Countermeasure on Preventing Line Zero-Sequence Overcurrent Protection From Mal-Operation Due to Magnetizing Inrush

With the capability of limiting the increasing short-circuit current of power grid, high voltage built-in high-impedance transformer (HVBHT) has been widely used in recent years. However, due to its special structure, the magnetizing inrush with high magnitude and slow decay is likely to occur during no-load energization, which may lead to the mal-operation of zero-sequence overcurrent protection of the upstream transmission line. This phenomenon has become a serious problem in the actual production in China. To solve this problem, a modified time difference method is proposed based on the substation area information, so as to accurately identify the magnetizing inrush, internal fault as well as current transformer saturation. Subsequently, a countermeasure on preventing line zero-sequence overcurrent protection from mal-operation due to HVBHT energization is proposed. Simulation results based on PSCAD indicate that the proposed protection scheme can cope with various kinds of energization and fault situations effectively. Thus, the correct operation of zero-sequence overcurrent protection can be ensured. Compared with other existing identification methods of magnetizing inrush, the proposed method shows great superiority.