On Mon, 01 Oct 2012 16:45:31 -0500, Jon Elson
wrote:

Ignoramus350 wrote:

On 2012-10-01, Jon Elson wrote:
Ignoramus6882 wrote:



In this case, I would need to find a user of an old IBM mainframe who
needs a 415 Hz power supply. Which is not something that I hold my
breath for.
No, nobody is running that old gear. The Computer History Museum
might have such a machine, but it is extremely unlikely they would
try to run it, due to the power and air conditioning needs.

But, the aviation shops need modest amounts of 400 Hz power
to test all sorts of gear still in use. Depending on the
size of whatever they are testing, they could need multi-KW
amounts of 400 Hz 3-phase power. Basically, on commercial
and military aircraft, anything that uses over 1 KW runs off the
AC power system, and there's a HELL of a lot of loads in them.

Jon

But they have no use for 415 hz, do they?
415 Hz is 3.75% high, I can't believe the aircraft systems would
care. On the old planes (anything from F-4 to Boeing 707 to
pretty modern) they used multiple alternators that were driven
by hydraulic constant-speed drives. The alternators were
hard-synched, ie. they were just connected
to a couple common busses. When they start the engines on a passenger
jet and you see the lights blink, that is the alternators being added to the
bus. So, these constant-speed drives were very soft, to allow multiple
alternators to be synched, and I'd guess frequency varies by 5 - 10%
normally depending on load and the number of alternators supplying
the bus.

So, I am pretty sure any aviation maintenance outfit would find 415
Hz to be quite OK for testing aircraft hardware. The specific voltages
used on different planes were different, but 120/208 was pretty
common.

Jon

The aircraft we're dealing with have fixed voltage but variable
frequency.