线路电阻对SPD配合的影响分析

为了准确分析用于低压配电系统过电压防护的多级浪涌保护器(SPD)的配合问题,通过建立SPD配合电路的拉氏运算方程,求解并分析线路电压降的解析解,理论研究了线路电阻对低压系统SPD配合的影响,指出忽略线路电阻将使通过后级SPD的电流被夸大,造成配合分析的不准确。理论分析表明,在前级SPD的残压一定的情况下,2级SPD间的电压差主要由后级SPD的V-I特性曲线、线路电感和线路电阻共同决定。通过对多种线路模型的SPD配合进行仿真计算,验证了理论分析的正确性。

Analysis of Effects of Line Resistance on Cascaded Coordination of SPDs in Low-voltage AC Power Systems

To accurately analyze the coordination problems of cascaded SPD(surge protective device) located in the low-voltage AC power systems for over-voltage protection,the Laplace operational equations of lumped parameter circuit of cascaded SPDs are established.Some reasonable simplifications are adopted to simplify the calculation and analysis process.Among these simplifications,the waveform of residual-voltage of the SPD installed at the service entrance is approximately denoted by the three main phases: linearly ascending phase,saturation phase and the descending phase,and the first two phases are used in the analysis.Analytical solutions of the voltage drop on the line connecting SPDs are derived from Laplace operational equations and are analyzed to show the effect of line resistance on the coordination of SPDs,especially for the dissipated current through the downstream SPD.According to the analysis,it is found that if the line resistance is ignored,the current flowing through the downstream SPD will be magnified too much,so that the accuracy of coordination.Meanwhile,the theoretical analysis shows that it is far from enough for evaluating the coordination effects only according to the magnitudes of U1mA of the cascaded SPDs.The voltage drop along the connecting line and the coordination effects is mainly decided by the common effects of the V-I characteristic curve of the downstream SPD,line inductance and line resistance.For different lumped-parameter line models,the coordination schemes of cascaded SPDs are studied by using simulation software to prove the validity of theoretical analysis.