I have been studying the three phase induction motor and in the process I could not exactly understand the EMF generation in the rotor.

From figure(2) below, it is understood that the maximum EMF is produced in the rotor's coil when the maximum flux density is interacting with that particular phase.

So,does that mean the EMF so produced is in phase with the flux density wave?

View of three phase induction motor

sinosuidal waveforms in induction motor

From the figure below, if the induced EMF lags the RMF by 90 degrees then how come the EMF can be of maximum where the flux density wave is maximum in the first case ?

Phasor diagram

Does the above situation have anything do with understanding the term phase angle and mechanical angle?

If the induced EMF lags the flux wave that produced it by 90 degrees, then why do the figures above show that the maximum voltage is induced where the flux wave cutting action is maximum?

  • \$\begingroup\$ Please provide document or web links to the original text and diagrams. \$\endgroup\$
    – Andy aka
    Nov 17, 2021 at 10:58

1 Answer 1


From Fitzgerald, Kingsley, Umans, Electric Machinery, 4th ed.:

Fig 9-5(a) shows voltage in each bar induced by flux-density wave. Fig 9-5(b) shows current lagging rotation and voltage by power factor angle. Fig 9-5(c) shows MMF wave lagging rotation by 90 degrees plus power factor angle.

enter image description here

  • \$\begingroup\$ But i have a doubt regarding the phase difference between induced emf and rmf. \$\endgroup\$
    – Theja
    Nov 17, 2021 at 14:30

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