Will Tesla give up induction motors

The invention of the electric motor 1856-1893

Timeline 1856 - 1873: About the invention of the dynamo for the direct current motor

1856Werner Siemens (German) invents the power generator with a double-T armature and places a winding in two slots for the first time.

This invention marks a turning point in the design of electrical machines. In the decades that followed, all previous designs disappeared from the market. To this day, almost all electric motors are built with windings in slots.

In 1856 Siemens manufactured around 50 devices for the Bavarian railways. However, these first machines were operated by hand and supply voltage pulses for telegraphing, not continuous electrical energy.

Double T-anchor machine from Siemens
Poggendorff's Annalen der Physik 101 (1857), plate II 
James Clerk Maxwell (English) summarizes all previous knowledge about electromagnetism in 20 fundamental equations. Around 1882 Oliver reduced Heaviside (Englishman) 12 of the equations further down to only 4 equations with 4 variables, which are still valid today and comprehensively describe the theory of electrical engineering.
1866- 1867 Siemens develops the dynamo-electric machine based on the double-T armature. This means that a powerful power generator is finally available and the triumphal march of electricity can begin.
1871 The Siemens double-T armature initially has the disadvantage of generating a pulsating direct current.

Zenobe Théophil Grams (Belgians) solves the problem by inventing the ring armature (ring traveler) and can thus produce a smooth direct current. In the years that followed, Grammes' ring armature machines competed significantly with the Siemens double-T armature machines.

However, Grammer's construction is no longer used today.

Grammescher Ring, 1871
Photo: Wikipedia
Friedrich ofHefner-Alteneck(Deutscher), a close employee of Werner Siemens, starts developing the double-T anchor into a drum anchor.
To do this, he completely wraps wire around a cylindrical anchor.

It was not until 1875 that he got the problem of eddy currents under control by using iron wires for the magnetic core like Grammé.

Siemens drum anchor, ca.1872
(cut model)
Photo: Science Museum, London
1873 AugustePellerin (French) suggests dividing the iron core into many individual, mutually insulated sheets to avoid losses due to eddy currents. However, he does not pursue his idea any further.

With the Ritchie commutator, the drum armature from Siemens and Hefner-Alteneck and the sheet metal of the magnetic circuit, all the important design features of modern electrical DC machines are now known.

The later DC motor did not emerge from the developments of Jedlik, Jacobi, Davenport, Davidson, Page or other early inventors, whose designs ultimately all proved to be inferior, but from Siemens' dynamo.

J. Zöllner wrote in 1885: "The history of the electromagnetic power machine breaks off with its childhood, or it goes together with the history of the dynamo machine."


Timeline 1885 - 1893: The three-phase system and the induction motor

1882-1889NikolaTesla (Croat) worked on the multi-phase system as early as 1882 during his studies in Graz / Austria.
He emigrated to America in 1884 and founded his own company and development laboratory in New York in 1886.
In the meantime, Ferraris had succeeded in building a two-phase induction motor in 1885 (see below).
Tesla knows nothing about this and invents the induction motor a second time. He also builds a number of functional models.
Tesla fell out with his investors in 1886 and now has to earn his living as a laborer for two years while he continues to work on his inventions.
In 1887, Tesla files the first patents for a two-phase, four-line AC system consisting of a generator, a transmission system, and a polyphase motor.

George Westinghouse of Pittsburgh is presented in May 1888 by Tesla's notable lecture before theAmerican Institute of Electrical Engineersattentively and buys the now more than 40 patents for $ 1 million. He also hires Tesla as a consultant for a year.

However, Tesla still does not recognize the special advantages of three-phase alternating current and has subsequently concentrated on single-phase and two-phase machines with alternating current of high frequencies (125 Hz and 133 Hz). Ultimately, he failed to build a usable induction motor and left Pittsburgh and the Westinghouse Company unsatisfied in 1889. Westinghouse then stopped developing this type of machine entirely.

Only after AEG had proven beyond doubt with the Dobrovolsky machines (see below) that reliable three-phase induction motors could be built, Westinghouse began developing three-phase motors in 1892, which led to success in 1893. However, without the involvement of Tesla, who has meanwhile turned to other topics.

1885 GalileoFerraris(Italian) builds the first induction motor. Like Tesla, he uses two phases.
However, Ferraris wrongly believes that such engines can never go beyond 50% efficiency. He therefore loses interest and does not develop his engine any further.

Schematic representation of the Ferraris engine
from his patent specification, 1885
1887- 1889 Charles SchenkBradley (US-American) experimented with polyphase motors and generators even before Ferrari's work was published.
In 1887/88 he received several US patents on this subject (initially on two-phase, later also on three-phase systems), but was never able to put them into practice.


Bradley's induction motor
from his patent specification, 1887
Friedrich AugustHazel walk(German) in Offenburg / Baden in July 1887 was the first to come up with the idea of ​​using a three-phase alternating current.

He builds the first three-phase synchronous generator with pronounced poles. However, the postal authority prohibits the operation of the machine for fear of interference with the telegraph line. Haselwand's patent efforts also fail.

Haselwanders synchronous motor, 1887
1889-1891 MichaelDolivo-Dobrowolsky(Russian, naturalized Swiss), chief electrician at AEG in Berlin, develops the basic ideas of Ferraris and Tesla and uses them to construct the three-phase squirrel cage motor (induction motor) that is still widely used today. At the beginning of 1889 his engine ran perfectly.
The slip ring rotor with starting resistors was also invented by him later.

Dolivo-Dobrowolsky's first squirrel cage motor, 1889
Illustration from the ETZ, 1917 ([9])
1889-1893 JonasWenström(Schwede) describes in a British patent from April 1889 all parts of a three-phase transmission system.

Wenström's first three-phase generator was built in 1890 and the first 13 km long three-phase transmission system in Sweden in 1893.

He probably did not know the work of the other participants, because they were one or two years ahead of him.

Sketch from Wenström's patent application, 1890

The energy transfer

Dobrovolsky Be the first to recognize that a three-phase system in a suitable circuit (triangle or star) manages with only three conductors and is therefore even less complex than a two-phase system (four conductors).

in the August 1889 he receives the patent for the invention of the three-legged three-phase transformer. This marked the beginning of the triumph of three-phase alternating current.


1891 builds the AEG under the leadership of Dobrowolsky together with the Machine factory Oerlikon and their chief engineer Charles E.L. Brown the first three-phase long-distance electrical energy transmission over 175 km from Lauffen am Neckar to Frankfurt am Main, which later achieved the remarkable efficiency of 96%. The line can transmit up to 220 kW of power and was operated with voltages of up to 25 kV.


Five years later Late 1896, will be the first U.S. American high-voltage transmission line inaugurated. Built by Tesla and Westinghaus takes them from Niagara Falls to the city of Buffalo, New York State, over a distance of 22 miles (35 km). This line is also a three-phase system, which Tesla has come to appreciate in the meantime. However, three single-phase transformers must be installed at both ends because the advantageous three-legged three-phase transformer is patented by Dobrovolsky. The transmission line can transmit an output power of up to 750 kW and is operated with a voltage of 11 kV.





On the priority question, Franz remarksHillebrand In the name of the scientific committee of the VDE in 1959 after a detailed study of the matter the following [10]:

"... The solution to the problem (was) almost in the air, and so it is not surprising that in many heads very similar solutions were formed almost simultaneously on very similar lines of thought ...

One of them already has the solution in his hand, at least in principle, postpones its publication by a precious three years and, due to a mistake of thought, misunderstands its meaningFerraris); 

the other is very familiar with the matter, develops the solution step by step in a technically usable form, but only in patent specifications, he does not seem to think about implementation in reality (Bradley). 

Again someone comes to the right solution almost by chance, recognizes it immediately thanks to his technical talent, applies it correctly on a small scale for a modest special case in an astonishingly short time, but has neither the gift nor the economic backing to his Bring ideas to a breakthrough (Hazel walk). 

Another struggles for the solution in restless mental work, dreams of the fantastic prospects that his flight of thoughts opens up, of the shackling of the forces of Niagara Falls and other things, but does not have the ability to quickly find a technically usable form or employees for to inspire his ideas (Tesla). 

Someone clearly recognizes the problem, finds technically perfect, well thought-out solutions for the entire area, but appears one to two years too late in the race with his solutions (Wenström). 

Next comes someone who knows the situation in the field of energy supply very well, who has mastered the matter confidently, who is used to overcoming difficulties in the development of electrical machines, who combines courage with determination and who is very lucky with a far-sighted economist to be able to work together (by Dolivo-Dobrowolsky). 

... How difficult it is to distribute the merits correctly with this background! ...

Tesla be the first to deal intensively with the question of electrical energy transmission through a multi-phase alternating current system; he was the first to find the basis for such a transmission and was the first to specify the principle of a multi-phase induction motor.

Bradley was the first to apply for a patent on a two-phase AC power transmission with two-phase synchronous machines and four trunk lines. He also had the first patent for a three-phase induction motor with a completely short-circuited secondary part (cage stand).

Hazel walk was the first to design a three-phase power transmission with three-phase synchronous machines and three transmission lines. He was the first to build such a system and was the first to put it into practical operation.

OfDolivo-Dobrowolsky built the first simple, practically usable three-phase induction motor with a squirrel cage armature. In broad scientific lectures and papers he clarified the nature and properties of three-phase current and three-phase motors ... and two years after the construction of his first 1/10 HP three-phase motor, he handed over a 100-HP three-phase motor to normal operation ... Dobrowolsky is therefore to be seen as the pioneer for the introduction of three-phase current ... "



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