A section of a switchgear and protection book pdf switchgear panel, in this case, used to control on-board casino boat power generation. Oil-filled equipment allowed arc energy to be contained and safely controlled.
By the early 20th century, a switchgear line-up would be a metal-enclosed structure with electrically operated switching elements, using oil circuit breakers. The technology has been improved over time and can now be used with voltages up to 1,100 kV. The switchgear on the low-voltage side of the transformers may be located in a building, with medium-voltage circuit breakers for distribution circuits, along with metering, control, and protection equipment. 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.
The first models were very primitive: all components were simply fixed to a wall. Later they were mounted on wooden panels. 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. Switchgear for lower voltages may be entirely enclosed within a building.
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. A switchgear may be a simple open-air isolator switch or it may be insulated by some other substance.
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. Oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil along the path of the arc. Mineral oil has better insulating property than air. 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.
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. It is characterized by a compact and modular design, which encompasses several different functions in one module.