Proactive study and novel mitigation of MV power system damage due to sub-power-frequency ferro-resonance for a gas plant

Abstract

As projects to expand the processing capacity of a gas plant located in west Texas were pursued, engineering staff observed that the planned incoming medium-voltage power feeder possessed many of the risk factors that have led to increasingly common control-power transformer (CPT) and voltage transformer (VT) failures in industry due to switching. Such failures could involve significant damage and down time. To address these concerns, a computer simulation study was undertaken. As part of initial data gathering, sweep frequency response analysis (SFRA) measurements were performed in an atypical context to establish resonant characteristics of these instrument transformers. When the remote source breaker was modeled to open, connected VTs/CPTs went into severe sub-power-frequency ferro-resonance with probable catastrophic failure. This was verified by Electromagnetic Transients Program (EMTP) simulations as well as by field measurements. The focus of this paper will be on the determination of this unique form of ferro-resonance, identification of risk factors, novel cost-effective solutions, implementation, and field measurement verification of the proposed mitigation solutions. Field measurements have shown high correlations with the EMTP simulations and have verified the effectiveness of the proposed novel mitigation solutions.