consécutif à une surtension

16:50 Jun 6, 2015 

It's always useful to know what it is the writer is talking about. See http://en.wikipedia.org/wiki/Varistor, in which:
"A varistor remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its "clamping voltage", thus varistors are typically used for suppressing line voltage surges. However, a varistor may not be able to successfully limit a very large surge from an event like a lightning strike where the energy involved is many orders of magnitude greater than it can handle".
So yes, the current increases massively when the voltage rises above the design threshold.