The induction motor is one of the most important inventions in modern history. It turned the wheels of progress at a new speed and officially kicked off the second industrial revolution by drastically improving energy generation efficiency and making the long-distance distribution of electricity possible. Today, not only do the machines turn on the lights in your home but also power many mechanical gadgets people take for granted, from vacuum cleaners and electric toothbrushes to that classy Tesla Motors Model S.
The first induction motor was invented by the famed Nikola Tesla in 1887 at his workshop on 89 Liberty Street, New York. This gifted inventor is said to have had a vision of his A-C motor one sunny day in Budapest, 1882, while reciting stanzas from Goethe’s Faust.
“At that age, I knew entire books by heart, word for word. One of these was Goethe’s ‘Faust’. The sun was just setting and reminded me of the glorious passage, ‘Sie ruckt und weicht, der Tag ist uberlebt, Dort eilt sie hin und fordert neues Leben. Oh, da kein Flugel mich vom Boden hebt Ihr nach und immer nach zu streben! Ein schöner Traum indessen sie entweicht, Ach, au des Geistes Flügeln wird so leicht Kein körperlicher Flügel sich gesellen!’ As I uttered these inspiring words the idea came like a flash of lightening and in an instant the truth was revealed. I drew with a stick on the sand, the diagram shown six years later in my address before the American Institute of Electrical Engineers, and my companion understood them perfectly.
The images I saw were wonderfully sharp and clear and had the solidity of metal and stone, so much so that I told him, ‘See my motor here; watch me reverse it.’ I cannot begin to describe my emotions. Pygmalion seeing his statue come to life could not have been more deeply moved. A thousand secrets of nature which I might have stumbled upon accidentally, I would have given for that one which I had wrested from her against all odds and at the peril of my existence…”
In the summer of 1883, while in Paris, Tesla built his first actual induction motor and saw it run. Tesla sailed for America in 1884, arriving in New York, with four cents in his pocket, a few of his own poems, and calculations for a flying machine. After a few odd jobs, he got employed by Thomas Edison who tasked him with improving the dynamo for his DC motor. Neither Edison nor Edison’s investors were interested in Tesla’s plans for alternating current.
How a DC motor works
In a direct current motor, a magnet that supplies a magnetic field is fixed in place and forms the outside, static part of the motor. This is called the stator. A coil of wire is suspended between the poles of the magnet and hooked to a direct current power source, like a battery. The current running through the wire produces a temporary magnetic field (it’s an electromagnet), which repels the field from the permanent magnet causing the wire to flip over.
Normally, the wire would stop after one turn and flip back again, however, a key component called a commutator reverses the current every time the wire flips. This way, the wire can keep rotating in the same direction for as long as the current keeps flowing.
The DC engine was conceived by Michael Faraday in the 1820s and was turned into a practical invention a decade later by William Sturgeon.
After a fight with the American inventor, Tesla left Edison’s lab and partnered with George Westinghouse in 1888 to whom he sold the patent for Tesla’s polyphase alternating current technology. Their partnership became very lucrative, winning numerous contracts, including one that supplied the Chicago World’s Fair of 1893 with electricity.
However, the AC motor’s first big break came when Tesla’s polyphase alternating current design was chosen to harness the power of Niagara Falls that same year.
Since his childhood, Tesla himself had dreamed of harnessing the power of the great natural wonder. In his autobiography “My inventions” he told:
“In the schoolroom there were a few mechanical models which interested me and turned my attention to water turbines”.
After hearing a description of the great Niagara Falls:
“I pictured in my imagination a big wheel run by the Falls.”
He proclaimed to his uncle that one day “he would go to America and carry out this scheme.”
Despite Edison’s propaganda aimed at discrediting Tesla as an inventor and alternative current as a viable tech — things like public demonstrations in which animals were brutally electrocuted with AC — Tesla’s designs followed the natural course of progress. As DC current travels through transmission lines, the accumulated resistance in the wires greatly reduces the electrical power supplied to the consumer. AC, on the other hand, does not suffer the same loss and is able to travel great distances with far less loss of potential. Alternative current can also have its voltage increased or decreased by transformers, so electricity can be produced at high power at generating stations then reduced right at the point of local distribution.
How an AC motor works
Alternative current reverses its direction about 50 times a second (~50 Hz), so an electric motor needs a radically different design from the DC motor.
In an AC motor, the stator is comprised of a ring of electromagnet pairs which produce a rotating magnetic field. Unlike a DC motor where the power is sent to the inner rotor, in an AC motor the power is coupled to these electromagnets to induce the field. The brilliant trick lies in energizing the electromagnets at a time, in pairs. When one pair is fully active, the other is completely shut down.
When the coils are energized, they produce a magnetic field that induces an electric current in the rotor, which is an electrical conductor, per Faraday’s law. The new current produces its own magnetic field which tries to oppose the field that produced it in the first place, per Lenz’s law. This game of catch between the two magnetic fields is what ultimately turns the rotor.
In the 20th century, electrical power distribution witnessed a massive expansion all over the world. In the first decade of the century, for instance, a generating unit with a capacity of 25,000 kilowatts was considered large. But by 1930, the largest unit in the United States had a capacity of 208,000 kilowatts, with pressures exceeding 1,200 pounds per square inch. Driven by the economy of scale, the price per kilowatt-hour of electricity dramatically plunged which eventually helped electrify the whole nation. And with so much energy at our disposal all of a sudden, the world was ready to bloom technologically.