涌流引起换流变压器零序过电流保护误动的机理分析及对策

Mechanism and Countermeasures of Mal-operation of Converter Transformer Zero-sequence Overcurrent Protection Caused by Inrush Currents

针对高压直流输电工程中换流变压器空载合闸及外部故障切除引起零序过电流保护误动的案例,分析了换流变压器空投和外部故障切除时励磁涌流及恢复性涌流的变化特点及其对零序电流的影响机理。采用基于工程实际参数的高压直流输电的仿真模型,对高压换流站换流变压器空投及外部故障切除导致中性线零序电流幅值较大且衰减缓慢的现象进行了仿真分析,揭示了换流变压器零序过电流保护误动的原因。利用相空间重构技术提出了基于零序电流相空间分布重心幅值变化特征的换流变压器零序过电流保护闭锁新判据,并通过仿真验证了该方案的有效性。

Aiming at the mal-operations of the zero-sequence overcurrent protection due to the energization of unloaded converter transformers and the removal of external fault in the HVDC transmission project,the variation characteristics of the two inrush currents and their influences on the zero-sequence current are analyzed.The phenomenon that the zero-sequence current is provided with quite high magnitude and decays slowly during the two inrush currents is simulated.The reason of the maloperation of the zero-sequence overcurrent protection is revealed.Taking advantages of the phase space reconstruction technique,this paper proposes a novel blocking criterion of the zero-sequence overcurrent protection,which is based on the center-of-gravity amplitude of the phase space distribution of the zero-sequence current.The effectiveness of the proposed criterion is verified by means of simulation tests.