A Countermeasure for the Restraint of the Differential Protection in Converter Transformer

摘要

The differential protection is one of the most common main protections of the converter transformer. In order to deal with the mal-operation of the differential protection when magnetizing inrush occurs, it's highly recommended that the 2nd order harmonic restraint criterion should be introduced to restrain the differential protection when magnetizing inrush occurs. However, there will be a new problem after the introduction of the 2nd order harmonic restraint criterion when internal faults occur. When faults occur at the inverter side, the faults may cause the inverters happen commutation failure, which may produce abundant harmonic components. Then, the 2nd order harmonic, which is caused by the commutation failure, may be high enough to make the 2nd order harmonic restraint criterion restrains the differential protection in converter transformer. In order to avoid the restraint of the differential protection, this paper proposes an effective countermeasure by using the commutation failure protection, and proves the effectiveness of the countermeasure via simulations.