1. Need Of Switchgear:

A great demand for electrical energy is a notable feature of modern civilization. Most of this energy is needed for lighting, heating, domestic appliances, industrial electrical machinery and electric traction.

The importance of electric supply in everyday life has reached such a stage that it is desirable to protect the power system from harm during fault conditions and to ensure maximum continuity of supply. For this purpose, means must be provided to switch on or off generators, transmission lines, distributors and other equipment under both normal and abnormal conditions.
This is achieved by an apparatus called switchgear.

  • A switchgear essentially consists of switching and protecting devices such as switches, fuses, circuit breakers, relays etc.
  • During normal operation, switchgear permits to switch on or off generators, transmission lines, distributors and other electrical equipment.
  • On the other hand, when a failure (g. short circuit) occurs on any part of power system, a heavy current flows through the equipment, threatening damage to the equipment and interruption of service to the customers.

However, the switchgear detects the fault and disconnects the unhealthy section from the system. In this way, switchgear protects the system from the damage and ensures continuity of supply.

  1. How It Works :

The switchgear equipment is essentially concerned with switching and interrupting currents either under normal or abnormal operating conditions. The tumbler switch with ordinary fuse is the simplest form of switchgear and is used to control and protect lights and other equipment in homes, offices etc.

For circuits of higher rating, a high-rupturing capacity (H.R.C.) fuse in conjunction with a switch may serve the purpose of controlling and protecting the circuit.

However, such a switchgear cannot be used profitably on high voltage system (3·3 kV) for two reasons.

  • Firstly, when a fuse blows, it takes some time to replace it and consequently there is interruption of service to the customers. Secondly, the fuse cannot successfully interrupt large fault currents that result from the faults on high voltage system.
  • With the advancement of power system, lines and other equipments operate at high voltages and carry large currents.
  • When a short circuit occurs on the system, heavy current flowing through the equipment may cause considerable damage.
  • In order to interrupt such heavy fault currents, automaticcircuit breakers (or simply circuit breakers) are used.

A circuit breaker is a switchgear which can open or close an electrical circuit under both normal and abnormal conditions. Even in instances where a fuse is adequate, as regards to breaking capacity, a circuit breaker may be preferable. It is because a circuit breaker can close circuits, as well as break them without replacement and thus has wider range of use altogether than a fuse.


“Power system” by V.K. MEHTA.

Leave a Reply