The basic purpose of commutation is to ensure that the torque acting on the armature is always in the same direction. The voltage generated in the armature is alternating in nature, and the commutator converts it to direct current. In short, the commutator opens and closes the coil to control the direction in which the electromagnetic field points. On one side of the coil, the current should always "leak", and on the other side, the current should always "flow". This ensures that the torque is always generated in the same direction. Otherwise, the coil will rotate 180 degrees in one direction and then switch direction.
The commutator is a split ring made of copper, and each segment of the ring is connected to both ends of the armature coil. If the armature has multiple coils, the commutator will similarly have multiple segments-one at each end of each coil. The spring brushes are located on each side of the commutator and contact the commutator when the commutator rotates to provide voltage for the commutator sheet and the corresponding armature coil.
When the brush passes through the gap in the Changzhou commutator, the supplied charge will switch the commutator piece, thereby switching the polarity of the armature coil. This switching of polarity in the coil keeps the armature rotating in one direction. The voltage amplitude between the brushes fluctuates between zero and the limit value, but always maintains the same polarity.
DC motors have always been the backbone of electric traction drives on electric and diesel-electric locomotives, and many examples are still used around the world. The motor consists of two parts, a rotating armature and a fixed magnetic field. The fixed magnetic field consists of tightly wound coils installed inside the motor housing. The armature is another set of coils wound around the central axis.
The two parts are electrically connected through a commutator, which rotates with the armature, and provides a connection with the excitation coil through a brush. The commutator rotates with the armature and provides a connection to the excitation coil through the brush.
When a DC motor starts to rotate, the interaction of its internal magnetic field causes a voltage to be generated inside it. This "back pressure" relative to the applied voltage, the current flowing is controlled by the difference between the two. Therefore, as the motor accelerates, the internally generated voltage increases, the effective voltage decreases, and the current passing through the motor decreases, so the torque decreases.