Resistance Values; False Tri Pping- Breakers Equ Ipped With Ground Fault; Microversatrip - GE AKR-30 Series Maintenance Manual

FIG. 88 TEST SET, CAT. NO. TVTS 1
1 2.4.1 R ESISTANCE VAL U ES
For use i n troubleshooting the M icroVersaTri prM
cu rrent sensors, the resistance of the tapped and fixed
windings is g iven i n Tables 1 3 and 1 4 respectively.
TAB L E 1 3 - TAPPED SENSO R RESISTANC E
VALUES
Ampere
Tap
1 00
1 50
225
300
300
400
600
800
600
800
1 200
1 600
800
1 200
1 600
2000
TAB LE 1 4 - FIXED SENSOR R ESISTANC E
VALUES
Ampere
Rating
1 00
1 50
225
300
400
600
800
1 200
1 600
2000
The coil resistance of the MicroVersaTrip flux shifter
device is approximately 7 ohms.
Resistance in Ohms
Between Common
and Tap Terminals
7.0-8.2
1 0- 1 2
1 5- 1 8
20-24
20-24
27-32
42-50
58-68
42-50
53-68
93-109
1 30-1 54
74-88
1 1 6- 1 36
1 62-1 90
2 1 0-246
Resistance in Ohms
Between Terminals
6.7-7.8
1 0- 1 2
1 5- 1 7
20-24
27-32
42-50
58-68
92-108
1 29- 1 5 1
207-243
SECTION 1 2- MicroVersaTrip ™
Trip Device (Cont.)
1 2.4.2 FALSE TRIPPING- B R EAKERS
EQU I P P E D WITH G ROU ND FAU LT
When n u isance tri pping occu rs on breakers eq u i p ped
with the G round Fault tri p element, a p robable cause is
the existence of a false "g round" signal. As ind icated by
the cabling d iagram of Fig. 90, each phase sensor is
connected to su m m ing ci rcuitry i n the p rog ram mer. Un­
der no-fau lt cond itions on 3-wire load c i rcu its, the
currents in this circuitry add to zero and no g round
signal is develo ped . This cu rrent sum will be zero only if
all th ree sensors have the same electrical charac­
teristics. If one sensor d i ffers from the others ( i . e . , d if­
ferent rating or wrong tap setting), the ci rcuitry can
prod uce output sufficient to trip the b reaker. S i m i larly,
d iscontinu ity between any sensor and the p rogrammer
u n it can cause a false trip signal.
If n u isance tri p ping is encou ntered on any b reaker
whose M icroVersaTrip com ponents have p reviously
demonstrated satisfactory performance via the TVTS1
Test Set, the sensors and their con nections should be
closely scrutin ized . After d isconnecting the breaker from
all power sou rces.
a) Check that all phase sensors are the same type (am­
pere range) .
b) Ensure that the tap settings on all 3-phase sensors
are identical.
c) Verify that the harness connections to the sensors
meet the pola rity constrai nts i nd icated by the cabl i ng
diagram.
d) On G rou nd Fau lt breakers serv i ng 4-wire loads ,
check that the neutral sensor is properly connected (see
cabling diagram Fig. 91 ) . In particular,
( 1) Verify that the neutral sensor has the same rati ng
and tap setting as the p hase sensors.
(2) Ch eck conti nuity between the neutral sensor and its
equ ipment-mou nted second ary disconnect block. Also
check for conti nuity from the breaker-mou nted neutral
secondary disconnect bl ock through to the female harness
connector.
(3) If The b reaker's lower studs con nect to the su pply
sou rce, then tre :-�eutral sensor must have its LOAD end
con nected to the source. See Fig . 92.
(4) Ensure that th e n eutral conductor is carrying only
that neutral current associated with the breaker's l oad cur­
rent (n eutral not shared with other loads) .
e) If the preceding steps fail to identify the problem, then
the sensor resistances should be measured . Since the
ph ase and neutral sensors are electrically id entical , thei r
tap-to-tap resistances should closely agree . See Tables 1 3
and 1 4 .
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