[GreenKeys] History - Why voltages and frequencies are chosen (5v & 3.3v logic, 6.3v filaments, 120/220 VAC, 50/60Hz etc)

[Keith Mc]

Now that is VERY interesting.  

Ah, but that now begs the question, "why 16.7Hz"?   Why not 16.5, or 17?

Did that somehow zero in on EXACTLY the speed they needed for an app?
Did it somehow satisfy some nice integer number or physical need in 
a design (eg the maximum number of turns in a winding of the 
required wire gauge, that they could reasonably "stuff" into an
armature, etc)?

OR, was the choice totally arbitrary, "within a general range"
of acceptable numbers, and it just "felt right" once encountered?

I'm trying to get a sense of what drives SPECIFIC number choices 
for both the V&F that we see every day, yet never understand.
Especially when it comes to "the VERY odd numbers" you often 
see chosen (like your "16.7Hz"... ;-). 

At first glance many seem "totally arbitrary" numbers. But often they
have colorful stories behind them, or have VERY good (but often 
not well understood) reason for existence, that suddenly makes 
great sense once you hear it!   (Like this one...)

Some of those uncovered stories are amazing. Others are amusing.
...and in hindsight some are "just plain dumb, but now we're stuck 
with the choice because it would cost too {darn} much to FIX"... {grin}

Which is it, for the Swiss' "16.7Hz" decision?

- Keith Mc.
.
douglas-w-jones wrote:
> Railroads used lower frequencies because they wanted low RPM
> induction motors for their locomotives.  Lower frequency makes
> the motors run slower.  The Pennsylvania Railroad's choice of
> 25 Hz was on the high side.  The Swiss used 16.7 Hz.
>
> The low frequency also cuts down on eddy current losses and
> allows high inductance motor windings in "universal" (commutated)
> motors to still carry enough current to work well.