why three phase system is not preferred in aircrafts power circuits....

I don't know, Why?
In general, DC power distribution transfers the most power with the least amount of weight both in copper and in insulation than an AC system. Could that be the reason?

They use 400 HZ systems to power inertial guidance units that I used to work on. As I recall at one time the older analog units used small motors to do the calculations and the higher frequency allowed more accuracy.

They use 400 HZ systems to power inertial guidance units that I used to work on. As I recall at one time the older analog units used small motors to do the calculations and the higher frequency allowed more accuracy.
Yes, 400Hz was very common in aircraft especially during WWII and later. It was done because transformers, motors and so on are very much lighter than with lower frequencies like 60Hz. DC could not be easily be transformed with the technology then.
However, modern electronics allows DC to be converted (transformed) with very small magnetics operating at 100kHz or higher. This stuff trumps 400Hz. What do they do in modern aircraft?
I was basically referring to the power transmission and distribution. DC is more efficient and uses less material, insulation, with less loss than does poly phase AC. That's why ultra high power transmission lines like the pacific inter-tie are often DC these days.

This certainly cannot be the whole answer. I would expect that it would be fairly difficult to interrupt dc arcs if source voltage were much greater than 30V. Going to ac would allow better arc interruption at altitude. Higher ac voltage can reduce the amount of copper required for a given amount of power.
I am not really up to date on radar power supplies. I would expect that high power radar power supplies would be more advance than using dc and conversion. The same solid state technology that makes dc to dc conversion easy can also be used to rectify ac for feeding into dc to dc converters. After all, a three phase bridge rectifier is easily implemented and starts with relatively low ripple.
Bill

Who told you that? Three phase (400 Hz) is used extensively onboard aircraft.
28 VDC is used for systems where battery backup is provided.

Yep!
400Hz power was used in some US Navy Ships for "electronics." The main reason was that it reduced the weight of the iron needed in transformers and reduced the size of the filters in the power supplies. This would especially be inportant in an aircraft.
My understanding is that 60Hz is "standard" on ships today simply because much of the electronics is just re-packaged commercial stuff. Switching power supplies reduce the DC filtering needed.
Another advantage of 400 Hz or 60 Hz is that the minimum speed of a 2 pole/phase alternator is 3600 rpm with 60Hz but 24,000 rpm at 400Hz. 3600 rpm is a little on the slow side.
OTOH, direct current generators don't like high speeds as the comutators tend to fly apart.
Yep! At higher frequencies I don't thing it's important to have 3 phases available. Phase shifting caps, if needed, are a franction of the size needed at 60hz.
** Posted from **

| Another advantage of 400 Hz or 60 Hz is that the minimum speed of a 2 | pole/phase alternator is 3600 rpm with 60Hz but 24,000 rpm at 400Hz. 3600 | rpm is a little on the slow side.
Did you mean "or" in "400 Hz or 60 Hz" or did you mean "over"?
Why is that minimum speed relevant, given that a multi-pole/phase alternator could be used instead?
However, 3600 rpm for 60 Hz and 24000 rpm for 400 Hz do represent maximum speeds for syncronous motors, or near those speeds for induction motors. So 400 Hz has an advantage. It can be made for up to 24000 rpm or any lesser speed in multi-pole versions. There I do see an advantage of 400 Hz.
I'm curious how hard it might be to make a computer PSU that would run on any frequency from 50 Hz to 400 Hz (or maybe wider), compared to just the 50 Hz to 60 Hz range.
|> I am not really up to date on radar power supplies. I would expect that |> high power radar power supplies would be more advance than using dc and |> conversion. The same solid state technology that makes dc to dc |> conversion easy can also be used to rectify ac for feeding into dc to dc |> converters. After all, a three phase bridge rectifier is easily |> implemented and starts with relatively low ripple. | | Yep! At higher frequencies I don't thing it's important to have 3 phases | available. Phase shifting caps, if needed, are a franction of the size | needed at 60hz.
And in other cases a motor controller can be used (brushless DC motor).
So if they don't have a need for three phase, but do have a need for 60 Hz power on board (ship or aircraft, but consider each might have a different answer to this), what voltage(s) would be available? I would consider that at least for military purposes, they would want to have the ability to run anything they might get their hands on during "missions", and so they might want to be sure they have all common world voltages, or close to them, if not also frequencies. 120, 208, 240, 277, 416, 480?

Most of them made in the last 25 years or so already will. The first thing they do is rectify it to DC so the frequency is irrelevant within reason.

Most ATX power supplies use a simple rectifier first stage, fed directly from the power line. This is switched to a "doubler" when the 120/240V switch is set to 120V. This charges a capacitor, which supplies DC to the switching circuits. The newer ones work from 90-270V input and rely on the switching stage(s) to accommodate the varying DC developed.
There is nothing inherently related to the input frequency, unless it's the PF correction in some newer supplies.

Actually, it's a bit more involved than that.
You see, back in WW II and through the 1950's and 1960's, shipboard fire-control systems (the stuff used to aim guns, torpedoes and the like, not the stuff to put out fires) were all synchro servo systems. We used all sorts of analog computers to take the inputs from bearing readings on the enemy. These would be combined with inputs from the ship's log ('speedometer'), heading and even pitch and roll to electro-hydraulicly control the gun turrets. Or the to 'set' the gyro in torpedoes and the like.
All these analog computers used 400 hz because the servos and syncrhos could be made smaller running at 400 hz. My friend's dad worked for Sperry-Rand for years designing all this stuff.
But today's fire control is all digital computers that run on DC. So, as you said, switching power supplies for this stuff can be designed for 60 Hz input just as easily as 400 Hz.
It is very rare that such speeds are needed for anything. Pumps, fans, and other mechanical equipment certainly don't need such speeds. For the few specialized needs, servo motors or other DC machines work fine.
The speed of the generator is pretty much irrelevent.
daestrom

| |> I'm curious how hard it might be to make a computer PSU that would run on |> any frequency from 50 Hz to 400 Hz (or maybe wider), compared to just the |> 50 Hz to 60 Hz range. | | Most ATX power supplies use a simple rectifier first stage, fed directly | from the power line. This is switched to a "doubler" when the 120/240V | switch is set to 120V. This charges a capacitor, which supplies DC to | the switching circuits. The newer ones work from 90-270V input and rely | on the switching stage(s) to accommodate the varying DC developed. | | There is nothing inherently related to the input frequency, unless it's | the PF correction in some newer supplies.
So I can run them from 0.25 Hz power, then?
FYI, most of my PSUs do not have that "115/230" switch. They are labeled "100-240V 50/60Hz". So it's safe to run it on 400Hz in an airplane?

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Ah, but you have to generate and your prime mover may be a high speed turbine. There is then an advantage to 400Hz on aircraft in that the coupling of the generator to a high speed turbine is easier and lighter as a lot of gearing is avoided.

If you had large enough filter capacitors in the input circuit then yes, you could run it at 0.25 Hz, but where are you going to find that? A standard switchmode PSU will work fine on any realistic frequency, I don't think anywhere is less than 50Hz anymore, or greater than 400Hz.

| | snipped-for-privacy@ipal.net wrote: |> |> | |> |> I'm curious how hard it might be to make a computer PSU that would run on |> |> any frequency from 50 Hz to 400 Hz (or maybe wider), compared to just the |> |> 50 Hz to 60 Hz range. |> | |> | Most ATX power supplies use a simple rectifier first stage, fed directly |> | from the power line. This is switched to a "doubler" when the 120/240V |> | switch is set to 120V. This charges a capacitor, which supplies DC to |> | the switching circuits. The newer ones work from 90-270V input and rely |> | on the switching stage(s) to accommodate the varying DC developed. |> | |> | There is nothing inherently related to the input frequency, unless it's |> | the PF correction in some newer supplies. |> |> So I can run them from 0.25 Hz power, then? |> |> FYI, most of my PSUs do not have that "115/230" switch. They are labeled |> "100-240V 50/60Hz". So it's safe to run it on 400Hz in an airplane? |> | | | If you had large enough filter capacitors in the input circuit then yes, | you could run it at 0.25 Hz, but where are you going to find that? A | standard switchmode PSU will work fine on any realistic frequency, I | don't think anywhere is less than 50Hz anymore, or greater than 400Hz.
So _any_ 50/60 Hz switchmode PSU _will_ work fine on 400 Hz across the full range of voltage it is designed for (when switched properly for the case of those that have a "115/230" switch) ?

There's 25 Hz available between NYC and Washington DC, and 16 2/3 Hz in parts of Europe, but in both cases they are railroad traction power, and there's probably no such thing as a wall outlet supplied with either frequency.
I'm pretty sure the seatside outlets of the Northeast Corridor Amtrak lose power when the train hits a "dead" segment of catenary, but I'd be very surprised if the power doesn't go to a 60 Hz converter first (when it's running on a 25 Hz segment)

I have an electric shaver that has a "tuned" armature oscillating between two "stators" supplied with line power. It works on 50Hz in Europe, (It even has a 120/240V switch), but it does not work as well when using a frequency it's not tuned to.
I haven't had a chance to try it on 25HZ. I don't think it would work at all on 0.25Hz!

| James Sweet writes: | |>If you had large enough filter capacitors in the input circuit then yes, |>you could run it at 0.25 Hz, but where are you going to find that? A |>standard switchmode PSU will work fine on any realistic frequency, I |>don't think anywhere is less than 50Hz anymore, or greater than 400Hz. | | There's 25 Hz available between NYC and Washington DC, and 16 2/3 Hz | in parts of Europe, but in both cases they are railroad traction power, | and there's probably no such thing as a wall outlet supplied with either | frequency.
What kind of power is provided to electrical equipment aboard these trains?
| I'm pretty sure the seatside outlets of the Northeast Corridor Amtrak lose | power when the train hits a "dead" segment of catenary, but I'd be very | surprised if the power doesn't go to a 60 Hz converter first (when it's | running on a 25 Hz segment)
If this were a motor converter with a heavy flywheel, it might ride through the dead segment.

If I'm not mistaken, turbine speed on aircraft are anything but constant. So driving a 400Hz generator directly from them (or through any fixed gearing) isn't practical. But I'm not sure how they are driven on aircraft. A separate 'auxlilary power unit' (APU)??
On naval ships, they were often driven from 60Hz motors and variable-slip couplings. On subs, that have an abundance of DC systems anyway, DC motors were used to drive the 400Hz motor-generator sets.
daestrom

It's dangerous to say *any* because I'm sure there are *some* that have issues, but I would not be afraid to try one.