1gibson
That is an over simplified question to a very complex problem. I will try to give you a generalized answer without writing a book. Submersible motor basics:
1. Submersible induction motors used in the petroleum industry typically range from 1 kV to 4 kV nameplate volts at 60 Hertz.
2. Standard motor design used will be insulated between 4 kV and 5 kV regardless of nameplate voltage required.
3. The transformers typically used are multi-tap that allows 60 volt increments throughout the entire range. Basically any supply voltage is available.
4. Submersible motors are space limited; they must fit in a well. Typical sizes are 3.75, 4.5, 5.62 inch OD. The maximum length for a single housing can be up to 31 feet. Due to the OD size limitations we may manufacture a 450 HP, 5.62 inch OD, and 31 foot long motor.
5. Winding 20 to 30 foot long stators is a nightmare. Almost all stators must be hand wound. Submersible motor manufacturing is a labor intense process.
6. Most manufactures have a motor testing lab complete with dyno capabilities. You would think a onetime test is enough, but motor labs operate continuously year after year.
7. NEMA standards do not apply to submersible motors used in the petroleum industry. They are two different worlds.
During testing any motor manufacturer will make an efficiency curve by maintaining a constant voltage and varying the load. Submersible manufactures take this one off test a little further. We know the best efficiency with nameplate conditions. We can then vary the load and supply voltage to find the same best efficiency point at various loads. This sounds a little confusing, so I will use an example for a motor that I believe is no longer manufactured by any supplier.
Actual Nameplate Conditions:
70 HP,
1313 V
36.3 A
80.7 Efficient
If I want a lower rating for the same motor it would operate as:
56 HP
1218 V
32 A
80.5 Eff
I could go the other way with the rating.
87.5 HP
1412 V
43.1 A
80.8 Eff
The industrial world is limited to nameplate values simply because variable volts typically are not available. Realistically a motor does not know the nameplate value; it simply tries to drive the load attached to it. By adjusting the input we can match the motor to the load attached to it. We are not “simply supplying new paperwork” we are applying test data.
One thing I would caution you on as the load increases so does the internal heat rise. Any recommended adjustment should come from the motor manufacture. Manufactures know what their heat rise is, the effect of velocity past the motor, effect of specific heat of the produced liquid etc…
