Voltage escalation and reignition behavior of vacuum generator circuit breakers during load shedding

This paper focuses on multiple reignitions and voltage escalation that may occur during load shedding when vacuum circuit-breakers are used as generator circuit-breakers. The probability of multiple reignitions and voltage escalation is proportional to the arc angle and is very small. However, repeated reignitions and voltage escalation may be observed in vacuum switching devices after opening operations due to their ability to interrupt HF currents. The transformer side capacitance and the magnitude of the load shedding play a significant role in developing repeated reignitions and voltage escalation when vacuum circuit breakers are used as generator circuit breakers. Of particular concern is the case when a protective capacitor is connected to the system side of the circuit breaker. Although this capacitor reduces the magnitude of the of transient recovery voltage, it decreases the transient frequencies and increases the reignition current that flows through the vacuum circuit breaker after a voltage breakdown. In all the cases under study, the reignition/escalation problems are more severe with the protective capacitor connected to the power system for relative low load shedding at short arc angles. This paper reports on many simulated conditions analyzed by using the Electromagnetic Transient Program (EMTP). Ten generators in the range of 50 through 300 MVA have been considered.