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Application – All Motors
Distribution transformers must be adequately sized to
satisfy the kVA requirements of the submersible motor.
When transformers are too small to supply the load, there
is a reduction in voltage to the motor.
Table 4 references the motor horsepower rating, single-
phase and three-phase, total effective kVA required, and
Transformer Capacity - Single-Phase or Three-Phase
NOTE: Standard kVA
ratings are shown. If power
company experience and
practice allows transformer
loading higher than
standard, higher loading
values may be used to
meet total effective kVA
required, provided correct
voltage and balance is
maintained.
the smallest transformer required for open or closed
three-phase systems. Open systems require larger
transformers since only two transformers are used.
Other loads would add directly to the kVA sizing
requirements of the transformer bank.
During starting of a submersible pump, the torque
developed by the motor must be supported through the
pump, delivery pipe or other supports. Most pumps rotate
in the direction which causes unscrewing torque on
right-handed threaded pipe or pump stages. All threaded
joints, pumps and other parts of the pump support system
must be capable of withstanding the maximum torque
repeatedly without loosening or breaking. Unscrewing
joints will break electrical cable and may cause loss of the
pump-motor unit.
To safely withstand maximum unscrewing torques with
a minimum safety factor of 1.5, tightening all theaded
joints to at least 10 lb-ft per motor horsepower is
recommended (table 4A). It may be necessary to tack
or strap weld pipe joints on high horsepower pumps,
especially at shallower settings.
Effects of Torque
Table 4A Torque Required (Examples)
MOTOR RATING
TOTAL
EFFECTIVE
KVA
REQUIRED
SMALLEST KVA RATING-EACH TRANSFORMER
OPEN WYE
OR DELTA
2- TRANSFORMERS
CLOSED
WYE OR DELTA
3- TRANSFORMERS
HP KW
1.5 1.1
32 1
2 1.5
4 2 1.5
3 2.2
53 2
5 3.7
7.5 5 3
7.5 5.5
10 7.5 5
10 7.5
15 10 5
15 11
20 15 7.5
20 15
25 15 10
25 18.5
30 20 10
30 22
40 25 15
40 30
50 30 20
50 37
60 35 20
60 45
75 40 25
75 55
90 50 30
100 75
120 65 40
125 90
150 85 50
150 110
175 100 60
175 130
200 115 70
200 150
230 130 75
Table 4 Transformer Capacity
MOTOR RATING
MINIMUM SAFE
TORQUE-LOAD
HP KW
1 hp & Less 0.75 kW & Less
10 lb-ft
20 hp 15 kW
200 lb-ft
75 hp 55 kW
750 lb-ft
200 hp 150 kW
2000 lb-ft
4