Downsizing 550 kV GIS by applying dielectric coating

Abstract

SF 6 gas has been widely used in high voltage power equipment (HVPE) because of its high insulating and arc-quenching performance. However, the reduction of use of SF 6 is highly required, because SF 6 is a potent greenhouse gas. Thus, the improvement of SF 6 gas insulation system is indispensable in order to further downsize HVPEs with reduced SF 6 usage. In this work, we applied a dielectric coating to 550 kV gas insulated switchgear (GIS) and succeeded in downsizing it and reducing its SF 6 gas content.The rated specification and a schematic diagram of the developed 550 kV GIS are shown in Table 1 and Figure 1, respectively (1) . These rated values were decided so as to meet both domestic and foreign standards.A dielectric coated electrode shows better insulation characteristics. By being covered with a dielectric layer, the bad effects of micro protrusions on the surface of the electrode become reduced. This time, a thin dielectric coating whose relative permittivity was 4.0 and whose thickness was several hundred micrometers was applied (2) . Figure 2 shows the Weibull distribution of negative LI breakdown electric field (BDE) of the coated electrode. The BDE (breakdown probability 0.1%) of the coated electrode is normalized by that of the bare electrode. Effective electrode area of both electrode systems is around 10 5 mm 2 . The dielectric coating can improve the dielectric strength of bare electrodes up to 150%.In this work, we applied the dielectric coating to the high-voltage conductor of a current transformer as shown in Figure 3 and reduced the size and weight of the magnetic core and the tank of the current transformer.In addition, we changed the operating system of the gas circuit breaker from a solenoid system to a spring system and applied a new current quenching technique to a disconnecting switch and an earthing switch. Thanks to these new techniques, the size and weight of the GIS were reduced by about 20% and the amount of SF 6 gas use was reduced by 30%.