Why does wound rotor IM have the belt leakage but the squirrel cage rotor does not?

According to the description on page 159 of Prof. Lipo's book "Introduction to the AC Machine design":

It is important to mention that the harmonic leakage is important only for wound rotor machines. When the induction machine is equipped with a squirrel cage the harmonics in the air gap produced by the non-fundamental components of MMF will each induce a component of rotor current which will tend to “short” the harmonic inductance. Although belt harmonic fluxes still remain in the gap, they are now very small, being the summation of the harmonic stator fluxes and the opposing harmonic rotor fluxes.

However, I could not understand why such induced higher order harmonics rotor current, which cancel out the effect of higher order stator MMF in the case of squirrel cage rotor, cannot happen for wound rotor. After all, the current in the wound rotor is induced by the stator MMF, just the same as squirrel cage rotor.

• Voltage or emf is induced, not current. Current flows because of the induced voltage and a conductive path. I don't know why people say induced current in the context of magnetics; it seems to miss the point entirely; it's not like there are brand new electrons created. A bit like saying that light is conducted from an LED to our eyes. Dumbing down I guess. Rant over. Commented Jan 23, 2021 at 12:43
• and I always thought mutual inductance was Induced ! The current and voltage created are just ratios of the impedance transformer. Right? Commented Jan 23, 2021 at 13:13
• I think the induced current Lipo just means the induced rotor EMF divided by the rotor bar resistance. Thank you for pointing it out. But here the problem is focused on the analysis of harmonic leakage inductance. Commented Jan 23, 2021 at 13:48
• I found another thread about the phase number of wound rotor IM. The answer says that wound rotor IM is actually three phase. Is it the reason that it cannot be induced to generate higher order harmonic EMF/current? Commented Jan 23, 2021 at 15:44
• The squirrel-cage rotor does not have phased defined by windings. That prevents harmonics due to a difference between the stator and rotor windings that varies with relative angular position. It is the squirrel cage motor that has the advantage, not the wound rotor motor, I believe what you wrote reverses what Limo wrote. Look at my answer.
– user80875
Commented Jan 23, 2021 at 17:27