ingeneral explain me about DISCHARGE,the phenomenon due to which lightening is caused and ELECTRIC BREAKDOWN, or to put in simple, explain me under what conditions a dielectric could turn into a conductor and why?

t high electric fields, a material that is normally an electrical insulator may begin to conduct electricity – i.e. it ceases to act as a dielectric. This phenomenon is known as dielectric breakdown.

For each material, there is a characteristic field strength needed to cause dielectric breakdown. This is referred to as the breakdown field or dielectric strength. Typically values of the dielectric strength lie in the range 10⁶ – 10⁹ Vm^-1. The exact value of the dielectric strength depends on many factors – most obviously the size of the energy gap, but also the geometry and microstructure of the sample and the conditions it is subjected to.