Speed of a Permanent Magnet Synchronous Motor (PMSM)

1 rotor, 2 rotor, 3 rotor, 4, ..................................

i believe the synchronous speed of a rotating field in a motor is 120xf/p EVEN if there is no rotor at all ?

Your doubt is valid, why do you think that the length of the rotor has any effect on its synchronous speed when it is the speed of the rotating magnetic field in the stator that the rotor follows.

ok then the speed depends on length of the stator???

My goodness. .... no.it.does.not.

Please keep your engineering degree, if any, in a safe place.

Thanks for your comment,

Do u think my question is very basic??? If so, please excuse me, i am trying to design motor by fixing a particular length for it. That is why i got this doubt. You may think the length of stator & rotor are same, but what i actually mean was length of rotor means length of permanent magnet.

Sorry if my comment was offensive, i wanted to take it back, but could not....

i was taught a reasonable amount about synchronous motors, induction motors, and many other types in the pre-final year of my engineering course (1966). Things could not have deteriorated to such an extent today that you would not have learnt the same thing....

Anyway, a synchronous motor, as the name implies, will run at 120xf/p. Nothing else will affect.

Yes sir, things are worsened so much that, i didn't studied about permanent magnet synchronous motors in my engineering subjects (2010 pass out), but got a work to design it so i am posting many silly questions (if you feel such) about PMSM....

Anyways thanks for your answers sir

sharath

SHARATH:

The problem you have is basic electricity and the lack of paying attention to the basic principles and at the same time NOT recognizing what to do, because the lack of attention to the basic principles.

You have a basic PMSM -- please define what is PMSM for you. !!

That have magnets that define the magnetic field of the motor or generator that as a motor the RPM has to be defined by the number of poles and the frequency of the power applied to it of : RPM = (60 seconds * Frequency ) * 2/poles.

Then You need to think how is the power that the motor may be able to produce -- this is a basic problem of metal volume and magnetic flux available -- the diameter time the volume of the core and rotor plus other oddities produce the watts that the motor can handle -- so the length is a consideration for power available .

One needs to study motors if you are using them, even if this is done sparingly and rarely -- well at least this was the way I did even when I was 12 or 13 years old I studied the motors to understand them and how to use them.

Permanent magnets - brushless -- are synchronized to the frequency by definition -- and for sure such fact was included in the university courses for many decades -- specially the last 20 years.

We know that Power = (2*pi*speed*Torque) / 60
If torque remains constant, speed is the only variable parameter, So i think i can relate length to speed since the length is a consideration for power available.
Please, Can u clarify me??? (if i am wrong also)
Sharath

Electrical Power depends on the inductance of the motor windings which are related to the windings turns generating a magnetic field in the metal volume of the motor that has to be kept within the metal magnetic saturation capabilities to produce the necessary energy to be fed to the rotor .

So the necessity of having certain minimum volume to have enough magnetic field to produce the desired KW output or HP.

Often, I can not attend the requests and supply answers , though I am retired I am quite busy and often away from the PC.

You need to study the electrical equations that generate the necessary power with relation to the core metal volume which are different from the electro-mechanical .

http://www.control.com/thread/1026233123 this another place where you could get responses to your questions,

http://ww1.microchip.com/downloads/en/AppNotes/00887a.pdf

http://www.ece.auckland.ac.nz/~kacprzak/PE2.html http://www.pdhonline.org/courses/e176/e176content.pdf http://charming.awardspace.com/induction_motor/induction_motor.html

Read this as well -- specially the electrical terminology

http://uotechnology.edu.iq/dep-eee/lectures/3rd/Electrical/Machines%202/IV_I.Machines.pdf

Thank You Mr.Nando37

The last time I looked, synchronous meant synchronous, as in lockstep with the rotating magnetic field. No ifs, no buts. A phase difference will occur depending on the load etc., and will remain in a given application relatively constant.

An induction motor on the other hand relies on the slippage to get current induced into the rotor, to function at all.