It's very likely capacitance. At 200kV even a couple dozen meters above ground the capacitance would be enough to get a couple microamps over an arch (it would

It's very likely capacitance. At 200kV even a couple dozen meters above ground the capacitance would be enough to get a couple microamps over an arch (it would likely tickle a bit). AC makes isolating rather complicated since increasing your resistance to ground naturally turns you into a capacitor which acts like a resistor in AC (which is why thin rubber soles on your shoes don't protect you, you want think ones to increase resistance and decrease capacitance) so a small current will flow. At high voltage this small current can still be transmitted over an plasmaarc.