Efficiency loss associated with a HIGH or DRASTIC reduction in CM/A.

[petronila]

Happy Holidays,

There are some cases when the redesign of a winding from concentric to lap, specially in 2 pole machines, results in a HIGH or DRASTIC reduction in the wire area per turn and sometimes the reduction may range from 5 % to 7 % or above. My question is if there is a formula or rough calculation for estimating the efficiency loss associated only with such wire area per turn reduction.

Thanks in advance

Petronila

 

[waross]

At any reasonable value of I, I²R₁ minus I²R₂

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[zlatkodo]

First of all it is not clear how the result of such a redesign could be a high or drastic reduction in the wire area per turn!?!?
This is only possible with a poorly performed redesign.
You need to give a specific example of when this happened, with all the data for both windings.

Winding Redesign

 

[petronila]

Hi Zlatkodo,

My post is related to 2 pole machines redesign (concentric to lap) such redesigns are not necessary when the repair center is equipped with the concentric molds (heads) for manufacturing the coils but when a concentric to lap redesign is necessary you should consider also the new data be practical.

Here the example reuested:

50 kW, 2 pole, 460 v, 77 A, 60 Hz. 48 Slots

Winding data: 6 groups, 6 coils/group, 5,4,5,4,9,9 turns, pitch: 1-14,16,18,20,22,24, 1 Delta connected. 10 wires of 1.6 + 4 wires of 1.4

Core sizes in mm. Lenght= 222, Inside diameter: 219, Back Iron:51, Toth Width: 6.35

I know the best redesign will be using 9 turns 1-21 pitch two delta and 5 wires of 1.6 + 2 wires of 1.4 but just try to use a 1-21 pitch in a circunference of 219 mm. How long will take to rewind that motor??

For this example, please calculate a new lap winding using a 1-17 pitch an evaluate wire area per turn reduction calculated for the new winding.

Thanks

Petronila

 

[zlatkodo]

Hi,
Double-layer winding with 1-17 pitch is not an adequate replacement for the original winding.
You should not do that way at all, because you will reduce the motor power by one third approximately.
It is important what you will get as outcome, not just how to convert one winding to other.
The only solution is to replicate the genuine winding in a workshop that has all the necessary equipment.
BTW, I'm a little surprised you're asking such a question.
Probably you are prompted by dilemmas related to the claims of author of one unverified software. Am I right?

 

[petronila]

Hi Zlatkodo,

Thanks for your inputs. I don't know why are you a little surprised by my question.

In my first post, my question was: [highlight #FCE94F]If there is a formula or rough calculation for estimating the efficiency loss associated only with such wire area per turn reduction[/highlight] and your answer was "You need to give a specific example of when this happened, with all the data for both windings". Then I have provided an example where I have clarified: I know the best redesign will be using 9 turns 1-21 pitch two deltas and 5 wires of 1.6 + 2 wires of 1.4 but just try to use a 1-21 pitch in a circumference of 219 mm. How long will take to rewind that motor?? thus I disagree with your statement: "The only solution is to replicate the genuine winding in a workshop that has all the necessary equipment" the 9 turns and 1-21 pitch will provide the same performance without efficiency sacrifice also lap winding allows a better winding cooling because all coils had the same size so with the original concentric the smaller pitched coils will not be cooled as much as the largest pitched coils.

The winding data were provided for example only. I already knew the 1-17 pitch will drop the wire are per turn 6.5 % but that reduction will not reduce the output in one-third. Such reduction will increase the I2R losses in the winding and the motor will run hotter, accordingly with some EASA/AEMT Rewind Studies the I2R loses in the stator are about 30% of total losses so the 6.5 % reduction will increase the I2R stator losses, that´s why I am asking for a formula in order to calculate the efficiency drop:[highlight ] My question is if there is a formula or rough calculation for estimating the efficiency loss associated only with such wire area per turn reduction.[/highlight]

I am not trying to verify any software or similar. Again, the 1-17 pitch redesign example provided was only to show you a possible redesign that will show my concern and why I am looking for the formula. However, there are some tips that may allow using a 1-17 pitch redesign:
1. Use the right MLT
2. Use insulation class H
3. Use Inverter duty wire

The last two tips will help to avoid early damage to the insulation because the overheating.

Best Regards

Petronila

 

[zlatkodo]

Hi, Petronila,
I stick to what I have already written.
Double-layer winding with 1-17 pitch is not an adequate replacement for the original winding because after such a redesign the motor has about 40 kW (instead of 50).
What about

the efficiency loss associated only with such wire area per turn reduction

In this case, it is superfluous to talk about it, because such a redesign must not be done. If the customer is going to reduce the load to 40 kW, there is no any loss of efficiency.

the 1-17 pitch will drop the wire area per turn 6.5 %

I don't agree. The percentage is more then 11 %. I assume you miscalculated the winding factor of the original winding.
Regards
ACW

 

[petronila]

Thanks ACW,

Recall: I am not telling the 1-17 pitch is an optimum and recomended redesign. It is just an example.

From the beguining I have recomended the 1-21 pitch redesign. I am looking for a formula for estimating the efficiency loss related with the area per turn reduction.

Petronila

 

[zlatkodo]

Hi, Petronila,
Still I think the area per turn reduction (associated with increased number of turns) will cause the motor-derating rather than efficiency loss?