Gas Insulated Switchgear(GIS) mainly combines busbars, circuit breakers, CTs, PTs, isolating switches, and arresters. It is the switch station we often see, also called high-voltage power distribution devices. There are three types of high-voltage power distribution devices: the first is air-insulated conventional power distribution devices, referred to as AIS. The exposed busbar is in direct contact with the air, and the circuit breaker can be of porcelain column type or tank type.Gezhouba Power Plant adopts this type. The second is a hybrid power distribution device, referred to as H-GIS. The busbar adopts open type, and the others are gas-insulated switchgear of sulfur hexafluoride. The third is the sulfur hexafluoride gas-insulated fully enclosed power distribution device. Its name is GAS—INSTULATED SWITCHGEAR, referred to as GIS. The advantages of GIS lie in its small footprint, high reliability, strong safety, and small maintenance workload, and the maintenance interval for its main components can be greater than 20 years.

C-GIS is increasingly used in petrochemical metallurgy, mines, development zones, urban road traffic, high-rise buildings and high-altitude areas because of its small footprint, unaffected by external environment, and high reliability. At present, the top 8 foreign companies and their joint ventures with C-GIS market dominance are ABB, Siemens, Areva, Tamco of Malaysia, Hyundai Namzi of South Korea, and AE of Japan.

There are two types of C-GIS structure: cylinder type and cabinet type. Cylinder types such as 8DA10/8DB10 of Siemens, WIA and WIB of Areva.The current structure is developing towards the cabinet type. For example, Siemens has developed the cabinet type 8DC11 and Nxplus type, and Areva has also developed the cabinet type GMA and WS type. Cabinet C-GIS accounts for about 70% to 85% of the total demand. In the arrangement of its internal components, according to the relative position of the busbar-isolating/earthing switch-circuit breaker, there are 3 arrangements: upper, middle and lower arrangement, lower middle and upper arrangement and rear middle and front arrangement. As the voltage level, there are mainly 12 kV level and 40.5 kV level, and 24 kV level; as a current-carrying capacity, foreign C-GIS also achieves a rated current of 2 500 A, while in China it generally achieves 1 250 A, and some achieves 2 000-2 500 A; as an insulating medium, the current mainly uses lower pressure SF6 gas, but other gases have also been used, such as dry compressed air, N2 and SF6+N2 mixtures; as the components used, vacuum circuit breakers, isolating switches and grounding switches are currently used to form combined three-position isolation/grounding switches, and busbars are made into plug-in structures, etc.; as air chambers, there are currently single air chambers, double air chambers and multiple air chambers. C-GIS is a high-tech product, which often requires modern processing equipment, processing technology and welding technology, so it has high requirements for processing and manufacturing.