LIGHTNING LOCATION SYSTEMS IN JAPAN Fukumune ... - Vaisala

in power equipment maintenance and thedevelopment of lightning-proof designs. TheLPATS or time of arrival (TOA) type LLS wasfirst installed in Japan in 1989. At the time,each electric power company was usingCIGRE type lightning discharge counters toobserve lightning occurrences in their area.Those systems were gradually replaced byLLS networks. By 1989, LLS systems ownedby the nine Japanese electric powercompanies covered the main areas of Japan.The location of those LLS sensors in 1991 isshown in Figure 4 (7) .Although each electric power companyLLS was operated independently, a systemthat collected the data from the networks wasdeveloped in 1999, and it became possible torecord national lightning data continuously,and evaluate lightning frequency andcharacteristics without regionaldifferences (8)(9)(10)(11) . A national Japanthunderstorm day map was created with datafrom the past decade (Figure 5). Although thisthunderstorm day map was almost equivalentto the conventional IKL map (Figure 6), thenew lightning frequency map showed regionaldifferences in much more detail, and it wasconcluded that the lightning frequency mapobtained using the LLS was a more suitabletool for the design of power equipment thanthe conventional IKL map.Figure 5. Lightning stroke frequency mapcreated using the electric power company LLSnetwork data in the summer, 2000 (11)Figure 6. The conventional IKL map (11)Figure 4. Location of Japanese LLS sensorsin 1991 (7)In the meantime, system evaluations wereperformed in parallel with lightningobservations. Detection equipmentimprovement and replacement and networkexpansion resulted in improved locationaccuracy and system reliability. The IMPACTsensor that combined MDF and TOAtechnology was introduced for the first time in1994, and it was confirmed that it providedimproved location accuracy (12)(13) . Moreover,the IMPACT sensor made it possible to detect