The demand of electrical energy is increasing day by day. It has become so essential in everyday life that it is now almost important as air and water.
A few hours without power is difficult to survive. Therefore, it is desirable to protect power system from harm during faulty condition and to ensure maximum continuity of supply. For this purpose, the apparatus are used to open (ON) or close (OFF) the electrical circuits and electrical equipments under both normal and faulty conditions. These operators are known as switchgear.
Definition: In electrical power system switchgear is the assembly of operators employee for switching, controlling and protecting the electrical circuits and equipments.
Function of switchgear
Switchgear has ability to open and closer the electrical circuits under both normal and conditions.
During normal condition, the Switchgear can operator manually. Generally, it is used to energise or De-energies electrical equipments and open or closed electrical circuits.
In this way, switchgear ensure the safety of worker and also proper utilisation of electrical energy.
During faulty condition, the switchgear operates automatically. When a fault occurs, the switchgear detect the fault and disconnect the unhealthy part from the power system.
In this way, switchgear protect the system from damage and and ensure continuity of supply.
Switchgear covers all the apparatus and equipment employed for switching, controlling, metering and protecting electrical power system. It includes switches, fuses, circuit breakers, relays, isolators, bus bars, current transformer, potential transformer, lighting arrester and other associated equipment.
Switch: A switch is the most simplest device to on or off the electrical circuits and equipment. It is design to operate manually and can not protect to electrical system from any fault. Switches are used for low voltage applications to control the power supply.
Fuse: Fuse is an another important device used for the protection of electrical circuits and equipment.
It is a piece of metal wire which is connected in series with load. When excessive current flow through fuse, it melt and disconnect the power supply. It is design to operate manually.
Circuit breaker: It is very important power system device design to open or close various electrical circuits under both normal and faulty conditions. In can operates manually under normal condition and automatically under faulty condition.
Isolator: Isolator is device which is used to open or close electrical equipment and circuits under no load conditions. It is design to operate manually when there is no current flow through power system. It ensure the safety of worker while maintenance of circuit breakers and other equipment.
In our home, the switch is used to manually open and close the electrical equipments and electrical fuse/MCB is used to protect household wiring.
In the same way, higher voltage electrical power system needs switching and protecting devices. But in high voltage and extra high voltage system, these switches and protective devices becomes complicated and large.
Classification of Switchgear
Switchgears can be classified on the basis of voltage level into the following
1. Low voltage switchgear: The Switchgear rated upto 1 kV is termed as low voltage switchgear.
2. Medium voltage switchgear: The switchgear rated between 1 kV to 35 kV is termed as medium voltage switchgear.
3. High voltage switchgear: The switchgear rated above 35 kV is termed as high voltage switchgear.
Although, switchgear are also classified on the basis of current rating, voltage class, operating methods, type of current, interrupting device, insulation tape, application and purpose.
Features of Switchgear
1. When fault occurs, the switchgear must operate to isolate the faulty section from healthy section. Hence, to ensure the quantity of supply and improve reliability.
2. Switchgear must able to carry normal current and also faulty current for short period.
3. When the fault occurs, the switchgear must operate quickly so that no damage is done in power system.
4. A switchgear must have provision for manual control.
5. A switchgear must simple and have good quality of design.