Analysis on performance of inrush current identification algorithms under sympathetic inrush

This paper is concerned with sympathetic interaction between two transformers caused by inrush transients in order to discuss whether the existing inrush current identification algorithms are applicable to sympathetic inrush. Based on models of two transformers in parallel and in series operation, the influencing factors such as system resistance, switching time, residual flux and the load of a connected transformer are investigated. Then the inrush current identification algorithms including the scheme of second harmonic restraint, dead angle restraint and waveform symmetry principle are used to test their validation under various conditions of the transformer sympathetic inrush. It is believed that the study will provide a theoretical basis to improve the principle of transformer protection and then reduce the possibility of mal-operation of relays. (6 pages)