4 / 2019-09-02 09:25:26

Added Protection for Limiting Medium Voltage Regulator Circulating Currents

single phase regulators; medium voltage substation regulators; bypass switching of voltage regulators

Abstract — Distribution utilities know the inherit risks of bypass switching of medium voltage regulators. When bypassing a regulator in any position other than neutral, dangerous circulating currents can develop due to the voltage across the series regulating winding which is in parallel with the shorted regulator bypass switch. Conventional distribution substation protective relays do not adequately protect for circulating currents until the regulator, bypass switch, or leads fail internally and short to ground. This paper will explore a new approach to protect distribution service personnel, regulators, & other equipment from potential harm. The approach would involve the addition of a high saturation current transformer in the primary circuit ahead of the regulators. The protective relays would provide instantaneous tripping of substation high side protection or low side bus tie breaker(s). The relay pickup would be set high enough to avoid instantaneous tripping for downstream distribution faults or normal low side bus faults but would operate in the calculated range of regulator bypass circulating currents. This would serve as an attempt to minimize damage caused when regulators are switched off neutral, enhancing the safety of distribution service personnel while limiting catastrophic damage to substation equipment.
Index Terms —single phase regulators; medium voltage substation regulators; bypass switching of voltage regulators; regulator switching safety