400 Hz
- Thread starter A1cbr
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electricalperson
Senior Member
- Location
- massachusetts
my teacher used to work on airplanes in vietnam he said the conductors were hollow. i believe it has something to do with the size of the power supply but im probably wrong
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
One big reason is that inductive equipment (transformers and motors) can be smaller and lighter for a given power rating.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Hollow conductors suggests compensating for (or rather, taking advantage of) skin effect.
electricalperson
Senior Member
- Location
- massachusetts
he said the conductors didnt need the middle because of the high skin effect from 400 hertz
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Right, although it matters more at much higher frequencies. Skin effect is dependent on both frequency and current.
zog
Senior Member
- Location
- Charlotte, NC
400Hz is used on submarines too, so much for the "lighter' theory. I used to maintain the 400hZ MG sets and they are not smaller and lighter for the power output, huge communtators.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
At higher frequencies, the power units are significantly smaller. I once worked on a test stand for the 400Hz alternators that are on the GE engines used on Boeing 777 aircraft. The entire 400kW alternator assembly is about the size and weight of an average 50HP industrial AC 4 pole motor.
ohmhead
Senior Member
- Location
- ORLANDO FLA
Well in the navy all aircraft are 400 hz in the commercial civilian world aircraft are also all 400 hz and the wiring inside a aircraft or generator is not hollow tubing !! 400 hz is not high freq to the point of hollow tubing i worked on the flight deck in the navy .
Our support power to aircraft was 400 cycles but we never had hollow wires . The avionics and electronics need this 400 cycles to operate its dc rectification less power supplies for electronics and power thats part of the weight issue its also the jet engine speed mechanical part from a rotation stand point gearing to generator to transmission of power . 400 hz is better in many ways on aircraft. Smaller parts on everything electrical ! we also had 800hz stuff in the navy and no hollow tubing or wires . take care
- Location
- Massachusetts
I agree and will add that everything in life is a trade off. The higher frequencies do make for lighter equipment but voltage drop becomes much more of an issue. Of course on a plane or a sub the circuit length has some inherent limitations. :smile:
On the other hand I think some old railroads used 20 cycles, voltage drop becomes less of an issue but motors become huge, not a problem for trains.
50-60 cycles is a mid ground trade of, reasonable voltage drop and reasonably sized motors and transformers. :smile:
At least that is my limited understanding of it. :smile:
- Location
- Massachusetts
One big advantage of 400 HZ is it is much easier to filter obtain a smooth DC voltage. Picture a full wave rectifier with a capacitor across its outputs. The capacitor only has to hold enough charge to sustain the output voltage for 1.25 ms with 400 Hz. With 60 Hz. the same cap would have to hold the output for 8 ms.
If you think about the types of instruments and electronics on airplanes and submarines (radar, radios, avionics, etc.) I think the DC filtering is pretty important.
P.S. I guess its possible that a very large wire, or a power feeder might have been hollow, but I'm a little skeptical about it. Are you sure he wasn't refering to fiber optic signal wires?
If you think about the types of instruments and electronics on airplanes and submarines (radar, radios, avionics, etc.) I think the DC filtering is pretty important.
P.S. I guess its possible that a very large wire, or a power feeder might have been hollow, but I'm a little skeptical about it. Are you sure he wasn't refering to fiber optic signal wires?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
They are pretty impressive looking when you consider how much power they can generate. I have seen a similar 200kW generator on a test stand.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
It's easier to filter, not rectify.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I owned the 400 HZ MG sets on a couple aircraft carriers. There were four MG sets, and (going from very old memory here) each was about 2 feet in diameter, and about 6 feet long. I?d call it big. But even if the power source is large, operating at 400 HZ does make the served equipment smaller and lighter. Also, and this is not based on anything other than a guess, but it is my guess that the high degree of precision needed for weapons-related radar systems can be achieved more easily, if your power source has a higher frequency.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Two motors of the same power rating and the same _speed_ will be approximately the same size, 60Hz or 400Hz. So in a M-G set the 400Hz alternator will be roughly the same size as the 60Hz driving motor, unless there is gearing between the two.
400Hz motors can be smaller for the same power level if you let them operate at higher speed. For example, a 50kW 2 pole 400Hz motor will be significantly smaller than a 50kW 2 pole 60 Hz motor, but it will spin at 24000RPM to get there.
-Jon
400Hz motors can be smaller for the same power level if you let them operate at higher speed. For example, a 50kW 2 pole 400Hz motor will be significantly smaller than a 50kW 2 pole 60 Hz motor, but it will spin at 24000RPM to get there.
-Jon
zog
Senior Member
- Location
- Charlotte, NC
I agree, the size/weight advantages seem to be in the loads rather than the sources.
thats what I meant when i said easier to rectify to clean dc. easier to get clean dc when rectifying. i guess i worded poorly, but yes easier to filter to a cleaner dc than 60hz. same reason stuff that needs super clean DC such as telco gear and ion laser power supplies use 3ph rectifiers..
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