The coupling between coils in power transformer causes the complexity of external characteristics of internal short circuit faults. In order to design and adjust the relay protection correctly

it is necessary to model and simulate the internal short circuits in details for different type of power transformers. An equivalent circuit model and an algorithm for modeling internal short circuits in power transformer windings are proposed. The several kinds of faults including short circuit to ground

inter-turn short circuits and inter-phase short circuits are simulated for a doublewinding power transformer and the external characteristics with the fault position variety are given.