Breakdown Mechanism of Double Breaks in Air Under Lightning Impulse Voltage

The objective of this paper is to reveal the breakdown mechanism of double breaks in air under lightning impulse voltage. Two sphere-to-sphere air gaps was connected in series to model double break circuit breakers. The two air gaps in series underwent standard lightning impulse voltage (1.2/50μs). The two air gaps in series was vertically arranged to form a upper break and a lower break and the total gap distance was 50 mm. Gap distance of the upper break was manually adjusted from 5mm to 45 mm with a step of 5mm. The breakdown photographs were captured by a Canon E80D camera. Experimental Results shows the breakdown phenomenon can be classified into three types. The first type is the breakdown only occurred in the upper break, while there was no breakdown occurring in the lower break. It happened when the upper gap was in the range between 5mm to 15mm The second type is that breakdown occurred in both breaks almost simultaneously. It happened when the upper air gap distance ranged from 5 to 45 mm. The third type is the breakdown only occurred in the lower break, while there was no breakdown occurring in the upper break. It happened when the upper air gap distance was 45mm. The results implied that the breakdown in the double breaks in air was determined by a competition between a dielectric recovery time of a breakdown in one break and the voltage withstanding time of the other non-breakdown break.