dangerous student electricity project?

On Wed, 12 Dec 2007 19:58:43 -0800, ChairmanOfTheBored


ERrr... that would be BPA.
BCA is the Billiard Congress of America.
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wrote:

That's Ok- I got it- point to point bulk transfer but with a T junction, as I recall. 500KV with possibly some 765KV stuff on the AC sides.
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Don Kelly snipped-for-privacy@shawcross.ca
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Rice cake looking thyristors from Siemens? That are about 8 inches in diameter. Stacks of them to convert the AC to DC.
Used to be huge vacuum mercury arc rectifiers. Prolly some of the biggest "vacuum tubes" in existence.
Up in abse I posted a pic.
My caption is usually: "Mine is bigger than yours" :-]
Note the desk and chair in the picture for scale.
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----------------------------
wrote:

------------- ---------- These aren't breakers and aren't meant to interrupt current- they are isolating switches. If one attempted to use one to clear a fault- then there would be real fireworks (and likely destruction of the switch without clearing- opening on normal load current is also not recommended but spectacular). The breakers have contacts completely enclosed (no fireworks unless it explodes) and use forced oil, pressurized air or Sulphur Hexafluoride and can be quite compact. In these the gaps are fairly small. The idea is to build up pressure which is held back by the arc plasma and when this dies at current zero- replace it with good dielectric by blasting air, oil or SF8 through a few fairly small series gaps of the order of 1 inch ( a 1950's air breaker operated at 400psi and 161KV had 4 gaps of the order of 1 inch each). With an air breaker, there is a big bang but no fireworks. The others are quieter. Breakers are fascinating as at high voltage brute force opening of a switch is simply not adequate. A movie made may years ago showed a test where a grounded wire was thrown across a 230KV line. The wire vaporised and the arc wandered all over the place-extending 30 ft before it was quenched.

---------- They don't have breakers on the DC side but can gate off the thyristors so that when the supply current goes to 0, the thyristor leg stops conducting in order to kill a fault quickly. There will be breakers on both AC sides. There have been many attempts to make HV DC breakers but so far the results have been poor- Basically they use an AC breaker and with a lot of added complications superimpose an AC current across the breaker contacts to force current zeros. This has been found to be very expensive. With AC, the effectiveness of the breakers means that one can have a network but with DC, that is out of the question and even a T connection may involve 3 rectifier/inverters "back to back". So DC is point to point long distance bulk transfer or ties between two systems which may be at different frequencies (or not connected by AC for stability reasons) or for long underwater cables. Economics of DC vs AC favor these applications and the ease of voltage level optimisation with transformers is available only with AC --------------

-- look at a 765KV substation some time-Take your binoculars. Do it in a "wet" snow storm and start estimating the distance from the hot end to where you are and the distance from you to where the insulator is "winking".
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Don Kelly snipped-for-privacy@shawcross.ca
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----------------------------

----------- This is also true with low voltage AC and, in fact the problem with arcing is decreased.
The key point is low voltage, not AC vs DC.
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Don Kelly snipped-for-privacy@shawcross.ca
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No shit.
However, in the setting he is in, with the things that are available to him, like the wall outlet, which is a fairly HIGH voltage source for this application, or a DC source, like a dongle from Radio Shack, which is most assuredly of a low enough voltage not to matter.
Unlike those of us with labs and all manner of voltage sources at hand, he has very few choices, so my mere mention AC over DC is valid due to the fact that the voltage for the AC is a given to be rather high, and the voltage for nearly any DC source he would use would be a given to be a fairly low number.
I guess if all I did was mention the type of light bulb to include, you all wouldn't be nit picking like this. I did mention a DC light bulb socket, and nearly all of those are low voltage as well.
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ChairmanOfTheBored wrote:

And you also mentioned *low voltage DC* : " With low voltage DC, the most that can happen would be a hot wire causing a burn in the event of a short. Not really much else could happen."
It is clear that's what you were talking about. No need to identify the bulb.
Ed
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----------------------------

You did mention low voltage DC and the implication in what you said is that AC is dangerous and DC is not.
Quote:
"Yes, AC can be dangerous. If there are any exposed contacts, then the

This is what you said and as it stands- is subject to interpretations that have been given. It may not be what you thought or intended to say but as it was expressed, left a lot for others (particularly the person who in following your advice, then lugs in an automotive battery ands finds that a short is anything but minor).
So, on the basis of what you initially said, not what you modified it to be, your mere mention is not valid as it is misleading.
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Don Kelly snipped-for-privacy@shawcross.ca
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----------------------------

Exactly! The person who asked the question doesn't know or he wouldn't have asked the question. I know what you meant even if you were incapable of stating it clearly, but he didn't and could make some dangerous assumptions.
My point stands. Have a good day
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Fuck you. I am quite capable of detailing every little iota. I just didn't think it necessary to go beyond the quick observation I made at the moment, and I think he understood just fine.

Doubtful.

No. You mouthyness stands.

I will... laughing even.
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Bayou Self wrote:

Assuming that this is intended to be a learning experience, I would suggest that there are two alternatives:
1) Learning by trial and error and experimentation
2) Learning from an expert (eg book or person)
The first is arguably more fun. However, allowance has to be made for errors. Either there needs to be someone present to step in when things get potentially dangerous - or the capacity for danger has to be intrinsically low. This means having someone present if the energy source is powerful enough to kill, seriously injure or cause a fire. Which "household current" is. A potential fire risk exists, even with GFCI and a circuit fused at 1A.
The second is arguably more efficient and certain. However, a book without tutorial support can lead to misunderstanding and error.
Thus, if someone is present with enough expertise to protect the student from errors which could be fatal - by all means let him use mains power, wiring and equipment. The "someone present" could simply be someone that the student calls when he is ready to apply mains power - who examines the system and gives the OK to apply power.
If no such person is available - then a low voltage, low energy, power source will ensure that his learning experience of terminals isn't terminal. Note "low energy" - giving students multi ampere hour "car batteries" to play with is arguably more dangerous than a mains outlet..
As is common, I learnt by trial and error using 240v 15A outlets, large lead acid batteries, etc. In days when Boots the chemist would sell a teenager flowers of sulphur, saltpetre, etc over the counter. A teenager with the odd burn or two could go to casualty without the parents being given the third degree by Social Services.. My parents were of the "Better drowned than duffer - if not duffer, won't drown" school. However, in the UK at least, society has moved on to more "enlightened" attitudes..
--
Sue











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| My son needs me to help him with a school project--a simple circuit | with a switch. He said he wants to use a light bulb, a switch, and | have it plug into the wall. Is this inherently dangerous? BTW, he's in | 9th grade and says he saw a setup like this on the teacher's desk.
I thought they quit using the Darwin effect to raise the average IQ.
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|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On 9 Dec 2007 17:21:44 GMT, snipped-for-privacy@ipal.net wrote:

So much for you thinking, Darwin boy.
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wrote: | On 9 Dec 2007 17:21:44 GMT, snipped-for-privacy@ipal.net wrote: |
|> |>| My son needs me to help him with a school project--a simple circuit |>| with a switch. He said he wants to use a light bulb, a switch, and |>| have it plug into the wall. Is this inherently dangerous? BTW, he's in |>| 9th grade and says he saw a setup like this on the teacher's desk. |> |>I thought they quit using the Darwin effect to raise the average IQ. | | | So much for you thinking, Darwin boy.
OK, so they still use the Darwin Effect. How did you get past it?
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|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On 10 Dec 2007 01:20:18 GMT, snipped-for-privacy@ipal.net wrote:

It had to be the same way you slipped through mensa's fingers.
The only difference is that I am a rising star, and you are on your way over the event horizon of the black hole of Darwinism.
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wrote: | On 10 Dec 2007 01:20:18 GMT, snipped-for-privacy@ipal.net wrote: | |>On Sun, 09 Dec 2007 09:29:28 -0800 ChairmanOfTheBored
|>|
|>|> |>|>| My son needs me to help him with a school project--a simple circuit |>|>| with a switch. He said he wants to use a light bulb, a switch, and |>|>| have it plug into the wall. Is this inherently dangerous? BTW, he's in |>|>| 9th grade and says he saw a setup like this on the teacher's desk. |>|> |>|>I thought they quit using the Darwin effect to raise the average IQ. |>| |>| |>| So much for you thinking, Darwin boy. |> |>OK, so they still use the Darwin Effect. How did you get past it? | | | It had to be the same way you slipped through mensa's fingers. | | The only difference is that I am a rising star, and you are on your way | over the event horizon of the black hole of Darwinism.
I avoided that foolish group by simply not going anywhere near them. So you stayed away from anything dangerous?
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On 11 Dec 2007 15:10:03 GMT, snipped-for-privacy@ipal.net wrote:

Stars are, by their very nature... dangerous. So are black holes. One is simply more fun than the other.
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