wrote:

On Saturday, 14 April 2018 19:29:43 UTC+1, The Natural Philosopher wrote:

The OP is convinced that slow voltage surges are the problem not
fast high-voltage transients. However, this is just an
assumption - there might be fast transients causing insulation
breakdown. Nobody actually knows.

Therefore it would make sense to try and achieve a reasonable
bandwidth if it can be done with little extra effort.

It might be something completely different such as corrosion of the
elements.

Its an interesting problem. I will have a rummage around for a
suitable transformer and make some measurements and report back
in a few days.

John

Just to generalise, and by no means to accuse the OP, the commonest
cause of submerged element failure is probably allowing the water level
to get too low, or possibly displaced sideways if the vessel is not kept
horizontal.


--

Roger Hayter