17-04-2012, 04:05 PM
Protection of Power system against transient overvoltage due to switching and lightning
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Introduction
Protection of transient is a critical task because the exact nature of transients in the real world is at best only statistically defined, so that the choice involves technical and economic decisions based on calculated risks rather than certainties.
Protection against lightning effects includes two categories:
(1) direct effects concerned with the energy, heating, flash, and ignition of the lightning current.
(2) indirect effects concerned with induced overvoltage in nearby electrical and electronic systems.
Striking Distance
The distance between the tip of the leader and the object about to be struck is called striking distance.
The length of this distance is affected by the field established by the leader.
Conversely, very low amplitude flashes have an even shorter striking distance, which means that they will seem to ignore "attractive" points of termination.