I've read that it's because they don't require commutators but i couldn't understand that part .. can someone please explain in some details or offer me a useful link
Wrong , high power high torque motor is series motor, not the induction motor. AC induction motor is widely used because it is simple to make and less maintenance. Its rotor just a piece of iron core without the need of winding, no need the brushes like DC motor, therefore it does not need maintenance from time to time like other type motor.
It has good power factor at high load thats why..IT has 0.8 lag p.f at full load
