field map about Ia & If of DC motor(separate If)

[boydli]

Hi all,
i have a problem about the test method and calculation method of field map about the Ia(armature current) & If(separate pole winding current) of DC Motor.our customer need that field map. The field map is to describe the disabled working area by If & Ia curve. For example when If less than 0.5A and Ia more than 100A then the motor should not work otherwise motor may get destroyed.
Any advices about that are much thankful.
thanks!
Boydli

 

[Skogsgurra]

By "map", do you mean a diagram?

If that is the case, do you mean a diagram showing torque vs Ie and Ia?

Or do you need a device where limits for excitation current and armature current can be set? And that makes the motor inoperative when certain limits or combinations of limits have been exceeded?

Could you, please re-phrase your question so we can understand it?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[sreid]

Assuming the "Field Map" is a safe operating area, most of the limits are probably calculated values.

Armature current limited by temperature and/or brush current.

Field current limited by temperature or magnetic saturation.

Decrease in field for operation above base speed; the limitations are rotor strength and brush arcing.

 

[boydli]

Sreid,
I undertand now.Thanks.
And I still have a question about the curve as below. There is a sample curve about If & Ia. Pls see "

http://e.simwe.com/28116/viewspace-5831".

It show that the minimum If keep same and the Ia get bigger,then the curve become inclined and at last it go to horizontal again(maximum If and maximum Ia). Now my question is how to calculate the first low end point of the inclined line. At this point the Ia is not the maximum current,why it can not go up.
And I also asked help from some engineers about that. They emphasize that generally the curve should be gotten by testing the motor. But i think it should be calculate out ,just not much exact. right?

Scogsgurra,
Yes,map may be diagram or cooperation.the curve is important for the customer to get a good device(controller) because if the device(controller) not (cooperate)mapped to motor properly then motor may run heavily or get destroyed in a short time.
thank you all very much.

Boydli

 

[Skogsgurra]

I guess that what you are saying is that you need to know the current limit, the minimum excitation current and perhaps also a speed-dependent current limit to avoid excessive arcing when running above base speed. Is that what you are asking for?

All drives that I know of have these settings available. Which drive do you use?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[boydli]

Yes.That's what I want to know how to calculate and test it, and send it to the controller designer,they want the curve to optimize their controller. I don't know the controller drive,maybe a DCVV system.
thank you.