THE ELECTRICAL ENGINEER
Sept 24, 1890
Tesla's New Alternating Motors
[139.)—I hope you will allow me the privilege to say in the columns of your esteemed journal a few words in regard to an article which appeared in Industries of August 22, to which my attention has been called. In this article an attempt is made to criticize some of my inventions, notably those which you have described in your issue of August 6, 1890.
The writer begins by stating: “The motor depends on a shifting of the poles under certain conditions, a principle which has been already employed by Mr. A. Wright in his alternating current meter.” This is no surprise to me. It would rather have surprised me to learn that Mr. Wright has not yet employed time principle in his meter, considering what before its appearance, was known of my work on motors, and more particularly of that of Schallenborger on meters. it has cost me years of thought to arrive at certain results, by many believed to be unattainable, for which there arc no numerous claimants, and times these is rapidly increasing like that of the colonels in the South after the war.
That writer then good-naturedly explains the theory of action of the motive device in Wright’s meter, which has greatly benefited me, for it is so long, since I have arrived at this, and similar theories, that I had almost forgotten it. He then Bays: “Mr. Tesla has worked out seine more or less complicated motors of this principle, but the curious point is that he has completely misunderstood the theory of the phenomena, and has got hold of the old fallacy of screening.” This may be curious, but how much more curious it is to find that the writer in Industries has completely misunderstood everything himself. I like nothing better than just criticism of my work, even if it be severe, but when the critic assumes a certain “l’état c’est moi” air of unquestioned competency I want him to know what he is writing about. How little time writer in Industries seems to know about the matter is painfully apparent when he connects the phenomenon in Wright’s meter with the subject lie has under consideration. His further remark, “He (Mr. Tesla) winds his secondary of iron instead of copper and thinks the effect is produced magnetically,” is illustrative of the care with which he has perused the description of the devices contained in the issue of The Electrical Engineer above referred to.
I take a motor having, say eight poles, and wrap the exciting coils of four alternate cores with fine insulated iron wire. When the current is started in these coils it encounters the effect of the closed magnetic circuit and is retarded. Time magnetic lines set up at the start close to the iron wire around the coils and no free poles appear at first at the ends of the four cores. As the current rises in the coils more lines are set up, which crowd more and more in the fine iron wire until finally the same becomes saturated, or nearly so when time shielding action of the iron wire ceases and free poles appear at the ends of the tour protected cores. The effect of the iron wire, as will be seen, is two-fold. First, it retards time energizing current; and second, it delays the appearance of time free poles.
To produce a still greater difference of phase in the magnetization’ of the protected and unprotected cores, I connect the iron wire surrounding the coils of the former in series with the coils of time latter, in which case, of course, the iron wire is preferably wound or connected differentially, after the fashion of the resistance coils in a bridge, seems to have no appreciable self-induction. In other cases I obtain time desired retardation in the appearance of the free poles on one set of cores by a magnetic shunt, which produces a greater retardation of the current and takes up at time start a certain number of the lines set up, but becomes saturated when the current in the exciting coils reaches a predetermined strength.
In the transformer the same principle of shielding is utilized. A primary conductor is surrounded with a fine layer of laminated iron, consisting of fine iron wire or plates properly insulated and interrupted. As long as the current in the primary conductor is so small that the iron enclosure can carry all the lines of force set up by the current, there is very little action exerted upon a secondary conductor placed in vicinity to the first; but just as soon as the iron enclosure becomes saturated, or nearly so, it loses the virtue of protecting the secondary and the inducing action of the primary practically begins. What, may I ask, has all this to do with the “old fallacy of screening?”