Regularity of breakdown of solid dielectrics after moisture absorption

The authors examine the usually encountered problems of environmental compatibility experiments on the breakdown of solid dielectrics after moisture absorption. These include: (1) the excessive reduction of dielectric strength and (2) an abnormal phenomenon in the case of which increases in moisture absorption cause the dielectric strength of the solid dielectric to increase at the start and then to decrease. Three essential types of phenomena involving the relationship between the increasing amount of moisture absorption and dielectric strength for different kinds of solid dielectrics are stated. These phenomena are as follows: the dielectric strength decreases slightly with increasing amount of moisture absorption: dielectric strength decreases abruptly at the beginning and then keeps steady; the dielectric strength increases at the beginning and then decreases or keeps steady. The occurrence of the three types of phenomena is chiefly due to the fact that, during the measurements, the effects of absorbed water film on the dielectric surface and permeated water into the interior of the dielectric distort the original distribution of electric field