Testing the Tripping Transformers
33
The tests described in the preceding sections verify perfor-
mance of the static trip device and the actuator.
The third link in the protection system is the circuit breaker
mounted tripping transformers. When secondary current
testing is done on the circuit breaker, the tripping transform-
ers are subjected to approximately their normal excitation so
that a transformer with shorted turns would show up in the
form of pick-up and/or time delay values above tolerance.
However, an open circuit in the transformer would not show
up at all. Therefore, it is desirable to test the tripping
transformers as described in the following.
Test Preparations
If the static trip device is on the circuit breaker, disconnect or
remove it. For STATIC TRIP II or III, disconnect by removing
the fanning strip from the terminal block. For first generation
static trips, remove the wiring from the terminal block on the
side of the trip device. For a circuit breaker with a Limitrip
device, disconnect at the sensor terminals.
Breakers that are wired for four wire ground fault protection
have a tripping transformer external to the circuit breaker,
either on the neutral or the ground strap. This external
transformer is wired to the circuit breaker through secondary
disconnect fingers. To test this transformer the circuit breaker
must be in the cubicle, in the “TEST” position. If in doubt, refer
to the circuit breaker wiring diagram. There are two tests that
can be made, winding continuity and exciting current.
Continuity Test
Except where the transformers exhibit evidence of overheat-
ing or other damage, a simple continuity test of the wiring and
the transformer winding may be all that is required. For
transformers rated 1000/1 and above, an exciting current
test can be inconclusive due to the low level of current
involved and in the case of some of the windings used with
the Limitrip devices, continuity is the only test that can be run
due to the very low voltage required.
An ohm meter is most suitable for the continuity test. For
STATIC TRIP II, test in turn across terminals 1 to 9, 2 to 9, and
3 to 9 of the trip device terminal block, for phase A, B, and
C respectively. For a first generation type device, test be-
tween each of the heavy black wires and the common white
wire. If the cubicle is wired for four wire ground protection, the
remote transformer should be checked also; this is between
terminal 4 and 9 for Static Trip II, and between the common
white wire and the wire that is connected to terminal 9 on
4WAG and 4WDG trip devices. The circuit breaker should be
in the “TEST” position so the terminals are connected to the
remote transformer.
For Limitrip the test is made at the sensor transformer and is
made between the O and Y (Orange and Yellow) and the B
and G (Blue and Green) at each set of terminals.
Exciting Current Test
An exciting current test can be run on the transformer. This
is done by applying an AC voltage to the secondary winding
and observing the magnetizing current. This test may reveal
shorted turns in the windings. Tables 5, 6, 7 and 8 show the
maximum allowable exciting current for the various trans-
formers and sensors used. Note, the “B” and “G” terminals
of the Limitrip sensors should not be tested for exciting
current; due to the small core used, the readings are mean-
ingless.
