Author Topic: Estimating spark length voltage  (Read 1843 times)

Offline oneKone

  • High Voltage Engineer
  • ****
  • Posts: 235
  • Karma: +3/-0
    • View Profile
Estimating spark length voltage
« on: September 06, 2017, 02:29:57 AM »
Hey,
A while ago (about 7 years) I read somewhere that a general rule of thumb for estimating a spark length is 1kv for 1mm. I've been blindly using this concept without actually looking into it. I've tried to find some answers but it seems my Google skills are not upto the task!

So basically the question is, is 1kv equal to 1mm or is this far from accurate....... I'm equating my 400mm spark length on my sstc is 400kv.

Cheers,
Chris
« Last Edit: September 06, 2017, 09:59:10 AM by Mads Barnkob »

Offline Mads Barnkob

  • Administrator
  • High Voltage Senior
  • *****
  • Posts: 926
  • Karma: +11/-0
  • Denmark
    • View Profile
    • Kaizer Power Electronics
Re: Estimating spark length voktage
« Reply #1 on: September 06, 2017, 09:58:05 AM »
The old 10 kV/cm rule does not apply here, I seem to recall that it is for DC current between pointy objects, the attached short description goes into further detail on the required breakdown voltage for different spark gap geometries.

Tesla coils does however operate quite differently. We charge up a topload, secondary top capacitance, with as many electrons as possible, before the voltage is high enough to break down the dialectric strength of atmospheric air. This can differ with temperature, moisture and pressure.

The topload voltage will always be the greatest just before there is a spark formed, as this is when the charge is at its highest, once the spark starts to grow it represents a larger and larger load to the topload and as current goes up while discharging the energy, the voltage drops significantly.

This is just a bold statement, that for a Tesla coil we are more in the league of 3 kV/cm for long sparks. Terry Fritz once made some measurements on this: https://deanostoybox.com/hot-streamer/TeslaCoils/MyPapers/planant/waveant3.html

Hydron also posted a lot of topload/breakout point current measurements, these numbers can be used to calculate the topload voltage: https://highvoltageforum.net/index.php?topic=117.msg735;topicseen#new
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline Uspring

  • High Voltage Experimenter
  • **
  • Posts: 80
  • Karma: +5/-0
    • View Profile
Re: Estimating spark length voltage
« Reply #2 on: September 06, 2017, 04:47:14 PM »
The differences between DC and AC arcs are mainly 2: An AC arc can end in midair and it usually lasts much longer. The AC arc can grow over many cycles by current flowing back and forth along it, keeping it hot. So once a small arc has broke out, it will establish a conductive channel to its tip from where the arc can grow further. The arc channel won't be a perfect conductor, so the voltage at its tip will gradually decrease as it gets longer. This will basically limit its length. In principle arc length and voltage don't even have to be linearly related. Probably higher frequency arcs are also longer for a given voltage, since charges are more often pushed back and forth, making it hotter and more conductive.

If you're into math, you might want to read https://www.pupman.com/listarchives/2012/Oct/msg00125.html

A back of the envelope calculation based on Hydrons data seems to indicate a voltage of about 300kV for an arc length somewhat above 2 m, i.e. 1.5kV/cm.

Offline oneKone

  • High Voltage Engineer
  • ****
  • Posts: 235
  • Karma: +3/-0
    • View Profile
Re: Estimating spark length voltage
« Reply #3 on: September 07, 2017, 01:40:46 AM »
Cheers for the replies and the links. Looking forward to understanding further

Offline AndreiRS

  • High Voltage Experimenter
  • **
  • Posts: 56
  • Karma: +0/-0
    • View Profile
Re: Estimating spark length voltage
« Reply #4 on: February 17, 2018, 12:12:40 AM »
I couldn't get an arc from a mot with 2kv output, at something like 0.3 maybe 0.4mm. It depends a lot on air humidity.

High Voltage Forum

Re: Estimating spark length voltage
« Reply #4 on: February 17, 2018, 12:12:40 AM »

 


* Recent Topics and Posts

post Re: WTS [EU]: UD2.7 thru hole pcb
[Sell / Buy / Trade]
FilipŠebík
Today at 08:39:46 AM
post Re: UD 2.7C Build
[Dual Resonant Solid State Tesla coils]
Thunderstruck
Today at 08:35:33 AM
post Re: Chinese MOSFETS/IGBTS
[Solid state Tesla coils]
flyrod
Today at 04:07:24 AM
post Re: Chinese MOSFETS/IGBTS
[Solid state Tesla coils]
Thunderstruck
March 23, 2019, 10:07:54 PM
post Re: WTS [EU]: UD2.7 thru hole pcb
[Sell / Buy / Trade]
Mads Barnkob
March 23, 2019, 04:07:55 PM
post WTS [EU]: UD2.7 thru hole pcb
[Sell / Buy / Trade]
Fumeaux
March 23, 2019, 02:12:48 PM
post Re: UD 2.7C Build
[Dual Resonant Solid State Tesla coils]
Thunderstruck
March 23, 2019, 08:03:58 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
March 23, 2019, 01:50:47 AM
post Re: Chinese MOSFETS/IGBTS
[Solid state Tesla coils]
Hydron
March 23, 2019, 12:11:10 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
badpeter
March 22, 2019, 08:19:21 PM
post Re: Chinese MOSFETS/IGBTS
[Solid state Tesla coils]
profdc9
March 22, 2019, 06:39:37 PM
post Chinese MOSFETS/IGBTS
[Solid state Tesla coils]
Fumeaux
March 22, 2019, 05:51:55 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
March 22, 2019, 03:46:16 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
kamelryttarn
March 22, 2019, 11:25:19 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
Mads Barnkob
March 22, 2019, 10:56:16 AM
post Re: looking for PCB creating software
[Printed Circuit Board]
Teravolt
March 22, 2019, 06:02:15 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
badpeter
March 21, 2019, 11:04:48 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
Hydron
March 21, 2019, 07:51:23 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
badpeter
March 21, 2019, 07:09:05 PM
post Re: looking for PCB creating software
[Printed Circuit Board]
kamelryttarn
March 21, 2019, 02:26:09 PM
post Re: GDT Experiments
[Solid state Tesla coils]
Uspring
March 21, 2019, 11:57:53 AM
post Re: GDT Experiments
[Solid state Tesla coils]
Teravolt
March 20, 2019, 11:15:50 PM
post Re: GDT Experiments
[Solid state Tesla coils]
Thunderstruck
March 20, 2019, 09:07:04 PM
post Re: Keep or throw away ?
[Beginners]
Teravolt
March 20, 2019, 05:18:07 PM
post Re: New small SSTC
[Solid state Tesla coils]
Bambinz
March 20, 2019, 03:52:15 PM
post Re: New small SSTC
[Solid state Tesla coils]
Mads Barnkob
March 20, 2019, 01:23:52 PM
post Re: GDT Experiments
[Solid state Tesla coils]
T3sl4co1l
March 20, 2019, 01:18:29 PM
post Re: GDT Experiments
[Solid state Tesla coils]
Mads Barnkob
March 20, 2019, 01:06:24 PM
post Re: cute-qcw Tesla Coil
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
March 20, 2019, 01:00:46 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
Mads Barnkob
March 20, 2019, 12:41:22 PM
post Re: Keep or throw away ?
[Beginners]
Thunderstruck
March 19, 2019, 10:02:41 PM
post Re: Keep or throw away ?
[Beginners]
Hydron
March 19, 2019, 08:14:33 PM
post Re: Keep or throw away ?
[Beginners]
Teravolt
March 19, 2019, 05:12:03 PM
post Re: Welcome new members, come say hello and tell a little about yourself :)
[General chatting]
Experimentonomen
March 19, 2019, 01:32:32 PM
post Re: Welcome new members, come say hello and tell a little about yourself :)
[General chatting]
Mads Barnkob
March 19, 2019, 12:20:34 PM
post Re: Strange gdt waveforms
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
March 19, 2019, 12:15:22 PM
post Re: Which varnish to use to coat the Secondary?
[Solid state Tesla coils]
Mads Barnkob
March 19, 2019, 10:46:50 AM
post Re: Keep or throw away ?
[Beginners]
Thunderstruck
March 19, 2019, 09:11:09 AM
post Re: Keep or throw away ?
[Beginners]
Mads Barnkob
March 19, 2019, 08:24:31 AM
post Re: Keep or throw away ?
[Beginners]
Teravolt
March 19, 2019, 01:51:51 AM
post Re: Keep or throw away ?
[Beginners]
Thunderstruck
March 18, 2019, 09:56:42 PM
post Re: cute-qcw Tesla Coil
[Dual Resonant Solid State Tesla coils]
Weston
March 18, 2019, 07:55:52 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
March 18, 2019, 06:11:07 PM
post Re: Strange gdt waveforms
[Dual Resonant Solid State Tesla coils]
Hydron
March 18, 2019, 02:27:35 PM
post Re: cute-qcw Tesla Coil
[Dual Resonant Solid State Tesla coils]
Uspring
March 18, 2019, 12:52:35 PM
post Re: Strange gdt waveforms
[Dual Resonant Solid State Tesla coils]
FilipŠebík
March 18, 2019, 12:22:58 PM
post New small SSTC
[Solid state Tesla coils]
Bambinz
March 18, 2019, 11:46:18 AM
post Re: Welcome new members, come say hello and tell a little about yourself :)
[General chatting]
Bambinz
March 18, 2019, 11:29:02 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
Mads Barnkob
March 18, 2019, 10:35:04 AM
post Re: Strange gdt waveforms
[Dual Resonant Solid State Tesla coils]
Marty
March 18, 2019, 05:32:43 AM

Sitemap 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30