Effect of the insulator size on the breakdown strength

The effect of the specimen size (S) on the dielectric strength E _Bb is a well known effect that exists whatever the breakdown type: pure vacuum, flashover, bulk breakdown. Eb varies as S^-n. S can be the insulator surface in case of flashover or the insulator thickness in case of bulk breakdown. This relation has received a statistical justification (weak links) and also has been explained from trapping-detrapping phenomena. n is often found to be equal to 0,5 but they are many results proving that n depends on the material. The work will review experiments on polymers and on ceramics. Considering the technological importance of this parameter for designing an insulating system, it will be suggested that n has to be extracted from Space Charge Measurements