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.
Skin Effect: tendency of the current to crowd near the conductor surface.
Skin effect is proportional to frequency, conductor diameter and permiability. Skin effect increases effective resistance of conductor. In DC, no skin effect.
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