Basic Structure
It is divided into two parts: the stator and the rotor. Note: Do not confuse the commutating poles with the commutator .
The stator comprises: main magnetic poles, the machine frame, commutating poles, the brush assembly, etc.
The rotor comprises: the armature core, armature windings, the commutator, the shaft, the fan, etc.
Rotor Composition
The rotor section of a DC motor consists of components such as the armature core, the armature windings, and the commutator. The following section provides a detailed introduction to each of these structural components.
1. Armature Core Section: Its function is to house the armature windings and serve as the path for magnetic flux. It is designed to minimize the eddy current losses and hysteresis losses generated within the armature core during the motor's operation.
2. Armature Section: Its function is to generate electromagnetic torque and induced electromotive force (EMF), thereby facilitating energy conversion. The armature windings consist of numerous coils, typically wound using glass-fiber-insulated flat copper wire or high-strength enameled wire.
3. Commutator (also known as the Rectifier): In a DC motor, its function is to convert the direct current (DC) supplied by the brushes into alternating current (AC) within the armature windings, thereby ensuring that the direction of the electromagnetic torque remains constant. In a DC generator, it converts the alternating EMF generated within the armature windings into a direct EMF output at the brush terminals.
The commutator consists of a cylindrical assembly formed by numerous segments (bars) insulated from one another by mica. The two ends of each coil in the armature windings are connected to two separate commutator segments. In a DC generator, the role of the commutator is to convert the alternating EMF generated in the armature windings into a direct EMF across the brushes; this allows current to flow through the load, enabling the DC generator to output electrical power to the load. Simultaneously, current inevitably flows through the armature coils themselves. This current interacts with the magnetic field to generate an electromagnetic torque-known as the reaction torque-whose direction is opposite to that of the generator's rotation. The prime mover (driving machine) must overcome this electromagnetic reaction torque in order to drive the armature's rotation. Consequently, while the generator outputs electrical power to the load, it simultaneously absorbs mechanical power from the prime mover, thereby fulfilling the DC generator's function of converting mechanical energy into electrical energy.
