A novel principle of energy directional protection for powerformer

In this paper, a new principle of stator single-phase ground fault protection for powerformers is proposed, based on the energy function of the fault component. Different from the traditional protection schemes, which need measurements of the zero-sequence fundamental frequency voltage and the zero-sequence third-harmonic voltage at both the neutral and the terminals, the proposed approach detects the ground fault by analyzing the energy direction. Zero-sequence current from the terminal of powerformer and zero-sequence voltage from the busbar are used in this scheme, which can protect 100% of generator windings. Simulation results using Matlab have shown that, under different fault conditions, the new scheme can obtain the high sensitivity and reliability that a large generator requires