Aging mechanisms of X2 metallized film capacitors in a high temperature and humidity environment

Abstract

Safety capacitors (usually denoted as X1, X2 or Y) are metallized film capacitors (MFC). Two kinds of capacitance loss mechanism typically occur in this metallized film structure: (1) caused by self-healing resulting in a very small electrode area loss; (2) caused by electrode oxidation by electrochemical corrosion under ac stress in a humid environment. This study focuses on the aging mechanism of X2 film capacitors working in high temperature and high humidity environments. Two types of X2 film capacitors have been stressed under an applied voltage of 270Vac at 85 ¼C, 78.68%RH. Capacitance and equivalent series resistance (ESR) were monitored during the experiment as parametric parameters that reflect the aging process. The aging mechanism including moisture ingress time were calculated and comprehensively analyzed with the capacitance change characteristics. It was found that capacitors with lower aluminum metallization has a better capacitance stability, the mean corrosion rate of Type2 (9.7% aluminum metallization) is more than 3 times of the Type1(6.9% aluminum metallization).The ingress time calculated by capacitance change and normalized ESR show reasonable agreement.