第四章第一节

The basic principle of operation of an induction machine is illustrated by the revolving horseshoe magnet and copper-disk experiment pictured in Fig.4-1. When the horseshoe magnet is rotated, the moving magnetic field passing across the copper disk induces eddy currents in the disk. These eddy currents are in such a direction as to cause the disk to follow the rotation of the horseshoe magnet. With the direction of rotation shown in the figure, the eddy currents will be as displayed in Fig.4-1 according to Fleming's right-hand rule

一台感应电机的基本工作原理如图4－1中的旋转的U形磁铁和铜圈盘的实验图所示。当U形铁旋转时，运动的磁场穿过铜圆盘从而在铜圆盘中产生涡流。这些涡流的方向是这样的以致于使圆盘顺着U 形磁铁的转向旋转。在图示的旋转方向下，根据弗莱明右手定则涡流的方向将如图4－1所示。

Fleming's right-hand rule: Place the thumb and the first and second fingers of the right hand so that all three are mutually perpendicular. With the hand in this position, the first finger is pointed in the direction of the field, the thumb is in the direction of motion of the relative motion of the conductor, and the second finger is the direction of the induced voltage. Note that the relative motion of the conductor is opposite to the rotation of the direction of rotation of the magnetic field.

弗莱明右手定则：伸出右手大拇指、食指以及中指并使它们相互垂直。保持右手处于这种状态，使食指指向磁场的方向，拇指指向导体相对

运动的运动方向，那么中指所指的方向就是感应电压的方向，要注意的是导体的相对运动与磁场的旋转方向的运动相反。

By applying Fleming's right-hand rule, the force on the copper disk is determined to be in the direction of rotation of the magnet.

通过应用弗莱明右手定则，我们确定作用在铜圆盘上的力与磁铁的旋转方向一致

Fleming's left-hand rule: Place the thumb and the first and second finger of the left hand so that all three are mutually perpendicular to each other. With the first finger in the direction of the field and the second finger in the direction of the current, the thumb indicates the direction of the force. 弗莱明左手定则：伸出左手大拇指、食指以及中指并使它们相互垂直。使食指指向磁场的方向，中指指向电流的方向，那么拇指所指的方向是力的方向

Whereas the copper disk will rotate in the same direction as the rotating magnetic field, it will never reach the same speed as the rotating magnet, because if it did, there would be no relative motion between the two and therefore no current induced in the copper disk. The difference in speed between the rotating magnetic field and the copper disk is known as slip, which is essential to the operation of an induction motor. In induction motors the rotating magnetic field is set up by windings in the stator, and the induced currents are carried by conductorsin the rotor. The rotating horseshoe magnet and copper disk are considerably different in structure

from today's induction motor, but the basic principles of operation are the same.

尽管铜圆盘将顺着旋转磁场的方向而旋转，然而它却永远也达不到旋转磁铁的速度，因为如果铜圆盘的速度等于旋转磁铁的速度，那么在两者之间就不存在相对运动因而在铜圆盘中不会感应出电流。旋转磁铁和铜圆盘之间的速度差被称为转差（率），转差（率）对于感应电机的运行是必要的，在感应电机中旋转磁场是通过定子绕组建立的，并且感应电流是由转子导体承载的。旋转U形铁和铜圆盘与目前感应电动机的结构有相当大的不同，但基本工作原理是一样的。

The rotating magnetic field is essential to the functioning of an induction motor. In practical machines this rotating magnetic field is achieved by a combination of a space displacement of the windings and a time-phase displacement of the exciting voltage.

旋转磁场对于一台感应电动机来说是必要的。在实际的电机中，旋转磁场是通过绕组在空间上的交替布置和励磁电压在时间相位上的相互交替这两者的结合来实现的。

The rotor is formed from laminated electrical steel punching, and the rotor winding consists of bars contained in slots punched in the laminations. These bars are short-circuited at both ends by a short-circuiting ring. A bar-end ring structure, without the laminated core, is called a squirrel cage, as shown in the Fig.4-2. In small- and medium-horsepower sizes, rotors are made by casting aluminum into the