Anatomy of Lightning Strike - RME111 - RWS200 - AWS310-SITE - AWS430 - RWCC - AWS310 - FOC201

Grounding and Lightning Protection in Vaisala Outdoor Installations Technical Reference

Document code
M211786EN
Revision
B
Language
English (United States)
Product
RME111
RWS200
AWS310-SITE
AWS430
RWCC
AWS310
FOC201
Document type
User guide

The potential difference between a thundercloud charge center and ground is estimated to be of the order of 10 million to 100 million volts.

Lightning strikes:

  • Only ~35 % of all lightning strikes are cloud-to-ground strikes in the northern hemisphere. Even less (~15 %) in the tropic.
  • Majority (80 … 85 % in Scandinavia) of cloud-to-ground strikes are negative. Positive strikes tend to double the current.
  • The average thickness of a bolt is 2.5 … 5.1 cm (1 … 2 in) and the temperature in the strike channel exceeds 30 000 °C (50 000 °F).
  • Single-strike discharges (which amount to about half of the negative strikes) or multi-strike discharges are possible.
  • Up to 42 separate strikes have been recorded with 10 … 90 ms intervals. A more common number of repetitive strikes is two. Positive strikes are usually single shots.
  • The current pulse rise time is about 1 ... 20 µs (10 … 90 %) and the duration (to half-value) is 50 … 700 µs. Ground potential rise caused by the strike can last even longer.

Lightning strike current distribution (according to IEC 62305-1) is:

  • 0.1 % > 600 kA
  • 1 % > 200 kA
  • 10 % > 80 kA
  • 50 % > 35 kA
  • 90 % > 10 kA
  • 99 % > 3 kA

Standards recommend the following maximum values to be used when designing a lightning conductor (99 % confidence):

  • Current 200 kA
  • Maximum di/dt 200 kA/µs

Typical down conductors have inductance of the range of 1.5 uH/m. The voltage difference over a 10 m (33 ft) down conductor can be several megavolts.