How does a Generator Work & How We Figured it Out

Most of our electricity comes from power plants that use a generator to, ahem, generate electricity.  OK, then, how does a generator work?  And how did anyone figure it out in the first place?  It’s time to get spinning.  Ready let’s go…

It all started in 1832.  That is when Michael Faraday published his work on his many ways of using magnets to create (or induce) electricity.  Faraday wrote that moving a magnet into or out of a coil of wire would create bursts of current and spinning a copper disk near a magnet made a constant but weak current.  A French instrument maker with the nearly unpronounceable name of Hippolyte Pixii read Faraday’s paper and combined their features into a single machine where he spun a u-shaped magnet near coils of wire with iron inside them.   When Pixii spun the magnet, an interesting thing occurred: the current would go one way and then, a half a turn later, the current would swing back the other way.  By spinning the magnet faster he could get more current, but it would also make the current swing back and forth faster.  We would now call that Alternating Current or AC.  At the time, however, the sinusoidal current seemed like a negative result. 

Pixii Machine

Pixii went to France’s leading electrical scientist, Andre Ampère, who suggested he could “fix” this problem with a funny device we call a commutator.  The commutator had brushes that connected to the coils so that sometimes the wires were connected one way and sometimes they were connected the opposite way.  The result of all of this is that it changed the alternating current to a current that pulsed but only went in one direction.  Even with the commutator, this machine was not useful for Telegraphs (as they needed a constant current – and Pixii’s was too “bouncy”).  Poor Pixii died in an accident two years after he created his invention at age 26 and, as far as we know, never made a dime off of his invention.

Not much happened for seventeen years until a Brussels professor named Floris Nollet made a generator with more and more coils, eventually creating a behemoth machine with forty magnets and sixteen coils, that he called “the Alliance” that could produce around 50 Volts of potential.  At the time, the only electrical lamp was made with a very bright spark between carbon rods called an arc lamp.  The Alliance machine would light up an arc lamp, but it was not practical for commercial use because the commutator would spark and would be destroyed by the brushes rubbing against a rapidly spinning machine.  After seven years of frustration and basically as a random attempt someone came up with the bright idea of using this generator without the commutator at all.  They found to their shock that the alternating current would light up an arc lamp!  This was the first instance of using the current that went back and forth (alternating or AC) instead of forcing the current to be in one direction (direct current or DC).  This was also the first use of AC current to create light.

The most significant innovation in generators has to do with something called an electromagnet.  Way back in 1831, an American scientist named Joseph Henry experimentally demonstrated that you could make the strongest magnet per weight with a simple battery by wrapping insulated wire tightly around a metal core and putting current in the wire.  In the 1850s two men said they independently thought of using electromagnets in their generators. 

Samuel Varley was a thirty-five-year-old English telegraph operator and “disciple of Michael Faraday” who had been playing with generators for fun on his own since he was seventeen years old.  In 1856, he created a generator with electromagnets although it took him ten years to file for a patent!  Varley might have been first, but he was mostly ignored as he was not well connected and he had had a bitter falling out with his older brother Cromwell Varley, who was well connected and apparently worked to obscure his younger brother’s accomplishments. 

nolet generator

Another Englishman named Henry Wilde, however, was well connected (& also his siblings did not work against him).  In 1866, Wilde wrote of his experiments with electromagnets and why he used them.  Wilde stated that since electromagnets demonstrated that electricity could produce a very strong magnet and generators demonstrated that magnets (and spinning) could produce a lot of electricity, it seemed logical to basically nestle these effects.  Use a generator with magnets to create electricity and then use that electricity to make electromagnets to generate even more electricity.  

Wilde, therefore, used a generator with bar magnets to electrify or “excite” the electromagnet.  This was called exciting the coil and the separate generator was called an exciter.  Wilde found his results to be “most splendid”, and had ecstatic descriptions of how his “compound” generator could produce incredible light or melt metal bars!  Note that energy is conserved, or you can’t get something for anything, meaning that these generators produced more power but were correspondingly harder to rotate. 

Wilde’s paper was a hit and two other scientists credited his work with giving them the idea of creating a generator with electromagnets powered by the generator itself!  The idea is to siphon some of the electricity produced by the generator back into wires of the electromagnets so the current that the generator produces creates magnetism.  This is called “self-excitation”.  Now, if you just spin wires near other wires you won’t produce any current, you need something to kick start the whole system.  Both men found that you could either give the electromagnets a start with some electricity from a battery or rub the iron bar in them with a magnet to make them weakly magnetic even just use the magnetic field of the Earth to magnetize the iron! So, in other words, electromagnets are given a little magnetism and then coils are spun near these weak magnets.  This causes current to be induced in the coil.  Some of that current is then siphoned off to the electromagnet, increasing its magnetism.  This causes more current to be induced in the coil to be fed back into the electromagnet.  This “feedback loop” is what makes electric generators so very powerful.

Self-excitation was the key to making practical generators to light up whole cities.  One of the scientists to “discover” self-excitation in 1866 was named Weiner von Siemens.  Siemens had started a company twenty years earlier called “Siemens and Halske” to manufacture long-distance telegraph lines in Germany.  Siemens had been manufacturing generators for many years (in fact, Wilde had used a Siemens generator in his experiments using electromagnets).  Siemens became the first company to manufacture self-excited generators which they called “dynamos” from the Greek word for power “dynamis” a name used for most DC generators for a good 50 years afterward. 

[Just to give credit where it is due, Samuel Varley, the guy with the pissed off brother, discovered self-excitation in the 1850s and even patented it before either Siemens or the other scientist Wheatstone wrote about it, however, he was mostly ignored by the scientific community at the time.]

With dynamos, companies started using and manufacturing generators to drive motors in shops and towards the goal of lighting up streets and even homes.  Although it had been many years since it had been proven that you could use Alternating Current to create light most people used the commutators to get pulsed DC current.  Why?  Well, there was the mistaken belief that AC was more dangerous than DC.  Also, you couldn’t use self-excitation with AC at the time (the current in the electromagnets had to be DC).  Therefore, AC generators had to have separate exciters like Wilde used.  Siemens himself said that “there was nothing whatsoever in alternating current, it is pure humbug.”  In the late 1800s, there were only a few brave visionaries who wanted to use AC. 

One of those visionaries was named Nicola Tesla.  In 1887, Tesla invented what is called the multi-phase AC generator (and a corresponding multi-phase AC motor).  In this system, you spin multiple separate coils around the electromagnets.  The idea is that the different coils get the same alternating current but the current is out of step with each other.  The alternating current is then transmitted over more wires but with significantly more power as well.  For example, three-phase generators use three wires instead of two wires but also transmit three times the power as the two wires used to do.  In addition, multi-phase current can be used to make stronger motors as each coil pushes the motor at different phases.  For these reasons, we use three-phase generators in our power plants today! 

Nikola Tesla's ac induction motor
Nikola Tesla’s ac induction motor

After the invention of the diode, which is a one-way switch, we had a way of using self-excitation in our AC generators.  So, currently, we have generators that produce AC with self-excitation.  First, the electromagnets are charged with a battery, and then some of the generated currents are diverted (with a diode to make it DC) back into the electromagnets.  At its base, all generators generate electricity by spinning electromagnets near coils of wire.  That’s it.  So think of a power plant.  Coal plants burn coal and then have the steam spin electromagnets near coils of wire.  Nuclear plants use nuclear reactions to heat water so that the steam will spin electromagnets near coils of wire.  Dams block a river and then have pressured water spin electromagnets near coils of wire.  Windmills use the wind to spin electromagnets near coils of wire.  Ect. etc.  So this is where electricity comes from.

Thanks for watching my video, please remember to give it a thumbs up.  If you liked this video you may like my previous video on how Faraday discovered induction in the first place.  I will also, very soon, have a series of videos about Edison, Tesla, and Westinghouse and the battle over DC and AC.  First, however, I am going to tell one of my favorite stories in science, how a shy teacher invented the telephone because of his love for his father and for a deaf woman who could never use it.  The invention of the telephone, a love story is a next time on the secret history of electricity.

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