Oops! Misread the chart. Still seems counter intuitive. Increase in humidity also increases breakdown voltage. Now throw a bucket of water an high voltage circuit.
Water behaves differently in gas form, also pure water is a very good insulator so it's no surprise to me. It's only when condensation forms and dissolved ionic compounds start to cause tracking does humidity cause problems with HV circuits.
I wonder if water vapour is a better insulator than air? This evidence would suggest that this is the case.
Interesting discussion. Keep in mind that the spec for the transformer was based on a fixed set of conditions including input voltage and load on the secondary. Manufacturing tolerances along with slight departures from design conditions might explain why 7 volts when you expect 6.3 volts. If your measurements were no load or open circuit you might try adding some kind of load.
The reason the volts are higher on the secondary is because my house is a steady 120v not 115.
Also the max altitude is most likely because of it benign sealed oil. Exceed that height and the thing probably pops like a small grenade.
I use it for a varietal voltage supply. I use it for bench testing that requires high draw. Example, transmitters or amplifiers (audio and RF). Ill take some pics and post them.
I would disagree - certainly water vapour encourages arcing at the final anode of a TV set.
Also, to help find the exact point where arcing may be prone to occur it's common practice to breath on the suspected points, and the water vapour (or beer fumes ) in your exhaled breath will start the arc forming.