GE Industrial Solutions MicroVersaTrip Plus and MicroVersaTrip PM for Allis Chalmers, Siemens_Allis, and Siemens LA-600[F] and LA-1600[F] (Blue) - Manual (Page 15)

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SECTION 7. TESTING AND TROUBLE-
SHOOTING
WARNING: Do not change taps on the current sensors or
adjust the trip unit settings while the breaker is carrying current.
Testing
1. Verify that the trip unit is securely installed by performing a
continuity test on the CT wiring and the trip unit.
a. Disconnect the black CT wires at each phase sensor.
b. Check for continuity with a continuity tester or VOM from
the white lead of the phase A CT to the white lead of the
phase B CT.
c. Repeat this continuity test for the white leads of the phase
A and phase C CTs.
d. Measure the resistance across each phase sensor and
compare the values measured to the values listed in
Table 1.
e. Reconnect the black CT leads to all of the phase
sensors. Ensure that this is done before continuing with
performance testing of the breaker.
CAUTION: In addition to the continuity test described in Step 1
and before performance testing of the converted breaker, each
phase of the breaker should be primary injected with a current
level of about 10%, but no more than 20%, of the CT rating.
During the application of test current, activate the trip unit
screen by depressing the battery button on the trip unit face and
check that the test current is displayed on the screen for each
phase tested. If the trip unit fails to display the test current, stop
the test immediately and verify the installation of the trip unit and
wire harness before proceeding with any additional testing.
WARNING: If the converted breaker is energized or tested by
primary injection with a sufficiently high test current with a loose
or open circuit between the CTs and the trip unit, damage will
occur to the trip unit, wire harness, 36-pin trip unit connector,
and CTs. Failure to adhere to these instructions will void all
warranties.
2. Check the insulation on the primary circuit with a 1,000-volt
Meggar.
3. Measure the resistance across the line and load terminals for
each phase using a micro-ohmmeter or millivolt tester. If the
resistance differs considerably from phase to phase, the
electrical connections may not be properly tightened or it
could also indicate improper contact wipe.
4. To verify that the breaker has been properly retrofitted,
perform a primary injection test on each phase. This test will
check the CTs, bus, wiring harness, flux shifter, and trip unit
as a complete system.
a. A high-current, low-voltage power supply should be
connected across each line and load terminal to simulate
an overcurrent fault.
b. Set the long-time trip at 0.5 to minimize the breaker
stress.
c. When ground fault is installed, the test can be performed
by wiring two adjacent poles in series or by using the GE
Digital Test Kit, cat. no. TVRMS2. This will prevent the
breaker from tripping because of an unbalanced current
flow.
CAUTION: Do not attempt to use GE Test Kit cat. no. TVTS1
or TVRMS on this trip unit.
Trouble-Shooting
When malfunctioning is suspected, first examine the breaker and
its power system for abnormal conditions such as the following:
• The breaker is not tripping in response to overcurrent
conditions or incipient ground faults.
• The breaker is remaining in a trip-free state because of
mechanical interference along its trip shaft.
• The shunt trip (if present) is activating improperly.
Nuisance Tripping on Ground Fault-Equipped Breakers
When nuisance tripping occurs on breakers equipped with
ground fault trip, a probable cause is the existence of a false
ground signal. Each phase sensor is connected to summing
circuitry in the trip unit. Under no-fault conditions on three-wire
load circuits, the currents add to zero and no ground signal is
developed. This current sum is zero only if all three sensors have
the same electrical characteristics. If one sensor differs from the
others (such as a different rating or wrong tap setting), the cir-
cuitry can produce an output sufficient to trip the breaker.
Similarly, a discontinuity between any sensor and the trip unit can
cause a false trip signal.
The sensors and their connections should be closely examined if
nuisance tripping is encountered on any breaker whose
MicroVersaTrip Plus or MicroVersaTrip PM trip unit has
previously demonstrated satisfactory performance. After
disconnecting the breaker from all power sources, perform the
following procedure:
1. Check that all phase sensors are the same type (current
range).
2. Verify that the tap settings on all three phase sensors are
identical.
3. Verify that the wiring harness connections to the sensors
have the proper polarity (white lead to common, black lead to
tap), as shown in the cabling diagram in Figure 21.
4. On ground fault breakers serving four-wire loads, check that
the neutral sensor is properly connected, as indicated in
Figure 21. In particular, check the following:
a. Verify that the neutral sensor has the same rating and tap
setting as the phase sensors.
b. Verify continuity between the neutral sensor and its
equipment-mounted secondary disconnect block. Also
check for continuity from the breaker-mounted neutral