Single-Phase Ferroresonance in an Ungrounded System Causing Surge Arresters Failure during the System Energization

Ferroresonance often occurs in power systems during system switching actions, which can create overvoltages and pose great risks to the equipment safety. In this paper, a single-phase ferroresonance incident during a system energization is presented, which occurred at a single-phase station service transformer in an ungrounded system, causing surge arresters' failure. The incident is investigated through PSCAD simulations and analytical analysis. The relay field record is used to compare with the simulation results in order to validate the PSCAD simulation model. Several case studies are conducted using PSCAD simulations to evaluate various contributing factors to this ferroresonance incident. The root cause of the incident is found to be the lack of ground during energization in the system. Field practices are recommended to be implemented before the system energization to avoid such incidents, which were proved to be effective by successfully energizing the system in the field following these practices.