Comment by Animats | Hacker News Reader

Comment by Animats | Hacker News Reader

Yes, there's action in rotating electrical machinery again. For decades, this was a dull and boring field.

Tesla and Steinmetz figured out the theory of AC machines in the early 20th century. This was the first industrial technology where you needed advanced math to get anything to work right. Complex numbers. Calculus. Laplace transforms. That bothered some people, such as Edison. By the 1930s it was figured out, and generations of EEs struggled through rotating machine theory in college.

Then all the cool kids went off to radio and transistors and computers. Rotating electrical machinery was a mature field. Maybe a few people at GE in Schenectady worked on it.

Then came power semiconductors, and chopper-type motor control, where power was being turned on and off at moderately high frequencies. At first this was just applied to existing motor designs. But AC motors were designed for sine wave power. Choppers didn't produce clean sine waves. Much effort was put into making variable-speed controls that produced the nice sine waves motors needed. Classical AC theory was built around sine waves, and engineers knew how to do that kind of analysis. This worked, but it made AC motors buzz at the chopper frequency, and as chopper frequencies went up, whine. When you ride on BART, that's what you're hearing from the motors. The waveform mismatch also led to unwanted heating in the windings and inefficiency.

Variable-frequency 3-phase AC motors went from exotic to normal. Today, everything from a Tesla to a drone to a Diesel-electric locomotive uses such motors. The big power semiconductors required aren't that big. Here's one for a locomotive.[1]

In recent years, motors have started to be designed for the non sinusoidal waveforms that come out of chopper power supplies. This required new theory and much simulation of magnetic fields. There's plenty of compute power available and commercial packages for that kind of analysis. Now we're seeing more advanced motor designs that match well with their control electronics.

After most of a century, rotating electrical machinery design is cool again.

[1] http://www.ametrade.com/eng/electronics/products/IGBT_IGCT.s...

>When you ride on BART, that's what you're hearing from the motors.

https://www.youtube.com/watch?v=vdNCrj14cK0

That's brilliant!

There are some trains on the London Underground that use gate turn-off thyristors, which make a sort of Star Trek klaxon sound when they start up:

https://www.youtube.com/watch?v=pagB58tGpRY

That sounds similar to this, but with much less time spent on the intermediate frequencies: https://www.youtube.com/watch?v=NWEexwZSXF8

My favorite bit of electric locomotive technology: https://www.youtube.com/watch?v=yjMZ5qtyCUc

Closely followed by dynamic braking, or as it is more accurately and much more awesomely called in the UK, rheostatic braking.

Someone posted one of these on /r/electricians the other day running an elevator in New Zealand; very cool piece of tech.

https://www.reddit.com/r/electricians/comments/6vpg8n/the_me...

This melody is unique (on London Underground) to the Jubilee line.

Although the Northern line trains have an almost identical body design, they use a more modern IGBT traction system which, although presumably more efficient, has a little less character!

Yes, the 3-phase synchronous AC locomotives driven with IGBTs seem to be quieter.[1] But the real advantage is precise wheel control. Here's the biggest steam locomotive ever built being towed out of the Pomona Fairgrounds for restoration. They're towing it through a very tight turn on temporary track to get it out.

The locomotive doing the towing is a 2006-model Electro-Motive Diesel-electric locomotive. It's towing the old steam locomotive at a very slow speed, smoothly, with no wheel slip. Nothing special about it; Union Pacific has hundreds of them. Six axles, each powered by its own motor. AC synchronous, IGBT power control. The motors are run as servomotors, all locked together. No wheel can slip relative to the others. This is a huge win when you need to get a few thousand tons moving.

This boring but useful modern locomotive, although much smaller, has more drawbar pull than the Big Boy. Multiple locomotives can be ganged together with wheels locked in sync, if you need more pulling power. Here's Union Pacific overdoing that.[2] They put together a train 3.5 miles long, with 9 locomotives spaced throughout the train, and ran it from Long Beach to Denver. This was just a test; they don't normally run trains that long.

All this is made possible by modern electronic motor controls.

[1] https://youtu.be/JRoIrFgcIjc?t=894 [2] https://www.youtube.com/watch?v=jdIzRFOaTCY

I thought it was a PA jingle .. crazy.

Oh, that's cute. Siemens makes a locomotive that uses switching frequencies spaced one note apart and steps through them during acceleration. That has to be on purpose.

Likely due to some exponential thing with the switching frequency following the soft acceleration, as the speed as far as I know increases according to a cubic function until about half of full acceleration is reached, and from there on it goes over to quadratic until the train hits about 80 km/h, as they lack power at around that speed to keep the acceleration at the usual 0.9-1.1 m/s^2. And the harmonics are exponential, with log_2(#of_notes/12) giving you the relative frequency difference for a given number of notes spacing.

Yes, this was done on purpose :)

I always wondered what this sound was about.

https://youtu.be/TM0bOpwxxO8

Sounds like there is a steam engine inside (but the 451s are electrical)

Those are relay contacts selecting which field windings are getting power. As the locomotive accelerates, the number of enegerqzed coils is reduced in order to reduce back EMF (electro motive force)

And then there's "Somewhere" in NY:

http://www.nytimes.com/2009/02/21/nyregion/21about.html https://www.youtube.com/watch?v=WL436Qddigw

> Tesla and Steinmetz figured out the theory of AC machines in the early 20th century. This was the first industrial technology where you needed advanced math to get anything to work right. Complex numbers. Calculus. Laplace transforms. That bothered some people, such as Edison. By the 1930s it was figured out, and generations of EEs struggled through rotating machine theory in college.

It's always interesting to observe differences in history from different vantage points.

In Europe the story told goes like this: Some time in the early 19th century people noticed that a thing called induction exists. Then in the later 19th century a chap called Ferraris (also known for his AC energy meter) developed multi-phase AC and the general idea of an induction motor. Some bit later, a Russian guy named Dolivo Dobrowolsky, invented a two-phase induction motor. Meanwhile, some other folks started to build transformers. Not even a handful decades later and virtually everyone in Europe used AC and both synchronous and asynchronous generators and motors were used everywhere for everything in industry.

The reason for these differences is of course that in these few years key advancements were made by different people at the same time.

> In recent years, motors have started to be designed for the non sinusoidal waveforms that come out of chopper power supplies.

From what i remember, square waves are better for a motor. Thinking about it i see no benefit of it being sine (*with many poles, that is, as a square would shake the mechanical parts too much otherwise).

The trams here have 3-phase engines.

I think you're right. The thing with three phase motors is that you have a rotating magnetic field, which necessitates sinusoidal currents.

Depends on the windings. Synchronous motors have had windings designed for sq. wave drive for many years now, prominently for stepper, servo and BLDC motors. These still use some filtering to reduce the insulation stresses.

They use square waves for them because squares are much easier to make, not because they work better.

Good driver chips (e.g. https://www.trinamic.com/) still synthesize sinusoidal-like waves for these motors. It reduces noise and power consumption.

So where could I pick up similar motors to what Tesla uses in their cars?

A scrapyard. Both the rotor and stator are water cooled in Tesla motors. The motor shaft has two holes drilled down the length of it which is fantastically expensive to get done in units of less than tens of thousands. However there is a steady business of resold Teslas from crashes etc.

Shouldn't be much different than machining a gun barrel.

Iirc the term is "rifle drilling". :)

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