292 RPM induction motor on test stand 1

[antigfk]

Guys & Gals,

We have a 2000 HP, 292 RPM (24-pole induction), 4160V, 60Hz circulator motor on a test stand. It's an Allis Chalmers motor and is probably 30-40 years old.

I am trying to figure out some ballpark numbers for the no-load current and the rotor moment of inertia. Do any of you have access to motor data sheets of induction motors of similar speed and horsepower? Any help would be appreciated.

Another option would be to pay Siemens $1500 for engineering data, but I only need ballpark figures. For example, will the no-load current be about 25%, or 35%, or 45%, etc. of full load current?

 

[edison123]

For that no. of poles, I would expect more than 50%. How do you plan to start it ? Soft starter or direct-on-line ?

Muthu

http://www.edison.co.in

 

[electricpete]

We have a 22-pole (324rpm) 13.2kv 3500hp motor.
The WK^2 of the motor is 110,052 lbm-ft^2.
Data sheet doesn't have no-load currrent, but I think I can find it in a refurbishment report somewhere.

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(2B)+(2B)' ?

 

[antigfk]

Edison123, we'll be using a generator as a soft-starter most likely, but I was trying to determine if we could just start it D.O.L. using a the generator at full voltage. For that approach we'd use a "choke" transformer that would limit the current drawn from the generator. To do that though I needed to know for how long it would draw inrush current. I have the system modeled in ETAP and was planning to perform a motor accleration analysis once we can figure out a ballpark figure for wk^2 and no-load current.

 

[LionelHutz]

The no-load current will likely be well over 100% when no field is applied and then can change from almost no current to probably >50% current depending on the field current.

You should be able to adjust the field current to a level somwhere below rated where the power factor becomes close to 1 and the current reaches a very low minimum which is basically just to supply the losses of the motor.

 

[edison123]

Lionel, it's an induction motor.

Muthu

http://www.edison.co.in

 

[antigfk]

Lionel, you must have missed that it is an induction motor.

 

[LionelHutz]

Yes it is. I was thinking of all the Allis sychronous motor's I've seen over the years. OK, with an older slow speed induction motor such as that I would not be surprized to see a quite high no-load current, easily >50% of rated current.

Not sure why you want to know the no-load current but I'd assume it's to assure yourself that the motor health is OK. A much better measurement than the no-load current is to use the motor no-load power draw. You can make some assumptions from what you'd expect the motor efficiency is to assure yourself the no-load power draw is within an acceptable range.

 

[electricpete]

I was curious about the reason for wanting no-load current. Apparently from the 19 Aug 10 16:27 post, it is an input that ETAP wants for modeling some aspects of the motor.

Do you also input the motor torque/speed curve separately?
If so I guess it is just used to develop some simple model of current drawn by the motor as a function of speed.

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(2B)+(2B)' ?

 

[electricpete]

By the way, I have so far struck out in coming up with a no-load current that I mentioned. I have myself witnessed 3 full-voltage unloaded shop test runs in the past few years (we paid extra for the full voltage runs). I know I took notes and photographs of the screen where all the parameters were monitored.... can't find them....

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(2B)+(2B)' ?

 

[antigfk]

Electricpete,

We will be performing a full voltage uncoupled run on the motor, and I need to size my distribution components so that they can handle the motor's no-load current. The motor will be run by a 480V generator through a step-up transformer. I was trying to figure out a way to start the motor direct-on-line without having to parallel multiple generators. I was going to use the step-up transformer as a "choke" to limit inrush current... but the transformer also needs to be large enough to handle the motor's no-load current. I will probably end up soft-starting the motor.