Effect of the voltage pulse front steepness on the electric strength of polymers

We have studied the effect of the leading edge steepness of a high-voltage pulse front on the dielectric strength of 3-$\mu$m-thick polyethylene terephthalate film. It is found that its breakdown electric field strength increases logarithmically from 550 to 700 MV/m upon an increase in the voltage growth rate (pulse front steepness) from 2 to 70 GV/s. It is shown that the experimental data can be described using the concept of the ionization mechanism of polymer breakdown, which is not associated with the evolution of impact ionization in polymers, and accounting for the decrease in the overvoltage coefficient in a polymer dielectric upon an increase in the pulse front steepness.