Electrical Engineering ⇒ Topic : Construction of linear induction moter

Construction:- A linear induction motor, in its simplest form consists of field system having a 3 Φ distributed winding placed in slots as shown in Fig.(a) (short-single primary).

                                                                      Fig.(a) Short-single primary

The field system may be single or double primary system. The secondary of this type of induction motor is normally a conducting plate ¡nade of either copper or atuminium in which interaction currents are induced.

Depending upon the particular requirements either member can be the stator, the other being the rotor

The ferromagnetic plate, in a single primary system, is usually placed on the other side of the conducting plate to provide a path of low reluctance to the main flux. The ferromagnetic plate, however, gets attracted towards the primary when the field is energised; consequently unequal gap length results on the two sides of the plate. Double primary system can be used to overcome this problem.

The use of the motor decides which of the two primary and secondary will be shorter in length compared to other. The primary is made shorter than secondary when the operating distance is large (since winding a very long 3-phase primary is costly proposition.) and the short secondary is used when the operating distance is limited.