Switchgear Supplier In Kenya

Components
A switchgear has two types of components:

Power conducting components, such as switches, circuit breakers, fuses, and lightning arrestors, that conduct or interrupt the flow of electrical power
Control systems such as control panels, current transformers, potential transformers, protective relays, and associated circuitry, that monitor, control, and protect the power conducting components
Functions[edit]
One of the basic functions of switchgear is protection, which is interruption of short-circuit and overload fault currents while maintaining service to unaffected circuits. Switchgear also provides isolation of circuits from power supplies. Switchgear is also used to enhance system availability by allowing more than one source to feed a load.

History[edit]
 
Early switchgear (about 1910)
Switchgears are as old as electricity generation. The first models were very primitive: all components were simply fixed to a wall. Later they were mounted on wooden panels. For reasons of fire protection, the wood was replaced by slate or marble. This led to a further improvement, because the switching and measuring devices could be attached to the front, while the wiring was on the back.[3]

Housing[edit]
Switchgear for lower voltages may be entirely enclosed within a building. For higher voltages (over about 66 kV), switchgear is typically mounted outdoors and insulated by air, although this requires a large amount of space. Gas-insulated switchgear saves space compared with air-insulated equipment, although the equipment cost is higher. Oil insulated switchgear presents an oil spill hazard.

Switches may be manually operated or have motor drives to allow for remote control.

Circuit breaker types[edit]
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[edit]
 
Cutaway model of an oil-filled high-voltage circuit breaker
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[edit]
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[edit]
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[edit]
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[edit]
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)[edit]
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.[4]