relation between laminations and cage of bars inside rotor in induction motor

[aletric]

dears
regards
first let me explain this basic of principles : in an induction motor , an AC current will applied in the stator armature which generates a flux in the stator magnetic circuit . this flux induces an EMF in the conducting bars of rotors which are cut by the flux (E=BVL).
A current flows in the rotor circuit due to the EMF induced produces a force (F-BIL) , hence producing torque as the output.
the question now ? : can you verify to me , despite the laminations of rotor will aid the magnetic field to generate an emf in conducting bars , why not making short circuit between each other to the earth, as bars built inside laminations of rotor , even both have different materials but conducting.
thanks

 

[electricpete]

I have a hard time following your question.
We use rotor iron to enhance the flux path.
The rotor iron is laminated to prevent circulating currents

There is generally no electrical insulation between the bars and the rotor core (it would impede heat transfer from bars to core, vital during start).

There can be unintended currents but they are generally small due to a number of factors: bar-to-iron contact resistance and higher conductivity of copper than iron. In spite of these factors, I believe there is some small amount of current that flows in these iron paths. Some may flow in parallel with the bars, finding paths where there is a short between laminattions such as the id of laminations where they contact shaft or spider. Some may flow between bars of different potential ( google motor "interbar" currents). These are all secondary unintended effects, not important to the basic operation of the motor..... I suspect this is not what you’re interested in.

I don’t know if I have touched on your question or not. Please feel free to clarify exactly what you’re interested in.

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(2B)+(2B)' ?

 

[7anoter4]

The rotor torque is direct proportional with the field flux density multiplied by rotor bar current [Irot],as you-aletric- said .
In order to get more flux
density from the same stator mmf [wst*Ist] you have to reduce the magnetic flux path reluctance through the rotor surface where
the bar are spread by enhancing the material permittivity[Re=k/miu] as electricpete said.
If the cage will be air filled only a part of the stator
leakage field will reach the cage and not the main flux.
On the other hand, the energy transferred from stator to rotor contains, beside the effective power, the rotor cage losses ,the rotor laminate losses and the mechanical losses.
If you will produce short-circuit between laminates you'll rise the laminate losses by circulating currents-as electricpete said.
Nevertheless the laminate circulating current could produce a small torque- compared with this produced by cage,
in this way, you will decrease the remaining effective power and will increase the rotor-and the motor- heat.