Measurement and behaviour of partial discharge
for SF6 substitute gases in HVDC GIS/GIL

Abstract

Partial discharge measurement is considered as one of the most powerful monitoring and diagnostic tools for the detection and recognition of defects for high voltage equipment. It has been widely deployed in different kinds of equipment, including High Voltage Alternative Current (HVAC) Gas Insulted Switchgears (GIS) filled with SF6. However, SF6 is classified as one of the gas with very high greenhouse effect (Global Warning Potential – GWP) and has been included in the Kyoto Protocol list. Therefore, new fluorinated gases such as fluoronitrile (CF3)2CFCN – NovecTM 4710 (FN) and fluoroketone CF3C(O)CF(CF3)2 – NovecTM 5110 (FK) have been developed and today investigated in AC GIS as mixtures with different buffer gases such as CO2 or dry air. They present promising characteristics to replace SF6 including high dielectric strength, non-flammability and low GWP. The European Union (EU) funded project “Progress on Meshed HVDC Offshore Transmission Networks” (PROMOTioN) addresses the challenges for meshed HVDC offshore network development. The compactness, the high reliability and the resistance to extreme weather conditions of HVAC GIS have led to investigate the potential of this technology to HVDC network in PROMOTioN, Workpackage 15. It is thus necessary to anticipate the development of SF6 free DC GIS and its monitoring system based on PD measurement in order to reach the same reliability level as it is on AC GIS. The dielectric withstand of different FN and FK gas mixtures have been studied in different works but few works related to partial discharge behaviour were addressed. Moreover no information about the monitoring or defect detection by partial discharge and no service experience are available.

For this purpose, this paper presents in a first part an overview of different partial discharge measuring systems, including conventional and Ultra High Frequency (UHF) method and alternative measuring techniques such as light emission and also a new technique specifically developed for HVDC GIS based on the measurement of induced PD pulse current on the GIS enclosure by magnetic field sensor. In a second part, as the partial discharge experience feedback is still missing for HVDC and even more for SF6 alternative gases, partial discharge measurements with protrusion defect on high voltage.

C. TOIGO, T. VU-CONG, M. DALSTEIN, F. JACQUIER, A. GIRODET

Presented at CIGRE e-session 2020