Phase shift between stator and rotor

[mull982]

Is there a phase shift that exists in an induction motor between the stator EMF and the induced EMF in the rotor. The magnetic field of the rotor seems to be behind that of the stator (slip) and I was wondering if this was due to a phase shift in the induced EMF? How is this slip angle caused between these magnetic fields?

Are all induced EMF's in all other applications such as transformers etc.. subject to a phase shift?

 

[Lxnxjxhx]

From "Electric Machinery"

From "Electric Machinery"

They call things that change mechanical energy into electrical energy, or back, electromechanical transducers. A transformer isn't one of these.

Motor action induces a "slip frequency" in the rotor. They say the electrical behavior of an induction machine is similar to that of a transformer with the additional feature of frequency transformation, and they further say that a wound-rotor induction machine can be used as a frequency changer.

Hope this helps.

 

[coulter]

Is there a phase shift that exists in an induction motor between the stator EMF and the induced EMF in the rotor. The magnetic field of the rotor seems to be behind that of the stator (slip) and I was wondering if this was due to a phase shift in the induced EMF? How is this slip angle caused between these magnetic fields?...

Disclaimer: Not exactly my area of expertise. Explanation is likely to be considered simplistic by experts.

Assumption: you are talking about a standard induction motor as opposed to a synchronous motor.

Reference: Electric Machinery Fundamentals, Chapman, Chapter 7, Induction motors.

My first answer was ?Not exactly.? However after re-reading your question 10 times (or more) the answers are yes and yes. You really asked a tough one. At first I thought you were asking about the rotor turning slower than the stator mag field, and of course it does ? no slip speed, no torque ? but you knew that.

You are asking about the phase angle relationship between the rotor mag field and the stator mag field. And the rotor mag field turns the same speed as the stator mag field, and yes, the rotor field lags the stator field.

I attached a page from Chapman that explains it far better than I ever could. The last sentence on the attachment is really the important part.

...Are all induced EMF's in all other applications such as transformers etc.. subject to a phase shift?

Not really. A Delta-Wye connection gives a 30deg phase shift, but that is because of the method of connection. Sticking to an idealized two winding transformer (or D-D or Y-Y connected xfms), phase angle Vp = phase angle Vs. There are some inductances in the transformer that add small phase shifts, but I don?t think that is what you are asking about.

carl

 

[mull982]

Does anyone know if there are any teaching tool programs out there on the web, in which different motor variables can be entered, to see the effects on starting current vs torque plots? I'm trying to learn how different motor variables effect starting and running characteristics of a motor and was wondering if there was some simulation progam or spreadsheet on the web to help visualize this.