Induced Transient Voltage Performance Between Transformers and VCB. Severity Factors and Case Studies

In this paper, a new concept for analyzing the dielectric severity supported along transformer windings when a transformer is submitted to a nonstandardized transient voltage waveform induced by switching operation of a vacuum circuit breaker (VCB) is examined. There are two new factors considered for evaluating the severity supported by the insulation windings in factory and in service. One factor is based on the methodology suggested by the authors called time-domain severity factor and another one is the frequency-domain severity factor. Both methodologies are here applied to two case studies in order to show and compare their capabilities and sensibilities to detect the risk of dielectric failures. The analyzed case studies, performed as practical applications, consist of: 1) a power transformer submitted to damped oscillatory waves at the resonant frequency and 2) a power system consisting of a power transformer connected to a VCB.