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-   -   Why aircraft used 115v ac 400 hz (https://www.pprune.org/engineers-technicians/652888-why-aircraft-used-115v-ac-400-hz.html)

Danial9874 24th May 2023 11:57

Why aircraft used 115v ac 400 hz
 
Hello, Why aircraft used 115v ac 400 hz while household use 240v 50hz
Does anyone know why aircraft use 400hz but not 50hz?

​​​​​​​Thanks

Dave Gittins 24th May 2023 12:22

Google has an answer.

Why Airplanes Use 400 Hz Power | Blog- Monroe Aerospace

Uplinker 25th May 2023 09:47

Makes all the components, e.g. generators, transformers, smaller and lighter for a given power output, which is obviously important in an aircraft.

Also, rotating at 400Hz vs 50Hz means the generator does not need to be geared down as much, saving gearbox complexity and weight.

jimjim1 2nd Jun 2023 21:41

Much good information already.

I think the key is size. A power station generator is huge and will fly apart if spun too fast. Aircraft generators are much smaller and can be turned faster without disintegrating. Generators are usually turned as fast as they can tolerate because that means more power.

The generator's frequency is now almost irrelevant because the frequency can be efficiently and cheaply changed with modern electronics. Generate whatever frequency you want and feed it into the magic box, nice clean 400Hz (or whatever suits) comes out. Traditionally aircraft alternators (generators) used constant speed drives, but newer installations are able to dispense with these heavy and complex devices.

"A VFG on a A350 (Variable Freq Generator) ranges from 360Hz to 800Hz (idle to takeoff)"
If a piece of equipment can deal with this, e.g. a heater, it gets a direct feed, otherwise electronically altered to DC or 400Hz AC as required.


https://en.wikipedia.org/wiki/Constant_speed_drive
https://aviation.stackexchange.com/q...-ac-generators


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