Switchgear

Switchgear is a general term used to refer to a range of switches, circuit breakers, fuses, etc., which are used in an electric power system to control, regulate and switch the circuit on and off. By controlling the circuit, switchgear protects and isolates electrical equipment from the power supply, enabling testing, maintenance and fault clearing work to be undertaken.

Switchgear has two types of components:

• Power-conducting components: These conduct or interrupt the power flow; such as switches, circuit breakers, fuses, isolators, relays, lightning arrestors, and so on.
• Control systems: These monitor, control and protect the power-conducting components; such as control panels, current transformers, potential transformers, associated circuitry, and so on.

Although the circuit breaker is the main component, it is the combination of equipment within the switchgear enclosure that allows high voltage currents to be interrupted.

Switchgear is directly linked to the supply system and, based on the voltage level, can be classified as either:

• Low voltage switchgear (LV).
• Medium voltage switchgear (MV).
• High voltage switchgear (HV).

Switchgear can be a simple open-air isolator switch or can be insulated in another substance such as oil, pressurised sulphur hexafluoride gas, or insulated in a vacuum.

Lower voltage switchgear can be enclosed within a building, however, higher voltages (approximately over 66 kV) usually require the switchgear to be externally mounted and insulated by air.

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