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Categoria: ENGLISH ARTICLES

 

Polyphase Currents and Rotating Fields

The creation of the rotating magnetic field was “purely the work of scientific imagination”.

It has been identified as the greatest creation of the human mind since the invention of the wheel.

Tesla’s discovery of polyphase currents and “an invisible wheel made of nothing but a magnetic field” (the phrase is due to Reginald Kapp)(16) was the turning point from the past into the 20th century.

Tesla stands at the focal point of the important electrical discoveries of the 20th century. At the conferral of the AIEE’s highest award of honor, B.A. Behrend remarked, «Were we to seize and to eliminate from our industrial world the results of Mr. Tesla’s work, the wheels of industry would cease to turn, our electric cars and trains would stop, our towns would be dark, our mills would be dead and idle».(17)

When Tesla died in 1943, Yale University EE professor Charles F. Scott observed, «The evolution of electric power from the discovery of Faraday in 1831 to the initial great installation of the Tesla polyphase system in 1896 is ‘undoubtedly the most tremendous event in all engineering history’».(18)

And, the connection to the relativity of rotation (an issue still not put to rest today) was not overlooked: Yale physicist Leigh Page once said, «The rotating armatures of every generator and every motor in this age of electricity are steadily proclaiming the relativity theory to all who have ears to hear».(19)

Let us follow this central thread that runs through Tesla’s professional career back to its origin.

While Tesla had constructed the first rotating field apparatus in the summer of 1883 (one year before both he, and the Statue of Liberty, arrived from France), it was not until 1887 that a company was formed to exploit the phenomenon.

However, Tesla was unable to raise capital to commercially introduce his invention. (The enterprise was ‘undercapitalized’.)

He finally found a skeptical Wall Street lawyer that was somewhat interested, and this is the conversation as Tesla retells it.

Tesla: «Do you know the story of the Egg of Columbs? …Well, what I could make an egg stand on the pointed end without cracking the shell?”* “If you could do this we would admit that you had gone Columbus one better.” “And would you be willing to go out of your way as much as Isabella»? «We have no crown jewels to pawn», said the lawyer, who was a wit, «but there are a few ducats in our buckskins and we might help you to an extent».(20)

Tesla arranged for a demonstration the next day. He placed a copper-plated egg on a wooden plate above his rotating magnetic field (there is a photograph of the apparatus in the Secor article).

As soon as the windings were energized the egg began to spin.

[Tesla’s spinning egg is, in fact, a macroscopic analog of the Einstein-de Haas effect investigated almost thirty years later. The materials in Einstein’s WWI experiments spin because of molecular ‘amperian currents’ (although later Einstein did suggest using high frequency ‘rotating magnetic fields’ to Barnett). In Tesla’s experiments they spin because of induced eddy currents. See part V below.]

“… to their astonishment, it stood on end, but when they found that it was rapidly spinning their stupefaction was complete*… No sooner had they regained their composure than Tesla was delighted with their question: ‘ Do you want any money?’… That started the ball rolling. Tens of millions of horsepower of Tesla induction motors are now in use all over the world and their production is rising like a flood… Rotating fields of 15,000 horsepower are now being turned out… and ship propulsion by Tesla’s electric drive which, according to Secretary of the Navy Daniels’ statement, has proved a great success.”(21)

The electrical circuit which Tesla employed for the egg of Columbus used two phase AC energizing the coils in quadrature and the source frequency was varied from 25 to 300 cycles, “the best results being obtained with currents from 35 to 40 cyclas.”** The story was also mentioned in Fleming’s eulogy of Tesla. (22)

In 1893, 6 years after demonstrating the egg of Columbus to the attorneys and business investors in New York, a large egg demonstration was constructed for Tesla by Albert Schmid and Charles H. Scott, at the time both of Westinghouse. (Scott, subsequently an EE professor at Yale, served as President of both the AIEE and, later, the IRE.)

The egg occupied part of the Westinghouse exhibit in the Electricity Building at the great Chicago World’s Fair. The 1893 Fair celebrated the 500th anniversary of Columbus’ discovery of the new world and, ostensibly, it was intended to launch society into the 20th century.

There is a photograph of Tesla’s exhibit in the Martin book.(23) This was only a few months before Lord Kelvin was to choose the Tesla polyphase system for Niagara Falls, and 3 years before the first Niagara Falls plant was turned on.

While Tesla had been active in RF generation in the early 1890’s, the close of the decade saw him making great strides in the realm of high voltage RF power processing.

These experiments culminated in a cluster of patent applications and the construction of the Wardenclyffe laboratory. Mention should also be made of his turbine development and intense engineering consulting practice just prior to WWI.

From the comments above it is clear that he was actively promoting his patented ideas.

 

*The language used to describe the striking effect his 1892 lecture-demonstration had on the Royal Institution in London, was, “The scientist simply did not know where they were when they saw it.” (Anderson, 1992, pg. 95)

**Note that Tesla has recognized that he can characterize different spinning eggs with certain gyromagnetic resonance frequencies! This was in 1887.

READ ALSO:

1994 Tesla Symposium at Colorado Springs

RADAR AND ROTATING FIELDS

Why Tesla?

Tesla’s Reflections on Radar and Ships Wrapped in Coils of Wire

Radar

Sommerfeld on Electromagnetic Stealth During WW-II

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