800kV HV Gas Insulated Switchgear (GIS)

Protection Function Principles:

• GIS equipment is equipped with various protection functions to ensure the safe operation of the power system.

Overcurrent Protection:

• The overcurrent protection function monitors the current in the circuit using current transformers. When the current exceeds a predefined threshold, the protection device triggers the circuit breaker to trip, cutting off the faulty circuit and preventing damage to the equipment due to overcurrent.

Short-Circuit Protection:

• The short-circuit protection function quickly detects short-circuit currents when a short-circuit fault occurs in the system and causes the circuit breaker to act rapidly, protecting the power system from damage.

Additional Protection Functions:

• Other protection functions, such as ground fault protection and overvoltage protection, are also included. These protection functions use appropriate sensors to monitor electrical parameters. Once any abnormality is detected, the protection actions are immediately initiated to ensure the safety of the power system and equipment.

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.