The Air Insulated Substation Dissected

The Air Insulated Substation Dissected

Air Insulated Substation

The electrical substation is an often overlooked, yet integral part of power production. Regardless of the source, electricity goes through miles and miles of either underground or overhead transmission/distribution lines before reaching the consumer. Substations are located along these lines to ensure safe electrical distribution to the consumer.

Let’s delve into these parts and pieces, and how they work to keep the lights on.

The Occupational Safety & Health Administration (OSHA) has clearly defined the common elements of an electrical substation to include lightning arresters, air brake switches, circuit breakers, step-down transformers, voltage regulators, distribution buses, metal-clad switchgear and cutout switches. These items are responsible for safely converting high-voltage electrical power from transmission lines to lower voltage power for distribution to consumers.

There are two types of substations that branch this discussion in two different directions: Air insulated substations (AIS) versus gas insulated substations (GIS). In this article, we take a look at the air insulated substation (AIS).

AISs, which are more common, use air to insulate the different components of the substation from each other as well as for grounding the charge. Substations rely on copper grounding on equipment and in the ground to properly ground the system and make it safe. Since this type of system is exposed to the open environment, the elements can have a notable impact on the durability of the components.


  • The lightning or surge arrester works much like surge protectors in your home. If there is ever too much voltage in the system, surge arresters dissipate the excess or direct it to the ground.
  • Next, air break switches are used to isolate equipment or a circuit within the substation allowing the various equipment or lines of the substation to be maintained without the risk of electrocution.
  • Circuit breakers are automatic electrical devices that protect an electrical circuit caused by an overload on the line. For distribution substation use, vacuum technology is commonly used for extinguishing the arc caused by an overload inside a vacuum bottle. Other types of substation circuit breakers use oil or gas technology to insulate its components and help interrupt a fault.
  • The step-down transformer might be the most important component to the substation. It converts extremely high-voltage power into a lower voltage that can be transmitted down distribution lines until it is further converted by smaller transformers to usable voltage.
  • The voltage regulator maintains the proper voltage after it has passed through the t Voltage regulators are responsible for ensuring the correct electrical output travels across the distribution lines to the consumer.
  • The electricity moving through the transformer is sent to the high voltage bus, a junction of many different lines that disburse power in many directions. Since the high voltage bus is responsible for carrying incredible loads, it is yet another piece that requires great care to maintain proper function.
  • Metal-clad switchgear is the control center for the many distribution lines leaving the substation. This is where electricity can be distributed to certain destinations with and protected with the aid of the cutout switches, allowing lines to be isolated for required maintenance. The term metal-clad describes the housing which is metal enclosed to protect the sensitive equipment from the outside elements. In a lot of substations, engineers and utilities use an open-air secondary design using freestanding breakers instead of metal-clad switchgear which requires more maintenance. Coops might use ‘fused cutouts’ or ‘reclosers’ instead of switchgear to protect distribution circuits.


Any and all of these parts in an AIS environment are prone to environmental problems. Continued monitoring and maintenance are an absolute must to deliver reliable energy to consumers in a safe manner.


Image Source: Paul Chernikhowsky