This has to do with the physiology of the human hearing, just look at the Fletcher-Munson curves. At low frequencies, the threshold of hearing at 50/60 Hz is quite high, thus the humans can be subjected to quite strong audio levels at 50/60 Hz, but at 400 Hz the same level is easily audible.
Regarding audio system leakage problems, balanced systems would be much more common in a 400 Hz world than the stupid unbalanced systems (usually using RCA connectors).
On Sat, 16 May 2015 11:57:05 +0300, snipped-for-privacy@downunder.com Gave us:
Skin effect at 60Hz is near nil.
Multiple conductor runs negate the effect even further.
On Sat, 16 May 2015 11:57:05 +0300, snipped-for-privacy@downunder.com Gave us:
HV lines are bare for both DC and AC. AC and DC U/G lines are insulated. They have been doing it for decades, so they already know how to 'withstand'.
Can we withstand the memory loss you suffer from your educational past?
, s " l
That's not true at all. The steel rails and rail bed are far from ideal. If you ever take the time to observe a passing train, you'll see vertical rai l displacements as large as 6" when the train passes over, the rails bend like wet noodles under the weight, and the bed is just an approximation to a flat base. The heavier the cars, the deeper the rail deflection ruts they need to be pulled out of.
Forgot all about the wasted metal in those lines!
skin depth at 60Hz in copper is approx 1/3 inch and in aluminum [assuming the line is made up of aluminum wrapped around steel] is less than 1/2 inch. From memory those 1000A lines are about 1 inch diameter. Thus, there is indeed a lot of wasted material in those lines.
Also I forgot about the dielectric strain from AC high voltage applied across the insulators. Not just the 'peak' boltage being higher but AC applied.
I was just remembering how the transmission lines had to be 'resequenced' every so many miles, else the reactive loads per phase became way out of whack. ...For the lurkers, the 3 phase, a, b, and c are assigned to those
3 lines you see overhead. Usually two sets on each side. Every ??10 miles the lines are reassigned change from a, b, c to something like c, a, b, etc etc. That way each phase gets to see about the same capacitance to ground along the line.How did that experiment in Finland work out?
On Sat, 16 May 2015 05:39:53 -0700, RobertMacy Gave us:
Sure that you are not off by an order of magnitude?
Skin depth is a factor and is high AT high frequencies..
I cannot imagine that it is worse at power line frequencies, so a third of an inch sounds ridiculous.
I have a short piece of underground 245kV 60Hz transmission line. It has a copper center and outer protection and insulation layers. The center of the copper portion carries relatively little current, due to the skin depth at 60Hz.
--
Thanks,
- Win
eroUno:
-Lasse
"Amtrak President Joseph Boardman said Thursday the technology was installed where the crash occurred, according to The Associated Press, but it had not been turned on because the system needed to be tested further."
So the system was *not* fully installed since that is not complete until it is tested and verified.
-- Rick
I think that's mostly elastic, though, so the forward push on the back wheels balances out the backward push on the front wheels. It's only the inelastic part that causes drag.
Same thing with inviscid laminar flow around a sphere--the boost on the trailing side balances the push on the leading side.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
It is far from elastic. The movement is due to poor support of the cross-ties which allows them to move in the ballast. Lots of friction involved in moving rocks around.
-- Rick
It can't be very inelastic, or the tracks wouldn't survive long--in the inelastic case there's no restoring force to make the rocks move back under the ties.
Cheers
Phil
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
The ballast is like the molecules in the sea. They move around with others moving in to take their place with all the energy being dissipated as heat. I've seen this with my own eyes when working for the railroad. The ballast is supposed to be packed tightly around the ties so they can't move, but with time they get pushed out and the packing is not so tight allowing the ties to move in three directions.
This is no small part of why it is so hard to get a train moving from a standstill and why knuckles get broken in the process. There are smaller vehicles used on the tracks which require very little effort to get moving.
-- Rick
So, according to that, the 1/3 inch (8.47 mm) is correct. Most HV overhead power lines are constructed with a core of steel (or more recently, a carbon/glass composite with much less thermal expansion), so much more of the conductive aluminum is utilized.
Overhead lines are usually bare, although some might have a non-metallic covering to reduce corrosion.
The stress on insulators applies to the components that support and separate the power lines, and with AC applied there will be capacitive current through them and eventual deterioration that causes a resistive component that can lead to failure. Power factor testing is often performed on insulators, especially those on transformers and protective devices such as reclosers.
Paul
Skin depth is *small* at high frequencies. It's infinite at DC.
Skin depth is inverse on the square root of frequency.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The engineer claims that he was knocked unconscious by an object that struck the train. Still, there should have been a "dead man switch" that would have slowed or stopped the train and automatically signaled an alarm. Cheap, easy, and effective. No need for the expensive automatic speed controls and need for extensive testing before implementation.
Paul
It's not very surprising that a huge train is hard to get going from a stan dstill. That's not enough of an argument to establish the dependence of rol ling resistance on train mass.
If "Fred's" 6-inch deflection were even 1% inelastic, the roadbed would sub side by 0.06 inches per train. Assuming 10 trains per day, that's around 2 feet per year. The tracks would be level with the roadbed in at most 6 mont hs, which would lead to a fairly startling number of derailments.
Cheers
Phil Hobbs
I'm not going to argue this with you. Your logic is flawed. The fact that the rail comes back to level doesn't mean it is 100% elastic. Otherwise a ship would never stop bobbing. Either go do a little research or just be an armchair philosopher.
-- Rick
In a power distribution panel (or what ever that is called at your part of the world) it is no problem of using hollow bus bars instead of solid bus bars after 2 cm conductor diameter.
For HV overhead lines, it is more economical to use 3 or 4 wires for each phase instead of a thick conductor due to the skin effect at
50/60 Hz.The resequencing is about having equal capacitance to ground for each phase.
This started last autumn, so the interesting question is how it would survive the thunderstorms next summer.
If you want to Google, look for Technical University of Lappeemranta, they also have interesting ideas using rural electrification using ABC rural 1000 Vac low voltage feeds to your last substation instead of 20 kV open wire feeds across the woods.
Anything thicker than your thumb is more or less useless as an bus bar at 50/60 Hz due to the skin effect.
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