So if the max voltage is 28000 volts (rms) then the overhead lines have to be able to withstand a peak of almost 40,000 volts, yes it's only at a peak for microseconds but Electrical voltage is better understand as being Electrical Pressure.
If the insulation isn't up to 40,000 it will break down.
Now to clear a Myth, is Water a conductor?
Rain Water cann't be otherwise in every rain storm overhead lines would blow up.
As a matter of physics it depends on the voltage and the purity of the water. lots of ions (ie, sea salt) dissolved+ more conductivity, Higher voltage = more conductivity (because the H2O moleule becomes more ionized itself to H+ and OH-).
As a matter of engineering. Rain drops are small and don't conduct from the overhead line to the ground because there is no continutous stream of water. The insulators are of interesting shapes. i have always assumed that one reason for this was to prevent a continuous surface water film forming on them.
