Gas-insulated sealed switchgear (GIS) is a high-voltage power distribution device that encloses all high-voltage electrical components, including circuit breakers, disconnectors, grounding switches, instrument transformers, surge arresters, busbars, connectors, and outgoing terminals, within a grounded metal casing, using sulfur hexafluoride (SF₆) gas at a specific pressure as the insulating and arc-extinguishing medium.
Its core components typically include circuit breakers, disconnectors, grounding switches, instrument transformers, surge arresters, busbars, bushings, connectors, outgoing terminals, and control cabinets.
These components are separated into several independent sealed gas chambers according to their different functions. The main reasons for dividing the equipment into gas chambers include the different SF₆ gas pressures required by each component, facilitating unit-by-unit maintenance and repair, and preventing the escalation of accidents during faults.
In terms of structural components, SF₆ density relays are used to monitor for SF₆ gas leakage in each gas chamber of the GIS equipment; explosion-proof membranes serve as pressure relief devices, providing pressure relief windows to protect the equipment casing when an internal fault causes a sudden increase in pressure.