Overvoltages with remotely-switched cable-fed grounded wye-wye transformers

The system and transformer characteristics which can result in overvoltages and ferroresonance when energizing grounded-wye/ grounded-wye distribution transformers from a remote location with single-pole switches are defined. A qualitative analysis of a system typical of those installed today is presented to show how the overvoltages can occur during single-pole switching. Full-scale laboratory tests were conducted to determine maximum overvoltages and obtain a better understanding of the phenomenon. The results show that distinct responses occur during the single-pole energization, and ferroresonance can occur contrary to statements appearing in many references.