Dimensioning of protection devices for medium voltage transformers and shunt reactors against very fast front voltages

When interrupting small inductive currents by vacuum circuit breakers, so-called multiple re-ignitions can develop. This is the case when de-energizing medium voltage transformers or shunt reactors, especially if the circuit breaker and the inductive device are connected by a short line segment only. The resulting voltages can seriously affect the insulation of the transformer or shunt reactor, so that mitigation measures should be undertaken if multiple re-ignitions develop. One possibility to prevent multiple re-ignitions is the installation of RC snubber circuits. This paper outlines the theory behind multiple re-ignitions and gives a comprehensive procedure to design suitable RC components.