Mitigation of transformer inrush current associated with DER facilities connected on the distribution grid

Integration of Distributed Energy Resources (DER) to the distribution system brings technical challenges due to the inrush current resulting from the energization of power transformer. Besides impacting power quality, transients may cause undesired protection tripping. This paper compares different techniques used to mitigate these transients. It also presents results from research carried out on Hydro-Québec Research Institute´s distribution test line (IREQ). Outcomes of additional tests using Gang Operated (GO) circuit breakers (CB) and Controlled Switching Device (CSD) are also presented. This approach solves the problem of the re-energization of a windmill on a live windfarm, in order to minimize transients and sympathetic interactions between the transformers in the DER facility. Since the CS solution virtually does not require any installation footprint, it has the advantage of being easily adapted to the existing switchgear designs integrated at the base of the wind towers.