Re: Deane Kidd and the Metric System

Fabio Trevisan
 

Thanks Stefan,
For both explanations.
I realize that, although similar in construction, in the end the loops have
completely different reasons (i.e. on the transformer and on the motor).
Magnetics seems really like magic sometimes (to not say sorcery). So
counter intuitive at times.
I still have difficulty to think of gaps in cores to minimize the effect of
saturation...At first glance, one would just think that breaking the core
continuity would make it saturate even more...
So enters Mr. Maxwells' favorite child to prove the contrary.
Cheers to Physics!

2017-12-15 16:55 GMT-02:00 Stefan Trethan stefan_trethan@... [TekScopes]
<TekScopes@...>:



I am too lazy to log into yahoo and view the photo, but I suppose you
are talking about the single loop of wire that is wound around both
outside legs in a figure of eight pattern?

This is done to equalize the flux in the two legs on some Tek
transformers that have a winding on just one leg.
If the flux tries to be greater in one leg a compensating current will
flow in the loop, forcing it to be (almost) the same.

As for the AC motors, you are likely talking about split pole motors.
The shorted turn is wound around a split-off portion of the pole
(hence the name).
This causes a phase shift in the magnetic flux, so the motor
experiences a rotary moment and can start (and keep) turning in a
particular direction. This is the same effect as a capacitor in other
motors.
If you have just one single phase the field just pulses with no
momentum, and it wouldn't start, only sit there and buzz or vibrate.
Once it is turning it may keep going even without the shifted phase,
because it gets a push every time like a child on a swing, but very
low torque. Three phase motors create a rotating field and do not need
such inferior tricks.

The same split pole and shorting ring is used in many AC relays and
contactors. It maintains the pulling force through the zero crossing,
with decreased buzzing noise.

It's magic, really.

ST

On Fri, Dec 15, 2017 at 7:27 PM, Fabio Trevisan
fabio.tr3visan@... [TekScopes] <TekScopes@...>
wrote:
Hello Albert,
Don't know if I understand the joke, but it stroke me to ask...
What are those "equalizing loops" for? I always wanted to know.
Likewise, in some AC motors (Squirrel Cage type), there are usually one
or
two of those and it always puzzled me.
Rgrds,
Fabio

2017-12-15 15:36 GMT-02:00 aodiversen@... [TekScopes] <
TekScopes@...>:



Is this the consequence of mixing metric and imperial in one
transformer?
https://groups.yahoo.com/neo/groups/TekScopes/photos/
albums/1081764917/lightbox/596728073?orderBy=ordinal&
sortOrder=asc&photoFilter=ALL#zax/596728073


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Posted by: Fabio Trevisan <fabio.tr3visan@...>
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