TELECOM Digest OnLine - Sorted: Re: 25 Hz power

Re: 25 Hz power
Sun, 12 Mar 2006 20:33:07 EST

In a message dated Fri, 10 Mar 2006 11:07:14 -0800, Al Gillis <> writes:

> Hi Wes ...

> Sorry for the off-topic question but could you detail some of the
> advantages you mentioned?

> I know the Great Northern Railroad used electric locomotives through
> mountain passes in Washington State because electrical locos could out
> pull steam locomotives on the steep grades encountered there.

> Thanks!

> Al


These are summaries given to me by
two members of another (non-communication
related) list where this was a thread a few
months ago.

Interestingly, the first summary is from Bob
Gillis. Any relation?

Wes Leatherock


The lower the frequency the better an AC
commutator motor runs. A 0 frequency or DC
motor runs best.

When the electric industry was starting
here in the USA and Canada, two standard
frequencies were set. 60 Hz for lighting
and 25 Hz for industrial. (in Europe the
standards were 50 Hz and 16-2/3 Hz.)

Back in the 1950s visited the NY Central
Buffalo Station and you could see the
incandescent lights flicker. Most of the
electric power generated at Niagara Falls
was 25 Hz.

The first railroad AC electrfications had
commutator motors and so they were
electrified on the industrial frequency of
25 Hz: New Haven, PRR etc. Today AC
commutator motors are not often used. So
the common 60 Hz lighting frequency can be

The electrification's still using 25 Hz are
holdovers. Amtrak between New York and
Washington is 25 Hz because it ws too
expensive to convert the line to 60 HZ and
there was 25 Hz generating capacity

The New Haven line has been changed to 60

- - -

25 Hz was a standard for MOTOR loads,
because, as noted, these worked best on the
lowest acceptable frequency.

Lower frequencies have less 'inductive
transmission loss' than higher frequencies.
The differences are not huge, but, ca. 1910
were enough to make a difference.

Transformer and motor efficiencies (core
losses) were better at lower frequenciess,
though the devices were larger.

The first point has been superseded by
progress in design, and changes in
technology: e.g. use of rectifiers and
inverters to build the drives.

The second point has been superseded by the
cost benefits of using the standard grid.
(Its a bit more complex than that, but
leave it there for now....)

The last point has been superseded by the
first, and by progress in design and
application of transformer steels.


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