What Are Circuit Breakers?
Courtesy of Siemens |
Circuit breakers are mechanical
switching devices capable of making and breaking currents under
either normal or specified abnormal (short circuit) conditions on the
power system.
Though circuit breakers are primarily defined by their
protective capabilities and ratings under abnormal short circuit
conditions, they also perform switching duties under a myriad of
other system conditions, each of which has its own set of switching
stresses.
Circuit breakers are rated primarily by
power frequency voltage, insulation levels (BIL, switching impulse,
hi-pot voltage), continuous current, short-circuit current, and
interrupting time. Reference is made to IEEE C37.1001 for definitions
of ratings subjects, and to IEEE C37.042 and IEEE C37.063 for values
of ratings typically applied to circuit breakers.
Circuit breakers employ a variety of
media for high voltage insulation and/or current interruption. The
type of media employed in a specific design is often designated as a
prefix in the naming of the circuit breaker, for example, vacuum
circuit breaker, or sulfur hexafluoride (SF6) gas circuit breaker.
Circuit breakers are often categorized
as being of either “dead tank” or “live tank” design. In the
dead tank case, the interrupting contact system is enclosed in a
grounded tank, typically surrounded by an insulating fluid (oil) or
gas (SF6) (see Figs. 10-53 and 10-54 for examples of dead tank
circuit breakers).
The electrical current enters the tank
through high voltage entrance bushings, passes through the contact
system, and then exits through another high voltage entrance bushing.
In the live tank case, the interrupting contact system is supported
by insulators at some height above ground potential, but is not
contained within a grounded tank system.
There is no grounded tank or enclosure
surrounding the live parts. Dead tank design allows the placement of
current transformers, which are necessary for protective relaying
input signals, around the high voltage entrance bushing.
Live tank design offers no location to
place current transformers, and therefore must be independently
placed adjacent to the circuit breaker.
nice power circuit the tower is like the tower of tesla
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