Some aspects of tree initiation in solid insulation

It is largely within the last five years that treeing has been recognized as a possible mechanism in long time insulation breakdown. The term treeing is used here to indicate the growth of branching breakdown channels within insulation. Treeing differs from uniform field breakdown particularly in that the electric strength of the insulation is exceeded only locally at a concentration of electric stress. Treeing certainly involves time dependent processes and therefore proceeds at a finite rate which may be very slow. One aspect of treeing which adds to its interest is its common occurrence as the final phase of breakdown from corona erosion1,2.