Peris G. Halaris, John S. Katsanis, George K. Soulinaris, John D. Koustellis, and Aikaterini D. Polykrati
High AC Voltage Stress, Dielectric Ageing, Partial Discharges, Potential Steps, Polymeric Solid Insulators
This work examines the average value of electronic kinetic energy during the dielectric ageing of solid insulators. For this purpose, samples of various insulators with a relative permittivity er=2.5-4.5 (e.g. industrial bakelite) were electrically stressed by the imposition of a high AC voltage. The electrode set-up used was metal tip-sample-metal plane in insulating transformer oil environment. Thus, the imposed field was inhomogenous, such as those found in practical applications. Measurements were taken by increasing the imposed voltage in steps of 1 kV until the ultimate breakdown of the insulators and the charge which flows through the sample, as a result of partial discharges, was measured. The partial discharges appeared in the oscillographs in the form of potential steps of the measuring capacitor voltage, which were placed in series with the electrode set-up. From these measurements the increase of the average value of the electronic kinetic energy in relation in relation to the value of the imposed electric field was noted. The results for this material samples are in agreement with other results regarding DC or impulse voltage stress.
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