C.9.5 Internal dielectric discharge

In internally charged dielectrics, dielectric break-down (punch-through) occurs but does not generally penetrate fully through the material. Instead, it begins at a grounded point and fans out into the material, neutralising areas of high electric field. These discharges characteristically produce a ‘tree’-shaped discharge path called a Lichtenberg pattern.

Published breakdown electric fields for dielectrics are typically close to 10⁷V/m. However, in laboratory experiments (see [20]) pulsing has been observed at lower macroscopic field strengths (10⁶V/m), perhaps due to local microscopic field concentration.

Whilst the most immediate consequence is the production of transient currents through direct injection or electromagnetic coupling, breakdown can also cause a permanent change in the material properties which can cause the material to be degraded as an insulator.