Efficiency is one of the key technical and economic indicators of electric motors.

The operating load rate of low-voltage asynchronous motors is generally between 50% and 80%, mostly within the range of 60% to 70%. The variation of efficiency of asynchronous motors at different load rates is related to the distribution ratio of variable losses (stator and rotor winding copper losses) and constant losses (iron losses and mechanical losses) of the motor. In the total losses, variable losses increase while constant losses decrease, and the highest efficiency tends to approach the low load rate region. Therefore, when designing an electric motor, appropriately increasing the electromagnetic load will increase the variable loss, while the constant loss should be controlled as much as possible. This can enable the motor to have relatively flat efficiency characteristics over a wide range of load rates, which is beneficial for the motor to still have high efficiency at relatively low load rates.