Electric machines are devices for converting electrical energy into mechanical energy (and vice versa). The operation of a DC machine is based on the law of electromagnetic induction.
Typically, these units are used in industry for traction mechanisms such as cranes and winches. A significant drawback of the engine is the formation of carbon deposits from the brushes on the collector. To avoid excessive sparking, it is necessary to periodically inspect and carry out preventive maintenance. The design of DC machines is different from asynchronous and synchronous motors.
Between the poles creating a constant magnetic flux, there is an anchor made in the form of a steel cylinder. The coils of the copper conductor are laid in its grooves, and the ends of the conductor are connected to half rings that are isolated from other parts of the machine - this is the collector along which the brushes glide. They are connected to an external circuit.
Since electromotive force appears in the turns, the anchor of the DC machine begins to rotate when the field crosses its turns.
Due to the fact that the magnetic induction is distributed unevenly over the steel cylinder, the speed of the generated EMF depends on the current density in the gaps between the turns. Thus, the magnetic induction under the poles is maximum, and in the center of the armature (on the longitudinal axis) it is zero.
When the armature of a DC machine rotates every half a turn, the conductors change polarity, since they fall under the influence of opposite poles, therefore, the direction of the electromotive force changes to the opposite, and if the EMF changes in time and direction, then it should be attributed to a variable value. In order for the DC component to enter the external circuit, a collector is included in the device of the DC machine. This is a kind of switch. Fixed brushes, which are connected to the external circuit, slide along the half rings, rigidly fixed to the anchor.
When rotating, the anchor is in contact only with that brush, which is under a specific polarity. At a time when the direction of the electromotive force changes, the rings are switched, that is, for the external circuit, changes in the direction of the EMF do not occur. Thus, the collector is a kind of rectifier that does not allow the generated current to change.
To exclude the pulsation of the electromotive force, there are turns on the anchor that attach to the pairs of collector plates. The turns are shifted from each other by an insignificant angle, this allows you to compensate for distortions in harmonics and the current enters the circuit without ripples.
If DC machines operate in motor mode, then, on the contrary, voltage is applied to the brushes. Thus, passing through the collector, a current appears in the turns, which creates its own magnetic field. Interacting with the pole field, the armature begins to rotate, however, at the time when the direction of rotation should have changed when the conductors passed through the opposite pole, the collector still switches polarity. Thus, the direction of the current and, accordingly, its magnetic field changes. In this case, the collector is an
inverter, a DC to AC
converter .