Physical Examination of Dielectrics

In gaseous dielectrics, polarization is generally negligible ϵr≈1 and dielectric losses null. The mathematical properties of the field are thus the same as in a vacuum. The gas is only involved by way of phenomena of ionization, which it causes when the intensity of the field becomes sufficient. This chapter focuses on the study of these phenomena. This study is interesting because gases are used either as insulators in cables, or coupled with other dielectrics in the machines. In fact, they are the only insulators for which satisfactory theories on their ionization have so far been able to be put forward. The chapter talks about liquid and solid dielectrics and the breakdown of solid dielectrics. The problems posed by this breakdown are far more complex than those posed by gases.