Switchgear is a broad term that describes a wide variety of switching devices that all fulfill a common need: controlling, protecting, and isolating power systems.
The tumbler switch with ordinary fuse is the simplest form of switchgear, used to protect the light and other circuits in home.
But for high voltage above 3.3 KV any types of uses cannot be used profitably.
Firstly, when a fuse blows, it takes sometime to replace it and so there is a higher interruption period to the customers. Secondly, the fuse cannot successfully interrupt large fault currents.
Switchgear Equipment
- Switches:
A switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another at full load or at no-load, but it cannot interrupt fault current.
a) Air-break switch: Designed to open a circuit under load. Air-beak switches are generally used outdoors for medium capacity line or feeder supply.
b) Isolator or disconnecting switch: Designed to open a circuit under no-load. Its main purpose is to isolate the circuit. It operates to close before the breaker close(ON) or opens after the breaker open(OFF).
c) Oil switches: This is as normal switch but placed inside transformer oil. The effect of oil is to cool and quench the arc that tends to form when the circuit is opened.
2. Fuses: A fuse commonly consists of a current-conducting strip or wire of easily fusible metal that melts, and thus interrupts the circuit of which it is a part, whenever that circuit is made to carry a current larger than that for which it is intended. The screw-plug fuse was once commonly used in domestic electrical systems.
3. Circuit Breakers: A circuit breaker is an electrical switch designed to protect an electrical circuit from damage caused by overcurrent/overload or short circuit. Its basic function is to interrupt current flow after protective relays detect a fault.
4. Relays: A Relay is a simple electromechanical switch. While we use normal switches to close or open a circuit manually, a Relay is also a switch that connects or disconnects two circuits. But instead of a manual operation, a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit.