Originally Posted by
desbromilow
phase to phase fault started further up the line, and as the arc was established, the line impedance causes it to move towards the source (transformer) in order to reduce impedance - the closer it gets to the source, the more energy is released into the plasma ball, and it keeps moving until it gets to the source, or the supply protection (eg fuse) trips.
Given the flooding, I'd guess that the initial phase to phase fault may have been caused by a tree branch contacting the wires. - I was tree felling some years ago and a phase to phase fault caused by a 3/16" thick branch (with leaves) was enough to create this exact effect - it traveled about 400m before popping the transformer fuses.