Induction motor windings, number of turns per phase and per pole

[rulmismo]

Hi,
I have some question regarding windings on induction motors, if anybody can help.
Reviewing some literature (*), the usual formulae to get the number of turns per phase of a induction motor winding is

• Eph= RMS phase voltage [V]
• Nph= number of turns of phase winding
• f= frequency [Hz]
• FL="involved" flux (typically set by a limit of Bmean * involved area, being Bmean about 0.7T for a typical machine) [Wb]
• p=number of pole pairs
• K= winding factor

Nph= Eph / (4.44 * f * FL * K )

My question is regarding the flux to be used. Most of the books and references I found talk in this equation of a "per pole" flux, but voltage in the formulae is phase voltage (and you can have several poles per phase winding), so my current understanding is:
- if p=1 (2 pole machine), Nph shall be concentrated in one winding, and flux involved is the "mean" of the whole machine
- if p=2,(4 pole machine), flux loading (Bmean) must be the same so I think:
if poles are feed in paralel (is this the usual case?), Npole=Nphase of the p=1 machine, to keep same flux loading.
if poles are feed in series, Npole=Nphase/p, to keep same flux loading (so same total turns, but distributed between the poles.)
- p=3....

I would appreciate any insight or correction, any reference to a worked example of higher pole machine design or windings could also help.

Thanks!

(*) References just in case can help anybody
ref1
ref2
ref3

 

[Andrew Mason]

Does the 4 pole motor uses single phase power? I am not sure why you would have a 4 pole motor if you have 3 phase power. If it is a single phase motor, the pole windings will have to have different reactance in order to create a phase difference between the two pole pairs. So the windings will depend on how that phase difference is achieved.

AM

 

[rulmismo]

These are m-phase motor, in the usual case m is three, then phase windings are the same, but displaced 120º. My question is related to how many turns you would use per pole, so to keep flux within saturation limits.

A n-pole motor (with n>2) is used when you want a lower synchronous speed.