变压器是静止的电气设备，它的主磁场是脉动磁场，•一、二次绕组中的电动势和电流具有相同的频率。
Transformer is a static electrical equipment, its main magnetic field is pulsating magnetic field, and the electromotive force and current in primary and secondary windings have the same frequency.
而异步电动机则是旋转的电气设备，它的主磁场是旋转磁场，转子旋转时，定子、转子绕组中的电动势和电流iV有不同的频率。
The asynchronous motor is a rotating electrical equipment. Its main magnetic field is the rotating magnetic field. When the rotor rotates, the electromotive force and current iV in the stator and rotor windings have different frequencies.