The effects of lightning on structures and establishing the level of risk

The high levels of energy, current, charge and rate of current rise associated with a lightning strike can result in a structure being severely damaged if struck. A key stage in determining the type of lightning protection system (LPS) required by a structure is the estimation of the lightning strike frequency. For each strike, the probability of the energy/current/charge/rate of current rise exceeding a specific value can also be found mathematically. The IEC standard detailing lightning protection of structures, IEC 1024-1: 1990, provides a method of calculating the lightning strike frequency to an object of no more than 60 m height. Considering modern wind turbines may have a hub height greater than 60 m, this standard is inapplicable to such machines. Of particular importance in tall structures is the possibility of upward propagating lightning strikes. The assessment of the total lightning strike frequency, both upward and downward propagating, can be assessed using two independent models