[PRCo] Re: voltage and frequency

[Boris Cefer]

Now it is getting grade!

One of the advantages of low frequency is also lower trolley wire and feed 
impedancy, allowing for longer sections and fewer substations.

Boris
still non electrician but with some experience

----- Original Message ----- 
From: "robert netzlof" <wb3iqe at rocketmail.com>
To: <pittsburgh-railways at dementia.org>
Sent: Wednesday, August 29, 2007 7:39 PM
Subject: [PRCo] Re: voltage and frequency



> I've read some in old electrician's texts. Around the turn of the
> 20th century, "motors" were in effect DC motors. The rules of thumb
> for designers of electrical systems were:
>
> 1) For motors, DC is best. If AC must be used, the lower the
> frequency, the better.
> 2) For transformers, the higher the frequency, the better.
> 3) For lamps, the higher the frequency, the better.
>
> This boiled down to:
>
> If the major part of the load on your system is industrial (motors),
> use DC or a low frequency. If the major part of the load is
> residential and mercantile (lighting) use a high frequency. If the
> load is mixed, it may be worth considering separate facilities for
> the industrial and business/residential districts.
>
> The advantages of being able to step AC voltage up and down were so
> great that DC lost out (but note that it was within the past 2 or 3
> years that ConEd finally told their DC customers in NYC that DC would
> no longer be available).
>
> In the US and Canada, things eventually settled onto 25 Hz for
> industrial, 50 or 60 Hz for general use. Eventually 60 Hz became The
> Standard. Railroads, of course, were mostly motor loads, so 25 Hz was
> favored and once set up for 25 Hz, it would have cost a lot to
> change.
>
> Europe (where, we are told, everything is done better) went to 16 2/3
> Hz and 50 Hz although I vaguely recall reading of some other low
> frequencies, perhaps as low as 11 Hz, used in some early railroad
> applications.
>
> It may be interesting to note that at least in its later years, the
> Pennsylvania RR used 100 Hz AC to power signal apparatus. That was
> apparently chosen to avoid inductive coupling from 60 Hz AC, as well
> as the 2nd and 3rd (120 and 180 Hz) harmonics.
>
> Bob Netzlof
>
> Bob Netzlof a/k/a Sweet Old Bob