WHAT IS SWITCHGEAR AND GIVE ITS SOME CHARACTERISTICS TOO?

QUESTION:DEFINITION OF SWITCHGEAR
A switchgear is defines as the special assembly of components developed for protecting,switching and controlling the electric circuitry and equipment.Now a days modernization is creating more and more facilities and easiness to the people of the era.In the past we people had different individual devices and instruments used for different purposes and functionalities on individual bases,different devices performed different required tasks in a limited way and the device used for one purpose could not be used for other purposes but now a days due to huge progress in every field only single device can perform multiple tasks at a time with full accuracy and efficiency.

QUESTION:LIST OF SWITCHGEAR CHARACTERISTICS

a) instruments provision

b) quick operation

c) complete reliability

d) manual control provision

e) absolutely certain discrimination

QUESTION:LIST OF EQUIPMENT USED IN SWITCHGEAR
Normally a number of instruments and equipments are used in switchgear with the help of which protection,switching and controlling of different circuits and major equipments becomes possible.Every element or equipment used in switch is unique and has some special features of controlling,switching and providing protection to other instruments and high efficiency electric circuits.
Below is the list of components normally used in switchgear having unique features.

- switches

- fuses

- circuit breakers

- relays

QUESTION:FUNCTIONALITY OF SWITCHGEAR

A switchgear generally locates the fault and separates the faulty portion from healthy portion.

Circuit breaker types

A switchgear may be a simple open-air isolator switch or it may be insulated by some other substance. An effective although more costly form of switchgear is the gas-insulated switchgear (GIS), where the conductors and contacts are insulated by pressurized sulfur hexafluoride gas (SF6). Other common types are oil or vacuum insulated switchgear.

The combination of equipment within the switchgear enclosure allows them to interrupt fault currents of thousands of amps. A circuit breaker (within a switchgear enclosure) is the primary component that interrupts fault currents. The quenching of the arc when the circuit breaker pulls apart the contacts (disconnects the circuit) requires careful design. Circuit breakers fall into these five types:

Oil

TMW 50981 Schnittmodell Hochspannung-Leistungschalter HPF500F.jpg
Oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil along the path of the arc. The vapor released by the arcing consists of hydrogen gas. Mineral oil has better insulating property than air. Whenever there is a separation of current carrying contacts in the oil, the arc in circuit breaker is initialized at the moment of separation of contacts, and due to this arc the oil is vaporized and decomposed in mostly hydrogen gas and ultimately creates a hydrogen bubble around the electric arc. This highly compressed gas bubble around the arc prevents re-striking of the arc after current reaches zero crossing of the cycle. The oil circuit breaker is one of the oldest type of circuit breakers.

Air

Air circuit breakers may use compressed air (puff) or the magnetic force of the arc itself to elongate the arc. As the length of the sustainable arc is dependent on the available voltage, the elongated arc will eventually exhaust itself. Alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.

Circuit breakers are usually able to terminate all current flow very quickly: typically between 30 ms and 150 ms depending upon the age and construction of the device.

Gas

Main article: Sulfur hexafluoride circuit breaker
Gas (SF6) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the SF6 gas to quench the stretched arc.

Hybrid

Main article: Hybrid switchgear modules
Hybrid switchgear is a type which combines the components of traditional air-insulated switchgear (AIS) and SF6 gas-insulated switchgear (GIS) technologies. It is characterized by a compact and modular design, which encompasses several different functions in one module.

Vacuum

Circuit breakers with vacuum interrupters have minimal arcing characteristics (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched by a small amount (<2–8 mm). Near zero current the arc is not hot enough to maintain a plasma, and current ceases; the gap can then withstand the rise of voltage. Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 40,500 volts. Unlike the other types, they are inherently unsuitable for interrupting DC faults. The reason vacuum circuit breakers are unsuitable for breaking high DC voltages is that with DC there is no "current zero" period. The plasma arc can feed itself by continuing to gasify the contact material.

Carbon dioxide (CO2)

Breakers that use carbon dioxide as the insulating and arc extinguishing medium work on the same principles as a sulfur hexafluoride (SF6) breaker. Because SF6 is a greenhouse gas more potent than CO2, by switching from SF6 to CO2 it is possible to reduce the greenhouse gas emissions by 10 tons during the product lifecycle.Courtesy of wikipedia..