The use of 400hz electrical components in aircraft

[thruthefence]

Can someone enlighten me how the 400hz power common in transport aircraft came to be chosen?

 

[berkshire]

I am stumbling in the dark here, But I believe it had something to do with small wires and current losses.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[JohnRBaker]

Taken from the Wikipedia item below:

400 Hz

Frequencies as high as 400 Hz are used in aircraft, spacecraft, submarines, server rooms for computer power, military equipment, and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances, so 400 Hz power systems are usually confined to a building or vehicle. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft and ships. A United States military standard MIL-STD-704 exists for aircraft use of 400 Hz power.

http://en.wikipedia.org/wiki/Utility_frequency

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[IRstuff]

The 400-Hz question has been posted with varying degrees of success, all of them being less that completely successful:
thread16-34515
thread238-47291
thread248-26254

TTFN
faq731-376

 

[berkshire]

Looks like I had it completely Bass ackwards.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[BJC]

A three phase 2 pole motors runs at 24,000 RPMS. Good speed for a gyrocompass.
Sperry gyroscope had something to do with it ( way back in the 1920s i think ).
UH-1Bs had 400 cylce MG sets. 28 volts DC in, 400 cycle 3 phase out.
You could run your electric percolator on it. Easier to find and cheaper than a 28 volt DC coffee pot.

 

[IRstuff]

The 28Vdc that's aircraft power comes from the 400Hz AC. As described by one of the previous threads, 400Hz allows the generators to be smaller than if they were 60Hz.

TTFN
faq731-376

 

[IRstuff]

One of the other benefits, particularly from the 400Hz, embodied in the 3-phase aircraft power, is that the DC full-wave rectifier doesn't need as large a droop capacitor, since the duration of the droop is limited by the frequency of the input AC.

TTFN
faq731-376

 

[zeusfaber]

The 28Vdc that's aircraft power comes from the 400Hz AC.

That's how it is on modern aircraft. Older designs (I first came across this on Canberra and Scout) have 28V dc systems (very like the 24 V dc system on a truck, but specified in terms of the on-charge voltage rather than the "sucking off the battery" voltage). When you needed ac, you got it from the MG sets BJC described (we used to call them rotary inverters)

As well as a double ended battery shop (one end for Lead-Acid and one for NiFe or NiCd), most bases also had a soundproof inverter room where you could sit with your earplugs in underneath your duffs while setting up your screaming 100A inverter and still hear the anguished calls from people outside begging you to finish off quickly because they couldn't hear themselves think.

I remember an unscheduled landing in a field in the middle of Salisbury Plain 20+ years ago so I could look up which systems were fed off the inverter that had just wrapped its hand in.

A.

 

[JohnRBaker]

I think you will find that the so-called '12 volt' automotive system is closer to 14 volts. That being said there was much talk a few years ago about going to a 42 volt system as the new standard, which would also allow for lighter components, smaller gauge wires, etc. although the extra voltage could be a problem for the 'backyard mechanic' who sticks his hands into places under the hood without looking.

For some background on this issue and why it died, go to:

http://www.popularmechanics.com/cars/news/4226979

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[BJC]

"The 28Vdc that's aircraft power comes from the 400Hz AC. As described by one of the previous threads, 400Hz allows the generators to be smaller than if they were 60Hz. "

The 28 volt system was powered from a main generator mounted on the trasmission, a starter-stand by generator on the engine or the battery.
I think Blackhawks have 400 Hz main generators. there's air show comming up in a couple of months. I'll find a crew and talk to them.