Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations KootK on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Torque Production in Eddy Current Motors

Status
Not open for further replies.
shahvir

shahvir

Electrical
Nov 4, 2008
38
Hi guys,

The purpose of this post is to understand the actual phenomenon behind torque production in eddy current motors. This query is based on theoretical principles of torque production in AC motors.

Consider a simple eddy current AC motor with a disc type or cylindrical rotor (Watthour meter principle). The general theory of torque production explained in textbooks is that two stator magnetic fluxes, out of phase with each other, induce individual eddy currents in the rotor which in turn react with these magnetic fluxes to generate torque. But since these stator fluxes are out of phase, they will also create a net magnetic flux which will be rotating (or shifting) in space depending on the stator poles arrangement (induction motor principle). This in turn will also induce eddy currents in the rotor producing torque.

My query is, which of the above two phenomena are actually responsible (or both) for production of torque in such motors.

Thanks
 
Replies continue below

Recommended for you

Sort by date Sort by votes
Consider a shaded pole motor which uses a similar action.
The winding creates magnetic flux in the main pole which induces an eddy current in the rotor.
The shading coil creates a second pole that is phase shifted or lagging the main coil.
The flux from the shaded pole interacts with the flux from the eddy current and creates torque.
The shaded pole also causes eddy currents. The magnetic field from these eddy currents interacts with the flux from the main pole and adds to the torque.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
 
Upvote 0 Downvote
Yes. This is two field reaction theory (induction wattmeter principle). But there is another methid of torque generation by induction motor principle I.e. due to rotating or linearly shifting magnetic field (as per stator pole arrangement)
My query is, why induction motor principle of torque generation not applicable to induction type measuring instruments.
 
Upvote 0 Downvote
Same principle. The interaction of two or more field that are out of phase.
In the induction motor the eddy currents are developed in the squirrel cage winding.
A linear induction motor may be the heavy duty industrial equivalent of the Wattmeter application.
The linear induction motors that I am familiar with developed eddy currents in an aluminum strip, backed by a steel strip.
They developed about 400 HP and were capable of speeds of over 70 KPH.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
 
Upvote 0 Downvote
From the article in the link it is evident that torque production in such mechanisms is due to mutual interaction between the magnetic fields and 2 separate induced currents passing under the individual poles. In induction motor, currents are induced in the rotor due to sweeping of the stator flux in space. In my opinion the method of torque production in both these systems are different although both are induction machines.
 
Upvote 0 Downvote
I would politely disagree. The torque generation principle illustrated in the link and the induction motor principle are not exactly the same although they both operate on the principles of induction.
The above statement is also valid for a shaded pole stator because it is just a technique of phase splitting and in no way contributes to any similarities.
 
Upvote 0 Downvote
I don't believe everything that is put up on the internet. Unfortunately, the same drawing is in all EE textbooks on the subject. It is not about mechanisms or job skills, it's about working principle in theory.
 
Upvote 0 Downvote
To rephrase:
shahvir said:
My query is, which of the above two phenomena are actually responsible (or both) for production of torque in such motors(?)

1) The general theory of torque production explained in textbooks is that two stator magnetic fluxes, out of phase with each other, induce individual eddy currents in the rotor which in turn react with these magnetic fluxes to generate torque.

2) But since these stator fluxes are out of phase, they will also create a net magnetic flux which will be rotating (or shifting) in space depending on the stator poles arrangement (induction motor principle). This in turn will also induce eddy currents in the rotor producing torque.
Click to expand...

At first glance - these two phenomena are not separable.

Answer 1a: If there was no stator magnetic flux there could be no torque.
Answer 1b: If the flux were in phase they would cancel and there would be no net torque.
Answer 1c: If the rotor could not support an induced current, such as a nonconductive material, there would be no torque.

So all of (1) is required.

Answer 2: If the rotor doesn't rotate then the motor doesn't move and there is no rotation of the induced magnetic field in the rotor - the stators aren't moving so their magnetic fields cannot move.

So all of (2) is required to move, though there would still be torque due to (1) which is what initially moves the rotor.

In linear motors the effective radius for the rotor is infinite; that's the primary structural difference.

Is there some importance to the mathematics that is of concern in the different forms of induced electromagnetic force?
Are you designing some other kind of motor that is not either of the two originally suggested and for which you think no theory explains how to analyze it?
 
Upvote 0 Downvote
Ok then please provide some references or links representing the working principle you mentioned.
 
Upvote 0 Downvote
Can you please post a link or attachment?
 
Upvote 0 Downvote
Can you not simply Google the title waross suggested? Plenty of options there...

Dan - Owner
Footwell%20Animation%20Tiny.gif
 
Upvote 0 Downvote
Tried but cannot find, it's chargeable.
 
Upvote 0 Downvote
Pete and Dan. This is pointless. I give up. Let's hit the pub. The first round's on me.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
 
Upvote 0 Downvote
They won't come. They are busy helping me.
 
Upvote 0 Downvote
<Sorry, cannot answer right now. At the pub. Please leave a message.>
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

waveboy
  • Question
Comparator input bias current in STM32L073 micro?
Replies
5
Views
4K
IRstuff
IRstuff
J
  • Question
Tolerance for rated short time withstand current in MV switchgears
Replies
10
Views
6K
bacon4life
bacon4life
Dvhez
  • Question
Should secondary protection consider xfmr inrush current?
Replies
9
Views
3K
waross
waross
6
  • Locked
  • Question
Suggestions for a Display Unit in a Dusty Environment for Monitoring a Slip Ring Motor's Speed and Current
Replies
0
Views
1K
667Accord
6
FrankieAugust
  • Locked
  • Question
Current Leakage at 95% SCR Phase Control in Vacuum Sintering Press Process
Replies
1
Views
321
LionelHutz
LionelHutz

Part and Inventory Search

Sponsor

Back
Top Bottom