Rated Speed
The speed of a motor or gearbox specified for rated operation — expressed in min⁻¹ (also rpm) and the reference point for all other performance data of the drive.
Definition
Rated speed is the speed at which an electric motor, gearbox, or other rotating drive element can continuously deliver its rated power and rated torque under specified rated conditions (rated voltage, rated frequency, rated load). It is indicated on the nameplate and serves as the design basis for the entire drive system.
For induction motors, the actual operating speed (rotor speed) is slightly below the synchronous speed — the difference is called slip. For DC motors and brushless motors, the rated speed can be set directly. The output speed of a downstream gearbox is the rated speed divided by the gear ratio.
Practical Relevance
When designing drive trains, the rated speeds of all components must be matched to each other. A motor with 1500 min⁻¹ combined with a gearbox i=10 yields an output speed of 150 min⁻¹. Deviations from rated speed affect the efficiency, heating, and service life of the entire drive unit.