The rotation of the three-phase asynchronous motor principle

Three-phase asynchronous motor to spin the prerequisite is to have a rotating magnetic field, three-phase asynchronous motor stator winding is used to produce a rotating magnetic field. As we know, but that power facies phase difference is the voltage on the phase between 120 degrees, three of the three-phase asynchronous motor stator winding on the spatial orientation also sent 120 degrees, so, acmotortrading.blogspot.com when during a stator winding into the three-phase power supply, the stator windings creates a rotating magnetic field, its process is shown in figure 1. Figure to describe the points four moment of a rotating magnetic field to produce process. Current every change is a cycle, a rotating magnetic field in a week, i.e., the change of the rotation of the rotating magnetic field and electric current is synchronized. The speed of the rotating magnetic field is: n = 60 f/P type in f P is the power supply frequency, magnetic field of magnetic pole unit is logarithmic, n: revolutions per minute. According to the type we know, the speed of the motor and the pole number and the use of the frequency of the power supply, therefore, control of ac motor speed has two methods: 1, change the method of magnetic pole; 2, frequency conversion method. 

Use the first method, is now using the frequency conversion technology to realize infinitely variable speed permanent magnet generators for sale control of ac motor. Can also be found that the rotation of the rotating magnetic field direction is related to the phase sequence and the winding current. Phase sequence arrange A, B, C clockwise, magnetic field, clockwise if any two of the three power cord switch root, such as current bubbled into C phase windings, B C phase current into the B phase winding, the phase sequence into: C, B, A, necessary counterclockwise in magnetic field. Using this feature, we can easily change the direction of rotation of the three-phase motor. Rotor stator windings creates a rotating magnetic field, after conducting bar (cage) will cut the lines of magnetic force of a rotating magnetic field and induced current, the current in the rotor conducting bar and interact with a rotating magnetic field to electric motors price produce electromagnetic force, electromagnetic force produced by electromagnetic torque drive rotor rotating magnetic field along the direction of the n1 speed in the spin. In general, the actual motor speed n1 is lower than the speed of the rotating magnetic field n. Because suppose n = n1, rotor conducting bar and a rotating magnetic field, there is no relative movement, wouldn't cut lines of magnetic force, also won't produce electromagnetic torque, so the rotor speed gasoline generator n1 inevitably less than n. We called the three-phase motor asynchronous motor.