Experimental Study of the Breakdown Characteristics of a Gas-Insulated Bus

The area effect in gas-insulated systems on the breakdown voltages and V-t characteristics is studied, using a model bus section of 84 kV single-phase SF6 gas-insulated substation. The model bus, stretched along a straight line, has a number of conical spacers. The breakdowns occur at the shielding electrodes arranged near the spacers. Increasing the number of spacers means an increased chance of breakdown at these shielding electrodes. When switching impulse and ac voltage are applied to the above system including many spacers, the breakdown voltage distribution has a range somewhat lower than that of one spacer. This phenomenon is caused by the increase of weak points on the electrodes. When steep front impulse voltages are applied, the breakdown distribution of many spacers is very similar to that of one spacer, in contrast to the cases of switching impulse and ac voltage. This relative insensitivity of breakdown voltage to the system scale suggests a mechanism other than the statistics of weak points. The experimentally obtained overall V-t characteristic of this system is found to conform to the empirical formula proposed from small scale experiments.