Types of Weather Switchgear

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),  where the conductors and contacts are insulated by pressurized sulphur hexafluoride gas. 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 five types.


Oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil along the path of the arc. The vapour released by the arcing consists of hydrogen. 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 and ultimately creates a hydrogen bubble around the 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 circuit breakers may use compressed air 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..

Gas circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the gas to quench the stretched arc.
Hybrid switchgear is a type which combines the components of traditional air-insulated switchgear and gas-insulated switchgear l technologies. It is characterized by a compact and modular design, which encompasses several different functions in one module.
Circuit breakers with vaccum interrupts in the arc quenches when it is stretched by a small amount . 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.  Unlike the other types, they are inherently unsuitable for interrupting DC faults. . The plasma arc can feed itself by continuing to gasify the contact material.

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