The principle of operation of most plasmatrons with a power from several kW to several megawatts is practically the same.
Between the cathode, made of a refractory material, and an intensively cooled anode, an electric arc burns. Through this arc, the working body (PT) is blown-a plasma-forming gas, which can be air, water vapor, or whatever. The ionization of PT occurs, and as a result, the output is the fourth aggregate state of matter, called plasma.
In powerful apparatuses along the nozzle a coil of electromagnet is placed, it serves to stabilize the plasma flow along the axis and to reduce the wear of the anode.
In this article, the second design is described; The first attempt to obtain stable plasma was not a particularly successful one. Having studied the device "Alplaza", we came to the conclusion that it is probably not worth repeating it one by one. If anyone is interested - everything is very well described in the instructions attached to it.
Our first model did not have active anode cooling. As a working fluid, steam was used from a specially constructed electric steam generator - a sealed boiler with two titanium plates immersed in water and connected to a 220V network. The cathode of the plasmatron was a 2 mm diameter tungsten electrode that quickly burned off. The diameter of the aperture of the anode nozzle was 1.2 mm, and it was constantly clogged. It was not possible to obtain a stable plasma, but there were still glimpses, and this stimulated the continuation of the experiments.
In this plasma generator, the steam-water mixture and air were tested as the working fluid. The output of the plasma was intensified with water vapor, but for stable operation it must be heated to a temperature of not one hundred degrees, so as not to condense on the cooled nodes of the plasmatron. Such a heater has not yet been made, so experiments are still continuing only with air.
Photos of the interiors of the plasmatron:
The anode is made of copper, the diameter of the nozzle aperture is from 1.8 to 2 mm. The anodic block is made of bronze, and consists of two hermetically welded parts, between which there is a cavity for pumping a cooling liquid - water or antifreeze.
The cathode is a slightly pointed tungsten rod with a diameter of 4 mm, obtained from a welding electrode. It is additionally cooled by the flow of a working fluid fed at a pressure of 0.5 to 1.5 atm.
Here is the completely disassembled plasmatron:
Power is supplied to the anode through the tubes of the cooling system, and to the cathode through the wire, attached to its holder.
Start, i.e. ignition of the arc, is performed by twisting the cathode feeding handle until it touches the anode. Then the cathode should be immediately withdrawn to a distance of 2..4 mm from the anode (a pair of revolutions of the handle), and between them the arc continues to burn.
Power supply, connection of hoses of air supply from the compressor and cooling system - in the following scheme:
As a ballast resistor, you can use any suitable electric heating device with a power of 3 to 5 kW, for example, to select several boilers connected in parallel.
The rectifier should be rated for current up to 20 A, our specimen contains about a hundred turns of thick copper wire.
Diodes fit any, designed for a current of 50 A and above, and a voltage of 500 V.
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The air compressor for the supply of the working fluid is taken by the automotive, and for the pumping of the cooling liquid through the closed circuit, an automotive washer of the glasses is used. Power supply to them is supplied from a separate 12-volt transformer with a rectifier.
A little bit about the plans for the future:
As practice has shown, this design also turned out to be experimental. Finally, a stable operation was obtained within 5 to 10 minutes. But to the full perfection is still far away.
Replaceable anodes are gradually burned out, and making them out of copper, and even with threading, is difficult, it would be better not to carve. The cooling system does not have direct fluid contact with the exchange anode, and because of this the heat exchange leaves much to be desired. More successful would be a direct-cooling option.
Details are machined from the available semi-finished products, the design as a whole is too complicated to repeat.
It is also necessary to find a powerful uncoating transformer, without it it is dangerous to use a plasmatron.
And at the end, still pictures of the plasmatron when cutting wire and steel plates. Sparks fly almost a meter