Influence of humidity on conduction processes in gas-insulated devices

• Main Authors: Malte Tschentscher, David Graber, Christian M. Franck
• Format: Article
• Language: English
• Published: Wiley 2020-03-01
• Series: High Voltage
• Subjects: partial discharges; epoxy insulation; insulators; surface charging; flashover; electric strength; aluminium compounds; filled polymers; conduction process; gas-insulated systems; partial discharge inception voltages; homogeneous field arrangements; inhomogeneous field arrangements; insulator flashover voltage; ion currents; gas gaps; highly precise humidity control circuit; gas-insulated devices; insulation gas; insulator surfaces; low-field conduction phenomena; breakdown strength; frost-point; sulphur hexafluoride; al(2)o(3)-filled epoxy resin insulators; microdischarge intensity; technically rough electrodes; charge generation; electric field; surface-charge accumulation; pressure 0.45 mpa; temperature -25.0 degc to -5.0 degc; al(2)o(3); sf(6)
• Online Access: https://digital-library.theiet.org/content/journals/10.1049/hve.2019.0315

Humidity has been considered as one of the main influencing factors that determine the conduction processes and electric strength of gas-insulated systems. Whereas in the past, various studies focused on the change in the partial discharge inception voltages, breakdown strength of homogeneous and inhomogeneous field arrangements, and insulator flashover voltage, recent studies have investigated the changes in ion currents measured through different gas gaps. In the framework of this contribution, a highly precise humidity control circuit has been developed to analyse the significance of humidity in the range from −25 to −5°C frost-point, which is fully applicable to operating gas-insulated devices. Using sulphur hexafluoride (SF(6)) as the insulation gas at 0.45 MPa, Al(2)O(3)-filled epoxy resin insulators, and technically rough electrodes, the humidity was found to significantly influence the intensity of microdischarges at interfaces. Charge generation from microdischarges at the interfaces substantially increased with increasing humidity. For an electric field of 5 kV/mm that were applicable to the dimensioning of gas-insulated devices, humidity strongly influences the charge provision from technically rough interfaces and potentially contributes to the surface-charge accumulation at insulator surfaces. On the other hand, for low-field conduction phenomena, no increase in the ion currents from natural ionisation or electrophoretic conduction was observed. For the investigated range of parameters, humidity is expected to be highly relevant for the design of gas-insulated devices.