Simulation study of power transformer inrush current and internal fault

This paper is devoted to electromagnetic transient model and algorithm of inrush current and internal fault for power transformer. In the paper, it presents transformer model with excitation nonlinear characteristic based on the controlled source theory transformer simulation and damping trapezoidal algorithm. It simulates inrush current and internal fault by that model. When transformer inrush current phenomenon is simulated, usually piecewise linearization method will be adapted to solve the problem of transformer excitation saturation. However, after the comparison of simulated results with different step sizes, the paper finds it has overshoot distortion with larger step size and it increases simulation time with smaller step size. Therefore the paper proposes to predict next simulated exciting current during the simulation procedure. When predicted value is over the saturation threshold, exciting current revised formula will replace the original one. This method effectively solves overshoot distortion problem without decreasing simulation step size and improves simulation efficiency. On the basis of this simulation, it researches on transformer internal fault principle and modellings turn-to-turn short circuit internal fault for transformer. This model is able to simulate transformer turn-to-turn short circuit internal fault directly by setting up the parameter without any external circuit building. These models and algorithm are validated by test case.