Unbalance Examples; Example #1; Example #2; Ground Fault Current Functions - GE MM3 Instruction Manual

7 TESTING
a) EXAMPLE #1
Find the percentage unbalance given the following information:
VALUE PRIMARY
I 73 A
a
I 100 A
b
I 100 A
c
We have I given by: I
av
Since I < I , the following formula is used:
av fl
Since the unbalance is greater than 15%, an UNBALANCE alarm will occur if this condition persists for longer
than 5 seconds and the AUX Relay 1 will energize.
b) EXAMPLE #2
Find the percentage of unbalance given the following information:
VALUE PRIMARY
I
100 A
a
I
80 A
b
I 150 A
c
We have I given by: I =
av
av
Since I > I , the following formula is used:
av fl
Since unbalance is greater than 30%, a SINGLE PHASE trip will occur if this condition persists for longer than
5 seconds and the AUX Relay 2 will energize.
Test the Ground Fault CT (Residual / 50:0.025) in a similar manner to phase currents for accuracy at various
injected current levels. To check alarm and trip levels, make the following settings:
S1 CONFIGURATION \ CT/VT INPUTS \ GROUND FAULT CT INPUT: Residual
S2 PROTECTION \ MOTOR PROTECTION GROUND FAULT \ GROUND FAULT ALARM LEVEL = 40 %FLC
S2 PROTECTION \ MOTOR PROTECTION GROUND FAULT \ GROUND FAULT TRIP LEVEL = 80 %FLC
S2 PROTECTION \ MOTOR PROTECTION THERMAL\ FULL LOAD CURRENT = 100 A
While displaying A1 DATA \ MOTOR DATA \ GROUND CURRENT, begin injecting current into the 5 A Ground Fault CT
input. The Alarm LED lights and the AUX Relay 1 change state at 40 A corresponding to the 40% FLC alarm
setting. Change the display back to GROUND CURRENT and continue increasing injected secondary current.
When the measured Ground Current reaches 80 A, a Ground Fault Trip occurs. This trip causes the MM3 to
change its indicators and output relay status. The Running LED turns off, the Tripped and Stopped LEDs turn
on, and the Contactor A relay de-energizes. The AUX Relay 1 remains energized as long as the alarm is
present and AUX Relay 2 energizes after the ground fault trip. The MM3 displays a Ground Fault Trip mes-
sage. Turn the Ground Fault current off and press the reset key to reset the trip.
GE Power Management
SECONDARY (5A)
3.65 A
5 A
5 A
I + I + I
73 + 100
a b c
= ------------------------ - = -------------------------------------------- -
av
3
% unbalance
SECONDARY (5A)
5 A
4 A
7.5 A
I I I
+ +
100 80
+ +
a b c
=
------------------------ - -------------------------------------------- -
3 3
% unbalance
MM3 Motor Manager 3

7.2.2 UNBALANCE EXAMPLES

273
+ 100 A
--------- - A = 91 A
=
3
3
I I
–
×
n av
= 100
------------------- -
I
fl
150 A 330
= --------- - A = 110 A
3
I I
–
n av ×
100
= ------------------- - = ----------------------------
I
fl

7.2.3 GROUND FAULT CURRENT FUNCTIONS

7.2 FUNCTIONAL TESTS
73 91
–
×
= 100 = 18%
--------------------- -
100
150 110
–
×
100 40 %
=
100
7
7-3