The working principle of a DC motor is on the basis of the mutual effect of electricity and magnet. A DC motor basically includes the stationary poles and the rotating armature. And the stationary and the rotating parts both include some important elements. One of them is the commutator, which should be raised special attention. The rated value is a basis to ensure that the motor is working reliably and is provided with good performance. The rated values of a DC motor include rated power, rated voltage, rated current, rated rotational speed and rated field current. The armature winding is the main circuit of the DC motor, where the electromechanical energy is converted. Therefore, the armature winding is the heart of a DC motor.
The armature winding of a DC motor is a closed winding connected by many different winding elements according to a certain rule. The armature of a DC motor is virtually a multiple branch circuit. The magnetic field in the motor is the coupling medium of electromechanical energy conversion. The relative motion between the magnetic field and the circuit occurs to produce induced electromotive force, and the mutual effect between the magnetic field and the current produces electromagnetic torque. The induced electromotive force and the electromagnetic torque are both factors of electromechanical energy conversion. The magnetic field in the DC motor is produced by the mutual effect of the excitation magnetic potential in the poles and the armature magnetic potential. The armature reaction affects the induced electromotive force and the electromagnetic torque directly.
The feature of the shunt motor is that in case of constant field current, the flux remains unchanged, so there is little change in the speed when the load changes. It can be deemed as a constant speed motor. The feature of the series motor is that when the load (armature current) changes, the field current and the main flux change at the same time. So there is great changes in the speed when load changes. This motor has higher starting torque and better overload capacity. And the feature of the compound motor is between the two.
During operation, it is necessary to observe the commutation of the DC motor because bad commutation may cause damage to the motor. The commutation process is very complex that there are sever kinds of electric potentials in the commutating elements that delaying the commutation. When the commutation circuit is disconnected, some electromagnetic energy is released, which may produce sparks. A way to improve commutation is to install commutation poles. In order to prevent sparks of potential difference, compensation winding is installed in the main pole of the DC motor.