402 / 2017-04-25 20:31:19

Fundamental study on re-ignition process for CO2 blast arcs in a model circuit breaker using synthetic tests highly controlled by power semiconductors

13610,13574,361,IGBT

This paper reports fundamental measurement results on re-ignition process for CO2 arcs in a gas blast nozzle. Re-ignition of CO2 arcs was generated using the developed synthetic test system. The synthetic test system comprises a DC current source for an arc ignition, a half wave AC current source, a DC current source for artificial current zero point and an impulse-like voltage source for application of quasi transient recovery voltage (quasi-TRV). The electric current and voltage were switched by power-semiconductor-switches to guarantee high time-accuracy of the arc current injection and voltage application. In one test, a DC 50 A arc in CO2 gas flow at flow rate of 200 L/min was ignited and sustained in the gas blast nozzle. After the arc had become steady state, a half wave current with a peak of 1.4 kA and a frequency of 50 Hz was injected to the arc. Just before the current zero point of the half-wave AC current, DC 10 A current was intentionally injected to the arc to make an artificial current zero point. After generation of the artificial current zero point, a recovery voltage with a peak of 8 kV and rise rate of 1.8 kV/us was applied between the electrodes with a precise specified delay time td to judge arc re-ignition. During the above processes, the arc behavior and re-ignition process were observed by two high-speed video cameras. The results indicate that td = 25 us involves about 50% probability of arc re-ignition, and longer td decreases the probability. The re-ignition was inferred to originate in thermal mode from joule heating by a small current injection to the residual arc during the quasi-TRV application.