Partial dielectric discharges: Microbreakdowns in insulating materials which do not result in immediate total failure of the insulation. They may occur in zones of the insulation with extreme local field strength caused by material inhomogenities (e.g. gas bubbles, transition between materials). This becomes a problem in AC applications where, in the long run, the insulation is weakened and damaged, resulting in failure of the capacitor. Capacitors with no or very low level of partial discharges are much less likely to fail.