Higher current drawn by motor at Low Voltage - WHY ?

Hi all
If anybody gives the answer for this it is highly appreciable
I agree that an induction motor will draw more than the rated
nameplate current if the applied terminal voltage is less than the rated voltage
My question is as below
1) Why the above is happening in motor
2) This is the most important question - In the all manufacturer data sheet and curves the current at 80% of the terminal voltage shows lesser current that is drawn by the motor than at 100% Voltage- this is totally contracting with the above point (1)
pls give more clarity - Also tell me whether i am confusing both different entity pl.
Could anybody give the answer please
Regards N.A.Govind
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On Mon, 05 May 2008 09:27:01 -0700, Govind wrote:

Back EMF? Check it out!
Al
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The counter electromotive force created in the rotor is less, and current goes up to a limit then drops off as voltage is reduced.
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In article

If an induction motor works at all It will run close to but below synchronous speed. Lowering voltage may result in somewhat further reduction of speed but the motor will still run close to synchronous speed. The load still must still provide about the same amount of torque. Thus, mechanical output power will typically be reduced only slightly. To keep the power up at reduced voltage, in phase current must be increased.
Bill
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----------------------------
remove the X to answer

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Govind wrote:

There are a couple good answers to question 1.
For question 2, at 80% voltage there will be much lower speed and available torque, so there is much lower available horsepower, resulting in electrical power also being much lower.
Do they give 80% voltage for other than reduced voltage starting?
--
bud--

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Wowwwww
Thanks for all for posting their replies
(Mr. Bill answer is little favour to me - please give me more clarity by speaking about torque, i.e if applied voltage is less O/P has to reduce (in terms of torque) rather why motor drawing more current tends to supply rated torque - "motor is not knowing that voltage is less: :) :) ! )
I agree with all of your answers
Here i want to highlight my question again that
***If u observe "manufacture data sheet" - current drawn by the motor at 80% of voltage is less than the 100% voltage
this lead to my confusion
I again asking about here that what manufacture data sheet exactly indicates
please put some light on the above matter
"I agree that current drawn by the motor is more if the voltage reduces during running - by observation in site"
Please advise !
Regards N.A.Govind
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wrote:

One thing to keep in mind is not all motors are exactly the same. There are a few oddball designs out there like 'D' class that don't follow exactly the same rules. (well, in a nod to Don Kelly, they do follow the same formulae, but with a much higher rotor resistance, the resulting torque/speed curves don't look much like the others).
It might help us if you could tell us more about the specific example you have in mind. Or even find the data sheet on line and share it with us. Then we might be able to focus a bit more on your particular question.
daestrom
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