The nominal speed of rotation, corresponding to the nominal load on the natural characteristic, is usually either equal to or close in magnitude to the required operating main 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 regulation can be carried out by changing either e. etc. with. generator ET, or engine flux.
Rated speed of rotation
Since the generator in the nominal mode has a saturated magnetic circuit, change the e. etc. with. generator is possible only in the direction of decrease. At the same time, the speed control of the electric drive is provided downward from the main speed..
Mechanical characteristics corresponding to varying values of e. etc. with. generator, will be parallel to each other, since the decrease 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 armature circuit resistance are unchanged. By changing the polarity of e. etc. 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 circuit, so a change in its flux is possible only in the direction of decreasing. In this regard, speed regulation by changing the flux of a DC motor is called motor field weakening..
Using equations (1-7) and (1-9), it is easy to verify that when the field weakening in the area of normal working loads, the speed increases, i.e., the speed is controlled upward from the main one. By weakening the field for motors of normal design, which are not specially designed for deep weakening of the field, it is possible to obtain an increase in speed of one and a half to two times.
However, it must be borne in mind that the permissible load decreases with field weakening. From the formula (1-8) it follows that if, with a decrease in the flow, the load on the motor shaft is left unchanged and equal to the nominal, the armature current should increase above the nominal value in inverse proportion to the flux.