induction motor
The rotor in the squirrel cage induction motor are shorted end to end by aluminium bars; however the are placed parallel at a certain skew angle.
Wikipedia states that "The conductors are often skewed slightly along the length of the rotor to reduce noise and smooth out torque fluctuations that might result at some speeds due to interactions with the pole pieces of the stator ."
However I am unable to understand the above statement.
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.
The crawling effect failure of the motor to accelerate to full speed when starting. Rather than accelerating to the intersection of the load to the intersection of the load torque vs. speed demand curve and the motor torque vs. speed capability curve at a point near synchronous speed, the motor accelerates to a slower operating point. That operating point is at a low point in the motor curve where the curves cross at a lower speed. That low point is partly the result of harmonic torque subtracting from the fundamental torque of the motor. Rather than accelerating to point k on the curve shown below, the motor only accelerates to point g.
Skewing the rotor slots prevents a large area of a rotor slot from being aligned with a large area of a stator slot. When that occurs, there is less stator iron area that is only separated from the rotor iron by the narrow stater-rotor air gap. That means that some angles of the rotor position with respect to the stator have a higher reluctance. That reluctance variation causes the harmonic torque components that distort the motor's normal torque vs. speed capability curve.
The slot harmonics are influenced by the number of rotor slots compared to the number of stator slots, the width of the stator and rotor slots, the amount of skew and, to a lesser extent, the shape of the slots near the stator and rotor surfaces.
The impact of the harmonic torque components is influenced by the shape of the fundamental torque vs. speed capability curve, particularly any dip in the curve between the locked-rotor and pull-out points. That is influenced by the depth and shape of the rotor bars.
See also:
Why is there a pull-up torque during the starting of an induction asynchronous motor
Best Answer
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.