IMPULSE VOLTAGE BREAKDOWN IN SF//6 WITH AC AND DC BIAS VOLTAGES.

The paper deals with the test technique of applying superimposed voltages to a single-phase 420 kv coaxial bus duct. The coaxial cylinder arrangement is tested with lightning impulse voltage, while the ion densities in the electrode gap, and thus the statistical time lag, are affected by ac and dc bias voltages. The magnitude of the ac bias voltage has been chosen according to the highest voltage for equipment U//m in order to simulate working conditions. The impulse voltage is applied in different and well define phase angles of the ac bias voltage.