Monitoring of metalized film capacitors degradation with impedance nonlinearity measurement

Self-healing capacitors fabricated of metalized polypropylene film as the dielectric material are widely used in power electronics. Self-healing process makes elimination of local defects in these capacitors possible and extends the life-time of them. It was shown that the measuring of capacitor V/A characteristic nonlinearity is usable and effective tool for monitoring of capacitor quality. Six capacitors of this type were aged in an oven at the temperature of 90 °C for 1000 hours under normal ambient conditions and changes caused by ageing were monitored with the nonlinearity measurement. It was found that nonlinearity of capacitor grows with the time of ageing.