What is Switchgear ?
The apparatus used for controlling, regulating and switching on or off the electrical circuit in the electrical power system is known as switchgear.
- The switches, fuses, circuit breaker, isolator, relays, current and potential transformer, indicating instrument, lightning arresters and control panels are examples of the switchgear device.
- Switchgear refers to electrical tool that regulates the flow of electricity within an electrical system. It is used by utility providers and hidden facilities alike for two reasons: to prevent overloads and short circuits, and to de-energize circuits for testing and maintenance.
- The most familiar types of switchgear are circuit breakers and fuses, which interrupt the flow of electricity to a circuit when its current becomes too high; and power exchange switches, which exchange a buildings source of electricity from a primary source to a secondary source, such as accessing generator power while a power outage.
Essential Features of Switchgear
- Quick operation: When fault occurs at any part of the power system, the switchgear must operate rapidly so that no damage is done to generators, transformers and other equipment by the short-circuit currents. If fault is not cleared by switchgear quickly, it is likely to damage into healthy parts and its leads to shut down of the system
- Absolutely certain discrimination: When fault occurs on any part of the system, the switchgear must be able to discriminate between the faulty section and the healthy section. It should isolate the faulty section from the system without affecting the healthy section. This will ensure continuity of supply.
- Provision for manual control: A switchgear must have provision for manual control. In case the electrical (or electronics) control fails, the necessary operation can be carried out through manual control.
- Complete reliability: With the continued trend of interconnection and the increasing capacity of generating stations, the need for a reliable switchgear has become of paramount importance. This is not surprising because switchgear is added to the power system to improve the reliabil-ity. When fault occurs on any part of the power system, the switchgear must operate to isolate the faulty section from the remainder circuit.
Types of Switchgear
The switchgear is mainly classified into two types, the outdoors type (High voltage ) and the indoor type (low voltage ).
- Switchgear is initially categorized according to its interruption technology, the method by which it extinguishes its electrical arc.
- Using this categorization, there are five types of gear available on today’s market: oil circuit breaks, which vaporize oil in order to send a jet of oil straight through an arc; gas (Sf6) breaks, which stretch an arc and then rely on the Sf6 to extinguish it; vacuum breaks, which extinguish their comparatively small arc by stretching it; air breaks, which typically use a puff of air to extinguish an arc; and hybrid breaks, which use more than one type of breaking technology to extinguish an arc, such as gas and air.
- For voltage above 66kV, the outdoor switchgear is used. Because for the high voltage, the building work will unnecessarily increase the installation cost owing to large spacing between the conductor and large size of insulators.
- Below the 66kv there is no difficulty in providing the building work for the switchgear at a reasonable cost. The indoor type switchgear is of metal clad type and is compact.
- Because of the compactness, the safety clearance for operation is also reduced and thus reduced the area required.