# Why do utility companies supply at a frequency of either 50/60 Hz?

It just struck me that Utility Companies world-wide supply domestic users at either 50/60Hz. It could have been selected to be 10 Hz, or 100 Hz ... whatever

Was 50/60 chosen at random? Is there some rationale involved (efficiency, easier to construct/control etc) in restricting domestic supply to either 50/60 Hz?

In other words, if I were designing a power system, why would I pick 50/60 Hz instead of some other frequency?

• A possible reason: At lower frequencies (10 Hz) the incandescent lights would flicker Apr 9, 2012 at 20:29
• Just to say: I don't think that many people use the 50/60Hz supply as a clock, it's not the cleanest and most accurate signal... Apr 10, 2012 at 7:12
• @clabacchio: You'd be surprised how many systems use the mains as a frequency reference. (Even some non-electronic systems -- such as mechanical clocks and Hammond organs.) Apr 10, 2012 at 8:49
• @clabacchio: Actually a lot of home plug in clocks use the line frequency as a reference. The line frequency may drift a bit hour by hour, but some effort goes into getting the number of cycles over a 1 day to a few day period to be correct. Perhaps today using a 32768 Hz crystal is becomming more common, but there are still a lot of older clocks plugged in somewhere. Apr 10, 2012 at 11:35
• Interesting fact: Westinghouse 1st designed around 250 RPM turbine gen's. Electro-Mechanical issues limited the power cycle for commutation. Whereas Aeroplanes still use 400Hz. AC power. Apr 11, 2012 at 1:45

60 Hz was the result of engineering tradeoffs, I think made by or influenced by Nicolai Tesla. He was one of the early proponents of distributing AC, as apposed to Edison who wanted to distribute DC. The tradeoff had to do with size of the machines and transformers needed, which get smaller with higher frequency, and some losses, which go up with frequency. I remember reading that some careful study went into the decision to pick 60 Hz.

50 Hz, on the other hand, was due to marketing. There was a German manufacturer of power grid equipment that wanted to distinguish themselves and managed to get 50 Hz pushed thru as the standard in Germany and then much of Europe. This meant they didn't have to compete with the American 60 Hz equipment. The rest of the world ended up with 60 or 50 Hz depending on who they bought their equipment from and whether they were more economically tied to Europe or the US. Since Russia adopted the European 50 Hz standard, the soviet block all became 50 Hz countries.

• Do you have any sources for the marketing claim? Apr 10, 2012 at 5:32
• @Rasmus: I remember reading about that, and reading about the considerations that went into picking 60 Hz, but unfortunately that was so too long ago to remember where. Apr 10, 2012 at 11:31
• Olin: could you please cite sources? Apr 11, 2012 at 18:55
• @Jason: As I already said, I don't remember where I read that. Take it as coming from my memory, for whatever you think that's worth. Apr 11, 2012 at 18:59
• -1 I think this answer is biased, plus it does not cite any sources. Jul 10, 2012 at 11:42

This looks like what you're looking for:

http://en.wikipedia.org/wiki/Utility_frequency

In the early days of electrification, so many frequencies were used that no one value prevailed (London in 1918 had 10 different frequencies). As the 20th century continued, more power was produced at 60 Hz (North America) or 50 Hz (Europe and most of Asia). Standardization allowed international trade in electrical equipment. Much later, the use of standard frequencies allowed interconnection of power grids. It wasn't until after World War II with the advent of affordable electrical consumer goods that more uniform standards were enacted.

In Britain, a standard frequency of 50 Hz was declared as early as 1904, but significant development continued at other frequencies.[10] The implementation of the National Grid starting in 1926 compelled the standardization of frequencies among the many interconnected electrical service providers. The 50 Hz standard was completely established only after World War II.

By about 1900, European manufacturers had mostly standardized on 50 Hz for new installations. The German VDE in the first standard for electrical machines and transformers in 1902 recommended 25 Hz and 50 Hz as standard frequencies. VDE did not see much application of 25 Hz, and dropped it from the 1914 edition of the standard. Remnant installations at other frequencies persisted until well after the Second World War.[9]

• doesn't actually answer the question though: why 50/60Hz? Feb 5, 2013 at 21:13

In addition to the 1997 Edward L Owen column that Rasmus Faber cites, there's another good article here: "Technical origins of 60 Hz as the standard AC frequency in North America" IEEE Power Engineering Review, March 1999, Paul Nixon, p. 35-37. The full article is behind a paywall, but they post the first page as a png image, which I'll link to below.

The particularly interesting section here is:

By late 1889 and early 1890, direct-coupled alternators were coming into the experimental stage. These machines would prove to be much more reliable than the belt-driven generators, but would operate at much lower speeds. The need for lower ac operating frequencies [than 133.3Hz] was apparent, again driven by constructional and mechanical constraints. For example, an alternator direct driven by a 100rpm engine would require 160 poles to yield a frequency of 133 1/3 Hz. This type of construction was viewed as prohibitive. Around this time the Westinghouse Co. conducted an engineering study which considered both electrical operating characteristics with regard to the system components of the time and possible engine driven generator construction constraints, and recommended that 7,200 alternations per minute (60Hz @ 2 poles) was as high a frequency as would be desirable for the engine speeds which were then attainable. 60Hz was actually a carefully selected compromise. It was thought that higher frequencies would be better for the transformers then in existence, while lower frequencies might be better for engine-type generators. 60 Hz first appeared commercially in 1890. The earliest 60 Hz systems, like the earlier ac systems (140, 133 1/3, 125 Hz), were all single-phase.

By 1892, there were a large number of Westinghouse-designed 60 Hz central stations in existence, and 60Hz had taken over a share of the ac business from the higher frequencies.

(source: ieee.org)

So we basically have tradeoffs (transformers better at high frequencies vs. electric machines better at low frequencies, which is largely still true today) leading to a somewhat arbitrary compromise, then network effects solidifying the choices.

The Owen article also mentions that southern California was 50Hz up until conversion to 60Hz was completed in 1948. Japan still has half 50Hz and 60Hz: Owen states "In 1895, AEG sold a 50-Hz generator to the power company in Tokyo and the eastern half of Japan was put on the 50-Hz path. A little over a year later, GE sold a 60Hz generator to the power company in Osaka, and the Western half of Japan was put on the 60-Hz path." In the end it seems like it's mostly inertia/network effects -- it's just too painful to change large infrastructure projects.

From The Origins of 60-Hz as a Power Frequency (IEEE Industry Applications Magazine, Dec 1997, "History" column by Edward L. Owen):

"the choice was between 50- and 60-Hz, and both were equally suited to the needs. When all factors were considered, there was no compelling reason to select either frequency. Finally, the decision was made to standardize on 60-Hz as it was felt to be less likely to produce annoying light flicker.”

• If one produces more annoying light flicker than the other, then they aren't "equally suited to the need" after all. Apr 10, 2012 at 15:38
• +1: IEEE Industrial Applications Magazine's history column is really interesting and it cites sources. Apr 11, 2012 at 18:52

I believe after Tesla won the AC/DC fight with Edison he gained much influence and more or less dictated the 60Hz frequency in the US. He also had invented the fluorescent tube at the time and phosphor decay time was probably shorter then and had more flicker at 50Hz which emits light @2x this rate.

The German VDE dominated the standards in early 1900's and Europe standardized to 50 Hz after WW II as Matt said yesterday.

## 50 vs 60

The optimal choice is a tradeoff for costs, losses and expected revenue opportunities. The biggest consumers tend to be industrial smelting plants with massive arc currents and special transformers required, followed by industrial motors.

It depends on the cost of adds and losses such as added copper needed or thinner silicate-coated transformer-steel core materials losses due to skin effects in conductors and eddy currents losses in magnetics.

Also 60 Hz motors could yield higher RPM in induction motors 3600 vs 3000 RPM with no load.

Mutual coupling is lower at 50Hz for the same materials, light flicker is greater

Airplanes use a higher frequency usually 400Hz in order to reduce core weight to achieve high efficiency.

## AC vs DC

DC transformation was more expensive in large scale and with high voltage DC can be more problematic and needs more protection with latching effects and tribolectric charging effects.

HVDC is best suited for long haul distribution, where the Chinese are experts with 1GV technology installed around the world.

Why not change 50 or 60 Hz ? Cost of inertia vs savings is too great.

## Other power sources

Diesel trains use DC batteries and generators to drive DC traction motors. THey do generate a lot of EMI however.

The Russians & others have experimented with MagnetoHydroDynamic (MHD) generators with no moving parts and fields > 1 T. ** In some cases these generators run in the range of 4-6 kHz. **

The Chinese now have built a Fusion Reactor 100 times hotter than the inside of the Sun based on Russian technology.

If they knew how to distribute HVDC in Edison's day, Tesla would have lost the battle which he won based on improved efficiency of transformer step-up and step-down of distribution costs, reliability of induction motors over brush-type DC and other reasons.

The human eye's "refresh rate", per se, is right around 60hz. This was a determining factor in the frequency selection of power generation; It is engineered to be as low of a frequency as possible for feasibility, and thus ended up right around 60hz (50 in various parts of the world)

• AFAIK, the rate you are referring to is about 24 Hz, and you should quote at least a source because the earlier answers did, and there is no reference to your claim Apr 10, 2012 at 7:14
• The eye will perceive a 24 frame/sec as smooth (that's the frame rate in movies). Besides, this would be an argument when choosing a frequency for television (it was), not for mains power. Apr 10, 2012 at 10:21
• @FedericoRusso not exactly; it's true that some bulbs at low frequency may flicker, but I don't think it's the case of incandescent bulbs as they "lowpass" the power by heating, and may be an issue for fluorescent bulbs. Apr 10, 2012 at 13:43
• @clabacchio: I agree about the filtering. My point was that I disagree with Jay's answer. Apr 11, 2012 at 6:21
• Movie projectors have for many decades (probably a century) flashed each frame twice to minimize flicker, because flashing each frame one would cause very noticeable flicker. I would guess that early projectors did not do this, since early movies were often shot at much higher frame rates. Flicker at 30Hz is on the borderline between being something that's annoying and being something that can be tuned out. Apr 11, 2012 at 18:39

imagine 100 years ago the biggest high power turbine generator you can get is 250 RPM with 8 or 16 poles 3 phase and if you run it too fast it resonates and too slow , inefficient. then you decide to transmit using AC instead of DC and end up with 25 Hz then 50 Hz in one country while thinking, if we use 60Hz then all our clocks will be more accurate.

Later IBM's invents an automated re-synch magnetic clock that goes into every classroom to synchronize every hour because they used 60Hz power instead of 50 Hz long ago and invent the clocks. based on 60 HZ but Europe says who cares, turbines are better at 250 RPM and we can't afford to change everyone in Europe if we want to share power . Beside if more than 1 person has to agree, you never make a perfect same global answer.

I don't know exact answer, but I can imagine one based on history and liklihood of electromechanical cost issues of large machines

and if you want to share power back and forth in an AC grid..it has to be synchronous to 1 in 10^15th power and zero phase error, which is harder than it sounds... so there is regional differences based on many reasons... Some ways to share grid power is high voltage DC or use motor-generator or use synchronous invertors from HVDC with phase correction...

so EU is 50, North America is 60, and Japan is both and Africa has sync issues and many power failures. WHich tells you, whatever you decide on, don't change it with those you need to need to sell power to.

( MY brother worked a lot in Africa and told me one power failure burnt out every device in his house including the fridge motors and laptop supplies. in rural Uganda..

• This doesn't make sense at all! Apr 11, 2012 at 17:48
• Huh? How does 60 Hz make clocks more accurate than any other known fixed frequency? This makes no sense. You don't seem to know what you're talking about. Apr 11, 2012 at 18:50
• I know synchronous motors can be scaled to 24 pole at 60 Hz or 20 pole with 50Hz to give the same result but these weren't invented till mid'20's and 60Hz was preferred by Tesla, Westinghouse in 1890's and gained momentum for next few decades until WWII then 50 Hz was pretty much dropped in USA due to revenue issues. I doubt anyone can prove the exact reason as these decisions documents have not been found. Apr 11, 2012 at 21:39
• I'm starting to think that "Tony Stewart" is a Computer-based Word-Salad generator, like the ChomskyBot. May 5, 2012 at 22:48
• 10$^{-15}$ accuracy is ludicrous, even the 10$^{-10}$ from this answer was. I can't believe you're an engineer at all if you really think you can run a multi-megawatt turbine under varying load at better than 1 ppm accuracy. Or maybe knitting engineer. Jun 29, 2012 at 10:24