05-07-2012, 04:31 PM
GAS INSULATED SWITCHGEAR
ABSTRACT
The term Switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. High voltage Switchgear was invented in 19th century for operating motors and electrical machines. But with the advancement in technology, it has been improved over time to be used with high voltage. Earlier, the filling material used was air or vacuum only. Switchgear can be classified:
• By the current rating.
• By voltage class:
o Low voltage (less than 1,000 volts AC)
o Medium voltage (1,000–35,000 volts AC)
o High voltage (more than 35,000 volts AC)
• By insulating medium:
o Air
o Gas (SF6 or mixtures)
o Oil
o Vacuum
Nowadays, SF6 filled equipment, known as Gas Insulated Switchgear are generally used as circuit breaker to isolate electrical equipment. It is widely employed as a protection element in industries like BHEL, TATA, etc.
Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is important because it is directly linked to the reliability of the electricity supply. Today, oil-filled equipment has largely been replaced by air-blast, vacuum, or SF6 equipment, allowing large currents and power levels to be safely controlled by automatic equipment incorporating digital controls, metering and communications.