The power of the motor should be selected according to the power required by the production machinery, so as to make the motor run under the rated load as much as possible. Pay attention to the following two points when choosing: (1> If the motor power is too small, there will be a phenomenon of "small horse-drawn cart", which will cause the motor to overload for a long time, damage its insulation by heating, and even burn the motor. (2) If the motor power is too high, there will be a phenomenon of "big horse-drawn car". Its output mechanical power is not fully utilized, and its power factor and efficiency are not high (see table), which is not only bad for users and power grid. But also causes waste of electric energy.