Jim - 3/28/2017 21:48

A 600 kv line is a very high voltage power line. Maybe it's charged to "only" 350 kv but maybe not at all times. Even 350 kv is higher than most of the older lines.  What is most likely happening is that the current through the HV line above is inducing a current in your fence which is frying the chargers.  By the right-hand rule, a flow of current in a wire in the direction of your RH thumb causes an electrical field around the wire in the direction of your curled RH fingers. 

That field is doing the reverse in your fence: a field caused by the high voltage line will induce a current in your fence wire which is frying the electric fence chargers.

A current in a wire induces a field and a field induces a current in a wire.

I suspect the linemen you spoke with knew what the problem is, they just did not want to be the ones to tell you.

Some time ago there was someone on here who received a strongly shock when he was working on his combine feederhouse chain when under a high voltage line. If you take a standard flourescent lamp tube out under that line at night, the field will usually cause the flourescent light to glow just holding it in your hand.  The current in that line may vary through the day, depending on the grid demand where it serves.

I suspect the others that have not had problems under a high voltage line are running under one at less voltage, and/or running at a different angle to the line.

Is your fence running more or less parallel to the high voltage line above?  You might try crossing under the line at right angles and keeping any parallel fences a long way from the high voltage line. But still a matter of degree, especially when it does go up to 600 kv in the future.

It is NOT the fencer's fault, they are not designed to be back fed in from the fence.  Good luck.