利用时域波形比对的高压直流输电线路电流差动保护

高压直流输电线路电流差动保护受电容电流和数据不同步影响,选择性和速动性不高。通过对高压直流输电线路的故障特征分析发现,在时域平移一端数据,并对比差动电流的大小,可以进行区外故障数据同步的识别。对于区外故障,由于没有故障点注入电流的影响,差流在数据同步时最小,数据不同步时明显增大;对于区内故障,受故障点注入电流的影响,无论数据同步与否,差流的值总是很大。在分布参数模型下构造时域电流差动保护,利用上述差流特征可以获得区外故障实时的数据不同步时间信息,并在时域中实时调节差流和整定门槛,保证了差动保护不因区外故障数据不同步而误动。仿真验证表明所述方法能够可靠快速灵敏地识别高阻故障,不受分布电容影响,并且不需要两端数据严格同步。

A Current Differential Protection Using Time-domain Waveform Comparison for HVDC Transmission Lines

High voltage direct current (HVDC) differential protection is affected by distributed capacitance current and unsynchronized two ends data. A novel current differential protection unaffected by unsynchronized data is proposed. Based on an analysis of fault characteristics with transmission line two ends unsynchronized data, the data synchronization status of external faults can be identified by comparing differential current under a distributed parameter model in time domain. For external faults, free from the influence of fault point current, differential current reaches its minimum value when data is synchronized and augmented significantly when data is unsynchronized. For internal faults, with the influence of fault point current, differential current always has great value regardless of synchronization status. The criterion of the proposed approach is composed under the distributed parameter model in time domain, and data unsynchronized time of external faults is identified by using the characteristic above, which is used to adjust operation current along with the threshold to prevent false tripping. Simulation results have verified that the new approach can identify high resistance faults reliably and sensibly. The proposed approach is not affected by distributed capacitance current nor does it require precise synchronization of two ends data.This work is supported by National Natural Science Foundation of China (No. 51177128, No. 51477131) and Ph.D. Programs Foundation of Ministry of Education of China (No. 20110201110056).