On Mon, 19 Apr 2004 20:53:57 -0700, "Scott Gomez"
<scott@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>Which is exactly why many aircraft use (used to use?) 400Hz power.
>
>---
>Scott Gomez
>
>-----Original Message-----
>From: Adam [mailto:olympusom@xxxxxxxxxxxxxx]
>Subject: [OM] Re: [OT] 3 phase wiring
>
>Well you didn't mention that they use 60 Hz instead of 50Hz for exactly
>that
>reason ! I.e. higher frequency enables more power at lower voltage
>without
>the need for higher current or thicker wires.
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The real advantage of higher frequencies is that transformers can be
smaller and lighter. Broadly speaking, for a given rating the core
size of a transformer is inversely propoprtional to the frequency.
That's why 400Hz is used in aircraft.
The relativity of current and voltage for a given power is not
affected by the frequency. For example 1 kW needs 10A at 100V whatever
the frequency. In fact the actual current*voltage product is likely
to be higher at higher frequencies because of higher reactance (poorer
power factor).
I'm not sure why the US has 60Hz when most of the rest of the world
has 50Hz. It would be very hard for either US or the others to cahnge
now. It's probably no more than the reasons why railway guage in most
of the world is 4ft 8.5 inch but other countries chose 5ft 3in or 5ft
6in!
To return to a slightly more "on topic" note, the US television
standard uses 60 fields (30 frames) per second but all "50Hz"
countries use 50 fields (25 frames) per second. This is not mere
coincidence; in the old days TV power supplies were not what they were
and, if the field rate was not exactly the same as the mains
frequency, moving "hum bars" would scroll up and down the screen -
very disturbing!
John Gruffydd (Mold, Wales, UK)
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