Reasons for the Use of the Three-Phase Current in the Lauffen-Frankfort Transmission

The reports of The Electrical World upon the transmission of power from Lauffen to Frankfort give the impression that the application of the three-phase current alone renders such an installation possible, and that to its application is due the favorable issue of the experiment.

I wish, however, to call attention to the fact that the principal object of the experiment was to prove the possibility of producing and transmitting high tension currents over long distances by naked wires suspended from poles, and with such a degree of security against danger and such a small amount of loss by leakage as to demonstrate that this mode has commercially a right to exist.

The idea originated with me and was put to the test of experiment at Oerlikon with very encouraging results, which together with the lecture I delivered on the subject at Frankfort on the 9th of February last provoked the determination to carry out the Lauffen-Frankfort installation as it now exists.

In that lecture I propounded the view - in opposition to the general opinion at that time - that currents of 20,000 volts or more could be carried by naked wires suspended from poles on suitable insulators without excessive loss by leakage; further, I met all the questions that could arise concerning such an installation as that between Lauffen and Frankfort, and the proof of the correctness of the assertion I then advanced is that the installation in question has been carried out in accordance with my suggestions as given in my lecture referred to.

The adoption of the three-phase current only increased the difficulties to be met, since the generator, the transformer, switches and controlling appliances, as also the conductors - a most important disadvantage - became more complicated than they otherwise would have been had the usual alternating current been chosen. The only reason justifying the choice of the three-phase current was to demonstrate its advantages when applied to several small motors at the same time.

Examining closer into the three-phase current question, the only novelty which the Frankfort exhibition brings to light concerning it are important constructive improvements in its application, and these, almost without exception, I claim as my own, for the first large multiphase generator and transformer, as well as the first practical motor without moving or rubbing contact, were my constructions.

The three-phase current as applied at Frankfort is due to the labors of Mr. Tesla, and will be found clearly specified in his patents.

Baden, Switzerland, Oct. 12, 1891.

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Comments on Mr. Brown’s Letter by Carl Hering

In regard to the statement made in the beginning of this letter referring to my description of this transmission, I wish to say that I distinctly stated in those descriptions that the chief object of the three-phase currents, per se, was to enable alternate current motors to be run more readily than by the single phase system. I also stated, and emphasized it by repeating it in several places, that the chief object of the Lauffen-Frankfort experiment was to see whether it was practicable to transmit power on overhead lines by such high tension alternating currents, per se, irrespective of whether it was a three or a one phase current, as long as it was an alternating current. Nowhere do I recall having said or inferred that the “three phase current alone renders such an installation possible,” except perhaps that I implied that a high tension alternating current transmission, in combination with the three-phase motor, rendered a long distance transmission of power to a motor, practicable (not possible). I am well aware (which Mr. Brown might have supposed) that it could have been done with an ordinary synchronous alternating current motor, but I said then, and think so still, that the three-phase motor is a more practicable solution. Neither did I say or infer that “to its (three-phase system) application is due the favorable issue of the experiment” except as just explained. It is due to the combination of the two that the practical system of a long distance transmission and distribution to a motor (as distinguished from lights) by alternate currents was a success. The three-phase system is evidently not essential in a simple high tension transmission of energy, and nowhere did I say this, to my knowledge. What I did say about the high tension transmission portion of this experiment, per se, was almost exactly what he states in the second paragraph of this letter.

I would add that I do not think Mr. Brown does proper justice to the real inventor of this modification of the Ferraris-Tesla system, namely, Dobrowolsky, when he claims that “the only novelties which the Frankfort exhibition brings to light concerning it,” etc., are all his own (Brown’s). It is one thing to make an invention, and it is another thing to carry it out by the best details of construction. In the latter capacity, namely, as a constructor, no one who knows Mr. Brown’s works will question his ability as one of the first among electrical engineers of the present time. But without the invention of a new principle or a new modification, the ablest constructor would hardly be able to make any very great departures from well known systems. Due credit should therefore be given to the inventors as well as the constructors.