Protecting voltage transformers from switching induced transients and ferroresonance

摘要

While preparing a facility for startup, the commissioning process involved 25kV circuit switching that resulted in two voltage transformer (VT) failures. As a result of these failures, the authors conducted a comprehensive investigation of the VT failures. As the investigation proceeded, VT ferroresonance on circuit opening, and high frequency switching transients on closing, emerged as possible root causes of the VT failures. After incorporating extensive transient simulations and three rounds of field transient measurements, the authors designed and implemented a complete solution that included sizing of snubbers to overcome excessive switching transients, and the development of a saturable reactor to protect voltage transformers against the effects of ferroresonance. This paper describes root causes, simulation, field measurements, recommend solutions, and solution implementation. The correlation between field measurements and simulation results show the effectiveness of the implemented solutions.