Evaluation of Voltage Sag Mitigation by Resonant Grounding Comparing to Existing Direct Grounding in Provincial Electricity Authority

This paper proposes a practical mitigation solution to the voltage sag problem by resonant grounding for a 22-kV distribution system of Provincial Electricity Authority (PEA) at the Patumthani 1 substation in Pathumthani province in Thailand. A computer simulation by ATP-EMTP was carried out to investigate the voltage sag impact at the low voltage side of the delta/wye distribution transformer connected at a fault location in the existing solidly grounded system and proposed resonant grounded system. The results indicate that the proposed resonant grounding can help all customers connected at the same bus survive from voltage sag problems and also keep the customers on the faulty feeder connected to the system being continuously supplied for single-to-ground faults. To evaluate the benefits of the resonant grounding, the different voltage-tolerance curves are proposed by Information Technology Institute Council (ITIC) curve and laboratory testing of Personel Computer (PC) curve, Programable Logig Coltroller (PLC) and Adjustable Speed Drive (ASD). The saving from the cost of customer interruption and voltage sag is calculated comparing between the existing solid grounding and the proposed resonant grounding with different voltage-tolerance curves