The primary function of switchgear is the prevention of short circuits and overloading fault circuits in electrical installations.
Switchgear is usually found in power systems fitted to larger industrial and commercial facilities. The main purpose of switchgear is to ensure the continued operation of unaffected circuits while ensuring electrical hazards are kept at bay in the malfunctioning one.
Because there are a wide variety of applications for switchgear, it’s offered in several different configurations. Let’s look at some of the most common switchgear types and classifications.
A key component of many switchgear systems, like those offered by Schneider Electric, is a circuit breaker. Its primary function is to interrupt fault currents. This is accomplished by pulling contacts apart, which in turn disconnects (or “breaks”) the circuit. The insulation medium categorizes circuit breakers. These are the common types: pressurized sulfur hexafluoride gas (also referred to as SF6), oil, air, and vacuum.
Ideally, a circuit breaker should be capable of arresting the flow of current in as little as 30 milliseconds — but no more than 150 milliseconds. This, of course, will vary depending upon the circuit breaker’s age, design and construction.
Housed in metal-clad or metal-enclosed cabinets, switchgear systems typically contain both switches and circuit breakers. The switches can be fused or non-fused. They can also be air break or vacuum break. Switchgear rated up to 1 kV is considered low voltage. Systems rated up to 36 kV are considered medium voltage, while anything above that rating is referred to as high-voltage switchgear.
Low-voltage switchgear sometimes employs a manual break, while medium- or high-voltage switchgear tends to be electrically actuated. A control power source and wiring are required in those instances. The power can be fed by a separate low-voltage source from outside the cabinet, or by transforming line power down to the appropriate control voltages inside the cabinet.
Switchgear is classified based upon the following attributes:
- Current rating
- Interrupting rating
- Voltage class (low, medium, high)
- Insulating medium (air, gas, oil, vacuum)
- Construction type (indoor, outdoor, industrial, utility, marine, draw out, fixed, live-front, dead-front, open, metal-enclosed, metal-clad, arc-resistant)
- IEC degree of internal separation
- Interrupting device (fuse, air breaker, oil breaker, gas SF6 breaker, etc.)
- Operating method (manual, motor, solenoid, etc.)
- Type of current (AC/DC)
- Application (transmission, distribution)
- Purpose (isolating switch, load-break, grounding)
As you may have observed, there are also categories within many of those classifications, such as low, medium and high voltage, as noted above. Because they are offered in a variety of types and classifications, equipment designers and engineers can precisely tailor switchgear to a prescribed usage. Additionally, many different switchgear configurations can be combined in a single line-up.
Naturally, switchgear must meet several different standards and specifications. If you’re designing an electrical system for a new facility, you’ll want to look for equipment adhering to the directives issued by the IEEE (Institute of Electrical and Electronics Engineers) and ANSI (American National Standards Institute) within North America, and the IEC (International Electrotechnical Commission) for applications in other countries.
This primer on common switchgear types and classification is intended to help you gain a fundamental understanding of how they work, what they do and how they’re classified. Switchgear is a critical link in the chain ensuring safe operation of large-scale power systems. In preventing overloads and fires, they also save human lives. With this in mind, it’s very important to understand all of the requirements a system must fulfill to match the most appropriate switchgear to the need at hand.