The Basics of Switchgear

For those who don’t know, electrical switchgear (sometimes just called ‘switchgear’) is a fairly broad, generic term that includes a variety of switching devices used to protect your power system from overloads. By extension then, the definition could also include devices used to regulate, meter, and control your power system.

You’ve seen switchgear before, even if you perhaps didn’t realize it. In a small scale, simplified form, that’s what fuses and low voltage switches in your home are. It’s the same basic thing, but scaled up to be of use industrially. Just like the home fuse that opens and closes to keep the system from overloading, the high voltage electrical power systems used by business need the same basic kind of protection. Of course, as you scale this equipment up, these switches and other protective measures become more complex, and of course, in business, electricity (like any other resource) needs to be carefully controlled, monitored and measured, if for no other reason than cost controls. As such, it may be the case that your business will need something custom designed to see to your specific needs.

Switchgear protection is pivotal in any modern power system network. From power generation, to transmission to distribution at your place of business where it actually runs the machines that turn a profit for you, at any point in that chain, there is the possibility of overload, and if that happens (especially if it happens once the power is actually delivered to your site), if not for having a robust switchgear system in place, it can have catastrophic consequences leading to the burn out or destruction of your expensive equipment. That’s why a robust system is so important!

One of the most pivotal components of switchgear is a current interruption (switching) device, also called a circuit breaker. The circuit breaker can be operated manually if and when required, but is also designed to ‘trip’ automatically in the event of an overload or any type of fault or abnormality in the system. The circuit breaker ‘senses’ the fault through a protection relay and triggers before damage can occur.

There are five basic “types” of circuit breakers: Oil, air, gas, hybrid, and vacuum. Each type performs essentially the same function, with the key difference being their operating mechanism. For example, an oil circuit breaker relies on oil vaporization to blast a jet of oil along the path of the arc, breaking it, while an air based circuit breaker uses a puff of compressed air to break the arc, and so on.

But of course there’s more to switchgear than just the circuit breaker. In addition to that component and functionality, the system also has to be able to carry and switch (route) it to different subsystems and specific machines inside your facility. It also needs some means of metering, and performing similar functions. From end to end then, the switchgear system would need (at a minimum) to include one or more Circuit Breakers, a current transformer, a voltage transformer, some kind of protection relay and a measuring instrument. It would also need electrical switches, fuses, a lightening arrestor (like an industrial surge protector), and an electrical isolator.

As you might imagine, this type of equipment is essential at every switching point along the path of the electrical power system. Given varying voltage levels, there are varying fault levels between the generating stations and the load centers, and because of that, different switchgear assemblies are required, depending on the specific voltage level of each system.