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 cm{sup}2 were used and 40-100 individual measurements per electrode area per sample were performed. All measurements were performed in air. The Weibull function parameters α and β 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 α-parameter values were stable and repeatable over a period of several years. The average β-parameter values varied ±10-30, 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.
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