GE Industrial Solutions MicroVersaTrip Plus and MicroVersaTrip PM DS-206, DSL-206,DS-416, DSL-416, DS-420, DS-632 - Manual (Page 18)

18
SECTION 7 TESTING AND
TROUBLESHOOTING
(CONTINUED)
False Tripping Breakers Equipped with
Ground Fault
When nuisance tripping occurs on breakers equipped with
the ground fault trip element, a probable cause is the
existence of a false “ground” signal. Each phase sensor is
connected to summing circuitry in the programmer. Under
no-fault conditions on 3-wire load circuits, the currents add
to zero, and no ground signal is developed. This current
sum will be zero only if all three sensors have the same
electrical characteristics. If one sensor differs from the
others (i.e., different rating or wrong tap setting), the
circuitry can produce output sufficient to trip the breaker.
Similarly, 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 components have previously demonstrated satisfactory
performance. After disconnecting the breaker from all
power sources, perform the following steps:
Step 1.
Check that all phase sensors are the same type (ampere
range).
Step 2.
Make sure that the tap settings on all three phase sensors
are identical.
Step 3.
Verify that the harness connections to the sensors meet the
polarity constraints indicated by the cabling diagram (Fig.
25).
Step 4.
On ground fault breakers serving four-wire loads, check
that the neutral sensor is properly connected. See cabling
diagram Fig. 25. In particular, check the following:
a. Verify that the neutral sensor has the same
rating and tap setting as the phase sensors.
b. Check continuity between the neutral sensor
and its equipment mounted secondary dis-
connect block. Also check for continuity from
connect block through the female harness
connector.
c. If the breaker’s lower studs connect to the
supply source, then the neutral sensor must
have its load end connected to the source.
See Fig. 25.
d. Make sure that the neutral conductor is
carrying only that neutral current associated
with the breaker’s load current (neutral not
shared with other loads).
Step 5.
If the preceding steps fail to identify the problem, then
measure the sensor resistance’s. Since the phase and
neutral sensors are electrically identical, their resistance’s
should closely agree.
Table 7-1. CT Resistance Values
Breaker
Ampere CT
Rating
Resistance in
Ohms
DS-206
DSL-206
DS-206H
150A
225A
400A
600A
800A 4.7-5.8
6.2-8.3
10-14
14-20
20-25
DS-416
DSL-416
DSL-416H
800A
1600A
1600A
20-25
40-50
40-50
DS-420 2000A 84-103
DS-632 3200A 44-60*
* CT’s have .4A output at rated input current.
SECTION 7 TESTING AND
TROUBLESHOOTING