The gas-insulated switchgear (GIS) is a substation unit compromising switchgear and buses enclosed in a ground metallic sheath and filled with pressurized SF6 gas. This construction can minimize total substation size, improve safety and economy, and attain high reliability and labor-saving maintenance, using the merits of insulation space reduction and simplicity. Although the GIS has many excellent features as described below, some care should be taken in practical applications to make the best use of these merits.
By adopting the GIS, which has several times higher insulation capability than air insulated apparatus. The volume and occupied space can be considerably reduced in reverse proportion to the operating voltage level increase. If the entire substation is made up of GIS units, including buses, the size reduction effect is much more significant. Since all live parts of switchgear are contained in a grounded metallic sheath, electric shock danger and damage to dust particles’ equipment can be avoided. By the rational arrangement of the components and bused, operation safety is increasingly assured.
Using noninflammable materials, such as SF6 gas, insulators and structures, and enclosing equipment in the metallic sheath, GIS is practically free from fire hazards. Since the GIS is wholly enclosed, no external conditions, such as contamination, weather condition, and atmospheric pollution, affect it. Thus, a highly reliable switchgear can be obtained. All switching devices are operated in the metallic sheath, there is no arcing outside. A lower noise level can be attained compared with a conventional system.
What are the Features of GIS
The single-pressure gas circuit breaker is adopted for all ratings as standard since it has a more straightforward operating principle than the double-pressure gas circuit breaker. Therefore, gas construction is simple, and there are fewer components, and gas pressure is lower. Consequently, there is no fear of gas liquefying
Thus, the unit has reliability, low cost, and easy maintenance. Higher quality is attained by standardization and mass production of parts commonly used with independent tank gas circuit breaker.
A General Requirement for Gas-Insulated Switchgear
(1) All live parts of 132kV components included 3 Phase bus bar, are contained in the grounded metal enclosure with pressurized SF6 gas.
(2) For the Gas-Insulated Switchgear layout, refer to the GIS plan, view the layout drawing.
(3) The cable termination flange will be provided for Transmission & Transformer feeder for Company to connect the underground cable and cable sealing end.
(4) The supporting structure and base for GIS will be supplied. Still, we will not provide the embedded material, cable conduct in the GIS foundation.
(5) The local panel for GIS will be supplied. Still, the remote protection & control panel and the cables and its tray will not be provided.
(6) The GIS will be provided bellows joint for more flexibility and endurable for earthquake shock.
The gas control seal off system is adopted as standard based on development and operation results obtained over the past ten years. No complicated piping and gas compressor is required. Piping becomes simple, and the number of parts needed is significantly reduced.
The breaker up to heavy current rating standardized systematically for all the following voltage classes. All equipment is highly reliable and self-cooled.
It is usually necessary to inspect and maintain the circuit breaker when a specified number of switching operations have been reached. In this case, the inspection usually dines in the site without movement. If required, units can be dismounted structurally for inspection and maintenance.