Overvoltages on five-legged core transformers on rural electric systems

Abstract

Five-legged core grounded-wye three-phase transformers can cause overvoltage conditions on an open phase when the primary is cable fed and single-phase switched. Field and lab test results on the overvoltage condition are given. An equivalent circuit of the transformer is evaluated and used to simulate lab and field test conditions. Mitigative techniques to minimize the overvoltage condition are discussed.