The working principle of the commutator is the principle of converting the alternating electromotive force generated in the armature coil into a direct current electromotive force by the commutator in cooperation with the commutation effect of the brush.
No DC voltage is applied to the brush, and the armature is dragged with the prime mover to rotate it counterclockwise at a constant speed. The two sides of the coil respectively cut the magnetic lines of force with different polarities, and the electromotive force is induced in them. determine. This electromagnetic situation is shown on the figure. Because the armature rotates continuously, the coil sides ab and cd that the current-carrying conductor is exposed to in the magnetic field must alternately cut the magnetic field lines under the N and S poles, although the induced electromotive force in each coil side and the entire coil The direction is alternating. The induced electromotive force in the coil is an alternating electromotive force, but the electromotive force at the ends of the brushes A and B is a direct current electromotive force (to be precise, it is a pulse electromotive force with a constant direction). Because, during the rotation of the armature, no matter where the armature is turned, because the commutator cooperates with the reversing effect of the brush, the electromotive force drawn by the brush A through the reversing sheet is always in the coil edge cutting the N-pole magnetic field lines. Therefore, the brush A always has a positive polarity. For the same reason, the brush B always has a negative polarity, so the brush end can draw out the pulse electromotive force of the same direction but the size changes. If the number of coils per pole is increased, the degree of pulse vibration can be reduced, and DC electromotive force can be obtained. This is how the DC generator works. It also shows that the sub-DC generator is essentially an AC generator with a commutator.
From the perspective of the basic electromagnetic situation, a DC motor can work as a motor and a generator in principle, but the constraints are different. Add DC voltage to the two brush terminals of the DC motor, input electrical energy into the armature, mechanical energy is output from the motor shaft, drag the production machinery, and convert the electrical energy into mechanical energy to become the motor. For example, use a prime mover to drag the DC motor If the DC voltage is not applied to the brush, the brush terminal can draw DC electromotive force as a DC power source, which can output electrical energy. The motor converts mechanical energy into electrical energy and becomes a generator. The same motor can be used as a motor or generator. It is called the reversible principle in motor theory.
