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.
2, of single-phase AC motor rotate principle
Single-phase AC motor has a winding only, rotor is squirrel-cage. When single-phase sine electric current passes stator winding, electromotor is handed in with respect to meeting generation change magnetic field, the rule of sine of the intercrop when losing by force to be followed with direction of this magnetic field changes, but be fixed on dimensional azimuth, weighing this magnetic field again so is to hand in become pulsatile magnetic field. This is handed in become pulsatile magnetic field is dissoluble it is two to be contrary whirl with each other of identical rotate speed, direction of rotation magnetic field, when rotor is dormant, these two rotate magnetic field generates two volume in rotor the torsion with equal, opposite way, make synthetic torsion is 0, so electromotor cannot rotate. When making with outside force when us electromotor rotates to some direction (rotate like the clockwise) , at this moment rotor and the whirl that arrange hour hand direction of rotation the decrescent of motion of cut lines of force between magnetic field; The whirl of rotor and anticlockwise direction of rotation the motion of cut lines of force between magnetic field greatens. Such balances were broken, the total electromagnetism torsion that rotor place produces will be no longer 0, rotor general down drive direction to rotate.
3. The principle of synchronous electromotor
Synchronous electromotor is to belong to alternating current machine, stator winding and asynchronous electromotor are identical. Rotate speed coming back spends its rotor to arise with stator winding place rotate the speed of magnetic field is same, call synchronous electromotor so. as a result of such, the electric current of synchronous electromotor is in phasic going up is lead at voltage, namely synchronous electromotor is a load that allow a gender. For this, in a lot of moment, synchronous electromotor is the power element that in order to improves power supply system.
Synchronous electromotor has two kinds roughly on the structure:
1, rotor undertakes excitation with dc. The rotor of this kind of electromotor is shown 1 times like the graph, can see from inside the graph, its rotor make it is shown extremely of type, installation is in the magnetic field coil above magnetic pole core is mutual series connection, receive have alternant and contrary polarity, two down-lead join outfit above two slip ring on the axis. Magnetic field coil is by small-sized dc dynamo or accumulator come incentive, in most synchronous electromotor, dc dynamo is to install what go up in electromotor axis, in order to supplies the excitation electricity of coil of rotor magnetic pole.
Because this kind of synchronous electromotor cannot be started automatically, still serve as what electromotor starts of squirrel-cage winding to use on rotor so. Squirrel cage winding puts in rotor all round, structure and asynchronous electromotor are similar.
Should connect in stator winding on when three-phase alternating current source, one arose to rotate inside electromotor magnetic field, lines of force of cut of squirrel cage winding and generation is faradic, make electromotor rotates thereby. After electromotor rotates, its speed slowly heighten arrives a bit under rotate the rotate speed of magnetic field, right now dc of by of coil of rotor magnetic field comes incentive, make certain magnetic pole is formed above rotor, these magnetic pole dog with respect to the purpose the whirl on stator magnetic pole, the rate that raises electromotor rotor so till with rotate till magnetic field synchronism rotates.
2, the synchronous electric machinery that rotor does not need excitation
Rotor not electromotor can apply the synchronism of excitation to go up at single-phase power source, also can apply go up at polyphase power source. In this kind of electromotor, the stator that has a kind stator winding and split phase electromotor or polyphase electromotor is similar, have rotor of a squirrel cage at the same time, and the surface of rotor cuts plane, if pursue,2 are shown. It is to belong to so show extremely rotor, rotor magnetic pole magnetizes steel make it by a kind, and often can keep magnetic. Squirrel cage winding uses generation to start torsion, and when the rotate speed with rotate certain when electromotor, rotor is shown extremely achieve synchronism with respect to the voltaic frequency that follows stator coil. Show extremely polarity comes out by stator induction, should go up with stator because of its amount extremely number is equal, when electromotor turns to its due speed, squirrel cage winding lost action, maintain rotating is recumbent rotor and magnetic pole follow stator magnetic pole, those who make is synchronous.