Measurement and Analysis of Partial Discharges in HVDC Gas Insulated Substations

The measurement of Partial Discharges (PD) in Gas Insulated Substation (GIS) enables to identify and analyse various types of defects that can result in electrical breakdown. Unlike the case of alternative current, the measurement techniques of PD in direct current are less mature and require more investigations for the development of suitable recognition tools; the mechanisms involved in direct current being different from those of alternative current. This paper deals with experimental characterization of a real-size part of a 320 kV GIS filled with various gases (SF6, N2, Air), at room temperature and for a pressure range from 0.1 to 0.5 MPa. To characterize the partial discharge signatures of existing defects, a protrusion fixed on high voltage conductor and a free metallic particle are considered. The test are achieved according to IEC 60270 recommendations. The experimental results reveal different regions with characteristic apparent charge distribution and PD pulse frequency. It is also evidenced that the variation of pressure and the voltage polarity influence the succession of regions. Different PD patterns are identified depending on the considered defect and polarity.