Urban areas and densely-populated towns in the US are often powered via gas-insulated substations, but what are they and what are they used for? Let’s take a look.
What Are Gas-Insulated Substations?
Gas-insulated substations (GIS) are high-voltage substations that contain major conducting structures within a sealed environment. Gas-insulated substations also contain an insulating medium, which could be sulfur hexafluoride gas or a dielectric gas, known as SF6.
Gas-insulated substations are often confused with air-insulated substations or conventional substations which use atmospheric air as the dielectric gas medium. However, air-insulated substations are always located outdoors, and gas-insulated substations are required to be protected from environmental aggressors.
GIS technology is often used in desert or arctic locations, as they can be enclosed in protected buildings with a Faraday cage, which also protects the system from lightning strikes.
What Are Gas-Insulated Substations Used For?
Gas-insulated substations are used as a part of electrical distribution, transmission, and generation systems. GIS technology is designed to transform voltage from low to high or from high to low.
Before electricity can reach the consumer, it may flow through several different substations at various voltage levels. Gas-insulated substations may contain transformers to adjust these voltage levels.
Superior Dielectric Gas
SF6, or super dielectric gas, is used in gas-insulated substations at moderate pressure for phase-to-ground and phase-to-phase insulation.
The voltage transformers, switches, high-voltage conductors, current transformers, and circuit breaker interrupters are surrounded by SF6 gas inside grounded metal enclosures. This protects the elements from deterioration due to exposure to contamination, moisture, and atmospheric air, and allows them to be placed much closer together.
How Much do Gas-Insulated Substations Cost?
On average, a single leg or bay of a half substation and a 138kV breaker, without protective relays, will cost up to $500,000.
However, gas-insulated buses alone cost $2,600 dollars per foot, but this will vary between vendors.
As an area’s voltage requirements increase, gas-insulated technology becomes more desirable. A 765kV conventional substation, for example, will take up a significant amount of space, but if it were to employ GIS, it would be more compact.
GIS technology is often used in areas where the safety or aesthetic appeal of an area is a priority, particularly in areas with high real estate costs.
Purchasing land for a conventional AIS station in a densely-populated area can be difficult to locate, as well as potentially politically sensitive and cost-prohibitive. One solution to expand existing AIS technology is to create a hybrid GIS, or mixed technology switchgear system, which does not require large areas of land.