Lightning Voltage Surges
The most severe lightning stroke is that which strikes a phase conductor on the transmission line
It produces the highest overvoltage for a given stroke current.
The lightning stroke injects its current into a termination impedance Z, which in this case is half the line surge impedance Zo since the current will flow in both directions as shown
In Figure1.3. Therefore, the voltage surge magnitude at the striking points = (½) IZo The lightning current magnitude is rarely less than 10 kA.
For typical overhead line surge impedance Zo of 300 Ω, the lightning surge voltage will Probably have a magnitude in excess of1500 kV.
The impedance of the lightning channel itself is much larger than 1/2Zo (it is believed to range from l00to 3000 Ω).
· Lightning voltage surge will have the same shape characteristics.
· In practice the shapes and magnitudes of lightning surge waves get modified by their
· Reflections at points of discontinuity as they travel along transmission lines.
· Lightning strokes represent true danger to life, structures, power systems, and
· Communication networks.
· Lightning is always a major source of damage to power systems where equipment
· Insulation may break down, under the resulting overvoltage and the subsequent high-
· Energy discharge.
Lightning has been a source of wonder to mankind for thousands of years. Scotland points out that any real scientific search for the first time was made into the phenomenon of lightning by Franklin in18th century. Before going into the various theories explaining the charge formation in a thunder cloud and the mechanism of lightning, it is desirable to review some of the accepted facts concerning the thunder.
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