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converting double layer windings

converting double layer windings

converting double layer windings

(OP)
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.

RE: converting double layer windings

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

RE: converting double layer windings

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)' ?

RE: converting double layer windings

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.

RE: converting double layer windings

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.

RE: converting double layer windings

[b]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)' ?

RE: converting double layer windings

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.

RE: converting double layer windings

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.

RE: converting double layer windings

(OP)
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".

RE: converting double layer windings

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.

RE: converting double layer windings

(OP)
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?

RE: converting double layer windings

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

RE: converting double layer windings

Quote (lyen12)

What is the effect of having 2 times volts/coil?
First let me know the motor voltage and connection (Wye or Delta).

RE: converting double layer windings

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

RE: converting double layer windings

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?")


RE: converting double layer windings

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.

RE: converting double layer windings

(OP)
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.

RE: converting double layer windings

lyen12,
Do you have some pictures of this winding?

RE: converting double layer windings

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.

RE: converting double layer windings

lyen12 - That is one weird looking notor. It looks like the stuff that plays the role of end turns is some type of cable ?
Can you explain more about it?

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

RE: converting double layer windings

Wow, they say that if you keep your eyes open then you can see something new every day. Well, I have seen something new here.

Pete, it would appear the it is not just the end turns, it is the entire winding that is made of 'cables'.

All I can say is that I would hate to have to wind that, especially considering that the slot opening is smaller than the cable and this is truly a 'pull through' winding.

My other comment is; why would you design something like that? I could almost imagine this as being a re-design from low voltage to medium voltage but, it is hard to imagine that the stator slot would be big enough to accomodate that amount of increased (cable) insulation while still allowing for enough circular mils of copper to carry the current.

I m interested to hear lyen12's explanation of the reason behind this design.

RE: converting double layer windings

I think, the stator of submersible pump is shown on the picture.

RE: converting double layer windings

(OP)
That is a stator of a type of submersible motor, which will be rewind from an OEM. The whole of the motor when running is filled with plain water. Winding cables are all fully insulated to withstand the rated voltage to earth. To wind the stator, it must be pull through as the stator slots have narrow opening. I am not sure about the design of such motor as I do not design motors. I supposed with all submersible motors filled with water, the insulation system is plain simple - there is no need to have ground insulation, turn to turn insulation fault does not happen as any leaking current will go to ground through the fluid, the type of insulation does not need the stator to be VPI-ed. I also supposed that the copper cross section area would be smaller than in conventional motors because cooling is excellent in water than air. Maybe those who are experienced in submersible motor can comment on the design.

RE: converting double layer windings

While the winding wire does appear to be a type used for high voltage water filled motors, the entire design does not seem too efficient for that purpose. First, that winding is a pain in the butt and very hard to keep the winding tight in the slot to keep it from rubbing in the slot. You are correct that VPI is not performed, as it would provide no benefit. However, you should still have phase seperators as the voltage difference between phases can really do a number on the insualtion on the end turns without it.

The copper cross section is about the same, as the wire insulation required to keep the water out also traps heat effectivley, as well as has a lower allowable operating temperature.

Another thing, not winding related, is why the heck would you have holes in the stator that allow the water to leak in and out. From what I can see of that design, there seems to be much better ways to do it, but I can not see the whole system it is used in and may be missing something that makes it practicle.

RE: converting double layer windings

(OP)
As mentioned in my previous post, I did a random search on the internet to find for a picture to post as zlatkodo requested for one. I certainly do not know why the stator has holes around it.

I have never thought of the phase separators. If all of the winding wires are insulated against 4kV, for example, shouldn't the windings are protected against the line-to-line voltage? You have raised a good point. Is there any equations that I could use to determine the voltage gradient of the insulation?

RE: converting double layer windings

To my way of thinking, if conductor insulation is rated for phase to ground then there is no problem putting two conductors next to each other. Phase separators are important for random wound where we have only enamel wire insulation...relies on slot liner in the slot section and phase separator in the endwinding. There is certain difficult-to-quantify effects associated with local stress concentration but I tend to think it is much worse where unshielded conductor comes close to ground (especially at a corner of core or vent duct) than where it comes close to another unshielded conductor. I'm open to correction if I'm looking at it wrong.

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

RE: converting double layer windings

It looks like there is slot liner in there, but my guess if for mechanical protection. Anyway, I don't know details of this motor at all so feel free to disregard my comments

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

RE: converting double layer windings

Quote (Lyen12)

If all of the winding wires are insulated against 4kV, for example, shouldn't the windings are protected against the line-to-line voltage? You have raised a good point. Is there any equations that I could use to determine the voltage gradient of the insulation?

The theory says yes, but there are too many variables. In practice, we have seen most failures on this type of winding (other manufacturers, as we prefer the lap winding for ease of use and installation) with a small recorded voltage spike on more than one phase cause failure of the insulation between phases with no phase seperators. The cost of the phase seperators is so small, why not use the cheap insurance. As a personal choice I would also say use slot liners, more as a mechanical protection than electrical. Most of my caution comes from the fact that our motors may be in a hole 2000+ft down, and we do not want to see it again until the pump it is attached to is the failure from old age.

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