How low have mains frequencies gone? What areas once used 30 Hz, and why? [closed]

Question

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?

Answer 1

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.

Answer 2

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

Answer 3

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.

Answer 4

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.

Answer 5

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.