Chapter XI ceramic insulation

Lewis and Bickford (1) presented a method for determining the resistivity of lossy material using dielectric measurements but making use of interfacial polarizations at low frequencies. Measurements were made on glasses using mica as the boundary material. Results agree quite well with those attained by direct measurement. Taylor (2) studied the dielectric relaxation spectrum of several glasses. Dielectric measurements were made in the range 100–16000 cps and at temperatures up to 450°C. It was concluded that the relaxation was due to alkali ion movement. Vermeer (3) evaluated the impulse breakdown strength of Pyrex glass. He found that in the range of 50 to 100°C, the breakdown is independent of temperature, impulse duration, specimen thickness and electrode material. A value of 9200 v/cm is believed to be the intrinsic electrical strength of Pyrex.