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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