About 3 phase AC motor 1

[goodhong7]

Dear
I have a question in rotor portion behaviour of 3 phase simple motor. I know the stator portion has autometic rotating magnetic field by applied 3 phase AC power. But in rotor section, there are no connection like brush with power that I know of. How could rotor have magnetic field?
Thanks.

 

[electricpete]

Current is induced in the squirrel cage rotor by relative motion between stator field and rotor.

 

[Marke]

Hello goodhong7

Consider that the motor is like a transformer with a short circuited secondary. The rotor is the shorted secondary and current is induced in the same way as in a transformer. The frequency of the current induced in the rotor circuit is equal to the difference in the stator field rotation and the rotor rotation. i.e. if the rotor is stationary, the rotor current is at line frequency. If the rotor is at half speed, the frequency of the current induced in the rotor is half line frequency. If the rotor is at 99% synchronous speed, the frequency of the current in the rotor is 1% of line frequency.
Best regards,

Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Suggestion: Visit

http://www.engr.uconn.edu/ece/courses/ee214/fall2003/214ln06.pdf

http://www.geocities.com/vijayakumar777/inductionmotor/inductionmotor.html

etc. for more info