Dielectric Strength & Breakdown Potential

Dielectric Strength:

As we know that the dielectrics are the insulators which don't have free charges to conduct electricity. To get free charges from the atoms of a material we will have to apply some energy from some external source. Let us consider we apply an external electric field to the dielectric .But as an insulator works the dielectric opposes any transfer of charges through it. We keep increasing the field to conduct charges through it and we ll find at some extent the dielectric strat passing charges through it .i.e. it starts conducting charges.

We define the Dielectric Strength of an insulator as the maximum electric field, it can withstand without allowing charges to pass through it ( without becoming a conductor ).

Breakdown Potential:

To set up the field across the dielectric to find the dielectric strength, we must set up an electric potential between two sides of the dielectric. As we increase the electric potential, the electric field across the dielectric increases and finally reaches to dielectric strength. 

So we define the Breakdown Potential as the minimum Electeic potential required to conduct charges through the dielectric, i.e. to breakdown it's insulation property.