A Tutorials On The Operating Mechanism Of Power Circuit Breaker

Opening and closing of power circuit breakers under service conditions is seldom performed manually, since most breakers are installed in systems designed for remote control providing specific redundancy.

Various means of operation are used, such as
(1) dc solenoids,
(2) solenoids operated from an ac source through a dry-type rectifier,
(3) compressed air,
(4) high pressure oil,
(5) charged spring, and
(6) electric motor.

Automatic reclosing of breakers in overhead line feeders is frequently used to restore service quickly after a line trips out because of lighting or other transitory fault. Instantaneous or time-delay reclosing may be provided with a lockout to prevent more than one to several successive reclosures, as desired.

If the fault is cleared before the lockout feature operates, the reclosing device resets itself, permitting a complete cycle of reclosing at a subsequent fault.

The circuit-breaker-operating device has to cope with the increasing requirements in interrupting and current-carrying capability as well as with shorter operating times. Simplicity of design, robustness, and reliability have to ensure safe operation of this vital link between the electrical system controls and the interrupter.

The principle of a pneumatic drive is sketched for an extra high voltage circuit breaker which functions according to the differential piston principle in figure below.

A pneumatic interlocking device in connection with the SF6 gas system ensures that the breaker always remains in the defined open or closed position even on loss of air pressure. Besides opening and closing functions, effective damping of the highly accelerated moving parts is incorporated.

Principle of the drive system for an SF6 outdoor breaker: (a) closed position; (b) open position.

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