Tech Brief
Circuit Breaker Trip Defeat Switch
by Jim Bowen
Powell Electrical Manufacturing Co.
T
out of the circuit and replaced with
he circuit breaker trip defeat switch allows the owner to take the functional
an indicating light and a dropping
testing of the protective relay scheme and extend it all the way to the trip
resistor. The dropping resistor is
coil without opening the circuit breaker, thus confirming that the relay’s
sized to make the circuit draw the
output contacts will indeed pick up the lockout relays and that the lockout contacts will energize the trip coil of the
circuit breaker. This action combined
with a healthy coil monitor device or
a healthy coil light tests the circuit
CS
HEALTHY
86-1
86-2
86-3
86-4
T
to the final element without openR
ing the circuit breaker. With the
increased reliability of relaying and
the pressure for extending the main95 ISW
tenance intervals, more equipment
95 ISW
95 ISW
NOR
DEF
DEF
owners are asking for the capability to
do final element functional testing on
RES
52/a
the circuit breakers feeding loads that
they can not afford to de-energize
TRIP
TRIP
SIMULATOR
DEFEATED
LT
LT
on a regular basis. As the failure rate
LIGHT
POSITION
TC
of relays goes down, the equipment
owner would prefer to functionally
95 ISW
95 ISW
check the protective relay scheme
NOR
DEF
and setpoint yearly and then pull
the relays for a full calibration check
every second or third year. The circuit
breaker trip defeat switch requires
Circuit Breaker Trip Defeat Switch
a two-position control switch (95
Switch Shown in the Normal Position
device). Position one is the normal
trip mode (see sketch). In this position the trip coil is in the circuit. The
95 ISW
DEF
second position is the trip defeated
mode. In the trip defeated position
the circuit breaker’s trip coil is cut
ANNUNCIATOR WINDOW
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same amount of current as the trip coil. Due to the critical
nature of defeating the trip coil, a separate contact should be
wired to the substation annunciator and to an amber light
mounted in the front of the breaker panel to indicate when
the breaker is in the trip defeated mode. With the switch in
the trip defeated position, the technician can function the
relays and trip lockouts to see that the lockout would have
energized the trip coil by observing the indicating light.
Once the testing is complete the technician confirms that
the lockouts are reset and the trip light is de-energized.
Then the circuit breaker trip defeat switch can be transferred
back to the normal mode. Now for my note as a circuit
breaker manufacturer, this scheme allows a much more
comprehensive check of the protection system than we
have done in the past, but don’t forget the circuit breaker.
NETA WORLD Winter 2006-2007
Yes, we have tested the protective logic all the way to the
trip coil, but the breaker has just gone another year without
functioning and the grease, without exercise, hardens over
time. Granted, in an air-conditioned substation, the interval
between maintenance can be extended but not indefinitely.
If we can help with this or any other topic please don’t
hesitate to call.
Jim Bowen graduated from Texas A&M University in 1976 with a
BSEE. He has worked for SIP Engineering as a Power Engineer and for
Exxon in all facets of electrical engineering in the petrochemical process.
He held the position of regional engineer for Exxon Chemicals Europe
for three years. In January of 1997, Jim joined Powell Electrical Manufacturing Company as Technical Director, providing leadership, training
and mentoring to both internal and external electrical communities.
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