Motor Heating 3

[busbar]

I attended a lecture on “Circuit Imbalances” where the presenter discussed a relationship where; e.g., in 3ø motors:

Per-Unit Temperature Rise = 2 x (Per-Unit Voltage Imbalance)^2

Is this correlation referenced in an IEEE or NEMA standard or guide? The presenter was unaware of its origin.
 

 

[electricpete]

That relation is given in "Managing Motors" 2nd ed by Richard Nailen page 4-19.

He mentions that it comes from "NEMA and various researchers" (nothing more specific.

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[electricpete]

And by the way.....

WELCOME BACK!

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[gepman]

Yes, welcome back. I remember your handle from several years ago when I had a different handle. I recently returned and tried to log-in and forgot mine but apparently you remembered yours.

From your member activity it looks like you fell of the face of the earth starting sometime in 2005 till about now!

 

[ScottyUK]

Hiya busbar,

Nice to see you back here. Been a few years hasn't it?



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If we learn from our mistakes I'm getting a great education!

 

[DanDel]

Hi busbar, go to see you back also. Now, we just need to find out where jbartos went!

 

[DanDel]

That was supposed to be 'GOOD' to see you back!

 

[stevenal]

http://www.webspawner.com/users/bartosphd/

 

[ScottyUK]

Now, we just need to find out where jbartos went!

Back to his village. There was a vacancy which needed filling.


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If we learn from our mistakes I'm getting a great education!

 

[stevenal]

Busbar's back just in time to defend his tipmaster title against dpc, who's closing fast.

http://www.eng-tips.com/tipmasters.cfm?pid=238

And right away he gets a star for his question.
Welcome back Scott.

 

[dpc]

I've just been using busbar's old answers.

Nice to have you back, busbar.

 

[jraef]

Welcome back busbar. I often wonder why people drop off.

Well, some people anyway... I was always curious if Jbartos was related to Frank Bartos of Control Engineering magazine.

gepman, that explains a lot. I thought you stepped in being a little too savvy for a newbie. What was your old handle?

 

[busbar]

Thanks for the positive responses, folks.

And thanks especially for the reference, e-pete. I'll look that one up.
 

 

[slavag]

Hello.
I would like ask other Q.
What is formula ( if any) for realtionship between current unbalance (imbalance) and Temp rise/ heating of motors.
Regards.
Slava

 

[electricpete]

It comes from:

Per-Unit Temperature Rise = 2 x (Per-Unit Voltage Imbalance)^2

For example,
1% volt unbalance -> 2% increase in temperature rise.
2% volt unbalance -> 4% increase in temperature rise.
3% volt unbalance -> 18% increase in temperature rise
4% volt unbalance -> 32% increase in temperature rise

I believe the relation applies the the temperautre rise at near full load which is the one of most interest in derating.

In Nailen's book, he says that the above relationship can be combined with an assumed load / temperature relationship to develop a relationship very close to the published NEMA MG-1 derating curves curves for voltage unbalance.
The load / temperature relationship that he gives is
1 + [fracitonal increase in temp rise] = [fractional increase in load)^1.7
(I believe this is based on fractional changes near full load).

I have plotted the method to combine these relationships to give the NEMA derating curves here:

http://home.comcast.net/~electricpete/eng-tips/UnbalanceDerating.xls

(you don't have to enable macro's - answer no)

You can see it's not too far from the NEMA derating curves which you can see on page 17/30 here:

http://www.joliet-equipment.com/pdf/techinfo/EASAHandbook.pdf

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[electricpete]

By the way, I have to say it again.

WELCOME BACK !!!!!!!!

[WAVEY][ROLL1][CHEERS][WAVEY2][WIGGLE][WAVEY3]




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[slavag]

Hello.
ElectricPete, thanks a lot, you are great!!!!
As EE, to one good answer I have two additional Q's .

Are possible say that relation between unbalance voltage and unbalance current is lineary and about
pu U2 ---- 5 x pu I2?
Best Regards.
Slava

 

[Marmite]

Slavag,
Have a look at Chapter 19, Section 19.7, of the Areva NPAG which you may find interesting, as it answers your question. The relationship is basically the ratio of starting current to rated current, 5 in your example.

Regards
Marmite

 

[slavag]

Hi.
Marmite, thanks a lot to you too.
Today is day of stars.
Best Regards.
Slava