Breakdown Characteristics for a Heated Busbar in a Gas-Filled Duct

Breakdown was studied for a 50 mm gap between concentric cylinders at a pressure of 1 atmosphere. The inner cylinder was heated up to 120°C with the outer cylinder at 20°C. Heating caused the alternating and switching impulse breakdown voltages of SF to fall by about 15%; with the inner cylinder at 40°C, the fall was 7%. With the inner cylinder positive and without heating, spark conditioning caused the direct breakdown voltage in nitrogen to increase greatly and the scatter to fall sharply; conditioning was much less effective for negative polarity. The alternating breakdown voltages of SF6 and nitrogen fell slightly with conditioning.