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Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
I'm kind of a newbie in the Tesla coil sort of area, but there's one thing thing that really baffles me:
When a Tesla coil (SGTC, SSTC, VTTC, DRSSTC etc) discharges into the air, how does it do that? In electronics, for a circuit to work the electrons must flow from one point to another to complete the circuit but in a Tesla coil it just discharges into the air?
How does this work? Has it got something to do with resonance?
Registered Member #4052
Joined: Thu Aug 11 2011, 04:43AM
Location: IN ,USA
Posts: 69
The way I understand it is, that the electricity in fact is flowing from one point to another. the topload of the coil is point #1 and the earth is point #2, the air acts as a highly resistive conductor. The reason a Tesla coil can do this is because its extremly high voltage and frequency allows it to over come the resistance of the air. I may be wrong though.
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
Józef C wrote ...
In electronics, for a circuit to work the electrons must flow from one point to another to complete the circuit
I suppose that's true, but it can be misleading! Capacitors pass an alternating current even though electrons are not flowing directly through the capacitor - the electric field is what drives current flow, so charge building up on one side of a capacitor can "push" charges away from the other side and cause a momentary current flow (this is a super-qualitative explanation of why capacitors generally like to pass higher frequencies). You can think of a Tesla coil discharge as a capacitor between the top of the coil and ground with the dielectric partially (or in the case of a ground strike) completely breaking down.
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
Daniel Kramnik wrote ...
Józef C wrote ...
In electronics, for a circuit to work the electrons must flow from one point to another to complete the circuit
I suppose that's true, but it can be misleading! Capacitors pass an alternating current even though electrons are not flowing directly through the capacitor - the electric field is what drives current flow, so charge building up on one side of a capacitor can "push" charges away from the other side and cause a momentary current flow (this is a super-qualitative explanation of why capacitors generally like to pass higher frequencies). You can think of a Tesla coil discharge as a capacitor between the top of the coil and ground with the dielectric partially (or in the case of a ground strike) completely breaking down.
I hope that helps!
Yes, that helps! There is still one thing. Like you said, the discharges of a Tesla coil are like "a capacitor between the top of the coil and ground with the dielectric partially (or in the case of a ground strike) completely breaking down." However, it doesn't seem to discharge to anything but air. The way I see your explanation is that the discharges somehow go to ground, but they don't appear to.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
Józef C wrote ...
Yes, that helps! There is still one thing. Like you said, the discharges of a Tesla coil are like "a capacitor between the top of the coil and ground with the dielectric partially (or in the case of a ground strike) completely breaking down." However, it doesn't seem to discharge to anything but air. The way I see your explanation is that the discharges somehow go to ground, but they don't appear to.
In a corona discharge like you describe, there is still a total electron flow going from the visible corona to the surrounding earth potential. It's just that there is an insufficient field remaining to cause an electron-avalanche plasma discharge in the atmosphere. Electrons continue to flow past the end of the visible light. Otherwise, KCL would be violated at the tips of the corona (as convoluted as circuit laws become in these instances, they still must always be obeyed, it just takes more thought to figure out exactly how they are fundamentally followed).
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
dude_500 wrote ...
Józef C wrote ...
Yes, that helps! There is still one thing. Like you said, the discharges of a Tesla coil are like "a capacitor between the top of the coil and ground with the dielectric partially (or in the case of a ground strike) completely breaking down." However, it doesn't seem to discharge to anything but air. The way I see your explanation is that the discharges somehow go to ground, but they don't appear to.
In a corona discharge like you describe, there is still a total electron flow going from the visible corona to the surrounding earth potential. It's just that there is an insufficient field remaining to cause an electron-avalanche plasma discharge in the atmosphere. Electrons continue to flow past the end of the visible light. Otherwise, KCL would be violated at the tips of the corona (as convoluted as circuit laws become in these instances, they still must always be obeyed, it just takes more thought to figure out exactly how they are fundamentally followed).
I'm getting it now, yeah. So the surrounding air acts as the earth potential when there is corona and it continues to discharge further beyond the visible light spectrum, and I presume this applies to streamers as well? No wonder they get thinner the further they stretch out...
There are always some electrons and positively charged ions floating around in the air. An electrode with a high e.g. positive voltage will attract the electrons and repel the ions. If the electric field is strong enough, the electrons will be accelerated enough on their way to the electrode to ionise air molecules, when they hit them. This creates new free electrons, which again are accelerated and so on. This avalanche leads to a visible discharge.
In a corona (DC) discharge from a positive electrode, the free electrons from the avalanche will be sucked into the electrode, while the ions are pushed away and eventually will reach the ground. So there is a continuous current from the electrode to ground. Ionisation takes only place near the electrode, where the electric field is high.
I believe, that streamers from a tesla coil (AC) are somewhat different. If, say, the breakout electrode is initially positive, it will create a cloud of positive ions around itself, like I described above. Then the voltage will reverse, so you have a negative electrode inside a local positive cloud. A discharge into the cloud will follow, electrons will be pushed away forming a negative cloud. Then the voltage will reverse again and so on.
There is not net charge transfer to the ground in this case. The charge will just oscillate between the toroid and the region around it. The streamers are more intensive than the DC corona due to the proximity of opposite charge near the electrode.
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Tesla Coil Discharge question
