Nonlinearity of Current-voltage Characteristic of PP Film Capacitors During Long-term Thermal Treatment

Nonlinearity of current-voltage characteristic of PP film capacitors was examined during their long-term exposition at the temperature of 100 °C and relative humidity of 54 %. The total time of thermal aging was 19,939 hours and was divided into 11 stages. The measurement of nonlinearity was carried out before the thermal treatment and at the end of every stage. Measurement of nonlinearity was done so that the capacitors were powered with a sinusoidal current having the frequency of 10 kHz and the voltage the first (u1) and third (u3) harmonics were measured. Capacitors of metalized polypropylene (PP) film with a value of 0.1 μF from five different manufacturers was measured. Nonlinearity was measured for six levels of the voltage U1 and the results were compared. Eight samples from every manufacturer were examined. It was found a weak dependence of the course of the nonlinearity of the current-voltage characteristic of the capacitors on the measuring voltage. Changes of nonlinearity were continuous without any extremes, indicating a progressive degradation of capacitors during thermal treatment.