High Voltage Conduction and Breakdown Phenomena in Dielectrics

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This work attempts to understand conduction, aging, degradation, and breakdown mechanisms in high field stressed gaseous, liquid, and solid dielectrics using new modern optical, electronic, and computer instrumentation to see charge transport effects inside materials that could not be seen before. Insulating dielectrics used in power apparatus, such as transformers and cables, and in pulse power technology, such as Marx generators and pulse forming lines, have their performance affected by injected space charge. The space charge distorts the electric field distribution and introduces the charge migration time between electrodes as an additional time constant over the usual dielectric relaxation and fluid transport times. Charge injection from high voltage stressed electrodes is measured by Kerr electro-optic field and charge mapping measurements. Such optical measurements have been performed for highly purified water, water/ethylene glycol mixtures, transformer oil, silicon oil, liquid and gaseous SF6, liquid nitrogen, and high voltage stressed and electron beam irradiated polymethylmethacrylate. In highly purified water, Kerr electro-optic measurements, voltage-current terminal measurements, and electrical breakdown tests have shown that the magnitude and polarity of injected charge and the electrical breakdown strength depend strongly on electrode material combinations and voltage polarity. Particular tasks are: (1) Kerr effect measurements including low-voltage prestressing of dielectrics; (2) electron beam irradiation of solids; (3) fractal mathematical modeling of electrical breakdown trees; and (4) electrokinetic pumping using traveling wave high voltages.