Diendorfer G., W. Schulz, C. Cummins, V. Rakov, M. Bernardi, F. De La Rosa, B. Hermoso, A. M. Hussein, T. Kawamura, F. Rachidi, H. Torres:
Review of CIGRE Report “Cloud-to-Ground Lightning Parameters Derived from Lightning Location Systems – The Effects
CIGRE SC C4, Colloquium, Kushiro, Japan, 2009
CIGRE TF C4.404 has recently submitted a comprehensive report for publication, dealing with the effects of performance characteristics of lightning location systems (LLS) on lightning parameters based on data from such systems. This paper will provide an overview and summary of this extensive report.
Lightning parameters are essential input variables to procedures for estimating the lightning performance of transmission lines. Parameters that are typically derived from LLS observations are the ground flash density (GFD), ground stroke density (GSD), peak current distribution, flash multiplicity, and polarity. LLS upgrades and/or LLS expansions are causing changes in the network performance that result in changes in LLS-inferred lightning parameters.
The CIGRE report discusses the effect of using different location methods in terms of required number of sensors to obtain a location. For example, median peak current (absolute value) increased by 47%, from -9.8 kA to -14.4 kA, when data from combined direction-finding and time-of-arrival sensors were reprocessed using only the time information and requiring 4 sensors to compute a location. This effect is reduced with shorter sensor baseline distances, or (equivalently) with greater sensor sensitivity.
Direct measurements of currents in lightning striking instrumented towers or in triggered lightning allow estimation of all three major performance characteristics of LLS’s - detection efficiency (DE), for strokes and flashes, location accuracy, and peak current estimation errors. By deploying most recent technology of sensors a flash DE of 95% or higher is achievable. In a network with small sensor baselines and low sensor threshold a flash DE close to 100% is possible. Corresponding stroke DE is generally lower, but can reach values in the range of 80-90%.
Peak current estimates given by LLS in the United States (NLDN) and Austria (ALDIS) are on average in reasonable agreement with the directly measured peak currents in triggered lightning and at electrically short towers, respectively, although significant differences (up to 50%) are observed for individual strokes, likely caused by the natural variation in return stroke speed.
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