Why did engineers choose 60 Hz in US and 50 Hz in Europe ??
unca cecil explains the voltage part…
I want to know the frequency part of it …
I think it was fairly arbitrary. There are some reasons to prefer different frequencies. In the US, for example (and maybe elsewhere), 20 Hz is the standard frequency for the electric power that runs trains. And 400 Hz is the standard frequency for the AC power in airplanes. I think 20 and 60 and 400 lined up the way they did because they represent different compromises between minimizing energy loss (lower frequencies heat transformer laminations less and/or let the laminations be thicker, which is cheaper) and allowing high power per weight ratios (an alternator generally has a power capacity that is an increasing function of the rotary speed, no matter how many poles it has).
But I think 50 and 60 are close enough the differences aren’t interesting. I think it was some sort of historical accident - but maybe somebody will have a better answer?
Really? All the trains around here run on DC as far as I know. Or is 20Hz AC used for the internal electric systems on the trains themselves?
Electric trains can use AC or DC systems. The normal rule is AC for long distance, high speed trains, DC for slower, suburban line. See this web-site for more.
>All the trains around here run on DC as far as I know.
Certainly some trains run on AC. You can often see transformers connected to the overhead wires in utility yards. Dopers driving along Interstate 95 near the Pennsylvania / Delaware border and alongside the Delaware river can see a particularly nice example.
But, I didn’t realize there were DC trains.
A little hunting on Google suggests that 20 Hz is by no means the only AC frequency for railroad electrification. I saw things about 16.??? Hz, 25 Hz, and various other things - apparently some of them coordinated in some such way with the 60 Hz power grid to reduce interferences and even more. It actually looks like a complicated subject.
This was discussed on another board.
(You’ll have to unbreak the link.)
physicsforums .com/archive/index.php/t-53692.html
Another site here.
I’ve never seen a good cite for how exactly we ended up at 60 Hz. There’s a lot of technical reasons to stay in the 25 to 100 Hz range or thereabouts. 25, 50, and 100 were common since they are even divisions of 100.
When I worked for a power company, an old engineer there told me that in one of the early test systems, they couldn’t get enough power out of the generator so they cranked up the RPMs a bit which put the output at 60 Hz instead of 50. They then delivered this system, and kept subsequent systems at the same frequency just to keep the equipment uniform. I’ve never seen another good cite that says the same thing, though. Other cites just say Tesla calculated out 60 as being the most efficient, which I’m not sure I believe.
There were a lot of different competing systems running at different frequencies, so in the early days things were far from standard. It wasn’t like the U.S. all started on 60 Hz. Eventually the 60 Hz systems became the most numerous, and when you go to make a standard, you generally take the most popular one and call it the standard. I believe there is still a 25 Hz system running in Niagra Falls (at least it was running a few years ago, not sure now). There may be some other oddballs at other frequencies still out there, but most stuff has been converted to 60 Hz by now. There used to be a lot of 50 Hz stuff in California. I’m not sure how much, if any of it, still remains in use.
In Europe, 50 Hz became the most popular probably mostly due to AEG. AEG was the largest supplier of electrical systems, and they dictated that all of their systems would run on 50 Hz because it was a nice round number (half of 100). There were other oddball systems in Europe, but again, popularity won out and when they started to tie all of the systems together, they picked the most popular frequency for the standard.
May be cecil should consider cracking this …
This is one case where Wiki is a good answer.
Please note the matter of why some frequencies ended up where they did.
Note for motor loads a low frequency is better. Trains have a low frequency because the main use of the power is in a motor.
HD,
thanks for the link …
I remember reading that a lot of Ontario was 25 Hz until after the Second World War, when the Ontarian government had a program for replacing appliances and motors to upgrade to 60 Hz. Those 25-Hz genenrators at Niagara Falls…
In those days, most loads would be resistive (incandescant bulbs and heaters), which wouldn’t care about the frequency), or motors (which could be swapped). There was not as much “electronics” connected.
Some parts of Quebec (Abitibi and such) used 25 Hz until the nationalization of electricity companies in 1962. It is a low frequency and apparently caused lights to flicker, but the private power company didn’t have much incentive to replace the outdated technology. This was used as one of the arguments for nationalization.