Linear induction motor and rotary induction motor in the principle of work is no essential difference. Just get the mechanical movement in a different way. But both in the electromagnetic performance there is a big difference drama, mainly in the following three aspects:
(1) Rotary induction motor stator three-phase winding is symmetrical. Thus if the applied three-phase voltage is symmetrical. The three-phase current is symmetrical. But the linear three-phase winding of the linear induction motor is asymmetrical in the space position. The coil at the edge is compared to the coil located in the middle. The inductance value is very different. In other words: phase reactance is not equal. Thus, even if the three-phase voltage is symmetrical. The three-phase winding current is also asymmetrical. The following are the same as the "
(2) Rotary induction motor set, the rotor asked the air gap is round, no head no tail, continuous. There is no beginning and end. But the linear induction motor between the primary and secondary air gap exists between the beginning and end. When the secondary end enters or exits the air gap. Will be in the secondary conductor to induce additional current. This is the so-called "marginal effect". Due to the influence of the edge effect, the linear induction motor and the rotary induction motor are quite different in operating characteristics. The following are the same as the "
(3) As the linear induction motor early, secondary in the direction of the straight line to continue a certain length, and the normal electromagnetic force is often uneven, so the mechanical structure of the general between the primary and secondary air gap done Longer. such. Its power factor is lower than the rotary induction motor.
Linear induction motor is divided into flat-shaped single-sided, flat-shaped double-sided, cylindrical, short stator and short rotor mode, the power can be single-phase or three-phase. To single-sided linear induction motor, for example, it consists of stator and moving body composition. The stator is also called the primary, which is formed by stacking the electric steel sheet of the cogging, and the groove is embedded in the groove. The moving body is also called a secondary conductor, usually made of copper or aluminum. There is a certain distance between the stator and the moving body, that is, the air gap. When the winding is connected to the single-phase or three-phase alternating current, the magnetic flux density B is expressed by the following equation: B = B0cos (ωt - πx / τ), ω = 2πf, x The distance on the stator surface, τ Pole distance. The moment is the half-wavelength of the magnetic flux density, which is equal to half the length of the cycle, and the magnetic flux density is a function of distance x. This kind of t and x as a function of the magnetic flux density called traveling wave magnetic field, which is the rotation of the motor with the rotating magnetic field is the same principle. As described above, the magnetic flux generated in the stator after the AC power is applied, and the eddy current is induced on the metal plate of the movable body according to Lenz's law. Let the induced voltage of the eddy current be E, the inductance L and the resistance R on the metal plate, the eddy current on the metal plate is I = E / z, the eddy current and the magnetic flux density will produce a continuous thrust F The There are positive and negative thrust, but the thrust is much larger than the negative thrust, the force acting on the body is mainly positive thrust, which is the working principle of linear induction motor. Linear induction motor drive device can use the inverter. The output frequency of the inverter can be controlled under the action of the control signal, which can be controlled by logic or closed loop. The frequency converter outputs a different frequency, and the resulting thrust will change accordingly. As the frequency of the two coils of the stator is different, the synchronous change of the traveling wave magnetic field is caused, so that the thrust of the motor is changed from 0 to the maximum.