高压直流输电线路电流差动保护新原理

A New Current Differential Protection Principle for HVDC Transmission Lines

通过分析直流系统控制特性作用下的输电线路故障特征,提出了一种新的高压直流输电线路电流差动保护原理。在分布参数模型基础上,利用两端换流站电压、电流量分别计算区内某点处两侧电流之和。区内故障时,得到的电流与故障支路电流相关,其值较大;区外故障及正常运行时,计算得到的是误差电流,其值很小。与行波保护相比,该保护能够可靠识别区内、外故障,可以在故障全过程投入,且具有可靠性高、对采样频率要求低、计算简单等优点。与现有的直流线路电流差动保护相比,该保护不受分布电容电流影响,故在暂态过程即可动作而无须等待暂态过程结束,动作速度快。仿真结果表明,在各种工况下,该保护都能灵敏、可靠地区分区内、外故障。

A new current differential protection （CDP） principle for HVDC transmission lines is proposed in this paper by analyzing the fault characteristics of DC transmission line. Based on the distributed parameter model, the current at any point of transmission line can be calculated with the voltages and currents measured at local and remote convert stations. When a fault occurs on HVDC line, the sum of the current calculated with each station’s data depends on fault current and can reach maximum at the fault point. When no fault occurs or a fault occurs beyond HVDC line, the sum of the current is small （it is near to zero in theory）. According to this feature, CDP can be implemented. Compared with traveling wave protection, CDP can effectively identify inner or external fault and can work in all fault process, and it features high reliability, lower sample frequency and simple algorithm. Compared with the traditional CDP used in HVDC line, it is independent of the distributed capacitance over the long transmission line, therefore it can operate well in the transient process and has high speed. The simulation results show that the method can identify inner or external fault reliably and rapidly.