Studies on stator single-line-to-ground faults protection for a Powerformer considering the winding electromotive force distribution

The Powerformer is very different from a traditional generator in terms of the stator winding material, the winding process and the grid-connection schemes. Therefore, the electrical parameters of the stator winding and the distribution characteristics of the electrical fault component are considerably different from those of a conventional generator. If the traditional protection scheme of a generator is simply applied to a Powerformer, the reliability and sensitivity of the protection will be lowered. Therefore, this paper carefully analyzes the tooth width of a Powerformer, the flux density distribution of the tooth, and the distribution of the electromotive force (emf) between the segments of the winding. A distributed parameter model of a Powerformer is established by considering the emf distribution of the Powerformer windings. Accordingly, the zero-sequence fundamental voltage distribution caused by the emf distribution is analyzed. Then, a stator single-line-to-ground (SLG) relay protection scheme is proposed for the Powerformer. The scheme considers the influence of the emf distribution on the fault characteristics and improves the suitability of traditional zero-sequence fundamental voltage protection for the Powerformer. The simulation results show that the scheme has good sensitivity and reliability.