converting double layer windings 1

[lyen12]

How do you convert from double layer lap 1-9 to single layer full pitch concentric and double layer concentric? What coil span would you recommend when converting to double layer concentric?
The stator has 36slots, 12 turns per coil, 2 parallel star. The coils are random wound pull through.

 

[Motorwinder]

I would wind it 8,10,12 pitch. Consequent connection. 24 turns. One coil per slot. Assuming it's a 4pole.

 

[electricpete]

I'm just curious, what is the benefit of converting a lap winding to concentric?

I wouldn't think the small savings in copper would outweigh the increased labor to design and wind the concentric winding.


=====================================
(2B)+(2B)' ?

 

[Motorwinder]

Less labor. Easier. Less copper. Some small motors can get quite tight, and hard to wind when you convert them from factory concentric to lap. To convert back, you just reverse the formula.

 

[rhatcher]

Pete, there is no savings in copper since you are using half of the number of coils with twice the number of turns of the same size wire. However, for small stators it is easier to wind concentric since you do not have to lap the coils. This is especially true for two pole motors.

For the OP, there is no benefit to using the double layer concentric but it would be a span of 7,9,11 with 12 turns, two wye connection with the same size wire.

 

[electricpete]

Thanks. I guess I can see some aspects that are easier to wind for concentric even though the whole thing is more complex (non uniform coils etc). We had an original concentric motor rewound and the shop elected to replace with lap since they said it was easier. I guess it's not a universal thing.

The copper savings I envison for concentric would be in the endwinding (not the slot) since the coil pitch is smaller, especially for the inner coils within a group.





=====================================
(2B)+(2B)' ?

 

[rhatcher]

Pete,
Keep in mind that the copper that is saved due to the smaller span of inner coils of a concentric windings is, more or less, offset by the additional copper that is required for the increased span of the outer coils.

With respect to which type of winding is easier to manufacture, for small diameter stators most winders will say that concentric is easier. This is because the difficulty of setting up to wind coils with different spans, and sometimes different turns, is offset by the reduced difficulty in laying concentric coils versus lap coils in a small stator.

For larger stators like you have, say >12" inside diameter, most winders will say that lap coils are easier since only one span and number of turns are required when manufacturing the coils and laying the coils under the lap is not as difficult.

 

[Motorwinder]

Consequent pole concentric motors have less copper, because they have half the groups. Half the groups mean less time to lay the coils in, and less time connecting. I've converted many small lap windings to concentric consequent. Not so much for salient windings. Continuity lap is easier for the larger stators.

 

[lyen12]

This is for a 4-pole stator. The winders are more familiar with concentric windings and it is easier to wind. The size of the stator is about 20".

 

[zlatkodo]

Hi, Lyen,
Replacement winding must be equivalent to the original.
The main condition for this is the equality of factor windings.
In this case there is no at all an absolutely equivalent single-layer replacement (lap or concentric) for double-layer lap winding with span 1-9.
Winding redesign can not be done just like that. Previous analysis has to be made​​.
If you change the winding factor you need to change the "turns / coil" and cross sectional area of wire.
Of course, this way you will also change the power and torque of motor.
Also, the ratio of "volts / coil" worsens (becomes 2 times higher) if the two-layer winding is replaced with a single-layer.
What is the impact of higher harmonics in the new winding, should be considered? Etc......
More on motor winding redesign is here.
In this particular case it's possible to replace the original winding with an equivalent double-layer concentric winding with step 1-11, 2-10, 3-9. But why would you do that? Electricpete is right, there is no any benefit .
My recommendation is: the change of original design should be avoided. However, if you want to do it, a previous analysis should be done.

 

[lyen12]

Thank you for all for the advice. These are all useful advices.
Motorwinder pointed out savings in copper, although this wasn't the main reason from rewinding the stator in single layer concentric, it may be a good reason for motor designers to consider single layer windings with 2 groups of coil per phase to save copper.

What is the effect of having 2 times volts/coil?

 

[lyen12]

btw, zlatkodo, the website you provided has lots of "eye-catching" diagrams.

 

[zlatkodo]

What is the effect of having 2 times volts/coil?

First let me know the motor voltage and connection (Wye or Delta).

 

[lyen12]

the motor voltage is 4kV, connected in two parallel star

 

[zlatkodo]

Ratio "turns / coil" is very important if winding is random wound, because there is a possibility that the first and last turn in coil are side by side.
Good design is limited to 50-60 V / coil.
If your winding is form wound that criterion is not important.
One example of poor design you can see here (see title "4 pole, 440 V; Is that connection OK?")

 

[rhatcher]

lyen12,
I have never seen a concentric winding using form coils as required by a 4kv connection. I imagine that such a thing is possible but, in my experience, it is not done.

 

[lyen12]

rhatcher, the coils that were wound was concentric, random wound. wires were manually pulled through. I have never seen form coils in concentric before. All of the pull through windings I have seen were done where the slot openings are too narrow for a drop in coils.

 

[zlatkodo]

lyen12,
Do you have some pictures of this winding?

 

[rhatcher]

So this is a random wound 4kv motor?? Are you sure it is not 400V? The extra zero between 400V and 4000V makes a big difference in winding design.

 

[lyen12]

I do not have a picture to show but it is very similar to this type of windings Link

It is 4000V.