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question about AC

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Minnow

New Member
I believe that the 60/50 Hz refer to the number of cycles per second. In other words the number of times the current changes direction. Picture it as a sine wave, top peak (max in one direction) and bottom peak (max in the other direction) would be one cycle. This happens 60 times/sec in the US and I think only 50 times/sec in Europe. Hope this helps.
 

wejos

Member
I believe that the 60/50 Hz refer to the number of cycles per second. In other words the number of times the current changes direction. Picture it as a sine wave, top peak (max in one direction) and bottom peak (max in the other direction) would be one cycle. This happens 60 times/sec in the US and I think only 50 times/sec in Europe. Hope this helps.

Minnow thanks for the info

i'll make further reading about them
 
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PatM

Member
50 or 60 Hz are not the only frequencies used.
Aircraft motors operate at higher frequency 400 Hz - 440 Hz. The size of a conponent can be reduced by operating at higher frequency. In aircraft weight and space are at a premium, so higher frequencies are used for reducing the size.
 
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Sceadwian

Banned
Their relationship is only their unit of measurement. The hertz. Or number of cycles per second. That's it.
2.0GHZ is 2 BILLION cycles per second. Which is how many times per second the main clock of a modern CPU ticks at. Each high and low cycle feeds the logic that makes the computer compute.
 

Styx

Active Member
50 or 60 Hz are not the only frequencies used.
Aircraft motors operate at higher frequency 400 Hz - 440 Hz. The size of a conponent can be reduced by operating at higher frequency. In aircraft weight and space are at a premium, so higher frequencies are used for reducing the size.

360 - 800Hz is used on more modern aircraft.
the 400-440Hz was via a proprietary,heavy,inefficient ~constant output speed gearbox that drove the generators.
To save weight they removed it and expose the generators (via gearbox) to the full speed variation of the fan
 

Diver300

Well-Known Member
Most Helpful Member
360 - 800Hz is used on more modern aircraft.
the 400-440Hz was via a proprietary,heavy,inefficient ~constant output speed gearbox that drove the generators.
To save weight they removed it and expose the generators (via gearbox) to the full speed variation of the fan

Surely the engine speed variation is larger than 800:360? I thought that only lawn mower engines have such a small variation, with about 1200 rpm tickover, which needs to be that high because it is only single cylinder, and 2400 rpm max to keep the blade tip speed low enough.

Also, wouldn't there be a problem with motors running from the AC supply? Their speed would vary with the engine. Or is AC only needed so that it can be transformed?
 

Styx

Active Member
Surely the engine speed variation is larger than 800:360? I thought that only lawn mower engines have such a small variation, with about 1200 rpm tickover, which needs to be that high because it is only single cylinder, and 2400 rpm max to keep the blade tip speed low enough.
Well iirc the generators are hooked up to the low-pressure fan via gearbox
The LP (it might be the HP I need to check my jet engine handbook) doesn't have such a wide speed variation. Also the gearbox steps down the speed.

Also, wouldn't there be a problem with motors running from the AC supply? Their speed would vary with the engine. Or is AC only needed so that it can be transformed?
That is very true and that is why for newer Aircraft (A380 and onwards) there is ALOT of motor-drives in the aircraft acting as essentially VFVF or VFCF converters.
 
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