الفهرس 
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Abstract
Due to the requirnnent of the modern age, the society found itself in need of a faster railway requiring minimum maintenance this need led to the use of electric traction which is found to be acceptable in many countries from the performance as well as economic do--’,nt of view.
The early types of motors used were the D-C motors due to the ease by which speed vcri-tion could be obtained . This type of electric rotors has the main disadvantages of rejuiring fre¬quent maintenance due to the problems associated with the current coromutati(,~n
Latter on the variable speed induction motor 1,vas used. Yet this type of motors as .,Tell as the D-C motors suffer from the limitation on the speed imposed by the centrifugal force acting on the rotor conductors, or the wear and stresses on the gear train used to increase the speed of the motor . In fact the limi¬tati,)n due to wear and mechanical stresses on the gear train is found to be more serious when an attempt to increase the vehicle speed above a certain limit . This limitation led to the develop¬ment of another type of motors which can be free from the gear train, i.e., a motor which is directly fixed to the train vehicle ivheels. The main function of the ;,jheej_s is therefore to reduce the friction force. This nr--,ij type of motors if directly fixed to the vehicle and not to the wheels has to provide a linear motion instead of rotary motion, this type of motors is known as linear motors .