What is Switchgear?
The Basics of Medium-Voltage Switchgear
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Switchgear is the collective of circuit protection and control components (fuses, switches, and breakers) housed in a metal structure called an enclosure. When multiple enclosures are in use, it is referred to as a switchgear line-up.
The function of switchgear is to control, isolate, and protect critical power electrical equipment commonly found in commercial and industrial applications. Switchgear distributes power and electrical loads within various sections of a facility. Additionally, a line-up provides crucial protection by limiting the flow of current to safe levels throughout the electrical system.
Medium-voltage switchgear refers to voltages above 1,000 volts and below 69,000 volts. The highest voltage metal-enclosed switchgear in general use in North America is generally 38 kV class, although there is a small amount of 44 kV.
There are six types of medium-voltage switchgear:
Gas-insulated
Metal-clad
Metal-enclosed
Pad-mounted
Vault or Subsurface
Arc resistant switchgear
Gas-insulated switchgear commonly referred to as (GIS), utilizes an insulating gas called SF6 (sulfur hexafluoride) or a combination of SF6 and other insulating gases, within a sealed metal enclosure(s). This application allows for a compact and low-profile line-up when compared to similar air-insulated switchgear.
Metal-clad switchgear is made up of separate metal compartments, each enclosing specific electrical components such as the incoming and outgoing bus, main breaker, and instrumentation. This application provides excellent safety, durability, and ease of upkeep. Metal-clad has rated voltage levels ranging from 5kV to 38kV. These line-ups are typically found in industrial facilities, as well as, power gen and transmission facilities.
Metal-enclosed switchgear is a common commercial and industrial solution specific to facilities with incoming electrical service is greater than 480/600V. The enclosure will house all circuited protection, controls, and metering equipment within a common compartment.
Pad-mounted switchgear is outdoor rated and features a low profile, tamper-resistant enclosure construction that is well suited for utility distribution, circuit protection, and feeder sectionalizing. This application is designed for underground distribution systems rated from 5 to 38kV that are required to be above grade operable and can be insulated with air, SF6 gas, fluid, solid-dielectric-in-air-technology, and solid materials.
Vault of Subsurface switchgear is designed to be operable from inside a vault or below-grade location, and id for electrical distribution systems rated 15 to 38kV.
Arc-resistant switchgear is designed to contain and safely redirect arc flash energy away from the operator. Standards are defined by ANSI/IEEE C37.20.7 which defines two levels of accessibility to switchgear assemblies, Type 1 and Type 2.
Type 1 - Only provides protection when the operator is in front of the gear.
Type 2 - Provides operator protection on all sides.
Type 2B - Must be arc-resistant around the entire perimeter of the equipment, even with instrument or control compartment doors open.
Type 2C - Must be arc-resistant between adjacent compartments within the assembly, as well as around the entire perimeter of the equipment.
CODES AND STANDARDS
Conventional switchgear is typically built to adhere to the standards set by the IEEE (North America) and IEC (Europe and other parts of the world).
IEEE C37.20.9 / IEC 62271 - Gas-insulated switchgear
IEEE C37.20.2 - Metal-clad switchgear
IEEEC37.20.3 - Metal-enclosed switchgear
IEEE C37.74 - Pad-Mounted and Vaul or Subsurface switchgear
ANSI/IEEE C37.20.7 Arc-resistant switchgear