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What Is Switchgear?

Mar. 15, 2021

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Switchgear is a generic term used to refer to a series of switches, circuits, circuit breakers, fuses, etc., which are used in an electrical system to control, regulate and switch circuits on and off. Switchgear protects electrical equipment and isolates it from the power supply by controlling the circuit so that testing, maintenance and troubleshooting can be carried out.

Low voltage draw-out switchgear is applicable for three-phase four-wire/five-wire AC power system with rated operation voltage 380V, used for electric power receiving and feeding, reactive power compensation, electric energy calculation, lighting and motor centralized control at the power plant, substation, mine enterprises, high buildings.

Low-Voltage Draw out Switchgear

Switchgear has two types of components.

Conductive components: conduct or interrupt the power flow; e.g. switches, circuit breakers, fuses, disconnectors, relays, lightning arresters, etc.

Control systems: These monitor, control and protect conductive components; for example control panels, current transformers, voltage transformers, associated circuits, etc.

Although the circuit breaker is the main component, it is the combination of the device's internal switching enclosure which allows high voltage currents to be interrupted.

The switchgear is connected directly to the power supply system and can be classified according to the voltage level as

Low voltage switchgear (LV).

Medium voltage switchgear (MV).

High voltage switches (HV).

Switchgear for lower voltages can be enclosed in the building, but higher voltages (approx. over 66 kV) usually require the switchgear to be mounted externally and insulated by air.

Types of switchgear

There are two main types of switchgear: outdoor and indoor. For voltages above 66 kV, output switchgear is used. This is because, for higher voltages, construction work will unnecessarily increase installation costs due to the large spacing between conductors and the large size of the insulators.

Below 66kv there is no difficulty in providing construction work for switchgear at a reasonable cost. The indoor type switchgear is metal-clad and compact. Due to the compactness, the safety distance for operation is also reduced and therefore the required area is reduced.

The switchgear can be a simple open-air disconnector or can be insulated with other substances such as oil, pressurised sulphur hexafluoride gas or in a vacuum.

In the event of a fault in the power system, high currents flow through the equipment, thereby damaging it and interrupting service. For this reason, automatic protection devices or switchgear are required to protect lines, generators, transformers and other electrical equipment from damage.

 

Automatic protection switchgear consists mainly of relays and circuit breakers. When a fault occurs in any part of the system, the relay in that part will start to operate and close the tripping circuit of the circuit breaker, thus disconnecting the faulty part. The normally operating part will continue to supply power as normal, so no equipment will be damaged and the supply will not be completely interrupted.

 


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