From the point of view of energy consumption in the speed control process, there are two types of efficient speed control methods and inefficient speed control methods.
- Efficient speed control implies that the slip rate is constant and therefore there is no slip loss, e.g. multi-speed motors, variable speed regulation and speed control methods that can recover slip loss (e.g. cascade speed control, etc.) .
- Speed control methods with slip losses are inefficient speed control. For example, in the case of rotor series resistor speed control, the energy is lost in the rotor circuit; in the case of electromagnetic clutch speed control, the energy is lost in the clutch coil. Hydraulic couplings in order to regulate speed, energy is lost in the oil of the hydraulic coupling.
In general, the slip loss increases with the speed control range. If the speed control range is not large, the energy loss is very small. The speed of the generator indicates the speed on the output shaft, not the speed of the generator rotor. Therefore, a gearbox is required if the motor speed is to be controlled. The rotor speed is, of course, the output speed of the shaft.