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article number 540
article date 03-24-2016
copyright 2016 by Author else SaltOfAmerica
Nikola Tesla Gives Us Modern Electrical Motors and Generators, 1896-Today!
by J. C. White, Dean Harrington and Karl Drexler

From the 1976 book, Nikola Tesla, Life and Work of a Genius

* * *


by: J. C. White, Manager, General Electric Co.

Nikola Tesla was unquestionably a genius. He was eccentric — but then most people of genius are. He was mystical. He had frequent flashes of intuitive reasoning which led him to an immediate understanding, in detail, of the solution to a problem which others might take years to realize.

He had an incredible memory. He seemed never to forget anything once learned, whether it be technical or otherwise. Late in life he could still recite long passages of the poetry of Goethe, which he had learned as a young man.

He had the remarkable ability to visualize, in his mind, complex mathematical or physical systems. This became evident at an early age when it was found that, to the early suspicion of his masters and to their subsequent admiration, he could write down the answers to quite complicated mathematical problems, without going through all of the intervening steps.

During all of his life as a practicing inventor and engineer, he found it unnecessary to commit much to paper, since he could envision complete systems or machines in his mind in total detail. He did not need drawings or other descriptive information.

And, he was a “loner”. He found it difficult to work with other people, and quite impossible to work for anyone.

All of these factors had a part in his first, and perhaps greatest, discovery — the induction motor.

In 1875, at the age of 19, Tesla went to Gratz, in Austria, to study electrical engineering at the Polytechnic Institute. Early in his second year at the Institute, there was received from Paris a piece of electrical equipment, a Gramme machine, that could be used as either a dynamo or motor. It was a laboratory model, direct current machine.

When the machine was demonstrated by a Professor Poeschl, Tesla was greatly impressed by its performance except in one respect — a great deal of sparking took place in the commutator and brushes. As Tesla himself described it in 1915:

“I ventured to remark that these devices might be eliminated. Professor Poeschl said that it was quite impossible and likened my proposal to a perpetual motion scheme, which amused my fellow students and embarassed me greatly.

"For a time I hesitated, impressed by his authority, but my conviction grew stronger and I decided to work out the solution. At that time my resolve meant more to me than the most solemn vow.”

"I undertook the task with all the fire and boundless confidence of youth. To my mind it was simply a test of willpower. I knew nothing of the technical difficulties.

"All my remaining term in Gratz was passed in intense but fruitless effort, and I almost convinced myself that the problem was unsolvable. Indeed, I thought, was it possible to transform the steady pull of gravitation into a whirling force? The answer was an emphatic no. And was this not also true of magnetic attraction? The two propositions appeared very much the same.”

In his mind Tesla constructed one machine after another, and as he envisioned them before him, he could trace out with his finger the various circuits through the armature and field coils, and follow the course of the rapidly changing currents. But in no case did he produce the desired rotation.

Practically all of the remained of the term he spent on this problem, but at the end of the term he was no nearer the solution than he was when he started.

Tesla spent a year at the University of Prague in 1879-1880, still working on his one big challenge, but still with no success. Thus far, his failure simply added support to Professor Poeschl’s contention that he would never succeed.

His father’s death, following his graduation from the University at Prague, made it necessary for him to be self-supporting. He went to Budapest, where in 1881 he was placed in charge of the new telephone exchange there. While in Budapest, in February 1882, he took a walk in the city park with a former classmate named Szigeti. There was a glorious sunset, and Tesla was engaged in one of his favorite hobbies — reciting poetry.

One of the works which he could recite from beginning to end was Goethe’s “Faust”. He was reciting some lines from this poem, and admiring the sunset, when suddenly he snapped into a rigid pose as if he had fallen into a trance. Szigeti spoke to him but got no answer.

Szigeti was about to sieze Tesla and shake him into consciousness, when Tesla shouted, “Watch me! Watch me reverse it.” In a flash of intuitive genius he had at last conceived of the idea of a rotating magnetic field. Again, in Tesla’s own words:

“As I spoke the last words of the poem, plunged in thought and marveling at the power of the poet, the idea came like a lightning flash. In an instant I saw it all, and I drew with a stick on the sand the diagrams which were illustrated in my fundamental patents of May, 1888, and which Szigeti understood perfectly.”

Nikola Tesla’s 1896 patent drawing for an alternating current motor.

During the next two months Tesla was in a state of ecstatic pleasure playing with his new toy. It was not necessary for him to construct models of copper and iron. In his mind he constructed them in wide variety.

A constant stream of new ideas was continually rushing through his mind. They came so fast, he said, that he could neither utilize nor record them all. In this short period he evolved every type of motor which was later associated with his name.

Shortly thereafter, Tesla went to Paris where he accepted a position with the Continental Edison Company, a French company organized to make dynamos and motors, and to install lighting systems under the Edison patents. He could find no one even slightly interested in his polyphase electrical system or his induction motor.

lt was while working for this company, while on an assignment to Strassburg in Alsace, that he had an opportunity to construct his first actual alternating current motor. The machine was built without benefit of drawings. His visualization of the construction was in such detail that drawings were not required.

When completed, and the switch thrown, the motor behaved exactly as his theory had indicated it should.

Being unable to interest anyone in Europe in his polyphase system, under the urging of friends, Tesla elected to go to the United States to work with Edison. This he did in the summer of 1884. His association with Edison, however, was rather brief, lasting only about a year.

It was the classic case of two very creative minds that could not work together. Edison was a proponent of direct current, and Tesla of alternating current.

After some financial ups and downs, Tesla obtained some financial backing and established a laboratory, in 1887, on South Fifth Avenue, in New York City. Here he was able to build many of the different kinds of electrical machines which he had envisioned during the two months following his revelation of the principal of the rotating magnetic field.

Within the next two years he applied for, and was granted, 29 patents covering various types of alternating current motors, distribution system, and transformers.

Then on May 16, 1888, he gave an invited lecture before the American Institute of Electrical Engineers, which has become a classic in the electrical engineering field. In it, he presented the theory and practical application of alternating current to power engineering, so broadly and completely, that it furnishes the basis for the entire electrical power industry today.

George Westinghouse was also a man of vision, and at the same time, a good businessman. He recognized the impact of the concepts which Tesla had announced to the world. Within a month after the AIEE speech, he visited Tesla in his laboratory and observed the operation of the machinery which he had built.

Westinghouse was immediately convinced, and on the spot offered Tesla one million dollars in cash and one dollar per horsepower royalty for the use of his patents. This offer was accepted, and he also arranged with Tesla to come to Pittsburg at a high salary for a year to act as a consultant in the commercial application of his inventions.

Tesla spent that year in Pittsburgh, expecting to clear up all problems within the year. He was uncomfortable in this environment, since he could not allow free rein to his creative mind but had to concentrate on the practical problems of getting the equipment into production.

Operational Tesla a-c motor, mid-1880’s.

Tesla succeeded in convincing the Westinghouse engineers that 60 cycles was the optimum power frequency, after much debate, and this is our standard frequency today.

After his year in Pittsburgh, when Tesla returned to his laboratory in New York, polyphase alternating current and the induction motor were well on their way toward successful commercial application.

In the years since Tesla invented the induction motor, the growth rate of the electric motor industry has been truly explosive. Much of this could be attributed to the general growth in our economy and standard of living. The electric motor, however, was instrumental in spurring this very growth. Without it, our industrial growth, and even our present standard of living, would be inconceivable.

The other day, just for fun, I counted all of the electric motors that I could find in my own home. I discovered 42, and I am sure that I missed some. The ubiquitous motor indeed!

The size of the motor market is indeed enormous. For example, it is estimated that there are presently in service, in this country today (1976), more than 30 million motors in the integral horsepower sizes, representing more than 400 million horsepower. In fact, if all of these motors were put on the line at one time, the power required would exceed the total electric power produced in this country.

As another example of the size of the motor industry, in 1974 nearly 17 million hermetic motors were manufactured in this country for use in refrigerators, freezers, dehumidifiers and air conditioners. This represented about 13 million kilowatts of connected load — about one-third of the increase in generating capacity in this country in the same year.

On the small end of the scale, approximately 50 million timing motors were manufactured in this country last year, of which nearly half were used in clocks and clock radios.

The growth rate in this industry has varied, from the early days, between 5 and 10 per cent per year, and that growth is continuing. For example, in the size range from 6 to 20 horsepower, three times as many three phase induction motors were built in 1974 as in 1947. In the size range from 21 to 200 horsepower, the ratio increased to four times, and in the range from 201 to 500 horsepower the factor is ten times. While this data is fragmentary and does not cover the whole spectrum, it does illustrate two important trends:

1. The growth rate is continuing unabated.

2. The growth rate for higher horsepower ratings is larger than that for the small machines, indicating a general trend toward higher horsepower applications.

Basic motor concepts have not changed appreciably since the time of Tesla. The same fundamental processes are at work in all motors today. However, the details have changed enormously, in terms of configuration, application, size, materials, cooling, and so forth.

Motor application has a profound influence on motor design. This can be seen graphically by looking at just a few of the near-infinity of applications for motors today:
— Motor for home washers and dryers.
— Oil burner motors.
— Small fan drive motors.
— Submersible pump motors.
— Business machine applications.
— Farm equipment drives.
— Gear motors for various applications.
— Vertical in-line pumping.
— Oil well pumping.
— Chemical plant pumping.
— Cement mill conveyors.
— Transcontinental pipeline pumping.
— Blower drives for sewage treatment.
— Reactor coolant pump motors for nuclear power plants.
— Wind tunnel drives.
— Chemical plant compressor drives.
— Pumped storage hydro-electric plants.
— Variable speed drive for generator component testing, fed by a solid state cyclo converter.

" The other day, just for fun, I counted all of the electric motors that I could find in my own home. I discovered 42, and I am sure that I missed some. The ubiquitous motor indeed!"

At the turn of the century, the electric motor was a new and exciting development. No one, perhaps not even Nikola Tesla himself, could have predicted at that time the phenomenal growth of the industry. It would certainly have been defined as a growth industry then, and today it would be described as mature.

It would be tempting to believe that all significant development in the industry is behind us. On the contrary, I believe that a very great deal of change will occur before the end of this century. Much of this change will not be so apparent to the casual observer as that which has occurred in the past. However, it will still be very significant and will require a continuing high level of engineering development effort to bring it about.

If you asked the man on the street today who invented the induction motor, you would most probably get no answer at all. If you asked the average electrical engineer the same question, you might very well get the name of any of the giants in the field at the turn of the century. You would probably not get the name of Tesla. This is indeed a pity. Hopefully this symposium will correct a deficiency, indeed an injustice, of long standing.


by: Dean Harrington, Manager, General Advance Engineering, General Electric Co. and Karl Drexler, Manager, Advance Electrical Engineering, General Electric Co.

The steam-turbine-driven generators of today represent the largest concentration of continuous power, as defined by rated output, of any electric apparatus yet devised by man. Those who are involved with these large machines are understandably proud of their achievements.

However, it is necessary, and humbling, to recognize that recent progress culminating in today’s machines could have been possible only because of the very great achievements which have been made in the past by ingenious, persevering, enterprising, and courageous engineers, truly giants of the engineering profession.

The engineers of today stand on the shoulders of those who did the essential basic work in understanding the fundamental principles which we now take for granted, and also those development engineers who made the required progress in magnetics, cooling, electrical insulation, and mechanical performance of generators.

Electricity is essential in the United States to our health, our comfort, our industry, our leisure, in short, our very way of life. Generators, of course, produce this electricity, and steam-turbine generators produce approximately three-quarters of all of the electric power consumed in the United States.

Therefore, the legacy left by the giants of the past, and Nikola Tesla in particular, has reached an importance and achieved a state of development which we are sure is far beyond even the fondest dreams of those who were responsible for the early progress which helped put us where we are.

The evolution of electric power, from the discovery of the principle of induced voltage by Faraday in 1831 to the initial great installation of the Tesla polyphase system in 1896 was pronounced by Edwin H. Armstrong in 1942 as “undoubtedly the most tremendous event in all engineering history."

In 1884, when Nikola Tesla came to the United States, electrical development was generally characterized by first inventing a useful device, such as a motor or a lamp, and then subsequently developing a “system” to operate this particular device.

Tesla provided a complete system in his concept of a polyphase alternating-current system for the generation, transmission, and utilization of electric power. With the associated generators, transformers, and motors. this terminated the “war of the currents” (ac vs. dc) which was ongoing during the 1880’s.

In May 1888, Tesla, in a paper before the American Institute of Electrical Engineers, announced his new polyphase system, consisting of two or three alternating currents from the same generator following one another in sequence.

In 1893, after the electrical engineers in the power industry had recognized the severe transmission limitations of the direct-current concept, two 3,725-kW generators based on Tesla patents were ordered for the Niagara Falls Hydropower Project, and the first of these generators was placed in operation in April 1895.

Nikola Tesla’s 1894 patent drawing of "Means for Generating Electric Currents."

In his historic announcement before the AIEE, May 16, 1888, Tesla proposed “an alternate-current generator having its field excited by continuous currents”. In further explanation of his proposed system, he described “the field of the generator being independently excited . . . the rotating magnetic field was placed in operation in April 1895.

TesIa continued to make improvements on his a-c generators, in the basic design, the frame structure, the direct-current excited field, the armature winding, the bearing arrangements, and machine improvements with regard to sturdiness, compactness, high efficiency, and better material utilization.

Only in a-c generators can the large ratings required by today’s power systems be accommodated. This is because of certain inherent limitations of d-c generators.

The armatures of both d-c and synchronous (a-c) generators (essentially by the definition of “armature”) carry the output power.

A d-c generator has its armature located on the rotor so that its output current can be rectified by a commutator, whereas the armature of an a-c generator can be located on its stator.

The stator winding concept employed in a-c generators, permits the use of the high voltage and the high current needed for large power output.

The commutator of a d-c generator, on the other hand, can not handle either the voltage or the current requirement.

Also, the laminated rotor construction required for a d-c machine imposes inherent mechanical limitations.

The solid steel rotor of a steam-turbine-driven a-c generator and the fabricated and assembled rotor of a hydraulic-turbine-driven a-c generator, are not affected by these limitations and hence permit much larger physical size than is possible for a stable-running laminated rotor. The large size is essential to carry the large magnetic flux for a large power rating.

The two types of a-c generators mentioned above generate essentially all of the electric power in the world. Hence, the adoption of the a-c system concept was essential for generating the power needed by the electric power industry.

Tesla’s vision of a rotor spinning in a magnetic medium is expressed in an autobiography written in 1915 where he states that the idea of the rotating electrical field came to him like a “lightning flash” while he was reciting poetry.

Today we are still concerned, as the early pioneers were, with an understanding of the magnetic flux fields and the way in which they do useful work in the machine. We will have more to say about this a little later.

As machines have become larger, and power concentrations in them have become more intensive, it has become increasingly important to understand and control the non-useful and potentially adverse side effects which the magnetic flux fields can produce. In some respects, we are as much concerned with stray leakage flux fields as we are with the flux which is produced to do the useful work of the machine.

One area in which modern large generators are in great contrast with the early pioneering machines is the levels of current which the windings now have to carry. Today, alternating currents in the range of 20,000 to 40,000 amperes must be provided for by the stator winding.

The magnetic force effects, the losses in the windings, and the parasitic losses due to voltages induced in structural parts in proximity to the heavy currents, are challenges requiring solutions of sophistication far beyond those which the early pioneer engineers needed.

Similar sophistication in concepts and design features of the rotor, collector, and excitation system of a large synchronous generator, to handle the thousands of amperes in the field winding, has also required the attention of some of the best generator engineers.

Nikola Tesla generator produced by Westinghouse.

Until recently, the electrical engineer had not much more than a good understanding of magnetic fundamentals to use to develop theories, and design generators. Armed with a slide rule and appropriate simplifying assumptions, he was able to find solutions to his problems and was able to continue the evolution of better and bigger generators.

Therefore, to the older engineers now in the generator business, it is very exciting to watch the development of new analytical techniques (such as numerical analysis using finite differences or finite elements) for determining the magnetic flux distribution throughout the cross section of the generator, and in many other areas of interest and importance to generator design.

In all such studies, our new ability to find quantitative solutions to important magnetic field problems and draw the flux plots, has greatly advanced the electrical engineering of generators.

In a sense, this is the culmination of a struggle by electrical engineers, including Tesla, for more than ninety years, to develop an understanding of the magnetic processes in a machine, in terms of where the flux is and what it is doing, as well as what the new things are that we can do to use and control this flux once we understand it.

One type of engineer which has been very important to the developments that have taken place to date and which is equally essential to the successes required for the future, is the engineer with an inventive mind, with tenacity to push his ideas to a practical conclusion, and with a critical eye to assure that a new approach is really an improvement to the generator. Tesla’s concepts of rotating magnetic flux, alternating current, and polyphase systems and windings, are early examples of the product of such an inventive mind.

As early as 1881 Tesla conceived the principle of the spatially rotating eletromagnetic field which is the basis for
all polyphase a-c generators and motors. However, even before 1881, at the age of 19 as a student at the Polytechnic Institute at Graz, Austria, when observing a demonstration of a piece of electrical equipment requiring a commutator to prevent changes in the direction of the current, Tesla realized that if current could be made to come out of the generator with an alternating sense, the commutator would not be needed.

When he voiced his thought aloud he was ridiculed by the instructor who said in a heavily sarcastic tone that "Herr Tesla was welcome to try it."

Tenacity based on believing in his concept, even in opposition to such outstanding personalities as Thomas Edison and Lord Kelvin, led to his final success for the benefit of the power industry and hence of mankind.

Similarly, today’s approach to armature end-winding support systems, generator gas and liquid cooling systems, high-current collectors, stator-core spring mounting, and modern excitation systems are areas where the inventive mind and the critical eye have brought us to a high state of generator development.

As a result, however, today’s challenges to make the needed further progress, which are faced by the young engineer as well as by the experienced generator engineer are even greater than in the past.

Today’s challenge and also that anticipated for the indefinite future is one of maintaining and even improving the record of reliability and availability of large turbine generators, maintaining or even increasing the high level of efficiency of these machines, and improving even further material and cost effectiveness in their manufacture.

Because of the increasing importance of reliability to the economics of power system operation, the past trend to larger ratings has largely abated, with the industry being willing to forego further potential economies of scale (economies of increased ratings) until sufficient experience has been gained at each new level of rating, before pressing forward to get a larger block of power into a single machine.

We anticipate that there will be future steps in machine rating, but each such step will be taken only when experience shows that it is prudent to do so. The challenge to today’s engineer remains, since the developments needed to maintain and improve generator reliability while improving material and cost effectiveness are equivalent to and very similar to solving the problems associated with increased rating.

We are where we are today because of the engineering giants who came before us. We generator engineers of today could not attain the achievements which have been possible without standing on the shoulders of the giants who were here before us.

One of the most significant of these giants was Tesla. His concept of the rotating magnetic field due to polyphase stator currents not only is basic to the a-c motor, but is essential to understanding the operation of a-c generators. We all take this for granted today. But Tesla had to hit upon the idea with little help, and mostly opposition.

To provide electric power in the quantities required in the United States and in the world today, Tesla’s concepts of alternating current and polyphase windings, are essential. The limitations of a commutator as well as the mechanical design of a laminated rotor, limit the power obtainable from a d-c generator to a small fraction of that which can be obtained from an a-c generator designed for the high voltage, and carrying the high current that are essential to the ratings of machines available today.

The future will require generators even better than today, and generator engineers competent in tomorrow’s technologies.

These engineers will need to benefit from the experience of the past, but not be limited by past approaches. They must also be equipped with the latest advances in engineering tools. This places a major challenge on the colleges to provide the required excellent education, and on the generator engineering organizations to work with the colleges to help provide the incentive and the direction for this educational excellence.

Nikola Tesla at the age of 55.
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