60Hz vs. 50Hz.

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zlinker1

Junior Member
Apr 11, 2005
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Before this 60 Hz bashing session gets out of hand, consider this:

Voltage and frequency

Europe and most other countries in the world use a voltage which is twice that of the US. It is between 220 and 240 volts, whereas in Japan and in most of the Americas the voltage is between 100 and 127 volts.

The system of three-phase alternating current electrical generation and distribution was invented by a nineteenth century creative genius named Nicola Tesla. He made many careful calculations and measurements and found out that 60 Hz (Hertz, cycles per second) was the best frequency for alternating current (AC) power generating. He preferred 240 volts, which put him at odds with Thomas Edison, whose direct current (DC) systems were 110 volts. Perhaps Edison had a useful point in the safety factor of the lower voltage, but DC couldn't provide the power to a distance that AC could.

When the German company AEG built the first European generating facility, its engineers decided to fix the frequency at 50 Hz, because the number 60 didn't fit the metric standard unit sequence (1,2,5). At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and only after World War II the 50-cycle standard was established. A big mistake, however.

Not only is 50 Hz 20% less effective in generation, it is 10-15% less efficient in transmission, it requires up to 30% larger windings and magnetic core materials in transformer construction. Electric motors are much less efficient at the lower frequency, and must also be made more robust to handle the electrical losses and the extra heat generated. Today, only a handful of countries (Peru, Ecuador, Guyana, the Philippines and South Korea) follow Tesla?s advice and use the 60 Hz frequency together with a voltage of 220-240 V.

Originally Europe was 110 V too, just like Japan and the US today. It has been deemed necessary to increase voltage to get more power with less losses and voltage drop from the same copper wire diameter. At the time the US also wanted to change but because of the cost involved to replace all electric appliances, they decided not to. At the time (50s-60s) the average US household already had a fridge, a washing-machine, etc., but not in Europe.

The end result is that now, the US seems not to have evolved from the 50s and 60s, and still copes with problems as light bulbs that burn out rather quickly when they are close to the transformer (too high a voltage), or just the other way round: not enough voltage at the end of the line (105 to 127 volt spread !).

Note that currently all new American buildings get in fact 230 volts split in two 115 between neutral and hot wire. Major appliances, such as ovens, are now connected to 230 volts. Americans who have European equipment, can connect it to these outlets.

http://www.pridelabs.us/adapters/

Originally posted by: blahblah99
Because we're the only ass-backward country in the world that likes to do things differently... left hand driving, 60hz, imperial units,...
 

nomadwind

Junior Member
Apr 11, 2005
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Interesting post; being one that's currently studying electrical engineering, I just can't help joining in :). Hi everyone.

Pertaining to the statement of Nikola Tesla's choice of 60Hz to avoid flickering, perhaps I may add, as I've read from the book "Tesla: Man Out of Time", it seems Tesla had some obsessive-compulsive tendencies, and preferred things that were divisible by the number 3 to produce round numbers. Looking at 50Hz and 60Hz, or 110Hz and 240Hz, it is quite obvious based on that factor, isn't it?

As for voltage frequencies, higher frequency would provide a better quality signal (when coupled with other necessary components, such as capacitors, etc) in the context of electricity usage. As a reference, let's consider the switching power supply. There's a pulse-width modulation circuit which is used switch the voltage on-and-off at a high rate. Generally, the switched voltage is about 40kHz. In a timeframe (let's say 1 second), the peak voltage (or rather, the signal flowing through) is achieved that many times.

Because of that, one could say that the current that flows is constantly switched on-and-off too. Supposing 40kHz, the amount of time for the current to flow is very small - in another way, the charge is less too (q=It or I=q/t). Taking the human body into perspective, with such high frequencies, there might not be enough of a charge to penetrate the body. Also, the "alternating" in A.C. isn't there for nothing - I'm not sure of how to explain that part in this context.

(To further illustrate, consider a friend who's splashing water on you. "High current" = bucket, "low current"=peewee water pistol. You'll definitely get really drenched by the bucket, while if your friend shot at you with the water pistol, you'll still get the water on you, but you won't be as drenched immediately; consider the evaporation as the "current's dissipation" through your body.)

Since there were discussions on power, I'd like to add that power can also be calculated using P=(I^2)R (current squared multiplied by resistance) - this equation is of higher importance than P=VI in dealing practical situations, as frequently it is called (I^2)R losses - heat losses (or production of heat). This equation is both a good and bad thing. Good in the sense that many appliances utilise heat for useful work - while bad being that in most circuits, heat is a byproduct. Also, consider electrical burns.

Also, remember that Ohm's Law, V=IR, isn't fully mathemathical - considerations need to be placed since all three values may be changing in a given situation.
 

PowerEngineer

Diamond Member
Oct 22, 2001
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This 50 Hertz vs. 60 Hertz question seems to be a recurring favorite (along with wireless power transmission). :)

I hadn't heard the metric explanation for 50 Hertz before, and that is interesting. I am familiar with Tesla's tendancy to favor multiples of three.

I have to take issue with the assertion that 50 Hz is "20% less effective in generation" and "10-15% less efficient in transmission". It is true that the iron cores of 50 Hz devices must be larger (i.e. contain more iron) because the slower frequency means that the magnetic fields persist longer in each direction during each cycle, and therefore tend to saturate the core iron at lower flux levels; more iron lowers the flux density and keeps the 50 Hz core from saturating. This means the 50 Hz devices should cost more initially. Otherwise, the efficency of generation and transmission is essentially the same. If anything, 50 Hz is a little more efficient because the lower freuency produces smaller eddy currents in the iron cores (and therefore lower losses) and it also produces less "skin effect" (which is the tendancy of alternating currents to produce higher current densities towards the surface of a conductor) and therefore less line losses (because a more even distribution means lower I^2 average).

It's also worth noting that most distribution circuits use volatges in the 12 to 14 kV range (before being stepped down for the household drops), which means that the choice of 120 volts or 240 volts for house wiring does not have any real impact on the problem of voltage level changes along the length of a feeder.

I'm afraid that 40 khz will never be a practical frequency for power delivery. While the "skin effect" might might save people from electrocution, that same effect would make it impossible to find a practical conductor for transmission. The rotational speed of a synchronous electric generator (or motor) is given by the formlua: RPM = 60*frequency/# of poles pairs. The speed for a simple three-phase synchronous motor with a single pair of poles (i.e. one North and one South) is 3600 RPM. It looks like you'd need 666 pole pairs to have a 3600 RPM motor at 40 khz.

Also remember that alternating current brings phase angles between currents and voltages [P=V*I*cos(phase angle)], and that reactances and capacitances must be included in determining impedances [Z = R + jX] where V=I*Z

:thumbsup:
 

jagec

Lifer
Apr 30, 2004
24,442
6
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Originally posted by: zlinker1
Today, only a handful of countries (Peru, Ecuador, Guyana, the Philippines and South Korea) follow Tesla?s advice and use the 60 Hz frequency together with a voltage of 220-240 V.

Ecuador is 110V, 60Hz.
 

Colin1497

Junior Member
Apr 25, 2005
3
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Can't resist:

Airplanes (and other miltary vehicles) use:

28VDC,
115V, 400Hz, 3ph, or
270VDC

See Mil-Std-704E
 

George Powell

Golden Member
Dec 3, 1999
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The reason for 115V 3 phase 400Hz on aircraft is to do with power factor.

By keeping the power factor as close to a particular value as possible it is possible to make the generation and transmission systems smaller and lighter thus saving fuel and money.

28V DC and 28V AC are used for instrument buses. 270V DC is not widely used, the only one I can think of is GMIS In flight entertainment.

 

JTWill

Senior member
Feb 2, 2005
327
0
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Originally posted by: ndolf
yeah, it is not the energy that kills you but the electric signal frequency, and WHO THE HELL CAME UP WITH SUCH A CLOSE NUMBER TO OUR HEARTBEAT?

Your heart beats at 60 times a second? :D