DC motors are powered from direct current (DC) power and are mechanically commutated machines. DC motors have a voltage induced rotating armature winding, and a non-rotating armature field frame winding that is a static field or permanent magnet.
DC motors use different motor connections of the field and armature winding to produce different speed and torque regulation. Unlike AC motors, DC motor speed can be controlled within the winding by changing the voltage applied to the DC motor armature, or by adjusting the field frame current.
Most DC motors today are manufactured to be controlled with industrial electronic DC drives. DC motors are still used in many applications across the globe, such as paper production machines, and steel mill rolling machines.
The AC motor’s stator has coils that are supplied with the alternating current and produce a rotating magnetic field. The AC motor’s rotor rotates inside the electric motor’s coils and is attached to an output shaft that conducts torque by the rotating magnetic field. There are two different types of AC motors, each of which uses different types of rotor. The first type of AC motor is called an induction motor (also known as an asynchronous motor).
An induction motor uses a magnetic field on the rotor of an induction motor that’s created by an induced current. The other type of AC motor is called a synchronous motor and rotates precisely at the supply frequency or on a sub-multiple of the supply frequency.
Synchronous motors can operate with precision supply frequency because it doesn’t reply on induction. The magnetic field on a synchronous motor is generated by current delivered through slip rings or a permanent magnet. Synchronous motors run faster than induction motors because the speed is reduced by the slip rate of asynchronous motors.
Dc motor is widely used in the field where the motor speed needs external control. Ac motors are most suitable for applications where long – term power performance is required. All DC motors are single-phase, but AC motors can be single-phase or three phases.
AC and DC motors use the same principle of using an armature winding and magnetic field, except with DC motors, the armature rotates while the magnetic field doesn’t rotate. In an AC motor, the armature does not rotate, and the magnetic field continuously rotates.
In some applications today, DC electric motors are replaced by combining an AC motor with an electronic speed controller, known as variable frequency drive. DC motors are replaced with an AC motor and an electronic speed controller because it is a more economical and less expensive solution.
A DC motor has many moving parts that are expensive to replace, and the maintenance of a DC motor is usually more competitive than using a new AC motor with an electronic controller.
So as far as maintenance is concerned, AC motors are used most as easy availability of AC supply DC motor has a constant maintenance problem.