Magnetic Theory 1

[lengould]

I have a question regarding magnetics which I can't find a definite answer for, hoped someone could help. The question is "If a static hoop of iron, eg. a horseshoe, is set near a rotating cylindrical permanent magnet which has north pole at one end and south at the other so that one end of the hoop approaches the north pole and one end approaches the south pole, is a torque imparted to the hoop? How much?"

N -]=[- S
U

The core issue is, does this setup cause the breaking of magnetic lines of force in a manner similar to eg. a claw-pole synchronous generator where the hoop is rotated 90 degrees and the magnetic shaft has alternate projections inward from each pole? BTW, I have little access to handbooks or texts, appreciate web ref's etc.

Thanks for your help


Pechez les vaches.

 

[electricpete]

You don't tell us which way the cylindrical permanent magnet is moving.

If A - rotating about it's axis so that the north and south pole stay in the same position, then that magnet generates a constant magnetic field and will not induce current in any loop.

If B - rotating so that N and S end swap - then it is capable of inducing a current. But your U-piece of iron does not constitute a loop so no current flows.

I both cases A and B there is no current flowing. Without current flowing there is no torque.


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[lengould]

electripete: Thanks for the reply. The first case is the one I am interested in, and (no torque) is the answer i had come up with by intuition. The reason I was asking is i was trying to validate a patent for a new configuration of electric motor. See

http://appft1.uspto.gov/netahtml/PTO/srchnum.html

application number 20040212259, or refer

http://www.ecologen.com/images/Wheelmotor_fig5.jpg

.

It covers three new configurations of synchronous electric motors, the second of which exploits the above configuration to excite the rotor pole pieces. eg see {images}, {drawings}, {Fig 5}. The exciter magnet is the stationary drum at the centre 14 with ring extensions 16 up each side of the stator to connect magnetically with the rotating pole pieces 6. Basically a "claw pole synchronous" machine with the "claws" separated from the exciter. Presuming eddy currents are defeated, how much power will be lost in transfering the magnetic field from the fixed exciter to the rotating pole pieces?

I take your response to be "none / negligable".

lengould (@) ecologen.com


Pechez les vaches.

 

[lengould]

What to make of Felipe Gonzales site, refered to by Texwiller? I assume he must be observing a result of an error in the software simulation. At least that's where i'd leave it until a prototype is built and proven. And no, the configuration i'm interested in is not really similar. I would SURE like to get some runs on a program like FEMM though, if it's reliable. Anybody know anything about how to arrange that? How reliable it is?

Pechez les vaches.

 

[electricpete]

Without reading in detail you have mentioned a syncronous motor. To me that suggests geometry B, ie. the N pole of the exciting field does not stay in one location, it rotates around the circumference of the airgap. (one north pole per pole pair). What part constitutes the U?

"Presuming eddy currents are defeated, how much power will be lost in transfering the magnetic field from the fixed exciter to the rotating pole pieces?"

That sounds reasonable to me. The only ways I can think of for a magnetic field to dissipate real power are:
1 - to create eddy currents as you mentioned you have discounted.
2 - to interact with an induced current in a loop such as the rotor of squirrel cage motor... I don't think you have a loop although I haven't looked loop?
3 - to interact with a forced current from some other source... I don't think you have any sources other than the field and the armature.
4 - hysteresis losses - most severe for high-frequency fields and ferrous material.

There is a separate question of reactive power... leakage impedacnes etc. Not related to real power.


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