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Home > Archive > Electrical Engineering > March 2007 > Motor Coil Design
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| Hey
Can somebody tell me, how Poles are formed inside the motor with the
windings?
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| Rheilly Phoull 2007-03-22, 3:25 am |
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"scant" <scant117586@gmail.com> wrote in message
news:1174478426.179446.300590@l77g2000hsb.googlegroups.com...
> Hey
> Can somebody tell me, how Poles are formed inside the motor with the
> windings?
>
Physically they are groups of coils connected together.
Imagine a set of "O's" decreasing in size stacked inside the bigger one.
That is how they would look, with each "O" being a coil of wire around the
laminations of the stator.
--
Cheers .......... Rheilly P
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| daestrom 2007-03-24, 5:25 pm |
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"scant" <scant117586@gmail.com> wrote in message
news:1174478426.179446.300590@l77g2000hsb.googlegroups.com...
> Hey
> Can somebody tell me, how Poles are formed inside the motor with the
> windings?
>
"...wants to be taught all the knowledge of the world while standing on one
foot."
AC or DC motor?
In typical polyphase machine, a small number of coils are connected to form
a pole-phase-group. These are used to create a 'pole'. But things get
tricky when you try and count them. Take for example a typical four-pole
three-phase induction motor. It has a synchronous speed of 1800 RPM (on
60Hz). We say it has 'four poles', but that really means that the A phase
winding has four poles, the B phase winding has four poles, and the C phase
winding has four poles. So it has 12 pole-phase-groups. Each one of these
may have six individual coils connected in series, for a total of 72 coils
in the machine (and probably 72 slots to put them in).
So in that example, six coils, in six adjacent slots are connected in
series. As current enters the first coil, passes around it, then the next
coil passing around in the same direction and so on, finally exiting the
sixth coil. The current flowing in the large number of turns creates a
magnetic pole of one polarity. When the current reverses, the magnetic pole
reverses polarity.
In small single phase machines, the windings might be different sizes
mounted concentricly as 'Phoull' suggested. Then each 'set' of windings
forms a magnetic pole of its own, and the magnetic polarity alternates with
the applied AC.
In a DC machine, the coils are mounted around a piece of iron to form a
large electromagnet. The current doesn't reverse, so the polarity is fixed.
For a 'four pole' DC machine there are simply four identical pieces of iron
situated evenly around the inside of the stator. Every other one is wired
up backwards from the others so the magnetic polarity alternates as you move
from one pole piece to the next.
daestrom
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