直流扰动对交流继电保护动态行为的影响

Impact of DC Disturbances on AC Protective Relaying Dynamic Behavior

针对直流系统对交流继电保护所带来的新扰动,分析了直流系统扰动在交流电网中传递的机理。在数字实时仿真系统(RTDS)上,以南方电网某直流系统为原型搭建了一次系统模型,通过接入实际保护装置,构成闭环的交直流混合仿真系统,分析了交流继电保护在直流系统3类扰动工况下的动态行为。结果表明,直流正常运行工况变化对交流保护的影响较小,不足以引起交流保护的误动。而在直流扰动及异常工况这类扰动中,以换相失败对交流保护的影响最为严重。换相失败时引起的快速功率倒向导致变化量方向元件及负序方向元件有误动的可能,并增大了零序过流保护的保护范围。在直流系统故障时,直流控制保护系统在故障后的快速响应比直流故障本身对交流保护的冲击更大,以双极闭锁最为严重,这会给交流保护带来一系列不良影响。所得结果为全面评估交直流混联系统中的交流继电保护提供了依据。

In allusion to new disturbances that are brought by HVDC system to AC protective relaying, we analyzed the spreading mechanism of disturbances in AC power system. We built a primary system based on an HVDC system in Southern Power Grid on RTDS, connecting with protection devices to constitute the closed loop AC and DC hybrid simulation system to analyze the dynamic behavior of AC protective relaying under three categories of HVDC system disturbance. The results show that the impact of changing HVDC system operating condition under normal operation state is too weak to lead to the mal-operation of AC protective relays. Among all the abnormal conditions, the impact of commutation failure on the communication protection is the most serious. Commutation failure will cause the fast power converse and lead to the mal-operation of the directional protective relays using variation and negative sequence components; it will also extend the protection range of zero-sequence overcurrent protective relays. When faults occur in the HVDC system, the rapid response of HVDC control and protection systems to faults bring greater attack to AC protection than the fault itself. Among all the HVDC system faults, bipolar blocking is the most severe, and it will bring a series of adverse effects to AC protection. The analysis in this paper provides a basis for the comprehensive assessment of AC protective relaying in AC-DC hybrid system.