Conversion from 6 to 2 pole

[EngRepair]

This is something weird that has never been done in our workshop.
Three phase, 72 slots, 6 pole, 60 HP, motor winding should be converted to 2 pole.
What would be an outcome (HP)? What issue could be expected?
Whether someone has already experienced such a conversion?
Thanks in advance.

 

[electricpete]

I haven't done it. I'll bet zlatkodo, edison, motorwinder will have some good ideas.

I'll just get started thinking thinking through it.

Original winding had 4 slots per pole phase group. 2-pole has 12 slots per pole phase group.

First simple view of the winding to maintain series turns per phase:
1 - If the original winding was single-circuit wye (with six series groups in each leg of the wye), there is 6*4=24 series coils line to neutral in each configuration, therefore no change to turns per coil or conductor area per turn.
2 - If the original winding was three-circuit wye with two series groups per phase with 2*4=8 series coil between line and neutral , then the new winding needs one third as many series turns per phase to give same number of turns when we connect 24 in series in the new winding. Presumably copper cross section of each turn is 3 times as large (maybe a little larger due to less insulation).

Above did not consider the endwindings which will be longer and may be a challenge to fit, especially in option 1.

Assuming we could implement option 1 and 2 as stated, we have roughly the same flux density and same current carrying capacity so same steady state torque rating of the stator which corresponds to three times as high power rating. Similar logic applies to rotor.

But lets look at unloaded DOL start. The heating of the rotor is equal to final kinetic energy of the rotor which increases by a factor of 3^2 = 9. The stator heating is not the same value but increases by the same factor 3^2*9. So it will be important to examine carefully the starting capability. For that we need some heavier analysis. My guess is the torque vs slip will also be lower during start due to higher leakage reactance which affects degrades starting performance and possibly breakdown torque. At this point I'm done, can't carry the analysis any further. Needs a careful look by someone far knowledgeable than me.


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

 

[electricpete]

Also you'll need to look carefully at the bearings. I assume they are greased. If you provide part number we can easily check speed rating. It's not a standard approach (maybe controversial comment) but in my experience greased bearings larger than 6313 on 3600rpm motors have lower reliability.

Are the rotor fan blades and other parts of the rotor able to handle the overspeed? Good questions for someone.

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

 

[electricpete]

Assuming we could implement option 1 and 2 as stated, we have roughly the same flux density and same current carrying capacity so same steady state torque rating of the stator which corresponds to three times as high power rating. Similar logic applies to rotor.

What was not mentioned was any change in cooling. My assumption is that it would go up (so conservative to assume that it remains the same). But may need someone to consider the cooling system and how it will perform at these higher speeds. If TEFC style it may be possible to change the external fan to be efficient at the new speed.

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

 

[zlatkodo]

It is possible but for HP estimation need more info (core / slot dimensions and previous winding data for comparison).
In fact, the complete winding data calculation must be done in order to get a proper new value of turns / coil and new HP rating.

[URL unfurl="true"]http://winding.wix.com/design[/url]

 

[edison123]

In theory, it can be done provided the no. of stator/rotor slots configuration allows it.

In practice, the rotor is likely fail due to centrifugal forces.

Also, what the speed change does to the load?

Muthu

http://www.edison.co.in