Self-generated overvoltages due to open-phasing of ungrounded-wye delta transformer banks

摘要

Disconnecting one phase of an ungrounded-wye delta transformer bank from the source can result in severe overvoltages due to neutral shift and ferroresonance. Neutral shift overvoltages are quantified and their impact on metal-oxide surge arresters are evaluated. Ferroresonance is shown by test data to occur when low-loss banks, 15 kV and higher, are open phased. Design and operating practices to eliminate or mitigate these self-generated overvoltages are discussed.