145kV HV Gas-Insulated 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.

The core difference lies in the scenario adaptability brought by the "hybrid application of insulating media": ① Compared with fully gas-insulated GIS, HGIS connects via air-insulated busbars, reducing reliance on a fully enclosed gas environment. It has more advantages in scenarios where installation space is relatively sufficient but the volume of core components needs to be controlled; ② Compared with fully air-insulated AIS, the core functional modules of HGIS adopt gas insulation, resulting in a more compact structure. It is suitable for scenarios with limited floor space (such as urban substations and offshore platforms) and reduces the impact of the external environment on core components.