We tend to think of all lightning strikes as being the same, but as is the case with other electrical currents, lightning comes in two flavors, negative polarity strikes and positive polarity strikes. The strong turbulence within thunderstorms tend to separate electrical charges in a storm leaving the lower portions of the cloud base with a negative charge and the upper reaches of a cumulonimbus cloud with a positive charge.
Because similar charges will repel, the ground tends to become positively charged eventually leading to the negatively charged cloud base to discharge to the ground. On occasion, usually less than 5% of all cloud to ground lightning, the positively charged upper portion of a thunderstorm will also send a lightning stroke to the ground, often well away from the base of the storm (where the ground tends to be more negatively charged).
These so called positive strikes last longer and are many times more powerful than a negative strike. Positive strikes are therefore more lethal and cause far more damage to our electrical grid than the weaker more common negative strikes.