Effect of UV treatment on the dielectric strength of BOPP capacitor film
The effect of UV treatment on dielectric breakdown strength of metallized biaxially-oriented polypropylene (BOPP) capacitor film was studied. Results from Weibull statistical analysis indicate that an optimal UV exposure level of ~3.4 J/cm2 (200-400 nm) increases the breakdown strength at 1% probability by ~20%. UV spectroscopic analysis indicates that the antioxidant in BOPP was consumed almost entirely. The results suggest that antioxidant remaining in the BOPP after processing may have an unfavorable effect on the breakdown strength of the film
Area dependence of breakdown strength of polymer films: automatic measurement method
An automatic method for determining the breakdown strength of thin polymer films was evaluated. The equipment consists of a scanning electrode arm with which the breakdown voltage over the film sample is measured. The measurement electrodes were of solid brass and the ground electrode was of thin aluminum foil. Five different electrode areas between 0.045 and 9.3 cm2 were used and 40-100 individual measurements per electrode area per sample were performed. All measurements were performed in air. The Weibull function parameters alpha and beta were fitted to the obtained data. Different features concerning the measurement system and conditions, e.g. the criteria for the automatic detection of the breakdowns, the effect of the electrode edge design, the DC ramp speed, partial discharges and humidity were analyzed. In order to control the reproducibility of the results, also another type of measurement setup was tested. It was concluded that the measured alpha-parameter values were stable and repeatable over a period of several years. The average beta-parameter values varied plusmn10-30%, more for the large than the small electrodes, and were also sensitive to changes in the sample, in the measurement conditions and the choice of the electrode system
Characteristics of Dielectric Fluids for Medium-Voltage Power Capacitors
Fluids used for the impregnation of mediumvoltage power capacitors made with polypropylene film must exhibit suitable gassing tendency, appropriate compatibility with the film in terms of wettability and limited solvent capacity, but in addition should withstand an endurance test. This test consists of two phases: during the first, repeated voltage impulses are applied which may generate partial discharges, then a subsequent overload run insures that soundness of the dielectric is maintained.