基于电流特征量相关系数的UHVDC线路高阻接地故障保护

Pilot Protection for High-resistance Grounded Fault of UHVDC Transmission Line Based on Correlation Coefficient of Current Variable

特高压直流输电线路距离长、跨越区域复杂,故障发生率较高,常规电流差动保护的快速性较差且耐过渡电阻能力有限,为此提出一种基于电流特征量相关系数的线路高阻接地故障保护新原理。首先利用状态空间分析得到直流线路两端稳态电流时域表达式;随后,分析电流成分,发现其衰减振荡项中的角频率可反映线路对地故障,且可用相关系数衡量。接着利用两端电流和、电流差进一步突出角频率特征,并计算两者的相关系数构造判据特征量。在此基础上,根据判据特征量在区内外故障的不同特征,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,且对信道要求低,利于工程应用。仿真结果表明,该方案耐受过渡电阻能力和快速性优于常规电流差动保护。

Ultra high-voltage direct current(UHVDC)transmission lines,crossing a long distance and complex regions,usually have a high fault rate.However,conventional differential current protection has shortages in tripping speed and adaptability to high-impedance faults.A pilot protection scheme based on correlation coefficient of current variables is proposed.Time-domain expressions of steady-state currents at both terminals of DC line are firstly derived by using state-space analysis.Then,the current components are analyzed,and the angular frequency of the damped oscillation term can reflect the grounded fault and can be measured by correlation coefficient.Moreover,the sum and difference of currents at both terminals are used to highlight angular frequency characteristics,and correlation coefficients of them are calculated,followed by the construction of relay criteria.Subsequently,by virtue of different characteristics of internal and external faults reflected by relay criteria,a pilot protection principle is proposed considering the effect of control features.The principle,without compensation requirement of distributed capacitor current,has lower requirements on communication channels,which is easier to be applied in the process of construction.Comprehensive simulation experiments demonstrate that the proposed scheme has better performance while dealing with high-impedance faults of UHVDC lines,and faster operation than the conventional differential current protection.