一种新的综合阻抗计算方法

Improvement of integrated impedance calculation

分析了线路相间电容对综合阻抗的影响,故障时健全相的综合阻抗会因线路相间电容的影响而较大程度偏离线路的对地电容阻抗,且随故障点和故障类型的不同而有较大波动。在整定综合阻抗纵联保护判据时要考虑此因素,灵敏度有所降低。提出了新的消除相间电容电流影响的综合阻抗计算方法,计算时在各相差动电流中减去该相流向其他两相线路的电容电流,使得健全相的综合阻抗计算结果仅与线路对地电容有关。而新方法对故障相的综合阻抗计算结果影响较小。EMTP数据仿真结果证明了新方法的有效性。

The influence of phase-to-phase capacitance on integrated impedance is analyzed. lhe integrated impedance of the sound phase becomes much lower when fault occurs because of the inter-phase capacitance and varies heavily with fault location and fault type ,which has to be considered during the parameter setting of integrated impedance pilot protection criterion and its sensitivity is thus reduced. A calculation method which eliminates the influence of phase-to-phase capacitance on integrated impedance is presented. The influence can be eliminated by subtracting the capacitive currents flowing to other two phases from the differential current of each phase,so that the integrated impedance of sound phase is decided only by the line to ground capacitance,which has little influence on the integrated impedance of faulty phase. Simulation with EMTP verifies its validity.