Estimating grounding resistance of medium voltage cables using measured sheaths current

Abstract

The online estimating of grounding resistances of medium voltage cable sheaths makes it possible to monitor their zero-sequence impedance. This paper proposes a cable grounding resistance estimation method for three-phase single-core cables. The method uses the phasors of measured voltage and currents of the cable sending end and the Pi-model of the cable to estimate the current of the main conductor at the receiving end. Then, using measured currents at the cable's receiving end, the sheaths' grounding resistances at both ends of the cable are calculated. A set of 1600 transient power system simulations proves the method is effective. The error is less than 71 $m$Ω varying short circuits level, X/R ratio, cable loading, voltage unbalance factor, and voltages and currents magnitude error.