At present more commonly used AC motor has two kinds: 1, three-phase asynchronous electromotor. 2, single-phase AC motor. The first kind multi-purpose go up in industry, and the 2nd kind multi-purpose go up in civil electric equipment.

One, of three-phase asynchronous electromotor rotate principle
The precondition that three-phase asynchronous electromotor should rotate is to have to rotate magnetic field, the stator winding of three-phase asynchronous electromotor uses generation to rotate namely of magnetic field. We know, but the voltage between photograph of get along with of bearing power supply is in phasic going up is to differ 120 degrees, 3 winding in stator of three-phase asynchronous electromotor are on dimensional azimuth also each other differs 120 degrees, such, three-phase power source should be told in stator winding when, stator winding rotates with respect to meeting generation magnetic field, the course that its produce is shown 1 times like the graph. A hour is divided to describe in the graph rotate the generation process of magnetic field. Electric current every change a cycle, rotate magnetic field rotates in the space a week, rotate namely the rotate speed coming back of magnetic field spends the change with electric current is synchronism. Rotate the rotate speed of magnetic field is: The unit of the magnetic pole logarithm that the F in N=60f/P type is power source frequency, P is magnetic field, N is: Rpm. According to this type we know, the rotate speed of electromotor and the frequency that magnetic pole is counted and use power source are concerned, for this, the rotate speed that controls AC motor has two kinds of methods: 1, law of change magnetic pole; 2, frequency conversion law. Before multi-purpose the first kind of method, use frequency conversion technology to realize the control of infinitely variable speeds to AC motor now.
Observation pursues 1 still can discover, rotate the appearance sequence of the electric current in the direction of rotation of magnetic field and winding is concerned. Appearance sequence A, B, C arranges hour hand to arrange, magnetic field clockwise rotates, the random in be like a 3 root power supply cord two exchange, in connecting B phase current C photograph winding for example, c phase current connects B photograph winding in, criterion appearance sequence turns into: C, B, A, criterion magnetic field certain anticlockwise way rotates. Use this one character we but very the direction of rotation that changes three-phase electromotor conveniently. ? ? ? Stator winding generation rotates after magnetic field, rotor guides (squirrel cage) rotate cut the lines of force of magnetic field and generation is faradic, rotor guides a medium electric current with rotate force of electromagnetism of generation of magnetic field interaction, the edge of rotor of electromagnetism torsion drive that electromagnetism force produces rotates magnetic field direction rotates with the rotate speed of N1. Usually, the N1 of actual rotate speed of electromotor under rotate the rotate speed N of magnetic field. Because of hypothesis N=n1, criterion rotor guides with rotate magnetic field did not move relatively, won't cut lines of force, also won't produce electromagnetism torsion, so the rotate speed N1 of rotor is less than N necessarily. For this we call three-phase electromotor asynchronous electromotor.
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