Transformer Sympathetic Inrush Characteristics and Identification Based on Substation-Area Information

Sympathetic inrush is a magnetizing inrush phenomenon between two or more transformers when one of them is switched on under no load condition. This phenomenon has caused transformer differential protection maloperation in several cases due to the failure of the second harmonic restraint algorithm. Sympathetic inrush is very different in both the mechanism and characteristics from general inrush generated by a single transformer. Hence, a special identification method is required. The physical mechanism of sympathetic inrush between transformers is thoroughly studied to understand its characteristics, especially the alternate saturation feature. A substation-area information-based identification method is proposed to identify sympathetic inrush of the in-service transformer (IT). The alternate opposite saturation characteristic is used in the method. Both locking and unlocking criteria are designed for current differential protection to prevent the IT protection from maloperation. The proposed method is verified to be effective under different system conditions by simulations conducted in PSCAD and RTDS.