False Tripping Caused By Faulty Ground Fault Detection; Magnetic Coil Assembly For Ak-3-50 Breakers - GE AK-2-50 Maintenance Manual

GEK-7303 Low· Voltage Power Circuit Breakers
Fig. 3· 2 (8039647) Magnetic Coil Assembly.for AK-3-50 Breakers
1. Carrying Fixture · · . . . 3. Transformer Taps
(In
Amperes)
2. Power Supply Coil, C. u z:ren~ Sensor Coil · 4. Disconnect Plug ·· . · .
continue carrying current without overcurrent 4..
If
·the breaker is equipped with ·ground
protection, it is recommended' that . the leads to fault protection, determine whether the false trip-
the tripping solenoid be removed to completely ping is the result of falsely answering an over-
eliminate the possibility of the breaker tripping. current trip or a ground trip. signal. This may be
Do not close breaker with power on the main determined by temporarily eliminating the.g~ound
contacts while the disconnect plug to the magnetic trip signal· by shorting out the ground signal points
coils is disconnected. ·
l
and 5 at the ground signal terminal board on the
1. Check · for the existence of overcurrent
or ground fa ult conditions that may be causing
the breaker to trip as a proper response to these
normal circuit conditions.
2. The possibility of the breaker. being trip
free by mechanical interferences along the trip
shaft or inadvertent shunt trip operations should
be positively eliminated before investigating the
Power Sensor. Successful operations in the test
p~sition should be obtained before proceeding
with the Power Sensor trouble shooting. ·
3. A PST-1 Power Sensor Test Kit must be
· available. (rig. 39). Check the -Power Sensor Unit
for correct function f<;>r each pick up setting and
one point on each time d~lay characteristic. Then .
check for the correct operation of each phase of the
Power Supply Unit. This procedure is described
in
the instruction manual (GEK-7301) for the
PST-1 Test Kit. If the test results for this test do .
: not deviate more than 10% froin the published ·· ·
. curves~__pz:oceed to ·step 4-.
If
the deviation is more
than 10% contact the factory for possible replace-
. ment of the Power Sensor Unit.
back frame of the breaker. Terminals 1 and 5
can be identified by the 0.15UF capacitor connected
between them. (See drawing 138B2454) (Fig~ 40).
With the breaker restored to service and with the
ground fault detector deactivated, establish whether
there is false tripping due to overcurrent. ·
FALSE TRIPPING CAUS.ED BY
FAULTY GROUND FAULT DETECTION
If
the breaker. is equipped for. four wire service
(fourth C. T. remotely (Fig. 37) itisimportant that
the shielding be effective by having continuityfrom
the disconnect plug at the Power Sensor Unit to the
external
C.
T. and further that this shield be isolated
from the signal conductors.
It
is also important that
continuity exists through the ground signal circuit.
Check these conditions as follows; referring to Fig.
40.
1. Remove connection plug at Power Sensor
Unit and check continuity between A and C (Signal).
Letters are located on end of plug.
.
.
2. Check to be sure no conµnuity exists be-
tween Rand C. ·
3.
Temporarily connect jumper from . shield