Cross-sectional study between SF6 and eco-friendly gases on dielectric coated electrodes for real-size gas insulated switchgear

The paper reports a new transversal study of dielectric coating effects on high voltage (HV) electrodes in SF₆ and eco-friendly gases like CO₂, dry air and N₂ for real-size gas insulated switchgear (GIS). From a practical viewpoint, the breakdown electric field (BDE) data of the following test conditions are collected; 1) large effective electrode area over about 5 × 10⁴ mm², 2) actual GIS cylindrical configuration of utilization factor of around 0.6, 3) high gas pressures up to 1.9 MPa for actual GIS. The BDEs of dielectric coated electrodes relative to those of bare electrodes (normalized BDEs) are systematically evaluated as a function of dielectric coating thickness and gas pressure. As a result, the normalized BDEs in percentage terms are 105-150% (average value of around 110%), which does not depend on the gases. Remarkable performances of the normalized BDEs of 120-150%, which correspond to nearly 90% of the theoretical BDEs of the gases, are observed in SF₆ and CO₂ for "thick casting epoxy coating", "thin coating of comparable dielectric performance to casting epoxy" and "hard anodic-oxide coating & PTFE-immersion" that have fewer defects inside. The normalized BDEs in N₂, however, show poorer dielectric performances than the other gases especially in the high pressure region above 1.0 MPa. The dielectric coating effects are more pronounced as increasing the thickness for all the gases. The pressure dependences of the dielectric coating effects are not clearly recognized for all the gases and all the coating conditions except for the "thick casting epoxy coating". The coating effect in N₂ decreases slightly as raising gas pressure. The application examples and application limits of the dielectric coatings to GIS are also presented. These new cross-sectional studies of dielectric coated electrodes are an effective approach to get new findings to re- lize a future eco-friendly compact GIS.