海上风电柔性直流送出线路的纵联保护方法

海上风电柔性直流送出系统常采用伪双极接线。当发生单极接地故障时,电流纵联保护不能可靠地区分区内、外故障。针对该问题,提出了一种适用于海上风电柔性直流送出线路的行波方向纵联保护方案。分析了伪双极直流系统的单极接地故障特征,提出了电流纵联保护在海上风电柔直送出线路的问题。基于行波原理,提出了不受暂态分布电容电流影响的保护方案。该方案利用线路两端的行波方向保护分别进行故障方向判断,然后通过方向纵联判断区内、外故障。PSCAD仿真验证了该方案能快速、可靠地识别故障,且具有较强的抗过渡电阻能力。

Pilot Protection Method for VSC-HVDC Outgoing Line from Offshore Wind Farms

The pseudo bipolar connection is often used in a VSC-HVDC transmission system for offshore wind farms.When a single-pole grounding fault occurs,the current pilot protection cannot reliably distinguish the internal fault from the external one.To solve this problem,a traveling wave directional pilot protection scheme for the VSC-HVDC outgoing line from offshore wind farms is proposed.First,the characteristics of a pseudo bipolar DC system under singlepole grounding fault are analyzed.Then,the problems with the current pilot protection of VSC-HVDC outgoing line from offshore wind farms are put forward.Based on the traveling wave principle,a protection scheme that is not affected by the transient distributed capacitance current is formulated,which uses the traveling wave directional protection at both ends of the line to judge the fault direction respectively,and identifies the internal and external faults through the directional pilot.PSCAD simulation results prove that the proposed scheme can identify faults quickly and reliably,and has strong capability to resist the transition resistance.