渝鄂柔性直流工程接入对500 kV交流线路差动保护影响分析

渝鄂背靠背柔性直流工程投运后可提高相邻区域电网的稳定性,但引入的电力电子设备也将改变系统的故障特征,因此有必要对原有交流保护进行重新校验。在不同的直流输送容量、功率传输方向以及STATCOM无功支撑等运行方式下,分析了柔性直流侧注入交流短路点的故障电气量特性:正负序故障电流幅值受直流控制策略影响较大,正序故障电流幅值随电压跌落程度的加深而降低、负序故障电流被完全抑制,但零序故障电流未受影响。分析发现,交流故障穿越期间的有功电流限幅环节是影响柔性直流侧故障电流幅值大小的主要原因。随后,针对该故障特性可能会影响交流线路差动保护启动判据、降低保护动作速度甚至造成保护拒动的缺陷,提出了交流强故障侧指挥柔性直流弱故障侧并辅以电压减量判据的启动元件优化策略。最后,基于实际柔性直流工程的控制策略及参数,利用PASCAD/EMTDC软件搭建仿真模型验证了所提优化策略的有效性。

Influence study of Chongqing-Hubei VSC-HVDC interconnection on 500 kV AC line differential protection

VSC-HVDC can improve the stability of AC grid, but the electronic equipment also changes the AC fault characteristics, so it is necessary to re-verify the AC line protection connected with DC system. Based on the different operation modes of VSC-HVDC, the fault characteristics on DC side are analyzed. The magnitude of positive and negative sequence fault current is greatly influenced by DC control strategy and the negative sequence fault current is completely suppressed, but the zero sequence fault current characteristics are not affected. The analysis of the AC fault traversal strategy of the project shows that the active current limiting link during the fault crossing is the main reason that affects the magnitude of the soft-side fault current. Aiming at the fault characteristics, an optimization strategy of starting elements is proposed, which is based on AC strong fault side commanding VSC-HVDC weak fault side and voltage reduction criterion. Finally, a simulation model is built in PASCAD/EMTDC software and the effectiveness of the proposed optimization strategy is verified. This work is supported by Science and Technology Project of State Grid Central China Division (No. SGHZ0000DKJS1800142).