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J. Mileski
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Message 1447184 - Posted: 27 Nov 2013, 0:23:47 UTC

I have been curious for a long time. If we were developing an electrical grid from scratch, would we choose 50 hz or 60 hz or some other frequency? Thinking about how our planet may look to others on another planet, as earth rotates there would be an alternating 50 hz to 60 hz and back. I recall reading, early AC in the USA started as low as 25hz to 30 hz. Does anyone know what would be most efficient for transmitting power over the grid?
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Message 1447211 - Posted: 27 Nov 2013, 2:04:22 UTC - in response to Message 1447184.

0 Hz (DC) has a lot of efficiency advantages, but the generating hardware (or rectifiers) adds cost and complexity.

If you're going with AC, lower frequencies result in less skin effect, but I think it's a matter of how low you can push the frequency and still make a practical and efficient generator. The minimum you can do is one cycle per rev, and generators have to turn at a certain minimum speed for various efficiency reasons.

It's probably safe to say there aren't large savings to be had going lower than 50-60Hz, or we would be doing it. And something in that range probably makes the hardware practical, if not simple.

If cost were no object you could produce with dynamos or use giant solid-state rectifiers.

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Message 1447212 - Posted: 27 Nov 2013, 2:11:44 UTC - in response to Message 1447184.

25 cycle AC power was commonly used in the New York Subway. The higher the frequency the more loss there would be in the wires. The advantage to higher frequencies is that transformers can be really small. When I was at GE we looked at 3000 cycle lighting, 60 cycles has many advantages over 50 cycles--in Europe the televisions (and the entire electric grid) used 50 cycles and you could notice a flicker in the picture especially if there was a light shining on the TV set and you were at a certain angle. I have never seen the problem in American TV. We used a different system (NTSC) rather than PAL, this may have also contributed to the flicker as NTSC interlaced half frames at 120 times per second (every other line out of 525 lines.

60 cycles also has an advantage for designing an electric clock--since our time is divided by base 60 thanks to the Babylonians.

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Message 1447213 - Posted: 27 Nov 2013, 2:15:17 UTC

A non-scientific observation would be frequency any lower and we could sense the lights pulsating with the AC swing. (^;

In the military we had planes that ran on 400Hz because of the ease of stabilization I believe. 5% drop at 400Hz vs. 5% drop at 60Hz.
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Message 1447240 - Posted: 27 Nov 2013, 3:40:36 UTC
Last modified: 21 Mar 2014, 23:02:57 UTC

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Message 1447289 - Posted: 27 Nov 2013, 6:06:59 UTC

Its a matter of checks and balances.
You need a higher frequency to reduce the size of the transformers, but increase the frequency too far and you increase the loses within the transformers and transmission lines. 50/60Hz is probably at the low end, but it was settled on as being easy to produce back in 190notverymany and we are stuck with it. The technical optimum is probably a few hundred Hz, but just think of the cost of replacing the whole generating infrastructure, and all the equipment that relies on it...
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Message 1447371 - Posted: 27 Nov 2013, 12:49:39 UTC

For absolutely new system, I would go with 400Hz, the same as aircraft. The technology and components are known and designed.

Linear DC power supply components would be smaller and lighter.

Fluorescent still glow, even when starter cct fails at 400Hz, could help safety and road signs.

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Message 1447576 - Posted: 27 Nov 2013, 21:38:04 UTC - in response to Message 1447240.

at 1.8 MHZ your wire would be an antenna and a lot of power would be radiated.

Voltage and current are not 180 degrees out of phase. VI cos θ is the power delivered. Usually the power companies like to keep the phase angle as close to zero as possible: because that is what they get paid for. That is why you will notice banks of pole-mounted Capacitors for power factor correction. Motors and transformers tend to mover the power factor (angle between voltage and current) in one direction while capacitors move it in the opposite.


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Message 1447611 - Posted: 27 Nov 2013, 22:20:23 UTC - in response to Message 1447576.
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Message 1447770 - Posted: 28 Nov 2013, 5:30:50 UTC

Williams post is correct but let me ask Guy a couple of questions. Perhaps guy can further elaborate.

Quote
I figured this out a few years ago and now use a balanced transmission line with an alternating current in the range of 1.8 Megahertz to 50 Megahertz and because I have the size of the wires and the spacing between those two wires set for a known impedence, and I feed it with a voltage sometimes in the range of 10,000 to 15,000 volts, I get really good results (very little loss.)
Unquote

Guy.....what do you do with this system? Are you sliding the frequency up and down between 1.8 MHz and 50 MHz? Wouldn't that be frequency modulation? (FM) I agree with Williams post that this sounds like a transmission antenna at those frequency's and voltage input. But knowing the purpose of this system may help my understanding. Can you elaborate?
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Message 1448181 - Posted: 29 Nov 2013, 1:33:37 UTC
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Message 1448202 - Posted: 29 Nov 2013, 4:06:20 UTC - in response to Message 1448181.

If you typically transmit at 5 watts, and designed your antenna for 2 kw, you've not optimized.

You could use that antenna to scare up worms.
The ends of a dipole can be at very high voltages, depending on the capacitive coupling of the antenna.
Drop a fine gauge wire down from the ends, connected to two insulated spikes into the earth with conductive spheres at the tips,
Juice the transmitter for a bit, shut down, go out an pick the worms.
You may have to lower the transmitting frequency into the khz, or hz, range.

Even given that Angela is reading AARL magazines, Shortwave RF transmission really isn't used much.
I'm sure that low tech terrorists still find it usefull. but it really is just a present-day historic anachronism.

Science has a knack for attraccting the brightest of humanity, discounting advertizing.
There be some smart people sellin religion, but "My God" Science is "So Much Sexier".

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Message 1448269 - Posted: 29 Nov 2013, 9:18:15 UTC

You guys are all talking rocket science to me! I view electricity down a cable as simply water down a pipe. The pressure is the voltage, the flow is the Amps, the diameter is the resistance, and the volume is the watts. Very roughly speaking of course :-0

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Message 1448274 - Posted: 29 Nov 2013, 9:34:53 UTC - in response to Message 1448269.
Last modified: 29 Nov 2013, 9:35:30 UTC

You guys are all talking rocket science to me! I view electricity down a cable as simply water down a pipe. The pressure is the voltage, the flow is the Amps, the diameter is the resistance, and the volume is the watts. Very roughly speaking of course :-0

All very roughly at room temperature for low voltage steady-state direct current (DC).

Add a few dynamics and it all changes! ;-)


One advantage of 50Hz or 60Hz for mains AC as opposed to a few hundred Hz is that you can work "very big" more easily... And 50Hz or 60Hz are nice speeds to couple directly to big generating machinery.

Also, coupling losses are minimized for long distance transmission. Or... You go new-fangled high voltage DC!


Keep searchin',
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Message 1448321 - Posted: 29 Nov 2013, 13:03:25 UTC - in response to Message 1448310.

... I sometimes put 1 Kilowatt into my transmission system...

Is that for moon-bounce?

Or something more esoteric?...

Sorry, no clue as to where your comment came from!


As for could ET detect our power grid... Doubtful unless we deliberately arrange and phase the power lines...

Far more likely would be for the various radars to be picked up.


Keep searchin',
Martin

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Message 1448354 - Posted: 29 Nov 2013, 16:02:37 UTC - in response to Message 1448310.

Here's the answer: The most efficient way of transmitting a lot of power over log distances is to use high voltage DC. I am talking about 750,000 to 1 million volts. At this high voltage the current could be quite small and require modestly sized wires,. This was a part of my scheme to locate Power Plants in the Powder-River Basin wastelands (which is the source of low-btu Lignite coal).

You would have to covert to DC at the power plant and then reconvert to AC at the distribution point.

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Message 1448357 - Posted: 29 Nov 2013, 16:14:58 UTC

My question stems from how we look to et, and what could we expect to find on other worlds. I have read a little about how our power transmission developed through history. I was wondering if what we would find on another world would be a lot different, or be close to what we do.

The ultimate question, "If we point Aricebo at the earth, would we find the same thing we are searching for out there?" I guess I am asking are we searching for the right rf from the other worlds? Sorry if I went from non-seti to (you know).
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Message 1448372 - Posted: 29 Nov 2013, 16:59:03 UTC
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Message 1448442 - Posted: 29 Nov 2013, 19:07:19 UTC - in response to Message 1448357.

If there were another intelligent society out there, we would not be looking to pick up their Power grid frequency. We would be looking at the possibility of high power/high frequency radar possibly from their aircraft and airports. We might also look to find a radio or TV broadcast.

If they were intentionally trying to reach another civilization we might look at the most promising Hydrogen absorption lines; or perhaps these frequencies times π. However if they are like us they would not be broadcasting a powerful beam of "we are here" type information.

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Message 1448503 - Posted: 29 Nov 2013, 23:21:06 UTC

The thing about electrical power transmission, no matter what the frequency, it is designed to transmit and not radiate. The electromagnetic fields around power lines store energy, they don't radiate. I don't think you could detect an extra-terrestrial civilization from their power leakage.

The wavelength of an electromagnetic signal at 60 Hz is about 5000 kilometers. So your typical transmission segment will be a lot less than a wavelength, and it won't act like an antenna. RF-type frequencies you would have to make sure your transmission lines are designed not to radiate.

The advantage that DC has is that the average current is the same as the peak value, whereas for AC is is less. Since you have to size your conductors for the peak values, your DC cables can be smaller.

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