Re: 50 hz VS 60 hz and a 120 HZ question


"bob" <bobt@xxxxxxxxxxx> wrote in message
news:1193750268.966019.222820@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Oct 30, 4:01 pm, Randy <rbraun...@xxxxxxxxx> wrote:
This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.


<snip>



Thank You,
Randy


<snip>

But that is not the only point to consider ! with high
voltage transmission lines the losses climb with frequency and
distance. The very big long ones even use DC !

Regards Bob


Aircraft use 400 Hz stuff because it weighs a lot less. And
aircraft can get away with it because they are "small."

When a transmission line becomes a significant part (more
than a few percent) of a wavelength, interesting things start
to happen with the greatest "strangeness" occuring at a
quarter wavelength. You can easily make a transmitting
antenna that will radiate most of your power. And, if you
put a significant load (low impedence) a quarter wavelength
down the transmission line, it will reflect an open at the
other end of the line and you won't get any power to go down
it at all.

In free space, a quarter wavelength at 60 Hz is 775 miles
(somewhat less in a transmission line...). So, a line of up to,
maybe, 50 miles can be constructed with little or no attention
paid to the details. For longer lines, an engineer is going to
have to start paying attention to the design, which, of course, is
pretty much standard practice. But a wavelength at 400 Hz
is only 15 percent of that at 60 Hz, so the typical line lengths
found, say, running around an average city would have to
be carefully engineered...

(And, yes, some of the numbers I used are SWAGs. But I'm
a radio guy. A power guy might use a sharper pencil. YMMV,
but you get the idea...)

Jerry


.

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