How many volts per meter of Arc for a DRSSTC?
nzoomed, Sun Apr 24 2016, 12:18AMOr any tesla coil for that matter?
I used to think it was 1 Million Volts per meter for an arc, now i read its 3 Million volts per meter.
AFAIK, this is for breakdown voltage and then once the air is ionized, you can lower the voltage can drop and still arc.
Anyway, if my DRSSTC can make 2M or long arcs, then with the 3 Million volts rule, it would have to produce at least 6 million volts for 2 metres.
What really confuses me here is that people are saying on here and other forums that their tesla coils are only putting out around 400 - 500 KV.
Does this sound right?
Is frequency dependant on the arc length?
Im interested to know the physics involved, because perhaps tesla coils physics are different at such high frequency?
Re: How many volts per meter of Arc for a DRSSTC?
DekuTree64, Sun Apr 24 2016, 04:40PM
3 million per meter is the maximum that air can support before breakdown. But to maintain that voltage without sparking, you need large polished spherical electrodes. Smaller spheres, rough surfaces and pointy things will spark at much lower voltage.
In the case of Tesla coils, these rules only apply until the streamer "breaks out". After that, the high frequency makes it propagate differently than a DC spark.
DekuTree64, Sun Apr 24 2016, 04:40PM
3 million per meter is the maximum that air can support before breakdown. But to maintain that voltage without sparking, you need large polished spherical electrodes. Smaller spheres, rough surfaces and pointy things will spark at much lower voltage.
In the case of Tesla coils, these rules only apply until the streamer "breaks out". After that, the high frequency makes it propagate differently than a DC spark.
Re: How many volts per meter of Arc for a DRSSTC?
loneoceans, Sun Apr 24 2016, 11:41PM
That's right, typical Tesla Coil voltages are closer to high tens, to hundreds of kV for the largest coils.
Some of the most unusual ones are in QCW sparks where voltages (measured) are below 100kV though with spark lengths >2m or more.
loneoceans, Sun Apr 24 2016, 11:41PM
DekuTree64 wrote ...
3 million per meter is the maximum that air can support before breakdown. But to maintain that voltage without sparking, you need large polished spherical electrodes. Smaller spheres, rough surfaces and pointy things will spark at much lower voltage.
In the case of Tesla coils, these rules only apply until the streamer "breaks out". After that, the high frequency makes it propagate differently than a DC spark.
3 million per meter is the maximum that air can support before breakdown. But to maintain that voltage without sparking, you need large polished spherical electrodes. Smaller spheres, rough surfaces and pointy things will spark at much lower voltage.
In the case of Tesla coils, these rules only apply until the streamer "breaks out". After that, the high frequency makes it propagate differently than a DC spark.
That's right, typical Tesla Coil voltages are closer to high tens, to hundreds of kV for the largest coils.
Some of the most unusual ones are in QCW sparks where voltages (measured) are below 100kV though with spark lengths >2m or more.Re: How many volts per meter of Arc for a DRSSTC?
nzoomed, Mon Apr 25 2016, 11:40PM
Ok this confirms alot what i have observed, as i have had much longer sparks than the 3MV per metre rule even from things such as an ignition coil.
And i take it there are some significant physics involved with high frequency sources such as a tesla coil that reduce the voltage required considerably?
nzoomed, Mon Apr 25 2016, 11:40PM
loneoceans wrote ...
That's right, typical Tesla Coil voltages are closer to high tens, to hundreds of kV for the largest coils. Some of the most unusual ones are in QCW sparks where voltages (measured) are below 100kV though with spark lengths >2m or more.
DekuTree64 wrote ...
3 million per meter is the maximum that air can support before breakdown. But to maintain that voltage without sparking, you need large polished spherical electrodes. Smaller spheres, rough surfaces and pointy things will spark at much lower voltage.
In the case of Tesla coils, these rules only apply until the streamer "breaks out". After that, the high frequency makes it propagate differently than a DC spark.
3 million per meter is the maximum that air can support before breakdown. But to maintain that voltage without sparking, you need large polished spherical electrodes. Smaller spheres, rough surfaces and pointy things will spark at much lower voltage.
In the case of Tesla coils, these rules only apply until the streamer "breaks out". After that, the high frequency makes it propagate differently than a DC spark.
That's right, typical Tesla Coil voltages are closer to high tens, to hundreds of kV for the largest coils.
Some of the most unusual ones are in QCW sparks where voltages (measured) are below 100kV though with spark lengths >2m or more.Ok this confirms alot what i have observed, as i have had much longer sparks than the 3MV per metre rule even from things such as an ignition coil.
And i take it there are some significant physics involved with high frequency sources such as a tesla coil that reduce the voltage required considerably?
Re: How many volts per meter of Arc for a DRSSTC?
GrantX, Tue Apr 26 2016, 06:10AM
Somewhat related (and very cool), here's a 150 meter spark created by a 5.2MV Marx generator. I guess the voltage ramp-up as all the Marx stages fire could be doing something similar to the ramped DC bus in a QCW coil?
GrantX, Tue Apr 26 2016, 06:10AM
Somewhat related (and very cool), here's a 150 meter spark created by a 5.2MV Marx generator. I guess the voltage ramp-up as all the Marx stages fire could be doing something similar to the ramped DC bus in a QCW coil?
Re: How many volts per meter of Arc for a DRSSTC?
Uspring, Tue Apr 26 2016, 09:26AM
nzoomed wrote:
With an AC source, the charges from the initial corona will be sucked back through it, heating it up, creating more charge carriers and then pushed again through it producing more heat. Basically the initial tip will be extended by the hot channel at the beginning of the next cycle, so the arc can grow with each polarity reversal. This growth will eventually be limited by the resistance of the arc channel.
The current in the arc is not limited by the drift velocity as in the DC case. In the AC case, the current is caused by the arcs space charge capacity. This space charge is pushed and sucked back and forth. Therefore AC arcs can end in midair, unlike DC arcs.
Uspring, Tue Apr 26 2016, 09:26AM
nzoomed wrote:
And i take it there are some significant physics involved with high frequency sources such as a tesla coil that reduce the voltage required considerably?Consider a pointed tip at a high DC voltage. There will be enough field near it to cause a breakout, yielding corona. The charge carriers will spread out creating a ball of charge at which boundary the field is too low to induce further ionisation. From there on the charge carriers will just drift away. The current in the corona is limited due to the small drift velocity.
With an AC source, the charges from the initial corona will be sucked back through it, heating it up, creating more charge carriers and then pushed again through it producing more heat. Basically the initial tip will be extended by the hot channel at the beginning of the next cycle, so the arc can grow with each polarity reversal. This growth will eventually be limited by the resistance of the arc channel.
The current in the arc is not limited by the drift velocity as in the DC case. In the AC case, the current is caused by the arcs space charge capacity. This space charge is pushed and sucked back and forth. Therefore AC arcs can end in midair, unlike DC arcs.
Re: How many volts per meter of Arc for a DRSSTC?
DekuTree64, Tue Apr 26 2016, 07:00PM
DekuTree64, Tue Apr 26 2016, 07:00PM
GrantX wrote ...
Somewhat related (and very cool), here's a 150 meter spark created by a 5.2MV Marx generator. I guess the voltage ramp-up as all the Marx stages fire could be doing something similar to the ramped DC bus in a QCW coil?
Wow! And that's even a DC spark. Just goes to show that 3MV/meter is only a limit on how much voltage you can sustain without sparking, and not a limit on how long of a spark you can make with a given voltage. But that still seems unbelievably long... if things scale linearly, that means you should be able to make a 1.5 meter DC spark with 50kV. Even with pointy electrodes, extremely fast voltage rise, and large amount of energy available, I wouldn't have thought you could get that far.Somewhat related (and very cool), here's a 150 meter spark created by a 5.2MV Marx generator. I guess the voltage ramp-up as all the Marx stages fire could be doing something similar to the ramped DC bus in a QCW coil?
Re: How many volts per meter of Arc for a DRSSTC?
GrantX, Thu Apr 28 2016, 09:14AM
It's certainly a bit peculiar. There must be some kind of non-linear relationship that only starts to show itself around 1MV<. I wish I could find it again, but I remember reading about measurements done with a big SGTC in the 90's. With a smaller topload, the peak voltage between the topload and earth was very high, but the sparks weren't incredible. Adding a big topload increased the available charge and spark length, however the peak voltage was significantly lower.
If you can get such long discharges simply with a quick rise-time, then I wonder if there have been flashovers or arcing on the huge 1.1MV AC transmission power line in Russia.
GrantX, Thu Apr 28 2016, 09:14AM
It's certainly a bit peculiar. There must be some kind of non-linear relationship that only starts to show itself around 1MV<. I wish I could find it again, but I remember reading about measurements done with a big SGTC in the 90's. With a smaller topload, the peak voltage between the topload and earth was very high, but the sparks weren't incredible. Adding a big topload increased the available charge and spark length, however the peak voltage was significantly lower.
If you can get such long discharges simply with a quick rise-time, then I wonder if there have been flashovers or arcing on the huge 1.1MV AC transmission power line in Russia.
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