HV arching within a semi enclosed space...

You seem to be describing a device known as a "Jacob's Ladder". The spark starts at the bottom of the "rabbit ears" and travels up to the top.

The corrosion you see is likely caused mostly by the buildup of ozone inside the plexi chamber. The arc exciteds the oxygen in the air and turns some of it into ozone, which is very corrosive in high concentrations. I'm not at all surprised that it corrodes items inside the plexi.

The liquid is another matter. It could be a residue from the ozone breaking down the copper or some other item(s) in the chamber. Or it could be a weak nitric acid compound formed by the arc and the nitrogen + humidity present in the chamber.

To lessen the corrosion, you could try drilling more holes in the chamber (especially down low, since ozone is slightly heavier than air). You may even have to mount a small fan to the chamber to force fresh air in. That won't stop corrosion completely, but it may slow it somewhat. The rabbit ears will degrade a little over time just from the arc itself.

And you won't stop acid formation unless you lower the ambient humidity. This may be more trouble than it's worth to you. You might prefer to just clean the unit on a frequent basis.

Hi,

The device you have is a often called a Jacob's Ladder or horn gap. Although "cold" corona discharges will generate ozone, hotter sparks and arcs (such as in your display) tend to generate generate various oxides of nitrogen. While ozone is a powerful oxidizer, it is not the source of your problems. Heat is the enemy of ozone - the hot arcing discharges will actually tend to destroy any ozone that may be in the area.

Hotter electrical discharges (such as arcs, sparks, and even lightning) generate various oxides of nitrogen that can ultimately create nitrous and nitric acids. The heat of the electrical arc breaks up the nitrogen-nitrogen bonds of the nitrogen (N₂) in the air, oxidizing it to create nitric oxide (or nitrogen monoxide) via the following reaction:

Electrical Discharge

N₂ + O₂ ------------------> 2 NO

The nitric oxide then quickly combines with oxygen in the air to form nitrogen dioxide, a brownish colored, and very toxic gas:

2 NO + O₂ ---------------> 2NO₂

Finally, the nitrogen dioxide then combines with water vapor in the air to form nitrous and nitric acids:

2 NO₂ + H₂O -------> HNO₃ + HNO₂

The resulting nitric and nitrous acids are responsible for corroding your copper rods and other metals in the vicinity, such as your transformer terminals and case. When the acid vapors condense on the surface of the Plexiglas, it causes the surface to become partially conductive, resulting in partial discharges, corona, and finally the electrical tracking that you observe.

You may be able to reduce or prevent these problems by changing the rod material to stainless steel, and increasing the ventilation in the chamber. You could also try operating the Jacobs ladder intermittently to allow the acid vapors to dissipate rather than building up. Finally, placing a tray containing a thin layer of a chemical base, such as calcium carbonate or sodium bicarbonate, may help to neutralize the acids that are formed. The tray may need to be periodically replenished if the system is used continuously.