BREAKDOWN CHARACTERISTICS FOR A HEATED BUSBAR IN A GAS-FILLED DUCT.

The breakdown characteristics of SF//6 gas at pressures up to 5 atmospheres are of importance for the design of power systems equipment, particularly metal-clad busbar installations and short lengths of gas-insulated cable. 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 degree C with the outer cylinder at 20 degree C. Heating caused the alternating and switching impulse breakdown voltages of SF//6 to fall by about 15%; with the inner cylinder at 40 degree 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 SF//6 and nitrogen fell slightly with conditioning.