AC Motors and Generators

AC Motor

交流电机

As in the DC motor case, a current is passed through the coil, generating a torque on the coil. Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave. It is called a synchronous motor. More common is the induction motor, where electric current is induced in the rotating coils rather than supplied to them directly.

正如直流电机的情况一样，电流通过线圈，产生对线圈的力矩。由于电流是交流的，电机只有在正弦波的频率下才能平稳运行。这种电机被称为同步电机。更常见的是感应电机，其中电流是通过旋转线圈感应产生的，而不是直接供给的。

One of the drawbacks of this kind of AC motor is the high current which must flow through the rotating contacts. Sparking and heating at those contacts can waste energy and shorten the lifetime of the motor. In common AC motors the magnetic field is produced by an electromagnet powered by the same AC voltage as the motor coil. The coils which produce the magnetic field are sometimes referred to as the "stator", while the coils and the solid core which rotates is called the "armature". In an AC motor the magnetic field is sinusoidally varying, just as the current in the coil varies.

这种交流电机的一个缺点是必须通过旋转接触点流过的高电流。这些接触点上的火花和发热会浪费能量并缩短电机的寿命。在常见的交流电机中，磁场是由一个由相同交流电压供电的电磁体产生的。产生磁场的线圈有时被称为“定子”，而线圈和旋转的实心铁芯则被称为“转子”。在交流电机中，磁场是正弦变化的，就像线圈中的电流一样变化。

AC Generator

交流发电机

The turning of a coil in a magnetic field produces motional emfs in both sides of the coil which add. Since the component of the velocity perpendicular to the magnetic field changes sinusoidally with the rotation, the generated voltage is sinusoidal or AC. This process can be described in terms of Faraday's law when you see that the rotation of the coil continually changes the magnetic flux through the coil and therefore generates a voltage.

当线圈在磁场中转动时，线圈两侧会产生动生电动势，它们相加。由于速度垂直于磁场的分量随旋转而正弦变化，因此产生的电压也是正弦的或交流电。这个过程可以用法拉第定律来描述，因为线圈的旋转不断改变通过线圈的磁通量，从而产生电压。

Generator and Motor

发电机和电动机

A hand-cranked generator can be used to generate voltage to turn a motor. This is an example of energy conversion from mechanical to electrical energy and then back to mechanical energy.

一个手摇发电机可以用来产生电压以驱动电机。这是一个将机械能转换为电能，再转换回机械能的例子。

As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil and that electric power being used is converted to the mechanical power to drive the load.

当电机转动时，它同时也充当发电机，产生一个‘反电动势’。根据楞次定律，由电机线圈产生的电动势将反对造成它的变化。如果电机不驱动负载，那么产生的反电动势几乎会抵消输入电压，电机线圈中的电流将非常小。但若电机驱动重负载，反电动势会减小，线圈中的电流会增加，此时所用的电功率将转换为机械功率以驱动负载。