Switch gears

In an electric power system, switch gear is the combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switch gear is used both to de-energize equipment to allow work to be done and to clear faults downstream.

This type of equipment is directly linked to the reliability of the electricity supply.

Typically, switch gear in substations are located on both the high- and low-voltage sides of large power transformers. The switch gear on the low-voltage side of the transformers may be located in a building, with medium-voltage circuit breakers for distribution circuits, along with metering, control, and protection equipment.

A switch gear has 2 types of components:

1) Power conducting components, such as switches, circuit breakers, fuses, and lightening arrestors, that conduct or interrupt the flow of electrical power.

2) Control systems such as control panels, current transformers, potential transformers, protective relays, and associated circuitry, that monitor, control, and protect the power conducting components.

Function of switch gear

One of the basic functions of switch gear is protection, which is interruption of short-circuit and overload fault currents while maintaining service to unaffected circuits. Switch gear also provides isolation of circuits from power supplies. Switch gear is also used to enhance system availability by allowing more than one source to feed a load.

Several different classifications of switch gear can be made

1) By the current rating.

2) By interrupting rating (maximum short circuit current kAIC that the device can safely interrupt)

a Circuit breakers can open and close on fault currents

b) Load-break/Load-make switches can switch normal system load currents

c) Isolators are off load disconnectors which are to be operated after Circuit Breakers, or else if the load current is very small

3) By voltage class:

a) Low voltage (less than 1 kV AC)

b) Medium voltage (1 kV AC through to approximately 75 kV AC)

c) High voltage (75 kV to about 230 kV AC)

d) Extra high voltage, ultra high voltage (more than 230 kV)