Circuits for Tesla Alternating Motors

M. Leblanc, a French electrician, makes an ingenious suggestion in the London Electrician for the suppression of the double set of leads of the Tesla motor. He says that it is only necessary to take a transformer and equilibrate the self-induction of its secondary circuit (including in this, of course, the external circuit) by interposing a suitable condenser. The current in this circuit will then be displaced in phase by precisely one-quarter wave length over that of the primary.

The primary coil of the transformer is placed in circuit with one set of the Tesla field coils, the ends of this circuit being connected directly to the two main leads; the secondary is connected with the other field circuit, a suitable condenser being interposed between secondary and set of field coils, and the ends of the circuit are connected together.

We can also, if desired, go a step further and balance the self-induction of the primary also, so as to suppress the apparent increase of resistance of the system with respect to the generator.

Another highly novel suggestion is as follows:

Having an alternating current of given period, to obtain a current of any other required period.

To do this, take a Gramme ring and divide the coils into three circuits a, b, c, in such a way that every alternate coil all round the ring is in circuit c, while the remaining coils in each alternate quadrant belong to circuits a and b respectively. In fact, so far as a and b are concerned, the circuits are placed exactly as in the Tesla motor, while a coil of circuit c intervenes between every pair of coils all round. Through circuits a and b two independent alternating currents are sent, which differ in phase by 90 degrees again as in the Tesla motor. The coils of circuit c are connected to the bars of a Gramme commutator, and upon this, according to M. Leblanc’s solution, a pair of brushes is caused to rotate. Now, while the brushes are at rest, the coils c are the seat of an induced E. M. F. equal in period and midway in phase to that of the currents in a and b; but now, if the brushes rotate upon the commutator, it is easy to see that the period may be either diminished or increased according to the relative velocity of the brushes as compared with that of the virtual rotation of the poles in the ring caused by the current a and b.