The influence of temperature differences in moist environments on surface discharges on solid insulation

Résumé

The electric breakdown strength of insulating surfaces in HV systems is known to be greatly affected by moisture deposited on the surface. This has been known for decades in relation to HV outdoor insulation. Another application range, where breakdown voltages as a function of moisture and temperature are relevant is the offshore industry. Subsea applications of high voltages systems can mean harsh temperature conditions in connection with moist environments, such that electrical breakdown conditions in these environments need special focus.
For gas insulated systems the moisture level is normally kept at a preferred minimum to avoid accumulation of condensation on the insulating surfaces, in particular on highly stressed areas.
In this paper has been investigated the correlation between the electric flashover voltage of an insulating surface in moist environments and the condensation process on the insulating surface, as dependent on the dynamic moisture/temperature conditions.
Under extreme environmental conditions, rapid temperature fluctuations can occur and cause accumulation of water droplets on surfaces. A series of tests were conducted on an insulation sample in air, showing the flashover voltage as a function of the temperature difference between gas and insulating surface.
The breakdown field was, as expected, dependent on the formation of condensation on the surface. At high moisture content in the gas no relation between temperature gradient and flashover voltage was found, at moderate moisture the dependency did not give a clear picture.