[GreenKeys] GreenKeys Digest, Vol 106, Issue 42

[John Nagle]

On 11/21/2012 1:28 PM, greenkeys-request at mailman.qth.net wrote:
> I don't know if I ever asked this before.  I had a VERY interesting question 
> arise (yet again) the other day, and STILL haven't yet found a good 
> explanation for MANY of the "made choices" by the engineers yet.
> 
> Question - What is the history behind the CHOICES for voltages and 
> frequencies - for logic, batteries, tubes (filaments & plates), 
> mains V&F, etc?  
> If arbitrary, then why do power supplies and load needs often NOT MATCH?
> 
> Does anyone have a link to any good "history of power supply voltage 
> and frequency choices" stories, that covers these subjects?
> (I'm sure this could fill books, but I'm looking for the Cliff Notes versions... :-)

    Google.

    There's an extensive literature on power line frequencies.
See

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

For an early discussion of the design tradeoffs, see

http://www.nycsubway.org/wiki/The_New_York_Subway:_Chapter_05,_System_of_Electrical_Supply

which discusses the tradeoffs which led to 25HZ distribution for
the New York City subway.  The generators were driven by large
reciprocating steam engines at 75 RPM.  Power distribution was
three-phase 11KV, converted to 600 VDC for the third rail system
with synchronous converters at substations along the system.

    					John Nagle