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pole inductance | 29 comments (29 topical, 0 editorial)

Re: pole inductance (3.00 / 0) (#2)
by Flux on Fri May 16th, 2008 at 12:50:35 AM MST
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I thought you got it last time but apparently not.

If you cancel winding inductance you get nothing. LEAKAGE inductance is what you are worrying about and is a different animal.

Your bifilar coil if connected as two windings will produce power but will do nothing for leakage inductance, that is related to slot geometry, flux path length, flux leakage paths and armature reaction.

If you connect your bifilar windings series opposing it will be non inductive and you get nothing out ( you will at least avoid the effects of the leakage inductance with no output).

Flux

Re: pole inductance (3.00 / 0) (#4)
by finnsawyer on Fri May 16th, 2008 at 08:09:19 AM MST
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I think what you and he are calling "leakage" inductance is really "mutual" inductance. I suggested he Google "Mutual Inductance", but apparently he did not. When I did, it looked like the third hit gave a decent treatment. But obviously, I'm not going to spend researching something I already know. I suggest further that he investigate the theory behind the ubiquitous transformer and how his coil arrangement would affect the performance of same.
GeoM
[ Parent ]

Re: pole inductance (3.00 / 0) (#7)
by bob g on Fri May 16th, 2008 at 08:41:14 AM MST
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finnsawyer

i understand the difference between mutual inductance and leakage inductance

but i am glad you mention it

perhaps this frames my question better

would there be a negative impact having two counter wound coils on one pole from a mutual inductance point of view?

would the induction of one coil serve to fight the other coils induction?

i guess that is basically my question.

bob g

[ Parent ]

Re: pole inductance (3.00 / 0) (#10)
by finnsawyer on Fri May 16th, 2008 at 09:18:30 AM MST
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No, and no. If the currents in the coils ran in opposite directions then the effects of the currents on the magnetic flux would cancel. But that can never happen, as connecting the coils in series for the currents to oppose forces the currents to zero, as you pointed out. Any other connection would mean that the coil currents run in opposite directions, which in turn would mean they act to change the magnetic flux in the same direction, but not necessarily by the same amount. That's tantamount to saying each coil always exhibits its own inductance.
GeoM
[ Parent ]

Re: pole inductance (3.00 / 0) (#6)
by bob g on Fri May 16th, 2008 at 08:36:24 AM MST
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my apologies for asking again, i get tied up with other stuff and forget where i post stuff,, comes with age i guess.

i am not referring to leakage inductance and yes that is a different animal
and i understand the double winding would do nothing to offset the leakage inductance as it would interact between the two windings, but
would the leakage inductance be worse with counter opposing windings? than it is between two windings of the same direction?

would the leakage inductance be lower because the iron has been theoretically taken out of play with the opposing windings?

i can do little about slot geometry, flux path, flux leakage, but
armature reaction there are a few things that can be done, reduce inductance in the pole being one, adding capacitance another, adding the opposing coil per pole.

i don't want to add the two coils in series, that i can see resulting in zero inductance with zero output,
but seperately rectified can i not still get the effect of zero inductance in that pole without zeroing the output power?

bob g

[ Parent ]

Re: pole inductance (3.00 / 0) (#9)
by finnsawyer on Fri May 16th, 2008 at 09:06:24 AM MST
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You are in error about making the inductance go away. Inductance is an inherent property for a given coil that depends on its construction. It never goes away. Just because you can connect the two opposite wound coils together to give zero voltage doesn't mean they have lost their inductance.

As far as the mutual inductance is concerned reversing one of the windings has no effect on the magnitude of the mutual inductance. Again, I recommend you study how a transformer works. Reversing one of the windings would not change the self inductance as that is independent of current direction. Since the output voltage and current would both change polarity relative to the input voltage and current, the sign of the mutual inductance would change, but not its magnitude.
GeoM
[ Parent ]

Re: pole inductance (3.00 / 0) (#11)
by bob g on Fri May 16th, 2008 at 09:24:16 AM MST
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a bifilar wound resistor has no inductance i am told

a bifilar wound iron cored inductor also has no inductance i am told as well.

yes each coil has its own inductance, but when they are wound together the effect is no inductance collectively? seperately yes, but together no?

i am not trying to get rid of the coil inductance, however i am trying to reduce the pole reactance, armature reaction

i am looking at having to rewind a stator anyway, perhaps the answer will come from just doing a test.

my hope was to get an understanding of the interaction of the two coils
carpel tunnel is no fun when it come to rewinding a stator.
but no pain, no gain i guess :)

thanks guys

bob g

[ Parent ]

Re: pole inductance (3.00 / 0) (#16)
by finnsawyer on Sat May 17th, 2008 at 08:33:39 AM MST
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Your two examples involve the reaction of the 'coils' to an external voltage source. Since the coils are wound in opposite directions the flux created by one coil opposes the flux created by the other coil, hence no measurable inductance, although each coil still has its own inductance. In the case of the alternator the time varying flux is already there, and it will induce a voltage in each coil. When the two coils are connected in some manner and a net current flows out, the principle of the conservation of energy kicks in. Since power or energy is coming out of the coils an equal or greater amount of power must be supplied at the axle of the rotor. The only way that power can be transmitted to the coils is through the magnetic flux. The process always acts to retard the motion of the rotor whether the current is 1 milliamp or 10 amps. I mention the milliamp current because you could conceivably connect the two coils together such that the voltages oppose each other. In that case, due to imperfect winding you could have a small current flow in a loop through the coils. No matter which direction that small current flows the axle must supply greater power to the rotor due to the power dissipated in the coils. This is not a "free lunch" universe. The energy equation must always balance.
GeoM
[ Parent ]

Re: pole inductance (3.00 / 0) (#17)
by bob g on Sat May 17th, 2008 at 09:32:12 AM MST
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Geo:

at least as far as i am concerned, i fully understand that there is no free lunch
as a matter of fact you cannot even break even! :)

i have been at this long enough to understand the basic rules of nature/physics/ohms law/etc...

that being if i want more power output (useable), i will have to do one of two (at least) things.

either input more power (mechanical), or
improve the efficiency of the alternator (electrically)

what i am after is a reduction in some of the losses within the machine i am working with, and alter the way it performs its function in a much different application than it was originally designed for.

not much different than the thinking behind all the other conversions on the forum,
but not specifically targeted for windpower use.
lessons learned from the process might very well have broader application for the diy'er wind generators,, who knows until you ask and experiment.

thanks

bob g

[ Parent ]

Re: pole inductance (3.00 / 0) (#22)
by finnsawyer on Sun May 18th, 2008 at 08:38:42 AM MST
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Since it's more power or shall we say more bang for your magnet dollar, I suggest you read my diary if you haven't already. I present arguments for a single phase design that should output more power than a three phase with the same number of identical magnets. The reason is fairly simple. It involves more coils for the same number of magnets with a larger rotor. Since the coils move past the magnets faster you get more voltage out per coil, which can translate into more power. The link is:

http://www.fieldlines.com/story/2006/4/21/16237/9933

GeoM
[ Parent ]

pole inductance | 29 comments (29 topical, 0 editorial)

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