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Number of windings clarification

electronicsman

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This is the image i saw, referring to the explanation of the 3Phase Synchronous motors. The doc says it is an empty stator containing just 3 coils, each 120 Degrees apart around the surface of the machine. But I see 6, like abc,a'b'c'. What are these a'b'c' coils? When it is referred to 3 coils does it always mean always 6 terminals. It can be different in different docs? Please advise.
1600585806529.png
 

KlausST

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Hi,

3 coils always have 6 wires.

For a motor you may connect them
* in star = 3 + 1 wires
* in delta = 3 wires

Klaus
 

electronicsman

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Is my understanding correct as shown
1600590109428.png
The terminals a,b,c are the actual phase winding's. The a',b',c' are the neutral points are ground? Can you please confirm if my understanding is correct?
 

KlausST

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Hi,

The connections are correct.

But your terminology is confusing.
Please call a'b'c' --> "Neutral", you already marked it with "N". It may be connected to earth ground or not.
You say one side is "motor" the other "load". But a motor is a load. But there is no source of power.
So either your motor is a generator, ...or your liad is a source, like mains grid, generator, source...

For equal load the current in "N" should be zero and thus may be omitted.

Klaus
 

electronicsman

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Hi,

The connections are correct.

But your terminology is confusing.
Please call a'b'c' --> "Neutral", you already marked it with "N". It may be connected to earth ground or not.
You say one side is "motor" the other "load". But a motor is a load. But there is no source of power.

So either your motor is a generator, ...or your liad is a source, like mains grid, generator, source...

For equal load the current in "N" should be zero and thus may be omitted.

Klaus
Yes i got confused. Yes my mistake motor is a load.

1600600651276.png
I need only one confirmation.
The a', b', c' i have seen in the document and posted in #1 are same as the a', b', c' i have shown in the diagram (which i have drawn on my understanding). Basically does both represent the Neutral?
 

FvM

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The figure shows a simplified stator cross section, not the winding terminals. In so far it's arbitrary and misleading to use the winding labels as terminal designator. A real motor or generator has of course windings with many turns, the windings can be either connected in star or delta circuit. Neutral won't be connected for a three-phase motor.
 

c_mitra

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Most large motors can be started in star mode and once it picks up speed, it is switched on to delta mode. Using the same coils, delta connection will provide a bit more power output. For the star delta change over at the starter box, all the six wires must come out of the motor. For small motors, it does not matter.
 

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