400Hz ?
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any particular reason?
What is the advantage to this new system on the A380? Are the constant speed units a common failure item?
What will be the effect of slightly different engine rpms, if the frequency varys with engine speed-will they be feeding separate buses? As I recall the generator frequencies and phases have to match before they can feed the same bus.
Also am I right in thinking the RMS voltage would vary with the frequency as the slope of the sine curve changes? (Or would a standard regulator also compensate?) Or am I completely off?
Possibly all easy problems for an electrical engineer these days, but you dont know until you ask!
Thanks,
FlyVMO
What will be the effect of slightly different engine rpms, if the frequency varys with engine speed-will they be feeding separate buses? As I recall the generator frequencies and phases have to match before they can feed the same bus.
Also am I right in thinking the RMS voltage would vary with the frequency as the slope of the sine curve changes? (Or would a standard regulator also compensate?) Or am I completely off?
Possibly all easy problems for an electrical engineer these days, but you dont know until you ask!
Thanks,
FlyVMO
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FlyVMO
What is the advantage to this new system on the A380? Are the constant speed units a common failure item?
A: Less weight and elimination of a possible failure source.
What will be the effect of slightly different engine rpms, if the frequency varys with engine speed-will they be feeding separate buses?
A: Yes, they will feed seperate buses.
Also am I right in thinking the RMS voltage would vary with the frequency as the slope of the sine curve changes? (Or would a standard regulator also compensate?)
A: Will be regulated to a constant voltage of 115V
regards
A: Less weight and elimination of a possible failure source.
What will be the effect of slightly different engine rpms, if the frequency varys with engine speed-will they be feeding separate buses?
A: Yes, they will feed seperate buses.
Also am I right in thinking the RMS voltage would vary with the frequency as the slope of the sine curve changes? (Or would a standard regulator also compensate?)
A: Will be regulated to a constant voltage of 115V
regards
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Variable frequency - ?
Many years ago a system called VSCF (variable speed, constant frequency) was proposed that used a "wild" alternator frequency, but processed this through a solid-state "chopper" to synthesize a constant-frequency output. Mechanically simple, let the electronics do the work.
I'm not sure what aircraft (if any) ever actually used this. Is it possible this is the A380 plan?
(Further research suggests Smiths and perhaps others are producing these systems)
I'm not sure what aircraft (if any) ever actually used this. Is it possible this is the A380 plan?
(Further research suggests Smiths and perhaps others are producing these systems)
barit1,
I have flown some 737-500's with VSCF's fitted. Identical in operation as far as the pilot is concerned, so identical that I think some aircraft even had a VSCF on one side and a CSD on the other.
We did have a UKCAA restriction on aircraft with VSCF's fitted that we had to stay within 45mins of a suitable airport rather than 1hr with CSD a/c, so maybe they were less reliable?
S&L
I have flown some 737-500's with VSCF's fitted. Identical in operation as far as the pilot is concerned, so identical that I think some aircraft even had a VSCF on one side and a CSD on the other.
We did have a UKCAA restriction on aircraft with VSCF's fitted that we had to stay within 45mins of a suitable airport rather than 1hr with CSD a/c, so maybe they were less reliable?
S&L
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Very low frequency
Fark'n'ell wrote:
Well, let's say we have 0.000011574 Hz. This would have been seen as DC "the entire day", and DC with reverse polarity during the night.
Now, the real philosophical question is: When (at what frequency) will AC become DC, and close to that limit isn't the AC "nearly DC" ?
I guess that depends who you are. For a mayfly a frequency of 0.000011574 Hz would surely feel like DC as it would not alter in it's entire life-cycle.
Bob.
HD
On the contrary, surely? It would be almost DC if it was 1 or 2Hz.... or is my aged brain playing tricks with my radio theory?
If it were 1 or 2Ghz it still a'int nearly DC
On the contrary, surely? It would be almost DC if it was 1 or 2Hz.... or is my aged brain playing tricks with my radio theory?
If it were 1 or 2Ghz it still a'int nearly DC
Now, the real philosophical question is: When (at what frequency) will AC become DC, and close to that limit isn't the AC "nearly DC" ?
I guess that depends who you are. For a mayfly a frequency of 0.000011574 Hz would surely feel like DC as it would not alter in it's entire life-cycle.
Bob.
I seem to remember reading that the 'new' F22 fighter uses 270v DC. Not too sure why - one problem with DC is the switchgear needed - with AC, as the volts go through zero, provided the power factor isn't too bad, any arc extinguishes.
800Hz was used in some WW2 airborne radar. There was appreciable weight saving in transformers - and, for that matter, a saving in transformer quality steel, which was another consideration.
800Hz was used in some WW2 airborne radar. There was appreciable weight saving in transformers - and, for that matter, a saving in transformer quality steel, which was another consideration.
Cunning Artificer
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To answer some of the questions posed:
The earliest A.C. systems were frequency wild at 208v which was then rectified to provide 112V D.C. for the main power busses.
So why 400 Hz? Early inverters were mainly used to provide power supplies for radio and radar equipment that 'liked' to have that frequency. It then became a standard. We actually used 1600 Hz single phase inverters for one particular piece of electronic kit in common military use back in the fifties and sixties. 400 Hz can be fed at high current loads without significant line drop caused by power cable inductance. At higher frequencies like that 1600 Hz I mentioned, line drop due to inductance is unacceptably high at the current ratings need by the aircraft power systems. As with everything in engineering, it is a compromise. Nevertheless the generator output is generally regulated at 208V which equates to 200V at the bus bar.
Most of the more powerful motors on aircraft are three phase and have no need to vary their speed - hydraulic pumps, flap and slat drives, fuel pumps even powered flying contol units (PFCUs) Three phase synchronous motors are more efficient than non-synchronous types.
The 115V 400 Hz outlet in galleys is a power outlet. Most electrical accessories - especially heating units and the cleaners' vacuum cleaners - are not frequency sensitive and work well on any frequency, as long as the voltage is correct.
D.C. is often quoted as being Zero Hertz but tackle it by Fouriers analysis and you soon see that it contains an infinite number of harmonics. In other words, think of it as 'Infinity' Hz.
The earliest A.C. systems were frequency wild at 208v which was then rectified to provide 112V D.C. for the main power busses.
So why 400 Hz? Early inverters were mainly used to provide power supplies for radio and radar equipment that 'liked' to have that frequency. It then became a standard. We actually used 1600 Hz single phase inverters for one particular piece of electronic kit in common military use back in the fifties and sixties. 400 Hz can be fed at high current loads without significant line drop caused by power cable inductance. At higher frequencies like that 1600 Hz I mentioned, line drop due to inductance is unacceptably high at the current ratings need by the aircraft power systems. As with everything in engineering, it is a compromise. Nevertheless the generator output is generally regulated at 208V which equates to 200V at the bus bar.
Most of the more powerful motors on aircraft are three phase and have no need to vary their speed - hydraulic pumps, flap and slat drives, fuel pumps even powered flying contol units (PFCUs) Three phase synchronous motors are more efficient than non-synchronous types.
The 115V 400 Hz outlet in galleys is a power outlet. Most electrical accessories - especially heating units and the cleaners' vacuum cleaners - are not frequency sensitive and work well on any frequency, as long as the voltage is correct.
D.C. is often quoted as being Zero Hertz but tackle it by Fouriers analysis and you soon see that it contains an infinite number of harmonics. In other words, think of it as 'Infinity' Hz.
