Theory of Dielectric Breakdown

The dielectric breakdown of an insulating material is a complex physical phenomenon but it may be generally characterized as a sudden change in the resistance of the insulation under test due to the applied voltage. Simply stated, the test voltage breaks down the insulating properties of the material.

The mechanism of dielectric breakdown begins with the application of a strong electric field to the insulating material by a high voltage. Different materials require different levels of electric field in order for dielectric breakdown to occur. Metals and other conductors have free electrons without the application of any electric field, but insulating materials typically require a very high electric field to allow electrical current to flow.

When the electric field is sufficient, it energizes the insulator’ s electrons until they gain enough energy to cross the band-gap and move into the conduction band, dramatically increasing the conductivity of the material. This transformation is called dielectric breakdown and the electric field necessary to start the breakdown is called the dielectric strength, or breakdown strength.

Thus, dielectric breakdown is a dramatic and sudden increase in the conductivity of a material due to an applied voltage.