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.

 

[electricpete]

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?

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(2B)+(2B)' ?

 

[rhatcher]

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.

 

[zlatkodo]

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

 

[lyen12]

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.

 

[KllrWolf]

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.

 

[lyen12]

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?

 

[electricpete]

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.

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(2B)+(2B)' ?

 

[electricpete]

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

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(2B)+(2B)' ?

 

[KllrWolf]

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.