Motor frame size

[SENGUTTUVAN]

For a given driven equipment ( Pump) , with the known GD2 value and torque requirement , how the frame size of the drive equipment ( motor) is selected? What are all the factors to be considered. In one of the Project , the client had changed the make of the motor from one vendor to another. Should there be any change in the Frame size? Is this applicable for both the LT and HT motors? Thanks to clarify.

 

[waross]

The frame size is selected by the motor manufacturer. You don't generally spec a frame size except to ensure that different branded replacements will fit physically. However, whet is the optimum frame size for one manufacturer is usually optimum for all manufacturers.
The following factors will affect frame sze;
HP
Speed
Cooling method (TEFC, ODP)
T-frame, U-frame, or, for very old installed equipment, NEMA-frame.
A multi-speed motor may be a different frame than the same HP motor in single speed.
Check the manufacturers specs to determine the frame size for the motor you require. If different manufacturers offer the same motor configuration in different frame sizes, consider designing for the larger frame. It is fairly easy to shim a smaller replacement motor, but difficult to install a larger motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

NEMA MG-1 2003 sections 13.1 and 13.2 give frame assignments based on horsepower and speed.

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[electricpete]

I should say sections 13.1 thru 13.5. There are various tables breaking motors into fractional and integral horsepower and into ODP and TEFC. So selection ODP vs TEFC affects frame size.

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[burnt2x]

I don't know how inertia and torque can be related to motor frame size.
What I know is that from the NEMA motor frame size, I get to know the shaft diameter (through the bearing size), mounting frame bolt center distances, etc. If you have a pump shaft, you measure the diameter and try to refer to the frame chart which motor frame has the same OD as your pump shaft.
I guess you could decide what type of material to be used as a shaft key based on your torque requirements inertia load. Other than those, let's wait for others to comment.
Hope this helps.

 

[edison123]

Agree with burnt2x. I don't see what motor frame size has got anything to do with inertia and torque (and why the motor inertia is important here ?). You specify the speed-torque of your pump and ask the motor OEM's to match it. You could even specify the frame size, if there is a site limitation.

 

[SENGUTTUVAN]

Thanks to all for replying. The present situation is , the detailed engineering of one of the refinery plant is half way through and based on one of the motor manufacturer ( which the client had entered into umbrella contract earlier) we have freezed the equipment GA drawings with the motor frame size. Now suddenly the client had indicated that the umbrella contract is cancelled and they are looking for alternate motor manufacturer. My concern is ,whether there are possibility of the change in the frame size if we go in for the alternate motor manufacturer ( The KW of the motor , speed and the Torque speed characteristics are already freezed for the equipment to be driven). All the motors are of LT motors only ( below 160 KW) Thanks to clarify.