Current Pulse Polarity Effect on Metallized Film Capacitors Failure

One of the main reasons of metal film capacitors failure in pulse modes is a degradation of contacts between film metallization and solid electrodes-contact edges. This paper presents the results of experimental investigations of modeled contact edges behavior under current pulses of varying amplitude, duration, and quantity. It was found that the contact edge degradation is caused only by metallization destruction and independent on metal of the solid electrodes ("shoopage"). Depending on pulse parameters and dissipated energy in the contact edge, the contact erosion rate is in the range of (0.4-2.7) x 10(-3) g/J. Current pulse polarity effect on contact edge degradation was found: mean time to failure (MTTF) of the contact edge depends on its polarity, i.e., on the direction of the current flow through the contact during charge or discharge of capacitor. For different contacts polarities the difference between MTTFs reaches 20%-60% depending on pulse parameters. Based on these facts, one makes a supposition that the timely changing of the capacitor's terminals polarity can lead to the increasing of capacitor lifetime.