Why 50/60 Hz?

But in the days before modern ferrites the iron losses would have been lethal. Also 1Khz implies a serious number of poles (or very high shaft speed), which makes useful induction motors harder.

50/60Hz was not a bad compromise given the technology of the time, and generating higher frequencies is easy and cheap now.

Personally I wish that 3 (or 6) phase was routinely available in a domestic setting, it would mean that switch mode power supplies would not need any input energy storage capacitor. Ohh and lets up the voltage to say

600/1000V makes the cables smaller and means that I get my tea more quickly in the morning (Also gives darwin some much needed help).

Regards, Dan.

Reply to
Dan Mills
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All over the world 50 Hz or 60 Hz is used as the frequency for AC voltage from the power stations. Why is that? Could it have been for instance 200 Hz or 1000 Hz or are 50/60 Hz superior for the purpose and why?

Reply to
Cubus

Hahhahaa I forgot the answer to this. maybe that was the frequency of one of the first AC circuits and then it remained like that throughout the years?

Yeah I wish AC current was 1000Hz then we wouldn't need such huge heavy transformers for our power supplies

Reply to
Brian Su

Ever been in a plane? Ever notice the "whine" during flight? It's not the engines, it's the 400Hz power supply, very annoying. Aside from many other reasons 50/60Hz is pretty low in the audible range, so it's easy to filter out.

Another big reason that comes to mind is the skin effect, it's bad enough at

60Hz at the power levels some lines are under, it must be much worse at 1000Hz. TTYL
Reply to
repatch

Supposedly it was a compromise between efficiency (very early large motors and transformers were more efficient at low frequency) and annoying light bulb flicker. The fact that low frequency motors were more efficient is supported by the fact that many subways, electric railroads and trolley systems used to operate at (and in some cases still use) frequencies like 25 Hz, 20 Hz and 16 2/3 Hz. Amtrak between NYC and Philly still uses either 25 Hz or 20 Hz (I forget which). Aircraft where weight is important use 400 Hz. (listen for the whine next time you fly somewhere).

Reply to
Michael Moroney

Here's a very very simplified answer without going into alternator theory and the math..

A 1000hz alternator is going to need to spin extremly fast to generate that frequency, that's hard on bearings, and is not very practical or efficent for our use, considering the amount of energy that would be required to do that. It's far more effeicent to have a slower moving alternator..

Reply to
Chris

That capacitor is a very good thing. It allows your equipment to ride very short power failures quite well. In fact, if not for that capacitor, UPS systems would be a lot more expensive because they would have to cut over instantaneously. The capacitor in the computer power supply rides the cutover time, along with any other power problems you might encounter.

That capacitor is a wonderful thing, it's not worth eliminating it to save a few lousy cents.

-Z

Reply to
Zorin the Lynx

It's more than just an alternator issue. Modern power systems have thousands of transmission and distribution transformers that may facilitate the transmission of power over hundreds of miles.

Transformers are composed of coils (inductors) that present an opposition to AC current flow (inductive reactance) beyond just the purely resistive component of current conductors. In addition, the laws of physics decree that the mere presence of simple conductors (transmission lines) will have a significant component of inductive reactance when operating on AC and these are often modeled as series coils.

The inductive reactance or opposition to the flow of AC current in a coil is proportional to the frequency. XL= 2 * pi * L * F

A relatively high Frequency (F) (of say 1000 hz) insures that the inductive reactance will be extremely high and it would be impractical to transmit significant quantities of power for any distance in a landlocked power system.

Beachcomber

Reply to
Beachcomber

On Tue, 13 Jan 2004 19:31:37 +0000 (UTC), snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) Gave us:

This guy gets the ribbon!

Reply to
DarkMatter

On Tue, 13 Jan 2004 23:39:54 GMT, Chris Gave us:

Just how fast do you think our 60Hz generators are turning?

3600RPM
Reply to
DarkMatter

On Wed, 14 Jan 2004 04:10:39 GMT, not snipped-for-privacy@nospam.xyz (Beachcomber) Gave us:

Another ribbon recipient!

Reply to
DarkMatter

Incorrect. The correct answer is that it depends on the frequency AND the number of poles for each particular generator.

Ever been in a hydroelectric plant? Typical Army Core of Engineers turbines run at between 60 rpm to 600 rpm depending on the head and design characteristics of the generator.

Don't believe me? Check out:

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Beachcomber

Reply to
Beachcomber

Actually the correctanswer is probably more dependent upon on what is driving the alternator.

Hydro driven turbines are probably relatively easy to build for slow speed, especially since the delta p is under a few hundred psi.

Steam driven turbines work best at higher pressures and higher rpms. Slow speed steam turbines become extremely large quite quickly unless reduction gears (expensive) are added to the mix. The Turbine generators I was/am familiar with were GE turbines connected to 2 pole Westinghouse alternators and ran at 3600 rpm. I can't recall, off hand, the poles and speed of our 400Hz MGs but rpms were in the same order or magnitude as the TGs.

ARM

Reply to
Alan McClure

And it gets *even* more complicated. For superheated steam units, 3600RPM is the norm. But for nucs that use saturated steam, the turbine has a hard time dealing with the moisture in the steam (causes a lot of erosion). So saturated steam units run slower at 1800 RPM.

Gas turbines use 3600 RPM generators, often through a gear box. The turbine itself runs higher, and 3600 is the highest speed for a 60HZ generator so the 'gear box' has the least gear ratio.

Some old-time diesel units run/ran at 900 or 600 RPM. Hydro I think are probably the slowest spinning, but with such large rotors (Niagara's are like 35 ft across), it's still a pretty good tangential speed at the pole face.

daestrom

Reply to
daestrom

You can spare me the lessons of basic transformer and alternating current theory.. .. think I might just have a handle on that ..

Reply to
Chris

Er yes and no.

It depends on what type and construction of the alternator..

Reply to
Chris

This is a recurring thread BUT

my WAG has always been the 60 Hz was chosen because there are 60 minutes in an hour, 60 seconds to a minute, so why not 60 cycles in a second?

The 50 Hz likely came about because the silly europeans wanted to be "metric". They might have preferred 100 or 10 Hz for "metric" purposes but since AC systems were first developed in the USofA they didn't want to re-invent the wheel too much.

Several of the lower frequencies for trains are obvious fractions of 60 or

50 Hz.
Reply to
John Gilmer

I guarantee you that the generators at Niagara Falls and the Hoover dam are not turning at anything like 3,600 RPM- one look at the armature and you can see that they would fly apart.

This page:

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says 187.5 RPM at Niagara, which would seem to work out to an odd number of poles for

60Hz, but for the original 25Hz it would be 8 poles.

Best regards, Spehro Pefhany

Reply to
Spehro Pefhany

According to that page, apparently 25Hz is still being generated on the Canadian side, and quite a bit, too. Who uses it, and why? (I guess two answers is everything is very very old/"if it ain't broke, don't fix it", and if the 25Hz generators were taken out of service there wouldn't be enough 60Hz capacity to take advantage of all the waterpower available)

Aside: I once worked in the former Digital Equipment "mill", and it had an old electric generator with a nameplate with a 1898 date and a 40 cycles/second rating.

Reply to
Michael Moroney

-------- You have hit it on the nose. The source characteristics determine the best speed range of the driver and the generator is designed with the right number of poles to put it in that range. Steam turbines are higher speed units so 1800rpm(4 pole) and 3600rpm (2 pole) units are used. Sure it would be nice to run a turbine at a higher speed but then it is necessary to increase the frequency - Hence 400 Hz for aircraft where high speed jet engines are the source, distance is short and weight is a major factor - cost and size advantages for short transmission distances but not much good for power grids. Diesel units like it about 900 rpm Hydro optimum speed depends on the head as a rough rule- the lower the head, the slower the best speed so that there may be 200 rpm 36 pole 60 Hz machines as well as 720 rpm 10 pole hydro machines (generally a different kind of turbine as the best turbine at 100ft head is quite different from the best turbine at 1200ft head) .

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

Reply to
Don Kelly

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