Thermal ageing of polypropylene film capacitors

Capacitors of metalized polypropylene film from four different manufacturers were aged at the temperature of 100 °C for 600 hours and changes of their capacitance and nonlinearity of the current-voltage characteristic were monitored. It was found that changes of the capacitance were very low. Significant changes were found in nonlinearity of the I–V characteristic of the capacitors. The reason of these changes is discussed and it is explained by changes of PP film metallization and by changes of quality of contacts on the foreheads of the capacitor coil. It was found that properties of capacitors from different producers differ. It was explained by quality of film and technology.