Study of thermal ageing of polypropylene film capacitors

Polypropylene film capacitors manufactured by five different manufacturers were aged at the temperature of 100 °C for 1600 hours. Changes of the capacitance, the loss factor and nonlinearity of the current-voltage characteristic were examined during ageing. It was found that changes of the capacitance are very low, whereas changes of the loss factor and nonlinearity are higher. But the loss factor of the capacitors is in the order of units of 10-4. Given the small value of the loss factor, even small changes in the structure of the capacitor could cause a large change in this parameter. As for current-voltage characteristic nonlinearity it was found that ageing can cause significant changes of this parameter. Therefore it can be used as an effective tool for evaluation of ageing of this type of capacitors. The highest value of nonlinearity was observed for capacitors Arcotronic. It is assumed that the cause is re-building of the metallization of the PP film by thermal ageing.