Modelling Lightning Results with an Equal Frequency

Lightning strikes and their present waveforms come in several types and are usually not solely predictable. Lightning strikes can both be upward or downward initiated and both adverse or optimistic polarity. Downward flashes happen in flat territory and to decrease buildings. Upward flashes are extra distinguished for uncovered or greater buildings. The likelihood of direct strike to a construction will increase with construction peak.

All impulse present parameters of upward flashes are lower than these of downward flashes and a better lengthy stroke cost of upward flashes shouldn’t be confirmed. Due to this fact, the lightning present parameters of upward flashes are thought-about to be lined by the utmost values for downward flashes.

About 85 to 95 % of the flashes to buildings having heights lower than about 100 metres on flat or rolling terrain are adverse downward. The opposite 5 to fifteen % are both adverse upward or optimistic. Thus, from {an electrical} transmission or substation viewpoint, aside from mountainous terrain or very excessive river crossing towers, the adverse downward flash is of main concern. Solely 2 to 10 % of complete flashes are optimistic polarity [ref. 1].

A lightning strike consists of a number of completely different strokes (typically mixed):

  • impulses (brief strokes) with period lower than 2 ms.
  • lengthy strokes with period longer than 2 ms.

Strokes have a polarity (optimistic or adverse) and a place (order) throughout the flash. A polarity ratio of 10 % optimistic and 90 % adverse strokes is at all times assumed within the absence of native data.


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