induction motor
Below is a squirrel cage induction motor's rotor and on the left shows only the shorted aluminum rotor bars; and on the right it shows the lamination disks are added to the rotor.
As far as I know the rotor can still rotate(as on the left) without those laminations. Those shorted bars are actually the structure which creates rotation. They form coils and pass currents and hence create torque and rotation ect.
But why are these limitations(on the right side) needed in construction of the rotor?
The problem is that the rotor and stator must have spaces called slots, in the iron for the conductors. The conductors and air in the slots have a lower reluctance than the reluctance of the iron. There are more slots than there are poles in the stator. The windings are distributed among the slots to form distributed poles. Their is a different numbers of slots used for the stator and rotor. Those two features prevent the rotor from becoming locked or "cogged" in the minimum reluctance position that would otherwise exist.
Even with proper selection of the number of stator and rotor slots, there can be reluctance variations at different rotor angles that cause torque fluctuations and inflections in the torque vs. speed curve. Skewing the rotor slots mitigates that effect.
Here is a picture of the rotor and stator of a 4-pole, permanent-split capacitor, single-phase induction motor.
The starting current and starting torque can be calculated from the per-phase equivalent circuit. The circle diagram is an aid for that calculation. You need to use the data from the no-load and blocked-rotor tests. However the DC resistance is also required and should be measured. You should be able to find the procedure for calculating the equivalent circuit component values in a text book or lecture notes that can be found on the internet. The procedure for calculating torque from the equivalent circuit can also be found.
The rated motor speed and current should be marked on the name plate. The rated torque can be calculated from the rated speed and power. With the rated torque and current, you can use the given percentage values to calculate starting torque and current.
The energy meter is not very useful beyond performing the no-load and blocked-rotor tests.
You should find the procedures mentioned above, work on the solution, then ask for assistance with any parts that you don't understand. The full solution can not be provided here as the answer to a single question.
Best Answer
An induction motor is basically a regular power transformer but the secondary is "shorted" and is allowed to rotate. Would you expect good efficiency if you had big air gaps in a regular power transformer? Maybe you don't know how power transformers work?
The bottom line with power transformers is that you want the primary magnetism (stator) coupled to the secondary winding (rotor) as much as possible and you therefore avoid large air gaps that would bypass the secondary winding.