特高压换流变故障性涌流产生机理及其对差动保护的影响

从磁链变化角度分析特高压换流变压器(简称换流变)阀侧发生单相接地故障时由换流阀单向导通性引起的励磁涌流(定义为故障性涌流)的产生机理和变化特点。以特高压直流输电系统中某一换流变为例,分析故障性涌流对换流变差动保护动作特性的影响。研究结果表明,故障性涌流容易导致换流变区外故障转区内时差动保护误闭锁。针对该问题,进一步分析发现,由于换流阀的单向导通性使得转换性故障发生后差动电流的直流分量存在由负极性到正极性反转的特征,进而利用该特征提出换流变差动保护闭锁逻辑改进判据。仿真结果证明了所提判据的可靠性。

Fault inrush current mechanism of UHV converter transformer and its impacts on differential protection

The inrush current caused by the unidirectional conductivity of the converter valve when the single-phase grounding fault occurs on the valve side of the UHV converter transformer is defined as fault inrush current, whose mechanism and variation characteristics are analyzed from the aspect of the flux variation. Taking a converter transformer in UHVDC transmission system as an example, the influence of fault inrush current on the operation characteristics of differential protection is analyzed. The results show that the fault inrush current easily causes differential protection of converter transformer to be locked improperly when external fault transfers to internal fault on valve side. Aiming at this problem, further analysis shows that the unidirectional conductivity of the converter valve causes the DC component of the differential current to be reversed from negative to positive polarity after the occurrence of the transferring fault, based on which, the improved logic criterion of lock logic is proposed for the differential protection of converter transformer. The simulative results verify the reliability of the proposed criterion.