基于电流特征量相关系数的UHVDC线路纵联保护新原理

特高压直流输电线路长、发生故障概率大,其常规纵联电流差动保护的快速性较差且耐受过渡电阻能力有限。相关系数可定量描述两个变量的变化趋势,且不受变化幅度影响。为此,首先立足直流线路故障暂态特性,利用两端电流和、差计算相关系数,构造了判据特征量。其次,基于判据特征量在区内、外故障的不同特性,计及直流输电系统控制特性,提出了纵联保护新原理。该原理无需电容电流补偿,耐受过渡电阻能力和快速性优于常规纵联电流差动保护;且对信道要求低,利于工程应用。最后,利用PSCAD/EMTDC仿真验证了新原理的有效性。

A new pilot protection for UHVDC lines based on correlation coefficient of designed current variables

Ultra High Voltage Direct Current (UHVDC) transmission lines usually go across long distance, and hence are exposed to high fault probabilities. Its conventional current differential protection lacks rapidity, as well as adaptability to high fault resistances. The correlation coefficient can be used to quantitatively describe the trend of two variables without being influenced by the magnitude of variations. Accordingly, based on the fault transient characteristic of DC lines, characteristic quantities for relay criteria are generated first by calculating correlation coefficients of the sum and difference of both-terminal currents. Subsequently, considering different characteristics in terms of internal and external faults reflected by relay criteria and the effect of control systems, a new pilot protection principle is proposed. The principle, without compensation requirement of distributed capacitance current, has better capability to discriminate UHVDC line faults with high fault resistance, and faster reaction than current differential protection. It also has lower requirements on communication channels, which means easier to be applied. Finally, the effectiveness of the proposed protection is verified by PSCAD/EMTDC simulation. This work is supported by National Natural Science Foundation of China (No. 51877084), Natural Science Foundation of Hebei Province (No. E2018502063), and Fundamental Research Funds for the Central Universities (No. 2017MS096).