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Tesla: Art of Transmitting Electrical Energy through the Natural Mediums (1900) (patents.google.com)
107 points by hownottowrite on Jan 12, 2018 | hide | past | web | favorite | 22 comments

Wouldn't it be better to post a link to the full patent here, since the OCR quality is so bad that it's almost unreadable on Google's site?

Here's that patent on the USPTO site:


Why do they publish each page in a separate file? Here are all pages joined together: https://a.pomf.space/sgpnalxtzbae.pdf

If you click the "Full Document" button on the left, it provides a single PDF.

Why that's not the default behavior though...

I started reading some of Tesla's speeches recently, and one thing that struck me was how he happily talks about enormous flaws in the implementations of his designs, but still went on to prove that they were POSSIBLE even if the practical design might have to wait.

His idea for ultra-efficient high-voltage, high-frequency AC power lines is a good example. It would probably work, but his proposed system required liquid insulation on the wires; it would be important to keep gases out of the medium, and the slightest break in a solid insulation like rubber or silicone (or gutta-percha) could basically turn the wire into the business end of a tesla coil.

So...I don't understand enough about the subject to say for sure, but we probably landed on 50-60Hz for a reason. I wonder why this one didn't wind up working out, but I'll bet it's described somewhere in the application which I've only skimmed.

Also, for anyone else trying to dive into it, 'condenser' = 'capacitor' in olde-speak.

The choice of 50/60Hz is an engineering trade off. Engines, Turbines and alternators are happiest spinning in 100s to 1000s of revolutions per minute range. At that RPM range, alternators with 2, 4, 6 etc magnetic poles translate to AC line frequencies in the 10's of Hz range. AC power on aircraft is usually at 400Hz because it makes equipment lighter.

It is similar with the choice of 3 phases for electrical power distribution, you can add more phases but it just adds to the cost with little benefit.

Another relevant trade off is transformer size vs. efficiency.

AC is used because it's very simple to step up to very high voltage for efficient long distance transmission and then back down to safer low voltages for use, while doing the same with DC requires significantly more complex electronics.

However, at very low frequencies you need to use very large transformers which cost a lot and look ugly, and at higher frequencies you lose efficiency due to skin effect [1].

50 Hz is a good compromise - transformers are of a practical size and skin depth is about 9 mm, which is larger than most conductors and therefore doesn't add much loss.

If you increase the frequency to just 10 kHz (which is still considered very low) the skin depth decreases to only 0.6 mm, and you would have significant loss on even moderate sized conductors.

[1] https://en.m.wikipedia.org/wiki/Skin_effect

Huh, cool; you learn something new every day!

Jeez, when it comes to electricity, it is just like peeling an onion with layers of ignorance...

You want low frequency for high efficiency in transmission lines. That's why HVDC is becoming more popular [1]. It wasn't really economical to use DC current for a long time because it's more difficult to step up/down the voltage than with AC (you just need a transformer). But power electronics and in particular power semiconductors have advanced so much that HVDC becomes more and more prevalent. As for AC: The higher the frequency the higher the losses, but you can use smaller transformers (without using any fancy power electronics).

[1] https://en.wikipedia.org/wiki/High-voltage_direct_current

We already use high voltage for power transmission. Step up transformers at the power plant bring the voltage up to 230kV for transmission and step down transformers within the city bring the voltage down to normal.

My guess for the frequency, is that it is a harder conversion to perform with acceptable loss. Compatibility reasons doesn't allow for just bumping it up. Also let's not forget that AC frequency actually comes from the revolutions per second the power generator does, so there may be some other physical limiting factors here.

Last, some underground high power transmission lines are actually emerged into oil, to keep them cool.

Higher frequency on power lines would be less efficient, not more. High voltage DC is the most efficient, but is most expensive because you can no longer use transformer for step-up and step-down.

> we probably landed on 50-60Hz for a reason

I'm pretty sure that's the minimum to prevent perceptible light flicker.

Incandescent lights were more forgiving in that regard due to thermal inertia: https://physics.stackexchange.com/questions/13400/what-invis...

Most remarkable are the number of very modern patents that cite this one! How surgical instruments benefit from earth-transmission technology is beyond my understanding.

The patent helps sensitive equipment work (think like an EKG monitor) during a lightning storm.

So this seems to be https://en.wikipedia.org/wiki/Extremely_low_frequency

Including "The attenuation of ELF waves is so low that they can travel completely around the Earth several times before decaying to negligible amplitude, and thus waves radiated from a source in opposite directions circumnavigating the Earth on a great circle path interfere with each other.[20] At certain frequencies these oppositely directed waves are in phase and add (reinforce), causing standing waves. In other words, the closed spherical Earth-ionosphere cavity acts as a huge cavity resonator, enhancing ELF radiation at its resonant frequencies."

Does anyone have a technical explainer of Tesla in modern terminology?

Which of those terms do you not consider modern? As far as I know all those terms are still in cirulation

Edit: sorry, I see you probably mean the content of the patent rather than the passage you quoted

Fascinating to read the text and know this was done nearly 120 years ago. Such an amazing genius.

Actually, it wasn't done. Every one of his Earth Conduction attempts ended up a spectacular failure.

The wording reminds me of this whimsical story that I read several years ago (before Tesla motors), about the electric car that he powered with vacuum tubes and an antenna: http://keelynet.com/energy/teslcar.htm

Come to your own conclusions, but there's evidence that it was a hoax: https://en.wikipedia.org/wiki/Nikola_Tesla_electric_car_hoax

Something I've always wondered about is whether the electrical charge of the earth is uniform across the entire surface, or of you could harvest electrical power by just running a (presumably really long) wire between two grounded spots. I guess if they don't do it the answer is probably "no", "not enough to pay for the wire", or "Where do you put the meter?"

It is common knowledge that a pair Earth stakes will pick up a small amount of current.

Hobbyists have been using the idea for years to run small radios.

Likewise that same ground current will screw up Telegraphs (etc) which try to use an earth-return path.

The problem for large scale energy harvesting is that the Earth is conductive, so any voltage differences are shorted out by the Earth itself and dissipated as heat.

To put it another way, the Earth is a lossy medium, so any signals are heavily attenuated by distance.

This is amazing

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