Analysis of Voltage Distribution in Transformer Windings During Circuit Breaker Prestrike

In this work, the circuit breaker prestrike effect that occurs during energizing a distribution transformer is investigated. An experimental test setup that consists of a supply transformer, a vacuum circuit breaker (VCB), a cable and a test transformer is built, and prestrikes in the VCB are recorded. The test transformer is a prototype distribution transformer, with installed measuring points along transformer windings in each phase. The transformer is modeled by lumped parameters extracted from telegrapher's equations in discrete form. Voltage oscillations during switching-in operations are recorded and calculated with and without a cable installed between the VCB and the transformer. Computed voltages show good agreement with the measured voltages. Described method can be used by transformer manufacturers to estimate voltage wave forms during switching or lightning, and to provide useful information for insulation coordination studies