Tổng quan về sét

7. Thang đo của sét và thiệt hại sét (đường dây điện)

If an electricity pylon is struck by lightning, the pylon’s voltage becomes very high, due to the lightning current, and if the voltage exceeds the withstand voltage of the insulators of the power lines, there may be a discharge from the insulators, causing a temporary power stoppage.

It has been proven that there is a correlation between power line lightning strike rates and IKL (number of thunderstorm days per year).

And, as shown in the figure at left, according to various statistics on the size of the lightning current, there are reports ranging from 5kA to 200kA. (515kA was observed in Poland.)

Most of the lightning current is negatively charged, with wave peak lengths often between 2 and 4μs, and mostly within a 1 to 20μs range.

Wave tail lengths fall within a 10 to 100μs range.
graf   Lightning damage especially affects power lines. Of all instances of damage to power lines, lightning accounts for over half.

The higher the voltage class, the higher the proportion of damage caused by lightning. For 500kV class power lines, lightning accounts for over 90% of power line damage.

Also, for this class of power line, a comparison of incidents in summer and winter shows that, for the total incident ratio, winter incidents occur 5.5 times more than summer incidents, and for 2 line multiphase incidents, winter incidents occur 25 times more than summer incidents, which gives some idea of the high rate of lightning strikes in winter.



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