Harmonics query: Inner magnet 3 phase induction motor vs. Inner magnet single phase motor 1

[gawnieonengineering]

Hello,

I am trying to compare the effects of harmonics on 3 phase induction motor against a single phase induction motor of the same size and under the same constant torque operation, negative torque (operation as a generator.)
Does anyone have any sources that could help me on this issue.
Also a source that compares the inrush current characteristics of both?

Cheers

 

[electricpete]

I don't know a lot about single phase machines. Here's what I think I know:

1 - In general, the single-phase machine with given number of slots and poles cannot be made to reduce spatial harmonics to the same extent as three-phase machine. Pitch and distribution factors will be lower for the single phase machine.

2 - In three phase symmetric machine, we only have to consider a positive or negative sequence for each harmonic. In single-phase machine, there is a positive and negative sequence component of every harmonic of interest. The fundamental negative sequence field is of particular interest. Also causes the pure single phase machine to create zero torque when not rotating.

3 - In three-phase wye connected symmetric machine, we are not concerned with triplen harmonics since the components of the three phases cancel. Single phase machines can have triplen harmonics.

I don't know about starting performance.

Many books describe harmonic performance of three phase machines. I haven't seen much on single phase except the following: Design of Rotating Electrical Machines section 2.13 covers some aspects of determining pitch and distribution factors for single phase machines. Some design options are also discussed (leave every 3rd slot empty to improve harmonic performance).


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

 

[gawnieonengineering]

Thanks for your response.
Could you give a brief explanation about why inner permanent magnet machines create less harmonics than their wound rotor equivalent? Or is this the case? I have "The Induction Machine Handbook" but find this quite daunting.

 

[YuriB]

The current produced by the supply emf in the stator of an induction motor induces an emf in the rotor. Current born by the induced emf in the rotor induces a further emf in the stator, and so on and on. Permanent magnet motors are free of this.