On the Rotary Magnetic Field and Multiphase Alternating Current Distribution

BY LUDWIG GUTMANN.

In the last few years a great deal of attention has been given to the rotary magnetic field, and a review of the principal workers and their devices may be of special interest. In 1885 we find the alternator almost forgotten. It had been abandoned and was found only in laboratories, but otherwise it had hardly any but historic interest. Very rarely such machines as the Ferranti-Thomson, for incandescent lighting, or a Siemens alternator, for either are or incandescent work, were met. The continuous current machines monopolized the market. They were the only salable devices for commercial lighting, when, unexpectedly, the great prize of the Turin Exposition of 1884 was awarded to Mr. Lucien Gaulard, of Gaulard & Gibbs, London, an eminent French physicist and chemist, for a distribution over long distances, by means of transformers and alternating currents. This result drew the attention of engineers again to the alternating current generators and high tension distribution, especially as it had been found meantime that, commercially, there were great obstacles in the distribution of low tension continuous currents over great areas. From this time on a great many engineers began to experiment and design transformers, as, for instance, Deri, Zipernowski, Ferranti, Siemens, Hopkinson, Kennedy, Kapp, Mordey and also the writer, who at that time was with Messrs. Gaulard & Gibbs. Among the early workers in America was Mr. Stanley.

It was in the early part of 1885 that Prof. Galileo Ferraris was engaged in testing the efficiency of transformers made by Gaulard & Gibbs, as also those of Ganz & Co., which tests were completed in July of that year. During these experiments the fundamental and far-reaching principles of the rotary magnetic field were developed, which were verified by experiments within the two following months. This eminent scientist did not make a secret of his work of obtaining rotation by alternating currents; on the contrary, he showed the devices and experiments, during the latter part of the year 1885, to many prominent workers, such as Mr. Gaulard (London), Mr. Deri (Budapest), Prof. von Beetz (Munich), Prof. G. Mengarini (Rome), Mr. P. Bellani (Italian representative of the Thomson-Houston Company), and many others. Before that time but a single alternating current had been used and studied, and little was known about it. Here, however, the action and laws of two alternating currents were explained and shown by experiments, which are now familiar to every student in the alternating current field. Prof. Ferraris produced his currents of displaced phase by means of converters; but was this clear sighted man ignorant of the fact that the difference in phase could not be accomplished by any other means than those adopted by him? By no means. He had intended to make modifications by building a generator producing currents of displaced phases and larger motors to be operated thereby, but he had been prevented, partly by reasoning, partly by circumstances.

We have here a similar case to that of Prof. Henry. Working in a scientific laboratory, with its limited means, no changes could be attempted with the Siemens alternator, as the winter term had just begun, and the machine was needed for other work by the students; besides, he was perfectly clear in his mind that the application of special designs of generators and the consequent complication of feeding wires would be a great practical inconvenience, which would tend to complicate the system, and considerably reduce its scope and utility. In spite of the advancements made in recent years, he still now maintains the same view, that the motor to solve the problem should be operative on the present systems of two wire distribution. These considerations, more than any others, may have influenced the professor to delay such special modifications and to produce the rotary magnette field by the simpler methods within his easy reach in using a transformer or derived circuits. The delay of communicating these experiments to the Royal Academy or otherwise publishing these results for almost three years was due to grave private misfortunes, or troubles, which influenced his mind for a considerable time.

As the transformer system developed during the next few years, the need of a meter made itself felt, and we read in 1887 (I think) in English periodicals remarks to that effect, the. Ferranti meter being then but little known and less used. Suddenly the great and slowly progressive work was interrupted by the communication of Prof. Ferraris, on March 18, 1888, to the Academy of Science at Turin. of the laws and actions of his "electro-dynamic rotation by alternating currents," which stirred up all constructing engineers, and brought new life and increased vigor for investigations in this unexplored field.

The publication was soon followed by translations in electric periodicals all over the civilized world. The first appeared on May 18, 1888, in the English "Industries," edited at the time by Mr. Gisbert Kapp. Since then this paper, owing to its extreme simplicity, clearness and importance, has now appeared so often in one form or another that we need not go over the ground once more at this place.

Ferraris "electro-dynamic rotation" can be condensed into the following short sentence: "Rotation of a magnetic field is the resultant of two or more magnetic or magnetizing forces of variable intensity acting at an angle to one another, whose maxima do not coincide, but whose periods are the same."

Two months later Mr. Tesla described his motor built on the same principles. We have here a great contrast: On the one hand a scientist in a great city of Italy, with limited means, and his only purpose, knowledge, light; on the other hand we find a young experimenter, backed by considerable capital, located in the busy metropolis, New York, where the chief motto is, "Time Is Money," and the principal aim "Dollars and Cents." The object, after having found rotation independently, was to get returns for the experiments by making commercial motors.

The respective characteristics are fully embodied in the important work of these distinguished workers. Prof. Ferraris lays down in beautiful and simple language the fundamental law governing this class of machines, while Mr. Tesla explains the action in his own way, which is not fundamental, but builds machines for practical purpose.

While these two men are the most prominent workers In this field, we have also to consider the work of others. Here we have to name first Mr. Bradley, who obtained a patent for a simple generator in October, 1888. It may be called a universal machine, inasmuch as it can be used as a continuous current generator or for alternating or multiphase currents. However, no statements are made in this patent that he expected rotation, or wished to operate motors by two or three alternating currents of displaced phases. This machine, which may be destined to do before long much valuable service, remained unknown to many, even to American workers, especially as there was no immediate demand for the same.

Naturally after a new subject is thoroughly understood we would expect some one to come to the front with a claim of priority, and sometimes with apparent right. In this instance such claims have been raised by the French engineers, M. de Fonville, M. Lontin and M. Marcel Deprez, and later M. Hasselwander, all of whom obtained rotation by either alternating currents or alternating and pulsating or continuous and pulsating currents. However, the question is not who made the first apparatus, but who understood first the subject, the principle of the device, and who in consequence thereof most benefited the world.

For instance, we name for historical reasons the first attempts in dynamo building, but the credit for fundamental and far-reaching work belongs to much later workers, such as Faraday, Hopkinson, Frohlich and Kapp. Similarly in this case, some early inventors may have built motors or small contrivances which produced rotation, but their work remained unnoticed, because the fundamental principle was either not understood by them or did not receive the deserved prominence. It can hardly be said that it was a fault of the time, because the subject has not been in advance of developments, as in those days we know that are lamps, and later incandescent lamps, were fed directly by alternators, especially of the Siemens and Ferranti types, and power transmission would have been attempted if there had been motors, or at least if the principle on which these early devices had been built had been understood.

It is therefore no surprise that the work of Prof. Ferraris, when explaining rotation by alternating currents in simple language, and based on principles so familiar to us, should sweep like a cyclone over all the civilized world. It is this work which made the understanding of the Tesla motor so simple. The explanations given by Mr. Tesla are as fundamental. However, the criticism by some English workers in their periodicals is often unjust, and based on observations or conclusions derived from a single diagram or a single patent or paper, and consequently erroneous. The writer himself agrees in many respects with Mr. Kennedy; however, he believes that the criticism is too severe, as it, is far easier to improve on the fundamental work of others than to do fundamental work oneself. Besides, only the first of Mr. Tesla's patents are based on the production of rotating the magnetic field. There are, however, enough other ones granted, at least in America, which speak of energizing fields, magnets whose poles, or what is the same, whose magnetic flux, do appear at different times without limitation to rotating fields, as Mr. Tesla himself has shown such magnets in parallel planes, instead of in one single structure.

As regards priority, Prof. Ferraris has the earliest publication and is recognized by most civilized nations as the father of the rotary magnetic field, and even should Tesla's applications for patents be taken into consideration, then, to be just, we would have to consider the unsolicited testimony of engineers like Mr. Deri,* which would give Mr. Ferraris the right to go back to 1885 and Tesla to 1887.

However, it is thought that publications only can be looked upon as just, as the main point to be considered at all times is, when the public first was made acquainted with a certain development and derived the benefit therefrom. However, there is sufficient and distinct merit in the work of either scientist. While Prof. Ferraris is the father of "electro-dynamic rotations," Mr. Tesla is the father of the system of distribution by multiphase currents and its applications.

However, in spite of the many weak points which exist at present in the rotary magnetic field, this principle has not been discovered nor this system of distribution been invented simply to be shelved. They both have come to stay, to form their department in power transmission.

The motor is open to improvements, and so is the system, and therefore Mr. Kennedy's statements must be read with reserve, because the case is by no means as hopeless as he describes it. It is only strange that Mr. Kennedy himself has a use for multiphase currents and combines a number of known devices into a system for commercial distribution. In a recent publication he rejects as hopeless everything else except multiphase currents, and instead of using a Tesla transformer he uses three separate converters, where a slight originality is gained at the expense of 25 per cent. more material.

No doubt it is unpleasant to see that a fundamental worker wishes to have all the glory and ignores the work of others necessary to make more economical machines, but this should not influence us not to fully recognize the importance of his work, even if we can devise a multiphase system without using transformers and not covered by his patents, as by their original design, their merits, or the meritorious results to be accomplished, have been brought to the notice of others.

Mr. Kennedy may abandon the use of a single alternating current for such distribution; others, however, will not do so, but will make use of single phase alternators of a safe potential, feeding by means of transformers high tension alternating currents from a distance into sub-stations and supply, aided by storage batteries, currents required for the devices in use at the locality, either low tension, continuous, alternating or multiphase, or all three if necessary. There is no doubt about it that to-day we can derive from a single alternating current all the various forms of currents; but however grand this distribution may seem, it is too complicated. We need simplification and not complication; therefore we should not strive to accommodate all apparatus now manufactured into one system. The solution lies in a simple alternating current motor. In this field there is an enormous scope, so wide even that in spite of the broad Tesla patents he must accustom himself within a year or two to find motors with a rotary magnetic field not covered by his patents, and some dozen other motors, with and without condensers, adapted to accomplish the same results far more economically than the original Tesla motors. To attack this question successfully, it is necessary to know the whole work of others, then devise other means as original, simple and far from their ideas and work as possible. Having accomplished the building of alternating current motors similar to the continuous current series and shunt motors, we will find the continuous current motors soon restricted to isolated plants, while multiphase or other complicated systems will stand on the level with continuous current distributions.