CAPACITORS AND DC

Imagine two large parallel metal plates, as described earlier. If you connect them to a source of dc, they draw a large amount of current at first as they become electrically charged. However, as the plates reach equilibrium, this current diminishes, and when the two plates attain the same potential difference throughout, the current is zero.
If the voltage of the battery or power supply is increased, a point is eventually reached at which sparks begin to jump between them. Ultimately, if the power supply can deliver the necessary voltage, this sparking, or arcing, becomes continuous. Then the pair of plates no longer acts like a capacitor. When the voltage across a capacitor is too great, the dielectric (whatever it is) no longer functions properly. This condition is known as dielectric breakdown.
In air-dielectric and vacuum-dielectric capacitors, dielectric breakdown is a temporary affair; it does not cause permanent damage. The device operates normally when the voltage is reduced, so the arcing stops. However, in capacitors with solid dielectric such as mica, paper, or tantalum, dielectric breakdown can burn or crack the dielectric, causing the component to conduct current even when the voltage is reduced below the arcing threshold. In such instances, the component is ruined.