420kV HV Gas Insualted Switchgear(GIS)

Insulation Principle:

• In an electric field, the electrons in SF₆ gas molecules are slightly displaced from the nuclei. However, due to the stability of the SF₆ molecular structure, it is difficult for electrons to escape and form free electrons, resulting in high insulation resistance. In GIS (Gas-Insulated Switchgear) equipment, the insulation is achieved by precisely controlling the pressure, purity, and electric field distribution of the SF₆ gas. This ensures a uniform and stable insulating electric field between the high-voltage conductive parts and the grounded enclosure, as well as between different phase conductors.

• Under normal operating voltage, the few free electrons in the gas gain energy from the electric field, but this energy is not sufficient to cause collision ionization of the gas molecules. This ensures the maintenance of the insulating properties.

Due to the excellent insulation performance, arc extinguishing performance and stability performance of SF6 gas, GIS equipment has the advantages of small footprint, strong arc extinguishing ability and high reliability, but the insulation ability of SF6 gas is greatly affected by the uniformity of the electric field, and it is easy to have insulation abnormalities when there are tips or foreign objects inside the GIS.

GIS equipment adopts a fully enclosed structure, which brings the advantages of internal components without environmental interference, long maintenance cycle, low maintenance workload, low electromagnetic interference, etc., while also having problems such as complex single overhaul work and relatively poor detection methods, and when the closed structure is eroded and damaged by the external environment, it will further bring a series of problems such as water ingress and air leakage.

• High Voltage (HV, 72.5kV-170kV): Mainly used in transmission systems, industrial plant power supply, distribution networks, and offshore platforms, adapting to medium-scale power transmission and distribution needs;
• Extra-High Voltage (EHV, 245kV-550kV): Core applications in large-scale transmission grids, major substations, and other key power hubs, undertaking large-capacity and long-distance power transmission tasks.