A Case of Abnormal Overvoltages in a Petersen Grounded 132 Kv System Caused by Broken Conductor

This paper analyzes stationary overvoltages in Petersen grounded systems resulting from a broken phase conductor. The analysis is done with basis in a real case where the overvoltages caused extensive damages and outages. It is shown that a requirement for high overvoltages to result is the combination of the following: The fault occurs on a radial connection that has substantial generation on one side only, the total compensation is close to 100%, and the compensation of the two subnetworks defined by the fault is far from 100% (one subnetwork is undercompensated and the other is overcompensated). These conditions were all met for the network subject to investigation. Overvoltages calculated by a simple model compare favorably with recorded results. The overvoltages are shown to be strongly dependent on the compensation level, the compensation distribution, and the shunt conductance to ground, and the load. A least squares method has been developed for estimating the shunt conductance based on a measured resonance curve.