Different switching devices in switchgear for power system

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What is switchgear?

In electrical system, switchgear is the combination of electrical switches, fuses and circuit breakers used to control, protect and isolate electrical equipment.

Switching devices are used to make or break electric circuits

     1. Classification of switching devices according to operation:

  • No-load switching
  • Breaking at operating currents
  • Breaking at short circuit currents

     2. Classification of switching devices according to function:

  • Circuit Breaker:
A circuit breaker is an electrical switch which designed to protect an electric circuit from damage caused by excess current from an overload or short circuit. Its basic function is to make, break and carry current under normal and abnormal conditions.
  • Switches:
Switches are used to switch current between two feeder or break current in circuit.
  • Disconnectors or Isolators:
Isolator is an offload mechanical device used to physically disconnect an electrical circuit to ensure electrical safety during maintenance.
  • Three-position Disconnector:
Three position disconnector combined the function of isolating and earthing in one device. Generally, it is used in Gas Insulated Substation.
  • Load Break Switch:
An isolator can be modified to load-break switch by including a series interrupter for higher voltage and current interrupting levels. These interrupters increase the load break capability of the disconnector. It is used to make and break load or rated current.
  • Contactors:
Contactor is a device which can be used to bypass the control circuit from the main source.
  • Earthing Switches:
Earthing switch is a mechanical switching device for earthing parts of a circuit, capable of withstanding for a specified time short-circuits currents, but not required to carry normal rated currents of the circuit.
  • Fuses:
Fuses contain a narrow strip of metal which is designed to melt when the current exceeds the rated value, thereby interrupting the power to the circuit.
  • Surge Arresters:
A surge arrester is a device to protect electrical equipment from over-voltage transients caused by external (lightning) or internal (switching) events.

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