To analyze the over-voltage between two arms of a tight coupling reactor in non-simultaneous breakingcondition for the parallel breaking scheme based on tight coupling reactor

this paper briefly introduces the scheme oftaking the tight coupling reactor-based parallel vacuum circuit breaker as large capacity laboratory test generator cir-cuit breaker（GCB）. The over-voltage between two arms of the tight coupling reactor in non-simultaneous breakingcondition is analyzed. A mathematical expression of the over-voltage is proposed

and the maximum over-voltage insteady state and transition process is calculated by adopting the circuit principle analysis. Moreover

an over-voltagesuppression method based on resistor-capacitor protection is also proposed according to the theoretical results. In ad-dition

a wiring mode of Chanzhou large capacity laboratory test generator circuit breaker and an over-voltage protec-tion measure are offered.