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This answer quotes from a book written by Jocelyn Bell Burnell who co-discovered the first pulsar in 1967 where the author mentions another astronomer who noticed a star was pulsing at around 30 Hz and recognized the frequency because

The Crab pulsar, with a period of 30Hz, is sufficiently fast that many people cannot see it; however some people can see 30Hz and Sue Simkin knows she is one of them – as a child she lived in an area where the main power supply was at 30Hz.

This page suggests that the area might be Detroit Michigan in the 1940's or 1950's.

But here I'm asking a more general question about mains frequencies well below 50 Hz.

Question: How low have mains frequencies gone? What areas once used 30 Hz, and why?

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    \$\begingroup\$ My point was larger transformers tend to be a bad thing which could explain the switch to higher frequencies. I think maybe I should have said "smaller transformers?" instead. \$\endgroup\$
    – DKNguyen
    Jan 2, 2020 at 1:27
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    \$\begingroup\$ TA Edison had the record of the low mains frequency. His company supplied 0Hz for substantial amount of customers. He didn't want to pay license fees for AC methods which were unfortunately patented by his rivals. \$\endgroup\$
    – user136077
    Jan 2, 2020 at 1:30
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    \$\begingroup\$ True. Exact 0Hz comes only from those which have never started supplying and never will start it. Unfortunately we can get from them only 0 volts. \$\endgroup\$
    – user136077
    Jan 2, 2020 at 1:36
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    \$\begingroup\$ @TonyStewartSunnyskyguyEE75 who said it was hard? Once in a while it is okay to ask a less than thoroughly researched answer in Stack Exchange in order to allow for an interesting answer to be posted; SE is primarily about good answers. I've asked well over 2,000 SE questions and nearly all are very well researched and probably half are too long. For this particular one I feel that this is enough to facilitate an answer along these lines that will be worth reading. \$\endgroup\$
    – uhoh
    Jan 2, 2020 at 1:56
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    \$\begingroup\$ archive.org/details/in.ernet.dli.2015.153641/page/n583 \$\endgroup\$ Jan 2, 2020 at 2:59

5 Answers 5

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The historical reasons for using 30 Hz and other frequencies is documented in the book Electrical Engineering Papers by Benjamin G. Lamme, published in 1919. In the article 'Story of the Frequencies' he explains that large generators and those powered directly by reciprocating engines ran at lower rpm, and therefore preferred a lower output frequency to reduce the number of poles required in the generator. Lower frequency was also preferred for long distance power transmission.

Finding all the areas that once used 30 Hz would take far more intensive research than this question deserves. My Google searches came up with nothing, however I did find some information that may be relevant.

In the 1880's electric power was used mostly for lighting, which preferred higher frequencies to reduce flicker, so frequencies such as 133⅔ Hz and 125 Hz were common. These higher frequencies enabled the use of smaller transformers. However the AC motors developed at that time required frequencies as low as 16⅔ Hz. This was a problem because converting from one frequency to another was difficult. So different frequencies were usually generated for residential and industrial use, with many factories having their own power plants free to run at whatever frequency they desired.

Around 1890 the 'compromise' frequency of 60 Hz was introduced, which eventually became a nationwide standard. However 25 Hz was still used in some places until quite recently.

In the article Early Electrification of Buffalo, it is mentioned that Westinghouse had adopted 60 Hz for lighting and 30 Hz for power, but for the Niagara Falls project they settled on 25 Hz. That service continued until 2006. Several other hydro stations on the Niagara river also ran at 25 Hz. I don't know if Detroit used Niagara power in the 1940's or 1950's, but it seems likely that at least some parts of Michigan did.

Sue Simkin might have lived an area which had a local power plant running at 30 Hz, perhaps attached to a factory. This could have been anywhere in the US. With so many private power plants involved I think it would be hard to rule out the use of 30 Hz in any area.

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    \$\begingroup\$ Excellent! I'm very happy to see that you squeezed this in before the close-voters made answering impossible. I'll spend some time reading through these in the next day or so. Thanks! \$\endgroup\$
    – uhoh
    Jan 2, 2020 at 6:36
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How low have mains frequencies gone? What areas once used 30 Hz, and why?

Mains frequencies are optimized around the requirements and constraints of their specific environment. The German railway for example uses 16.67 Hz (50/3). It comes down to a trade off: cost and size of transformers vs inductive and/or capacitive losses of the actual power lines.

Some modern high power distribution system actually use DC https://en.wikipedia.org/wiki/High-voltage_direct_current

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  • \$\begingroup\$ Another reason for the German railway system to run at 16.7 Hz (they changed the nominal frequence in 1995) is that locomotives at the time they introduced the system tended to use commutated series-wound motors. According to Wikipedia (en.wikipedia.org/wiki/15_kV_AC_railway_electrification): "High inductive reactance of the motor windings caused commutator flashover problems and the non-laminated magnetic pole-pieces originally designed for DC exhibited excessive eddy current losses. Using a lower AC frequency alleviated both problems." \$\endgroup\$ Jan 2, 2020 at 15:15
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I have seen an antique synchronous motor electric clock designed to use 25Hz mains. The Wikipedia article on Utility Frequency goes into some detail:

25 Hz origins

The first generators at the Niagara Falls project, built by Westinghouse in 1895, were 25 Hz, because the turbine speed had already been set before alternating current power transmission had been definitively selected. Westinghouse would have selected a low frequency of 30 Hz to drive motor loads, but the turbines for the project had already been specified at 250 RPM. The machines could have been made to deliver 16⅔ Hz power suitable for heavy commutator-type motors, but the Westinghouse company objected that this would be undesirable for lighting and suggested 33⅓ Hz. Eventually a compromise of 25 Hz, with 12-pole 250 RPM generators, was chosen.[2] Because the Niagara project was so influential on electric power systems design, 25 Hz prevailed as the North American standard for low-frequency AC.

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  • \$\begingroup\$ Why does this answer, which is the same as mine except it adds a quote from the article, get upvotes while mine gets downvotes? \$\endgroup\$
    – Barry
    Jan 3, 2020 at 3:06
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The technology of the prime movers probably influenced the frequency selection. Low frequency would seem to be easier for hydroelectric generators. Low frequency might also be better for AC motors for electric railways.

On the other hand, higher frequencies are better for eliminating flicker in incandescent lighting.

There are historical records of some studies and discussions about technical factors considered in selecting a standard frequency. There were likely both commercial and technical influences that are now unknown.

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  • \$\begingroup\$ Thanks, somehow I may have missed the notification for this answer back in January. I stopped by again today after seeing the activity in the linked meta. \$\endgroup\$
    – uhoh
    Mar 1, 2020 at 23:40
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The history and evolution of power line frequencies is given in the Wikipedia article: Utility Frequency. Over the years, the frequencies from 16-2/3 Hz up to 133-1/3 Hz have been used.

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  • \$\begingroup\$ If you check my questions on this site you'll see that I do do research. However, this question asks Why such a low frequency would be used as well as Where, and I'm looking for the engineering rationale for the "why" aspect. So far your answer doesn't address either one; perhaps change it to a comment? \$\endgroup\$
    – uhoh
    Jan 2, 2020 at 1:17
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    \$\begingroup\$ @uhoh I think it is explained in the Wiki article. “ Very early isolated AC generating schemes used arbitrary frequencies based on convenience”. We already have a whatever generating at whatever frequency; use what’s available. Save time, money. \$\endgroup\$
    – Tyler
    Jan 2, 2020 at 1:22
  • \$\begingroup\$ @Tyler so a historical map of early power generation color coded by frequency might show a somewhat random patchwork of frequencies, determined by whatever gear boxes could be obtained. That sounds like it could make for an answer worth reading. Thanks! \$\endgroup\$
    – uhoh
    Jan 2, 2020 at 1:25
  • \$\begingroup\$ @uhoh why the first generator in the area was x frequency, is well, because it was the first. Couldn’t just buy a power plant on e-bay. \$\endgroup\$
    – Tyler
    Jan 2, 2020 at 1:25
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    \$\begingroup\$ @Tyler I guess low-carbon iron was cheap enough, and the fabrication of laminations (to decrease eddy-current losses and heating) was difficult enough that low frequencies were attractive. I think there is some compelling electrical engineering to be expressed in an answer here. \$\endgroup\$
    – uhoh
    Jan 2, 2020 at 1:39

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