Dummy 차단기란

 

출처 : http://www.netaworld.org/files/neta-journals/NWwtr0809-Bridger.pdf

 

 

NWwtr0809-Bridger[2].pdf

 

Application of Dummy
Circuit Breakers in Metal-Clad
Switchgear

 

 

Dummy circuit breakers are used in metal-clad switchgear to provide a
method of disconnecting and isolating a circuit or circuits without using
a circuit breaker. A common use of a dummy circuit breaker is as a
temporary connection in a switchgear cell where a circuit breaker will be installed
as part of a planned future expansion. Another use might be to isolate one end
of a tie bus or cable from a switchgear bus. Because a dummy circuit breaker is
really a set of three jumper bars mounted on a breaker carriage, it has absolutely
no current interrupting rating. If an attempt is made to withdraw the dummy
circuit breaker with current flowing, arcing will occur at the primary disconnect
fingers. This may result in operator injury, equipment damage, or both. Therefore,
dummy circuit breakers normally are interlocked with other switching devices so
that the dummy cannot be withdrawn until the other devices are opened, insuring
that no current is flowing in the dummy. A particular application that can
be troublesome is isolating a tie cable that has been opened by a circuit breaker
at the other end. If the cable is still attached to an energized bus through the
dummy breaker, cable charging current will flow through the dummy. It only
takes a few hundred feet of 15 kV cable to draw a charging current of as much
as half an ampere. This highly capacitive current is difficult to interrupt. It is
recommended that the interlocking for any circuit involving power cable and a
dummy circuit breaker be arranged so that the cable is completely deenergized
before the dummy circuit breaker is removed to isolate the cable. Deenergizing
the unloaded bus of a lineup of metal-clad switchgear by withdrawing a dummy
circuit breaker is an acceptable application. The limited length and very low capacitance
of a switchgear bus structure keeps the charging current low enough
to be successfully interrupted by withdrawing a dummy circuit breaker.