The rated speed corresponding to the natural characteristic of the rated load is usually either equal to or close in magnitude to the required working basic speed of the mechanism. Therefore, the natural characteristic is the main characteristic of the drive. From equations (1-7) and (1-9) it follows that in the G-D system, speed control can be carried out by changing either e. d. With. generator Et, or engine flow.
Rated rotation speed
Since the generator in nominal mode has a saturated magnetic circuit, change e. d. With. generator is possible only in the direction of decreasing. This ensures the regulation of the speed of the electric drive down from the main speed.
Mechanical characteristics corresponding to changing values of e. d. With. generator, will be parallel to each other, since the reduction in engine speed due to the voltage drop in the armature circuit will be the same for all characteristics due to the fact that the motor flux and the resistance of the armature circuit are unchanged. Polarity reversal e. d. With. generator, characteristics corresponding to the opposite direction of rotation of the engine are obtained.
The electric motor in the nominal mode also has a saturated magnetic chain, so changing its flow is possible only in the direction of reducing. In this regard, the regulation of speed by changing the flow flow of a DC engine is called the weakening of the engine field.
Using equations (1-7) and (1-9), it is easy to make sure that when the field is weakened in the zone of normal workloads, the speed increases, t. e. speed control is carried out up from the main. By weakening the field for normal engines, not specifically calculated for deep weakening of the field, you can get an increase in speed by one and a half to two times.
However, it should be borne in mind that the permissible load is reduced as the field weakens. It follows from formula (1-8) that if, with a decrease in flux, the load on the motor shaft is left unchanged and equal to the nominal value, the armature current will have to increase above the nominal value inversely proportional to the flux.