Thursday, July 26, 2012

SF6 Gas-Insulated Switchgear

Gas-insulated switchgear (GIS) has come to be a major piece of substation equipment. Over that period, GIS has been improved by technological advancements that have increased the interrupting capacity of the circuit breaker (CB) and decreased the number of breaks per single CB without using an air condenser. 

The configuration of the GIS comes in several arrangements, such as the single bus, double bus, and ring-bus types. Because the arrangement is determined by a user’s specifications, we must create a different design each time.

Alstom 145kV Gas-insulated switchgear GIS

GIS offers high reliability, safety, and maintenance-free features in a much smaller space compared with conventional switchgear. The SF6 GIS  guarantees outstanding advantages for the planning and operation of high-voltage supplynetworks. For instance, the space requirement can be less than 10% of the space taken up by an equivalent conventional installation.

As all live parts are metal enclosed and hermetically sealed, the SF6 GIS is completely immune to atmospheric pollution (fog, sand, salt, etc.) and industrial pollution (dust, smoke, gas, etc.). With SF6 GIS, all foreign bodies (persons, animals, and tools) are prevented from coming into contact with live parts. This ensures maximum safety to personnel and increased continuity of operation.

 Main Features

  •  High reliability: The live parts are sealed in metal enclosures filled with pure SF6 gas. Thus, the switchgear is protected from contamination by smoke, chemical fumes, dust or salt-laden spray or by the ingress of small animals. This protection prevents the inside components from oxidation and rust caused by oxygen and moisture.
  • Space reduction: A medium-voltage GIS can be installed into a space about half that required for conventional air-insulated metal-clad switchgear.
  • High safety: All the live parts are fully enclosed in grounded metal enclosures. Thus, there is no danger of an electric shock. SF6 is an inert, nonflammable, nontoxic, and odorless gas used as an insulation and arc extinguishing medium. Therefore, it is safe for personnel and there is no fire hazard.
  • Short installation time: A GIS of about four panels can be transported fully constructed. The GIS can be energized by connecting external power cables to the prefabricated plug-in type terminals, thus shortening installation time.   
Example of specification and structure
 of line circuit of 550 kV GIS
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