Three-phase 2-poles windings for 72 slots 2

[zlatkodo]

Question for rewinders.
I'm interested in how often we can find three-phase 2-pole motors with 72 slots (also maybe with 90 slots), and which span is commonly used in these windings (in practice)?
Zlatkodo

 

[edison123]

The max I've come across is 66 in a 60 MW machine. 90 slots, I think, would breach the diameter limit for a 2 pole machine.

Muthu

http://www.edison.co.in

 

[zlatkodo]

Thanks Muthu,

I think the same , too.
In my practice I have seen 2-pole motors generally up to 60 slots.

But I have some unverified informations about the 2-pole motors with 72 slots for example:
Sterling 75 HP, GE 30 HP, Lincoln 125 HP, Toshiba 250 HP, Westinghouse 50 HP, Reliance 100 HP etc.
I would like to know which span is most often used in practice (I guess in double-layer ) in these windings?
It would be helpful to hear someone who has experience with these motors.

Zlatkodo

 

[edison123]

At that power range, I have not across anything over 60 slots, mostly it is 48 slots. All 2 pole windings have 2/3rd pitch.

Muthu

http://www.edison.co.in

 

[flandrax]

Along with Muthu I too have only seen 60 slot in that horsepower range.
Most 2 pole 60 slot GE that I've seen are interspersed. All the GE's I've seen have a pitch of 21.
I've also seen a Siemens 60 slot with a pitch of 14.
Don't know if this helps.

 

[electricpete]

In the category of unverified info... there is a spreadsheet of rotor bar numbers, stator slot numbers, etc for 1055 motors, mostly NEMA frame size, that I think came from Areva / Empath group. I found only one 2-pole that supposedly has 72 slots or more. It is as follows.
Manufacturer Louis Allis
Model 445US 54 2
Frame 445US
Speed 3530
HP 54
Voltage 306
Rotor Bars 34
Stator Slots 84

....Seems questionable given the voltage “306”.

===================

I think you have already seen the Reliance data which shows no 2-poles of 72 slots or more:

http://www.reliance.com/mtr/pcrssmn.htm

===================

EASA does list 72 slots as a valid combination for 2-pole machines (geared toward rewind) in the EASA Tech Manual table on coil grouping. It has annotation “6 groups of 12”, “12 12 12”, “1, 2, cir”. I know what the "6 groups of 12" means. I'm not sure exactly what is meant by “12 12 12”, “1, 2, cir” but I think it is just a simple description of the group connection. There is no mention of coil pitch in that table..

Of course we could post formula for pitch factor, but I’m pretty sure you know that one and just looking for actual built motors.


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[zlatkodo]

Electricpete wrote:
1/ "Of course we could post formula for pitch factor, but I'm pretty sure you know that one and just looking for actual built motors."

Yes.
I can choose the pitch and calculate the winding-factor for this pitch but I am interested in practical criteria for the selection of the optimal pitch. One of the criteria for the pitch selection is the value of winding-factor for this pitch but it is not the only parameter, because the highest value of winding-factor does not always mean the best winding.
Number of turns/coil (and also the motor power) depends on the chosen pitch.


2/ "there is a spreadsheet of rotor bar numbers, stator slot numbers, etc for 1055 motors, mostly NEMA frame size, that I think came from Areva / Empath group. "


By the way, whether that list is available?
Zlatkodo

 

[edison123]

pete - That "1,2 cir" means one or two circuits (max possible in a 2 pole machine) in a phase.

Muthu

http://www.edison.co.in

 

[zlatkodo]

For Flandrax:
"Most 2 pole 60 slot GE that I've seen are INTERSPERSED ."

I need some help in winding terminology in english.
What does mean the term "interspersed windings"?
Is this a winding with two half-group (with smaller span ) instead of one pol-phase group?
By the way, whether the term "interleaved windings" means the same or something else?
Zlatkodo

 

[flandrax]

Zlatkodo,
Here is some info on interspersed windings.
This should explain "interspered" better than i can.

Flandrax

 

[electricpete]

See this link for related info:

http://ifile.it/dg0wztp

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[edison123]

flandrax - are you sure that's not a copyrighted material ?

Muthu

http://www.edison.co.in

 

[zlatkodo]

Thanks for the explanation. I think I understand the difference between terms: "interspersed" and "interleaved". In attachment is a simple example of "interspersed winding" for single-layer, 2-pole, lap winding.
Maybe someone has a similar double-layer example for a number of slots of 54 or 60?
Zlatkodo