Torque Production in Eddy Current Motors

[shahvir]

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

 

[waross]

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!

 

[shahvir]

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.

 

[waross]

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!

 

[shahvir]

Please find the link below

https://www.electrical4u.com/induction-type-meters/

My only contention with reference to the above article is that why induction motor principle of rotating or linearly shifting magnetic fields not applicable to these types of mechanisms.

 

[shahvir]

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.

 

[shahvir]

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.

 

[shahvir]

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.

 

[3DDave]

To rephrase:

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.

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?

 

[shahvir]

Ok then please provide some references or links representing the working principle you mentioned.

 

[shahvir]

Can you please post a link or attachment?

 

[MacGyverS2000]

Can you not simply Google the title waross suggested? Plenty of options there...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[shahvir]

Tried but cannot find, it's chargeable.

 

[MacGyverS2000]

I'm not suggesting you'll find a free copy, only that the information is readily available...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[shahvir]

It's not.

 

[electricpete]

check this out for induction disk relays: The Art and Science of Protective Relaying

start at the bottom of page numbered 22 (which is 32/257 of pdf).
INDUCTION-TYPE RELAYS–GENERAL OPERATING PRINCIPLES

=====================================
(2B)+(2B)' ?

 

[waross]

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!

 

[shahvir]

They won't come. They are busy helping me.

 

[3DDave]

<Sorry, cannot answer right now. At the pub. Please leave a message.>

 

[shahvir]

Enjoy.