CHAPTER XI.

Another Method of Transformation from a Torque to a

SYNCHRONIZING MOTOR.

In a preceding chapter we have described a method by whichMr. Tesla accomplishes the change in his type of rotating fieldmotor from a torque to a synchronizing motor. As will be ob-served, the desired end is there reached by a change in the cir-cuit connections at the proper moment. We will now' proceedto describe another way of bringing about the same result. Theprinciple involved in this method is as follows:—

If an alternating current be passed through the field coils onlyof a motor having two energizing circuits of different self-induc-tion and the armature coils be short-circuited, the motor will havea strong torque, but little or no tendency to synchronism wdtlithe generator; but if the same current which energizes the fieldbe passed also through the armature coils the tendency to remainin synchronism is very considerably increased. This is due tothe fact that the maximum magnetic effects produced in the fieldand armature more nearly coincide. On this principle Mr.Tesla, constructs a motor having independent field circuits ofdifferent self-induction, which are joined in derivation to asource of alternating currents. The armature is wound with oneor more coils, which are connected with the field coils throughcontact rings and brushes, and around the armature coils a shuntis arranged with means for opening or closing the same. In start-ing this motor the shunt is closed around the armature coils,which will therefore be in closed circuit. When the current isdirected through the motor, it divides between the two circuits,(it is not necessary to consider any case where there are morethan tw r o circuits used), which, by reason of their different self-induction, secure a difference of phase between the two currentsin the two branches, that produces a shifting or rotation of theof the poles. By the alternations of current, other currents areinduced in the closed—or short-circuited—armature coils and the