The different dielectric strengths are defined as follows:
The dielectric strength of an isotropic insulating material in a
given physical condition is the maximum value of the electric
stress which it can withstand without breaking down [9]. The
puncture strength of insulators shows the value of AC voltage
which causes a puncture arc in the insulator. Impulse puncture
strength characterizes the insulator’s ability to withstand rapid
voltage impulses such as those caused by lightning. Practical
breakdown strength is an estimate of electric field strength that
most likely causes breakdown in a solid dielectric. It can be
used for theoretical estimations, but in real devices voltage
stresses only reach approximately 2% of this value for solid
dielectrics under normal operating conditions, to ensure
reliability of the insulation [5].