due to fractional pitch EMF can be approximately made into sine wave losses due to harmonics reduced saving in conductor material mechanical strength of coil is increased.
In all machine stator and rotor magnetic field rotates (stationary with respect to each other) at synchronous speed with respect to stationary observer.
slip ring motor have high starting torque compare to squirrel cage motor and have good speed control also have high over loading capacity, smooth acceleration under heavy loads.
EXAMIANS