The Impact of Series Capacitor on Transmission Line Current Differential Protection

This paper analyses the impact of series capacitor on transmission line current differential protection by means of theoretical analysis and digital simulations. The main influencing factors include series compensation degree, the equivalent impedance of transmission system, load current, the characteristics of MOV, the high current protection for MOV, fault type, fault location, and fault resistance. The simulation results show that The MOV and its high current protection will act to reduce the capacitor impedance significantly and even bypass the series capacitor, during the phase-to-phase fault, so the influence of series capacitor is eliminated. It is discovered that the series capacitor will decrease the sensitivity of the differential current protection for the internal fault, due to the phenomenon of the current inversion. To solve this problem, the measurements to improve the sensitivity of compensated transmission line current differential protection is proposed.