Analysis of Changes Due to Long-Term Thermal Aging in Capacitors Manufactured from Polypropylene Film

It has been found that the long-term thermal aging at the temperature of 100 °C and relative humidity 54 %, causes a low change of the capacitance and a high change of the loss factor of polypropylene (PP) film capacitors. The goal of the work has been to find main reasons of these changes. Dismounting of aged capacitors has shown that the metal layers on the PP film, which form the capacitor electrodes, near the metal contacts on the ends of the body of the capacitor are strongly corroded and sometimes even totally absent. On the other hand, the change of the total electrodes area is not significant, because the capacitance decreases only slightly during the thermal aging. Because the PP film as well as the sprayed contacts are resistant to heat aging, the main reason of a significant increase in the loss factor must be the increase the resistance of the metal layers that form the capacitor electrodes.