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.
These units are typically used in industry for traction applications 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, which create a constant magnetic flux, there is an anchor made in the form of a steel cylinder. Coils of a copper conductor are laid in its grooves, and the ends of the conductor are connected to half rings, which are isolated from other parts of the machine - this is the collector along which the brushes slide. They connect to the outer circuit.
Since an electromotive force arises in the coils, the armature of the DC machine begins to rotate when the field crosses itturns.
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, under the poles, the magnetic induction is maximum, and in the center of the armature (on the longitudinal axis) it is equal to zero.
When the armature of a DC machine rotates, every half-turn the conductors change polarity, as 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. In order for a constant component to enter the external circuit, a collector is included in the device of the DC machine. It's a kind of switch. Fixed brushes, which are connected to an external circuit, slide on half rings rigidly anchored.
Rotating, the armature is in contact only with the brush that is under a particular polarity. At the time when the direction of the electromotive force changes, the rings switch, that is, for the external circuit, there is no change in the direction of the EMF. Thus, the collector is a kind of rectifier that does not allow the generated current to change.
To eliminate the pulsation of the electromotive force, there are coils on the armature that are attached to pairs of collector plates. The turns are shifted from each other by a slight angle, this allows you to compensate for distortion in the harmonics and the current enters the circuit without ripple.
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 field of poles, the armature begins to rotate, however, at a time when the direction of rotation should have changed when the conductors pass 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/AC converter.
