Fundamental investigations on the partial-discharge behaviour in gas-solid insulating systems under DC voltage stress

• Applicant: Professor Dr.-Ing. Steffen Großmann
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 379542208

The transmission of large amounts of energy using low-loss high-voltage direct-current transmission takes into account the growing integration of renewable energy sources in a modern and sustainable power supply. Encapsulated gas-insulated systems satisfy to a vast extent, the simultaneous requirements of high reliability, independence from environmental conditions and compact systems for both offshore-usage and in densely populated areas. The reliability of these gas-solid insulating systems can be significantly reduced due to partial discharges at assembly or operational related defects. In comparison to AC voltage stress, DC operation forces a fundamentally changed partial discharge behaviour. Hence, the well-known physics of discharge processes are strongly influenced by additional effects. They are including an oriented charge movement, the accumulation of space and surface charges and a changed discharge formation due to pulseless pre-currents. For this reason, basic studies on the influence of these processes on defect-based partial discharges in gas-solid insulation systems become mandatory. For this purpose, the time-dependent discharge behaviour is studied in a model arrangement, under the influence of the insulation gas pressure, the electric field strength and the voltage polarity. Specifically, the influence of space charges on the partial discharge inception, the stability of the discharges and the charge and discharge behaviour of the gas-solid interface will be studied. Furthermore, a characterization of the type of the discharges with respect to conducted and field-bound optical and electrical parameters in time and frequency domain is planned. With respect to foreseeable technical and political developments, the investigations will not only be carried out with the approved insulation gas sulphur hexafluoride, but also with synthetic air as a natural alternative. Thus, new fundamental models for the partial discharge formation in insulating gases under DC voltage stress will be developed, which facilitate an accelerated development of a hybrid power supply infrastructure, including AC and DC components. It is expected that the findings of the investigations will allow reliable conclusions on partial discharge characteristics, which will enable the identification of defects under DC voltage stress. Additionally, the investigations provide an essential component for the calculation of transient processes for dimensioning and further development of gas-solid insulating systems. Due to the consideration of the long-term behaviour, an essential contribution for the currently missing standardisation of test procedures for DC equipment is accomplished. Overall, the investigations will ensure a reliable long-term service of the innovative energy supply infrastructure.

• DFG Programme: Research Grants