换相失败对换流变差动保护影响分析及对策研究

Influence of commutation failure on differential protection of converter transformers and its countermeasures

分析了换相失败造成换流变饱和的机理,针对故障恢复期间发生换相失败时换流变差动电流与故障电流特征,研究了故障恢复期间发生换相失败与故障差流共同作用时换流变的动作性能。研究结果表明,在故障恢复期间,换相失败对恢复性涌流具有助增作用。此时换流变若发生较轻微的区内故障,差动保护存在延时动作的风险,其速动性无法得到保证。最后,提出了一种基于离散Fréchet距离的保护方案,并通过仿真对该方案进行了验证。结果显示,在故障恢复期间发生换相失败与故障共同作用时,区外故障能有效闭锁,区内故障能快速进行识别,使差动保护正确动作。

The saturation mechanism of converter transformer caused by commutation failures of converters is analyzed first.Aiming at the characteristics of differential current and fault current of converter transformer during commutation failures under fault recovery,the performance of converter transformer differential protection when it is simultaneously affected by both commutation failures and fault differential current during the fault recovery is studied.It is revealed that,during the fault recovery,the commutation failure has a facilitating effect on the recovery inrush.Under this situation,when minor internal faults occur,the differential protection has the risk of delayed operation,and its rapidity is unable to be guaranteed.Finally,a protection scheme based on discrete Fréchet distance is proposed and its performance is evaluated by simulation tests.The results indicate that when commutation failures and faults simultaneously occur during fault recovery,the proposed scheme can effectively block the protection under an external fault,and rapidly identify an internal fault so as to trip the differential protection correctly.