| Fig. 78. | Fig. 79. |
A convenient arrangement for carrying out this invention is shown in Fig. 80, in which J J are the field coils of the synchronizing, and H I the field coils of the torque motor. L L' are the conductors of the main line. One end of, say, coils H is connected to wire L through a self-induction coil M. One end of the other set of coils I is connected to the same wire through a dead resistance N. The opposite ends of these two circuits are connected to the contact m of a switch, the handle or lever of which is in connection with the line-wire L'. One end of the field circuit of the synchronizing motor is connected to the wire L. The other terminates in the switch-contact n. From the diagram it will be readily seen that if the lever P be turned upon contact m, the torque motor will start by reason of the difference of phase between the currents in its two energizing circuits. Then when the desired speed is attained, if the lever P be shifted upon contact n the entire current will pass through the field coils of the synchronizing motor and the other will be doing no work.
The torque motor may be constructed and operated in various ways, many of which have already been touched upon. It is not necessary that one motor be cut out of circuit while the other is in, for both may be acted upon by current at the same time, and Mr. Tesla has devised various dispositions or arrangements of the two motors for accomplishing this. Some of these arrangements are illustrated in Figs. 81 to 85.
Fig. 80.
Referring to Fig. 81, let T designate the torque or multiple circuit motor and S the synchronizing motor, L L' being the line-wires from a source of alternating current. The two circuits of the torque motor of different degrees of self-induction, and designated by N M, are connected in derivation to the wire L. They are then joined and connected to the energizing circuit of the synchronizing motor, the opposite terminal of which is connected to wire L'. The two motors are thus in series. To start them Mr. Tesla short-circuits the synchronizing motor by a switch P', throwing the whole current through the torque motor. Then when the desired speed is reached the switch P' is opened, so that the current passes through both motors. In such an arrangement as this it is obviously desirable for economical and other reasons that a proper relation between the speeds of the two motors should be observed.
In Fig. 82 another disposition is illustrated. S is the synchronizing motor and T the torque motor, the circuits of both being in parallel. W is a circuit also in derivation to the motor circuits and containing a switch P''. S' is a switch in the synchronizing motor circuit. On the start the switch S' is opened, cutting out the motor S. Then P'' is opened, throwing the entire current through the motor T, giving it a very strong torque. When the desired speed is reached, switch S' is closed and the current divides between both motors. By means of switch P'' both motors may be cut out.
Figs. 81, 82, 83, 84 and 85.