A comparative study of arc behaviour in an auto-expansion circuit breaker with different arc durations

A computational study of the thermal interruption performance of a 145 kV, 60 Hz auto-expansion circuit breaker has been carried out. The pressure peak in the expansion volume has a delay of 2.8–3.4 ms with reference to the current peak when the arc duration varies. A reasonable indicator of the interruption environment is the average mass flux in the main nozzle. The short arc duration case (12.25 ms) is the most difficult case with the lowest critical rate of rise of recovery voltage (RRRV) of 10 kV µ s −1 , just above the initial system applied RRRV of 9 kV µ s −1 . This is a result of an insufficient gas flow cross sectional area between the live contact and the main nozzle to develop rapid gas flow for arc cooling. The auxiliary nozzle plays two roles. It provides blockage in the high current phase to reduce gas exhaustion from the main nozzle into the hollow contact; after current zero the hollow contact shares a considerable portion of the system recovery voltage, especially for the short arc duration case (36%). Therefore the proper design and use of an auxiliary nozzle is key to enhancing the thermal interruption capability of high voltage auto-expansion circuit breakers.