Which type of electric motors are more powerful a.c or d.c?
The strict answer to your question is neither; however, in a DC motor the armature wire utilization is not as good as the utilization of the rotor wire in an AC motor.
AC motors can convert more power per unit of mass and more power per unit of volume. In a DC motor, almost all of the input electrical power must pass through the commutator. The commutator adds size and weight and reduces efficiency. The design of the rotor windings also requires more copper and reduces efficiency. Lower efficiency means increased heat requiring a larger motor. In the case of a brushless DC motor, there are permanent magnets in the rotor making it more like an AC motor and possibly somewhat more powerful than an AC motor of equal physical size and mass. In addition, AC motors can be manufactured in power ratings that are not possible with DC motors. The commutator limits the maximum voltage and current. AC motors can operate at higher voltages. An AC motor has been manufactured for 101,000 kW (135,000 Hp). It has two 12,500 volt, 3-phase stator windings.
