The lightning strike is likely to happen any time and is the root cause of over voltage fault in electrical system. The lighting strike can be divided in to two group. One is direct lightning strike and another is indirect lightning strike.
Direct lightning strike
The lightning strike directly falls upon the over head line or electrical equipment. This sudden current injection creates voltage surges, traveling wave that propagates through the line make impact on other equipments.
Induced or Indirect lightning strike:
Here the lightning strike hits the surroundings of an electrical system. The voltage surge that produce by this indirect strike is loop between the line and earth.