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from the you're-not-just-bored:-the-wall-clock-IS-slow dept.
Electric clocks on continental Europe that are steered by the frequency of the power system are running slow by up to 5 minutes since mid-January according to a news release from the European Network of Transmission System Operators for Electricity ('entsoe'). The transmission system operators (TSOs) will set up a compensation program to correct the time in the future.
Many electric clocks rely on the transmission system frequency to provide a source that minimises long-term drift. Quartz crystals have good short term stability, but dreadful long term stability, so plant and machinery that requires power to be turned on or off at a specific time each day without maintenance over a long period historically used clocks slaved to the power-system frequency, which is kept long-term stable by the system operators to prevent problems in power generation and transmission across national and supra-national grids - for example, attempting to switch supplies to generators that are not synchronised to the grid frequency can severely damage the generator.
It is normal for transmission system operators to allow the frequency to drop slightly at periods of high demand, thus slowing clocks, but usually, the frequency is increased during periods of low demand to ensure the long-term average frequency remains stable.
(Score: 4, Informative) by DannyB on Tuesday March 06 2018, @10:55PM (18 children)
DC would be great for many uses at the building level. One large DC power supply. Lots of appliances and electronics within a building powered by DC. But what voltage? Electronics wants low voltages. But a vacuum cleaner still needs a LOT of power, and even, say 48 v is going to require thicker wires for higher amperage.
AC can go through transformers. This makes it possible to trade off current for high voltages for long distance transmission of power.
The lower I set my standards the more accomplishments I have.
(Score: 2, Disagree) by BsAtHome on Tuesday March 06 2018, @11:00PM (13 children)
Holding your finger on a DC wire is a lot more dangerous than the same voltage at AC. Your muscles will "turn on" at DC and you cannot release the wire, whereas AC allows you to get away from the wire again.
(Score: 4, Informative) by Arik on Tuesday March 06 2018, @11:05PM (2 children)
If laughter is the best medicine, who are the best doctors?
(Score: 4, Interesting) by edIII on Wednesday March 07 2018, @02:33AM (1 child)
Too Late :)
This was well tested with a couple hundred thousand volts (comparable to a high setting on a taser) on an innocuous looking capacitor that somebody tossed me. It was a like a grenade that you couldn't pry out of your fingers with a crowbar.
I almost shit myself, and the contact point was my hands. Caught it with both of them in just the right way that it arced through my hands, arms, and torso. Nearly every muscle in my body seemed to respond.
Never test this at home. Unless you want to look over your shoulder for a few years :)
Technically, lunchtime is at any moment. It's just a wave function.
(Score: 5, Funny) by anubi on Wednesday March 07 2018, @10:59AM
Tossing a plebe a charged capacitor, or leaving a charged one in the box, was the standard initiation ceremony at the school I went to.
I still remember sneaking up behind one guy thinking I was going to discharge a 40uF/450WV electrolytic behind him.
I scared the hell out of him all right.
I had forgotten the can was common to negative, and I touched the file I was using to discharge it to the positive terminal first.
Wasn't too bright that day. I never knew I could make that kind of noise. Ahhh, the stupidity of youth.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 3, Informative) by c0lo on Tuesday March 06 2018, @11:29PM (7 children)
I don't think this is true, given that physiological muscle relaxation time (30-75 ms for half relaxation) is longer than half the period of the AC we are using (10 ms at 50hz).
We** are electrochemical beings, the reaction speed is governed by the mobility of ions in acquatic solutions.
---
**Well, almost all of us, @bot may begin to differ.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by edIII on Wednesday March 07 2018, @02:35AM (4 children)
All I can say with authority, is that you cannot let go of DC. I desperately tried. Boy did I try.
Technically, lunchtime is at any moment. It's just a wave function.
(Score: 2) by c0lo on Wednesday March 07 2018, @02:47AM
Sorry, I missed blockquoting what I don't think is true. What my reply comment was addressing is the:
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 5, Informative) by martyb on Wednesday March 07 2018, @03:51AM (2 children)
Wit is intellect, dancing.
(Score: 2) by c0lo on Wednesday March 07 2018, @07:26AM (1 child)
Learnt this in highschool.
It'll still be a painful experience and a potentially (or does 'voltageusly' fits better in the context?) dangerous one.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by martyb on Wednesday March 07 2018, @01:49PM
Agreed. Tapping a live wire with the back of your hand is probably still a bad idea if your hands are wet and you are standing in water.
Wit is intellect, dancing.
(Score: 2, Disagree) by Nuke on Wednesday March 07 2018, @11:20AM (1 child)
c0lo said :
The point is not that you have time to withdraw your hand in 10ms. The point is that DC makes the muscle pull only one way (which may be to grip the wire harder), whereas AC is "neutral" with regard to muscle pulling direction in that the current direction cancels out on average as far as muscle movement is concerned.
I used to work for London Underground railways which has fourth rail electrification at 600v DC. I worked on the track sometimes, and the way the permanent way gangers I was with put it (from some experience) was that the positive DC rail was "sticky". I never experienced it myself.
(Score: 4, Informative) by c0lo on Wednesday March 07 2018, @12:10PM
The fact that the current goes one way or the other is irrelevant for the reaction of the muscle - it will contract anyway, the current mobilizes out the Ca+ ions, causing the proteins in the fibrils to contract. [opentextbc.ca]
If the muscles that are closing your fingers are involved, you won't be able to loosen the grip no mater if it's AC or DC.
To make the matter worse, an electric tetanus can let the muscle contracted for some minutes [allaboutcircuits.com], until the Ca ions repopulate the plasma inside the cells.
The only difference between AC and DC - AC is worse, it causes variable degree of contraction (it "shakes" the muscle) and makes the electrocution painful.
The DC contracts the muscle and keeps it that way in a single go - this is why the "stickiness" description, the muscle is contracted to the max and keeps this way no matter what your mind try to command it to do.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 3, Interesting) by RS3 on Wednesday March 07 2018, @04:16AM (1 child)
Ah, um, sort of not quite. Enough AC and your nerve electrical system is overwhelmed and you have no control of anything. You may want to, but agony is all you can muster.
There is a range of current that will cause heart fibrillation. Some quick research shows lots of differing opinions on lethal current levels. https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html [ohio-state.edu] It's not an easy thing to test, and even if you could, some people are quite strong, and some ready to die without electric shock helping.
Above that range you might survive because it's like getting hit by an electric shock defibrillator https://en.wikipedia.org/wiki/Automated_external_defibrillator [wikipedia.org]. They hopefully get the heart back into synchronized rhythm using a controlled electric shock.
There's some talk that AC is more dangerous to the heart. I've always feared DC because you don't feel it as much...
(Score: 3, Interesting) by c0lo on Wednesday March 07 2018, @07:49AM
Speaking of variability of human physiology, there are persons who can can touch live wired to 500V or thereby; thick skin on the fingers and palm and no sweating in the same areas - over 700kohm hand-to-hand measured resistance. Met one of them, he was working as an electrician and not even him would work unprotected - 'what if a wire punctures my skin' he said when I asked him.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by Grishnakh on Wednesday March 07 2018, @04:34PM (3 children)
DC would be great for many uses at the building level. One large DC power supply. Lots of appliances and electronics within a building powered by DC. But what voltage? Electronics wants low voltages. But a vacuum cleaner still needs a LOT of power, and even, say 48 v is going to require thicker wires for higher amperage.
Something like 200VDC would make sense, or maybe even 350VDC. (In countries with 120VAC systems, the peak voltage is about 170V, and in 240VAC countries, it's about 340V, so my numbers are pretty close to what we already use.) Electronics would have to be converted with a DC-DC converter, pretty much like we already do (except we currently use AC-DC converters that are really more like DC-DC converters with a rectifier on the front).
AC can go through transformers.
Except we don't do that any more. We use switching power supplies and converters for everything now. The only place we still use transformers is at the electric utility, for converting tens of kilovolts to the 120VAC your house uses (using a neighborhood transformer), or for stepping up/down power for transmission lines. And these are going the way of the do-do as they get replaced with HVDC transmission lines.
This makes it possible to trade off current for high voltages for long distance transmission of power.
You should look up HVDC. It's a really new technology used for transmitting power over long distance. It's only been in commercial use since the early 1950s though...
(Score: 2) by DannyB on Wednesday March 07 2018, @04:53PM (2 children)
I was not aware of HVDC. My mention of transformers was in regard to high voltage AC transmission.
Yes, I understand we using switching power supplies. And maybe that is an effective way to step down your 200 or 350 VDC to a stable 12 V or 5 V for many common uses. Although real isolation from the the electrical outlet would desirable. So maybe a DC to DC converter as you say. But this introduces additional inefficiency.
All this talk of DC only would please Edison.
Tesla would be spinning in his grave. (which would generate an AC current.)
I'm a software guy. I don't remember which end of a soldering iron to pick up. So maybe I'm all wet (and grounded), but it occurs to me that what if you could have a 2-stage switching power supply. You switch the main 350 VDC to a capacitor, and as its charge reaches the "stage 1 voltage" (> 5VDC) you disconnect the main, then as capacitor discharges below "stage 1 voltage", it is re-connected to the 350 VDC power. Now during the period while this first stage capacitor is disconnected from the electrical line, it is then possible to connect it to a 2nd stage capacitor to keep it charged up to a stable 5V. This 2nd stage is another switching power supply. At no point in time is the 5V output ever electrically in contact with either of the 350 VDC input wires. There is probably some reason why this won't work or is impractical.
The lower I set my standards the more accomplishments I have.
(Score: 2) by Grishnakh on Wednesday March 07 2018, @06:43PM (1 child)
I was not aware of HVDC. My mention of transformers was in regard to high voltage AC transmission.
They've been using HVDC since the 1950s now. It's not new technology.
Yes, I understand we using switching power supplies. And maybe that is an effective way to step down your 200 or 350 VDC to a stable 12 V or 5 V for many common uses.
Maybe???? That's the ONLY way it's done now, powering any 12V or 5V (or less) system. Everything uses a switching supply now.
So maybe a DC to DC converter as you say. But this introduces additional inefficiency.
No, it doesn't (at least not any inefficiency that could be avoided in some other feasible way). Again, everything now uses a switching converter for stepping down 120VAC to whatever your small device uses. They wouldn't be doing this if it were inefficient. Efficiencies for these things are well into the 90% range. High-quality DC-DC converters are well over 95%.
At no point in time is the 5V output ever electrically in contact with either of the 350 VDC input wires.
Switching power supplies already do not have outputs electrically in direct contact with inputs, and many designs use transformers for galvanic isolation. Maybe you're thinking of those cheap little transformerless power supplies that you can implement with basically a diode and a couple capacitors. Really you should go look up switching power supplies and read about them before you talk any more, if you're worried about or interested in safety aspects, feasibility in modern power systems, etc. Wikipedia [wikipedia.org] has a decent article to start with, though it does look like it's a little dated in places to me.
(Score: 2) by DannyB on Wednesday March 07 2018, @09:29PM
What you say is interesting. I am clearly uninformed about switching power supplies. And HVDC.
The lower I set my standards the more accomplishments I have.