Grundfos SP Installation And Operating Instructions Manual page 43

10.6.2 Other motor manufacturers
Refer to the other motor manufacturers'
application maintenance manual.
10.6.3 Correcting for three-phase current
imbalance
Example: Check for current imbalance for a 230
volt, three-phase, 60 Hz submersible motor,
18.6 full load amps.
Solution: Steps 1 to 3 measure and record
amps on each submersible drop cable lead for
hookups 1, 2 and 3.
Observe that hookup 3 must be used since it
shows the least amount of current imbalance.
Therefore, the motor will operate at maximum
efficiency and reliability.
Step 1 (hookup 1)
(T ) DL = 25.5 amps
1 1
(T ) DL = 23.0 amps
2 2
(T ) DL = 26.5 amps
3 3
Step 4 Total = 75 amps
Step 5 Average current
Greatest amp difference
Step 6
from the average:
Step 7 % imbalance
L 1 L 2 L 2 L 3
L 1 L 2 L 3
T 1 T 2 T 3
DL 1 DL 2 DL 3
M 1 M 3
M 2
Hookup 1
Fig. 18 Correcting for three-phase current imbalance
Step 2 (hookup 2)
DL = 25 amps
3
DL = 24 amps
1
DL = 26 amps
2
Total = 75 amps
total current
=
3 readings
(hookup 1) = 25 - 23 = 2
(hookup 2) = 26 - 25 = 1
(hookup 3) = 25.5 - 25 = 0.5
(hookup 1) = 2/25 x 100 = 8
(hookup 2) = 1/25 x 100 = 4
(hookup 3) = 0.5/25 x 100 = 2
L 1 L 2 L 3 L 1 L 2
L 1 L 2 L 3 L 1
T 1 T 2 T 3 T 1
DL 3 DL 1 DL 2 DL 2 DL 3
M 1 M 3 M 1
M 2 M 2
Hookup 2 Hookup 3
By comparing the current values recorded on
each leg, you will note the highest value was
always on the same leg, L
imbalance is in the power source. If the high
current values were on a different leg each time
the leads were changed, the imbalance would
be caused by the motor or a poor connection.
If the current imbalance is greater than 5 %,
contact your power supply company for help.
For a detailed explanation of three-phase
balance procedures, see section
with three-phase motors.
Step 3 (hookup 3)
DL
DL
DL
Total = 75 amps
75
=
3
L 3
Fused
disconnect
switch
L 2 L 3
Magnetic starter
Manual reset of thermal overload
with extra quick trip heaters
T 2 T 3
DL 1
Submersible drop cable
M 3
Motor
. This indicates the
3
7.1 Startup
= 25.0 amps
2
= 24.5 amps
3
= 25.5 amps
1
= 25 amps
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