Why The Speed Of The Physical Rotor And The Speed Of The Rotating Magnetic Field In The Stator Must Be Different?
The mechanical speed (speed of the physical rotor) and electrical speed (speed of rotating of magnetic field) are related as a function of the number of poles/pole-pairs. For example, in a 2-pole motor, one magnetic rotation (one flux cycle for the stator windings) will correspond to one mechanical rotation (one physical stator cycle). In a 4-pole motor, two magnetic rotations will correspond to one mechanical rotation. The relationship between the two is defined as follows: electrical speed is equal to the mechanical speed multiplied to half of the number of poles.