Improvement of dielectric performance of solid/gas composite insulation with YSZ/ZTA coatings

N₂ has been introduced to gas-insulated switchgears (GIS) as an environmentally friendly insulation medium for SF₆ gas. Considering the low breakdown strength of N₂, it's essential to apply a dielectric coating on part of the electrode in GIS. In the current work, yttria-stabilized zirconia (YSZ) and zirconia-toughened alumina (ZTA) ceramics are tactfully applied as dielectric coating materials and successfully coated on the surface of rod electrode via high efficiency supersonic atmospheric plasma spraying method. It is demonstrated that both YSZ and ZTA have excellent thermal stability. In the measured frequency range 10^-2-10⁶ Hz, the dielectric constant (ε') decreases with the increase in frequency. At measured temperatures (0-140 °C), ε' increases from 15.45 to 16.31 for YSZ ceramic at 1 kHz, while it varies between 30.23 and 39.34 for ZTA ceramic. As compared to that of bare electrode, the 50% BDV (U₅₀) of solid/gas composite insulation system is significantly improved when using YSZ and ZTA as coating materials. Furthermore, the U₅₀ increases with the increase of coating thickness. For the electrode coated with ZTA ceramic (500 μm), the U₅₀ value reaches to 86 kV, which is enhanced about 21.13% in comparison with that of bare electrode. With respect to YSZ ceramic coating (500 μm), a higher U₅₀ value of 88 kV is obtained. This is mainly due to that YSZ has a lower permittivity, which can generate a more uniform electric field distribution between the rod and plane electrodes, bringing about a higher breakdown voltage.