Which material has high enough ohmage to resist lightning?

[Sjouke Burry]

Damn, John, now you're REALLY going to send Radium, et
al, down a rathole.....

I'll get the popcorn...

Bob M.

I have already eaten it.

 

[Tim Williams]

Up to the breakdown point, I think you'll find that
the I vs. V curve for a reasonable amount of separation in a
vacuum is pretty damned flat...

Unless the electrodes are made of Mexican cobalt. ;-)

Tim

 

[Michael A. Terrell]

I have already eaten it.

Damn! It was for the rats, so they would follow Radium into the
hole.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[jasen]

Doesn't a vacuum has very *low* resistance?

heat the negatively charged end and it has a relatively low resistance.
(see thermionic tube)

when cold untill you get the voltage high enouh to extend the
electron orbitals across the gap or to strip ions off one electrode
it's an insulator.

Or are you referring to the
stuff around the vacuum? What is the insulation covering the vacuum
made of?

typically some sort of glass, a cheap, relatively good, insulator, only
problem is how brittle it is.

Bye.
Jasen

 

[Bob Myers]

heat the negatively charged end and it has a relatively low resistance.
(see thermionic tube)

Ummm...which is the "negatively charged end" of a vacuum?


Bob M.

 

[Radium]

heat the negatively charged end and it has a relatively low resistance.
(see thermionic tube)

when cold untill you get the voltage high enouh to extend the
electron orbitals across the gap or to strip ions off one electrode
it's an insulator.

Interesting, how some materials lose resistance when cooled while
others lose resistance when heated.

typically some sort of glass, a cheap, relatively good, insulator, only
problem is how brittle it is.

What is the breakdown voltage of the glass?

 

[w_tom]

Interesting, how some materials lose resistance when cooled while
others lose resistance when heated.
...

What is the breakdown voltage of the glass?

Breakdown voltage for air is about 75 kvolts per inch. For glass, it
could be as high as 3,000 kv per inch. But this becomes irrelevant.
Question was about voltages found in lightning. Other factors change
those numbers. Three miles of air - a best insulator - could not stop
lightning. We don't even try. We solve the problem by diverting -
shunting. Diversion means that voltage does not exist. Dominant
factor in lightning is not its voltage. Lightning is a current source
- an electrical concept necessary to better understand the problem.

Furthermore, you are asking about resistance - DC electricity.
Lightning is an AC source. Therefore ask about both resistance AND
reactance.

To better answer your question, provide what it is you are trying to
understand. Your question about insulating from voltages such as
lightning assumes lightning can be stopped - when even three miles of
air could not insulate sufficiently.

 

[John Fields]

Interesting, how some materials lose resistance when cooled while
others lose resistance when heated.

---
Yes, That's called the temperature coefficient of resistance of the
material in question.
---

What is the breakdown voltage of the glass?

What do you need it to be?

 

[Radium]

Furthermore, you are asking about resistance - DC electricity.
Lightning is an AC source. Therefore ask about both resistance AND
reactance.

Some sources describe lightning as being neither AC nor DC but *much*
closer to DC than AC. Others state that lightning is AC. Who should I
beleive?

 

[Radium]

Preferably infinite. LOL

 

[Homer J Simpson]

Some sources describe lightning as being neither AC nor DC but *much*
closer to DC than AC. Others state that lightning is AC. Who should I
beleive?

It's DC but it's an impulse.

 

[Radium]

It's DC but it's an impulse.

True. AFAIK, a smooth sine-wave current [DC or AC] can only be produced
artificially. Of course I could be wrong.

 

[Homer J Simpson]

It's DC but it's an impulse.

True. AFAIK, a smooth sine-wave current [DC or AC] can only be produced
artificially. Of course I could be wrong.

Think of a freight train hitting a cement wall. It mostly goes in one
direction but there's a lot more going on.

 

[John Fields]

Preferably infinite. LOL

 

[default]

Good idea. I remember reading about a small (relatively speaking)
Tesla coil that was supposed to be able to produce a few million
volts. It was in a large horizontal oil bath.

One of the benefits of oil - gets in all the tight spaces and prevents
corona which leads to insulation failure and lowers breakdown voltage.

Radium needs to build a few Tesla coils for an appreciation of
insulators.

 

[jasen]

Ummm...which is the "negatively charged end" of a vacuum?

the end with the negative charge attached.

 

[John Fields]

Good idea. I remember reading about a small (relatively speaking)
Tesla coil that was supposed to be able to produce a few million
volts. It was in a large horizontal oil bath.

One of the benefits of oil - gets in all the tight spaces and prevents
corona which leads to insulation failure and lowers breakdown voltage.

Radium needs to build a few Tesla coils for an appreciation of
insulators.

 

[w_tom]

A basic engineering and a basic mathematical concept: an impulse is a
sum of AC waveforms at many frequencies. The shorter that impulse,
then the more AC frequencies are in that impulse.

The term DC impulse is a contradiction or oxymoron. Either it is an
impulse - a sum of many frequencies - or it is DC.

For example, to determine the frequency response of a circuit, we
apply an ideal impulse. That ideal impulse applies every frequency to
the circuit. Circuit output is then captured to learn how well each
frequency transverses the circuit.

Many AC frequencies in lightning that make lightning challenging;
requires both resistance and reactance considerations. Those many AC
frequencies also appear as noise in radio reception. Lightning is AC.
Impulses are summations of energy in many frequencies - AC. That
concept is demonstrated in both advanced mathematics and in basic
engineering education. To appreciate the concept, get a first year
electrical engineering book and read about impulses. Concept is that
fundamental. A DC impulse is speculation often found where the math
and engineering were not first learned.

It's DC but it's an impulse.

True. AFAIK, a smooth sine-wave current [DC or AC] can only be produced
artificially. Of course I could be wrong.

 

[Radium]

A basic engineering and a basic mathematical concept: an impulse is a
sum of AC waveforms at many frequencies. The shorter that impulse,
then the more AC frequencies are in that impulse.

The term DC impulse is a contradiction or oxymoron. Either it is an
impulse - a sum of many frequencies - or it is DC.

For example, to determine the frequency response of a circuit, we
apply an ideal impulse. That ideal impulse applies every frequency to
the circuit. Circuit output is then captured to learn how well each
frequency transverses the circuit.

Many AC frequencies in lightning that make lightning challenging;
requires both resistance and reactance considerations. Those many AC
frequencies also appear as noise in radio reception. Lightning is AC.
Impulses are summations of energy in many frequencies - AC. That
concept is demonstrated in both advanced mathematics and in basic
engineering education. To appreciate the concept, get a first year
electrical engineering book and read about impulses. Concept is that
fundamental. A DC impulse is speculation often found where the math
and engineering were not first learned.

It's DC but it's an impulse.

True. AFAIK, a smooth sine-wave current [DC or AC] can only be produced
artificially. Of course I could be wrong.

AC -- by definition -- requires that the current reverse its flow.

A changing voltage isn't necessarily AC. Its only AC if the current
changes direction. Otherwise its still DC.

A DC impulse is a impulse that -- for a relatively short duration --
increases its strength of flow toward one direction and then stops,
without reversing its flow.

An AC impulse does similar but instead of stopping, it will increase
its strength of flow in the opposite direction and then stop at zero
volts.

 

[John Fields]

AC -- by definition -- requires that the current reverse its flow.

A changing voltage isn't necessarily AC. Its only AC if the current
changes direction. Otherwise its still DC.

A DC impulse is a impulse that -- for a relatively short duration --
increases its strength of flow toward one direction and then stops,
without reversing its flow.

---
No.
+V _
| |
This is an impulse: 0V__| |__

+V ___________________________________________
Strictly speaking, |
This is not: 0V__|

---