High-voltage circuit breakers:

Electrical power transmission networks are protected and controlled by high-voltage breakers. The definition of "high voltage" varies but in power transmission work is usually thought to be 72,500 V or higher, according to a recent definition by the International Electro technical Commission (IEC).

High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays operated through current transformers. In substations the protection relay scheme can be complex, protecting equipment and busses from various types of overload or ground/earth fault. High-voltage breakers are broadly classified by the medium used to extinguish the arc.

Bulk oil

Minimum oil

Air blast

SF₆

Some of the manufacturers are ABB, AREVA, Cutler-Hammer (Eaton), Mitsubishi Electric, Pennsylvania Breaker, Schneider Electric, Siemens, Toshiba, and others.

Circuit breaker can be classified as "live tank", where the enclosure that contains the breaking mechanism is at line potential, or dead tank with the enclosure at earth potential. High-voltage AC circuit breakers are routinely available with ratings up to 765,000 volts.

High-voltage circuit breakers used on transmission systems may be arranged to allow a single pole of a three-phase line to trip, instead of tripping all three poles; for some classes of faults this improves the system stability and availability.

Sulfur Hexafluoride (SF6) high-voltage circuit-breakers:

High-voltage circuit-breakers have greatly changed since they were first introduced about 40 years ago, and several interrupting principles have been developed that have contributed successively to a large reduction of the operating energy. These breakers are available for indoor or outdoor applications, the latter being in the form of breaker poles housed in ceramic insulators mounted on a structure.

Current interruption in a high-voltage circuit-breaker is obtained by separating two contacts in a medium, such as SF₆, having excellent dielectric and arc quenching properties. After contact separation, current is carried through an arc and is interrupted when this arc is cooled by a gas blast of sufficient intensity.

Gas blast applied on the arc must be able to cool it rapidly so that gas temperature between the contacts is reduced from 20,000 K to less than 2000 K in a few hundred microseconds, so that it is able to withstand the transient recovery voltage that is applied across the contacts after current interruption. Sulphur hexafluoride is generally used in present high-voltage circuit-breakers (of rated voltage higher than 52 kV).In the 1980s and 1990s, the pressure necessary to blast the arc was generated mostly by gas heating using arc energy. It is now possible to use low energy spring-loaded mechanisms to drive high-voltage circuit-breakers up to 800 kV.

Bearing: Supports revolving parts for stable revolution

7. Fan: Installed in the revolving area to feed in cooling air

The synchronous generator most commonly used, the revolving –armature type AC exciter is installed on the shaft used for DC excitation of the field coil. The output is converted to DC with the silicon rectifier for supply to the coil.

No. of Revs. And Poles

The relation between revolution speed and frequency in generators is represented by the following formula