Optical-Electrical Investigation of the Partial Discharge Behaviour of a Protrusion in Gas-Insulated Systems Under AC and DC Voltage Stress in SF6 and Synthetic Air

Abstract:
The transportation of electrical energy over vast distances is economically feasible only by using high-voltage direct current (HVDC) links. Gas-insulated systems can be used in these HVDC systems to reduce the footprint of the high voltage infrastructure and to ensure high reliability. Partial discharge (PD) measurements during development, factory, and on-site tests play a key role in satisfying the needs of reliable operation, as well as PD monitoring during operation. To achieve a sound interpretation of the measurement data, the PD behaviour of common defects in gas-insulated systems must be well understood. Therefore, optical-electrical investigations are carried out at a disturbed, weakly-inhomogenous electrode arrangement. The investigations are carried out at one common PD source in gas-insulated systems: a protrusion. An image intensifier camera is used to determine the illuminated area and a photo-multiplier tube to investigate the intensity of the optical emission as a function of the pulseless PD current. The experiments are carried out depending on the gas pressure, the polarity of the protrusion, and the type of the applied voltage. A prominent polarity effect has been shown regarding the apparent expansion and intensity of the discharge. A higher pulseless PD current results in a higher intensity of the discharge. Contrary to the expectations, no differences between AC and DC voltage stress have been shown. In order to contribute to the current developments regarding the usage of alternative insulating gases, the experiments are carried out in the insulating gas sulphur-hexafluoride (SF6) and synthetic air, as one possible alternative. The measurements proof, that optical investigations can be used to assess the intensity of a PD source within a gas-insulated system independent of the insulation gas used.