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IN VENTIONS OF NIKOLA TESLA
The currents in both primary and secondary coils in such a mo-tor will be retarded or will lag behind the impressed electro-motive force-; but to secure a proper difference in phase betweenthe primary and secondary currents themselves, Mr. Tesla in-creases the resistance of the circuit of the secondary and reducesas much as practicable its self-induction. This is done by usingfor the secondary circuit, particularly in the coils e, wire of com-paratively small diameter and having but few turns around thecores ; or by using some conductor of higher specific resistance,such as German silver ; or by introducing at some point in thesecondary circuit an artificial resistance b. Thus the self-induc-tion of the secondary is kept down and its resistance increased,with the result of decreasing the lag between the impressedelectro-motive force and the current in the primary coils and in-creasing the difference of phase between the primary and secon-dary currents.
In the disposition shown in Fig. 76, the lag in the secondaryis increased by increasing the self-induction of that circuit, whilethe increasing tendency of the primary to lag is counteracted byinserting therein a dead resistance. The primary coils n in thiscase have alow self-induction and high resistance, while the coilse f, included in the secondary circuit, have a high self-inductionand low resistance. This may be done by the proper winding ofthe coils; or in the circuit including the secondary coils e f, wemay introduce a self-induction coil s, while in the primary cir-cuit from the generator o and including coils n, there may be inserted a dead resistance b. By this means the difference ofphase between the primary and secondary is increased. It is evi-dent that both means of increasing the difference of phase—namely, by the special winding as well as by the supplemental orexternal inductive and dead resistance—may be employed con-jointly.
In the operation of this motor the current impulses in the pri-mary coils induce currents in the secondary coils, and by the con-joint action of the two the points of greatest magnetic attractionare shifted or rotated.
Iu practice it is found desirable to wind the armature withclosed coils in which currents are induced by the action thereonof the primaries.