Linear Induction Motor: It is a particular type of induction motor which gives linear motion instead of rotational motion of conventional induction motor.
Structure of Linear Induction Motor
If a Liner induction motor is cut axially at points a and b, as shown in figure (i), it takes the shape of a linear induction motor.
The simplest linear motor consists of a field plant with three-phase distributed coils inside slots. It acts as a primary. The secondary of the motor is a conducting plate which is made of copper or aluminum. The interaction in this secondary results in the formation of current. A stator can be made either primary or secondary. The second chariot automatically becomes the rotor.
A magnetic iron plate is placed on the other side of the conducting plate, as shown in figure (iii) so that the main flux can get a low resistance path.
But on energizing the field, the magnetic plate of iron gets attracted towards Prathanek. Due to which there is an uneven distance on both sides of the secondary. The dual primary is used to deal with this problem, as shown in figure (iv).
Which one should be made smaller in primary and secondary depends on the use of the motor.
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Working of Linear Induction Motor
Its working is similar to that of a conventional induction motor. When there is relative motion between the field and the short circuit conductors, a current is generated, producing electromagnetic forces. In the presence of these forces, the conductors start rotating according to the law of the lamp in that direction which can eliminate the current generated. In conventional induction motors, this motion is liner relative to an axis, whereas it is straight in linear induction motors.
When the primary electrical coil of a linear induction motor is energized by a balanced electrical plant, it produces a magnetic field rotating at linear synchronous speed (N) which moves from one edge to the other in a straight line.
synchronous speed,
Ns = 2 T fm/sec.
where, T = pole pitch (in m)
f = supply frequency (in Hz)
Therefore, the linear synchronous speed does not depend on the number of poles but the pole pitch and the frequency of the stator.
The flux moves linearly and pulls the rotor plate in the same direction. This reduces the relative speed between these two. If the speed of the rotor plate becomes equal to the magnetic field, the induction motor starts running at synchronous speed.
If the rotor plate is to be rotated at speed more significant than the synchronous speed, the direction of the force has to be reversed. For this, regenerative braking based on the principle of induction generator is used.
Characteristics of Linear Induction Motor
The speed of the moving field is proportional to the pole pitch at a constant frequency. The curve v(a) is shown between the speed and the pole pitch. It is clear from this curve that to achieve low speed, the pole pitch must be below, but in high capacity motors, it is difficult to adjust the heavy coil to low pole pitch. The thrust-velocity characterization is shown in Fig. v (b).
Uses of Liner Induction Motor
(i) In a trolley car for internal traffic in the workshop.
(ii) In cranes and conveyor belts.
(iii) Automatic sliding doors in electric trains.
(iv) in high potential circuit breakers.
(v) Ring test accelerators for vehicle performance
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Now you must know Structure of Linear Induction Motor, Working of Linear Induction Motor, Characteristics of Linear Induction Motor, Uses of Liner Induction Motor.