Partial discharges and breakdown in laminate insulation structures

There is a well-defined need for the development of very long-life, lightweight, high-energy-density capacitors.¹ These capacitors are made up of laminates of a dielectric material (such as polypropylene), impregnated in a liquid (such as silicone oil) and arranged between aluminum foils.² A basic capacitor section is shown in Figure 1. Some of our earlier experiments³ have shown that the failure of such a device occurs mostly due to dielectric punch at the foil edge. The failure mechanism consists of occurrence of partial discharges, which slowly erodes away the dielectric at the foil edge ultimately leading to a total breakdown. The presence of partial discharges and lifetime of these capacitors is found to be a function of the discharge pulse-repetition frequency. DC partial discharge tests on virgin capacitor samples showed large amounts of partial discharge activity during charge and discharge transient periods.