase to ground fault, a two phase to ground fault and a phase to phase fault, are presented. With the data generated by this internal fault simulation model, the protection scheme used for powerformer can be validated and improved accordingly.