dangerous student electricity project?

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---------- 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

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-- 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".

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.

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.

On Wed, 12 Dec 2007 19:53:50 -0800 ChairmanOfTheBored wrote: | On 12 Dec 2007 15:15:18 GMT, snipped-for-privacy@ipal.net wrote: | |>On Wed, 12 Dec 2007 01:26:44 -0800 ChairmanOfTheBored wrote: |>| On 12 Dec 2007 06:02:11 GMT, snipped-for-privacy@ipal.net wrote: |>| |>|>At a safe voltage level, yes, DC is actually a very good choice to work with. |>|>But AC is not that bad, either. Both have their uses in experimental study. |>| |>| |>| Not at the basic, lesson one, first learning experiment level. |>

|>Not what? DC or AC? |>

|>So, how much is it going to take to just get you to say "I should not have |>said that DC is safer than AC ... I should have said low voltage is safer |>than high voltage right from the start ... I knew that, really I did"? | | | How about: "F*ck off... really you should..."?

Sure, go ahead, say that. Then we'd know you a lot better. And more people would put your address in their kill file.

I am curious. What kinds of shocks have readers of this newsgroup experienced.

I started high school toward the end of WWII. Some vacuum tubes were difficult to get. One technique to repair (usually very temporary) open heaters was called flashing.

In my case, I used an old Philco as my power source. It used a type 80 rectifier in a full wave rectifier circuit. About 750VAC from the power transformer was applied between the two plates.

To flash, I plugged test leads into the socket connections for the plates. The idea was to momentarily connect the leads to the opened heater's pins. Most of the time, it was possible to connect across the heater's break. With a little practice, it was possible to weld the heater's break.

Well, one time I got across the transformer winding.

Bill

This is classic Dimbulb behavior. Killfile him and be done with it. ...or continue to poke it with a stick to see it flinch. It's all the same.

When I was in high school I got nailed, twice, by the plate supply on my 100ish watt transmitter. That was 750VDC. It must have been on, idling, on the bench all day because I came home from school and was poking around - ZAP => OW! That *hurt*!

I was working in one of the labs in college (I was a tech working for the EE department) and got nailed by the 120VAC on one of the benches. Some idiot had wired the switch in the neutral side. I got tingled once and thought it was a fluke, then *WHAM*! I spent a while walking that one off, before I could get myself go in and figure out what was happening.

I already related mine at 10kV. I'm sure it was a lot less with me as a load.

You're the only "it" in this group, f*****ad.

Damn! Wasn't enough to rid us of your retarded ass though.

Keep poking.

One can only hope.

I guess you were a dummy load.

Bill

No. I was smart before that event.

Now, (neck twitch)... I am the sanest (neck twitch) guy in the entire news(neck twitch) group. :-]

Nah, I'm better than that.

Yep, unlike you, I've learned a lot by poking. You should try it sometime (learning something, that is).

Apparently even the hopeless have hope.

Why don't you go play in mommy's laundry some more, Dimmie?

To increase the effectiveness of the GFI I suggest the student splash salt water on the concrete floor and stand barefooted in it. Otherwise I suggest you leave the GFI at the HomeDepot. Chuck

Some people won't have enough of a sense of humor to laugh at your joke - or even recognize that is what it is. I suppose, since it concerns safety, that they are right. Also, there are those who have no clue about how a GFCI works or the safety benefit it can provide, so they might actually believe what you posted.

It is probably wiser not to joke about safety, and it is definitely wiser to use the GFCI as Bill recommended.

Ed