LIGHTNING LOCATION SYSTEMS IN JAPAN AND THEIR APPLICATIONS TO IMPROVEMENT OF LIGHTNING PERFORMANCE OF TRANSMISSION LINES

摘要

In 1982, the first lightning location system wasrnintroduced in Japan by a university and an electric powerrncompany. Since then, lightning location systems hadrnbeen introduced rapidly, and Japan's nine regionalrnelectric power companies possessed their own lightningrnlocation systems in 1988, which covered almost all ofrnJapan. Because of the difference of policies and time ofrnthe introduction, different systems such as LLP system,rnLPATS, SAFIR are used in Japan at present. In additionrnto these, other lightning location systems are operated byrnweather companies and the Meteorological Agency.rnJapan is unique in that these different types of lightningrnlocation systems have been operated in parallel.rnDetection efficiency of the systems operated byrnthe electric power companies was investigated about fivernyears ago. At that time, by comparison with outage datarnof transmission lines, it was evaluated as about 80 % andrn60 % for lightning in summer and in winter, respectively.rnDue to the improvement of the systems, includingrnoptimization of sensor locations and waveformrndiscrimination criteria up to now, the present detectionrnefficiency and location accuracy of the systems arerngenerally more than 90 % and less than a few km,rnrespectively.rnThunderstorm days based on meteorologicalrnobservation have been used in Japan in the discussion ofrnlightning performance of transmission lines. Recentrnstudy shows, however, that the actual numbers ofrnlightning flashes in areas having same thunderstormrndays are sometimes quite different. The new lightningrnfrequency map using the data of lightning locationrnsystems of electric power companies clearly showsrnannual, seasonal and regional variations of lightningrnoccurrence. The lightning frequency observed byrnlightning location systems is better correlated with thernnumber of transmission line outages than that estimatedrnfrom the thunderstorm days. Furthermore, byrnconsidering a more reliable lightning frequency, it hasrnbecome possible to reduce the length of arcing horns of arn500 kV transmission line from 3950 mm to 3600 mm.rnRegional difference of estimated lightning current datarnsuggests the possibility of further rationalization ofrninsulation design.rnAnother application of lightning location systemsrnis the analysis of transmission line outages. Usually,rnlightning outages are categorized into shielding failuresrnand back flashovers. The distribution of lightningrncurrents observed by a lightning location systemrncorresponding to 187kV transmission line outages showsrntwo peaks, which seem to correspond to the two causesrnstated above. The simulation using EMTP confirms thisrnassumption.rnThe data of lightning location systems has alsornbeen used for fault analysis of UHV transmission lines.rnIn Japan, double-circuit UHV (1100 kV) transmissionrnlines were constructed and have been operated at 500 kV.rnThe height of transmission towers is usually more thanrn100m and the lines run through mountainous areas.rnRecently a couple of faults occurred in summer, and theyrnwere considered shielding failures. Waveforms ofrnincoming lightning surges into substations have beenrnrecorded with precise time stamps, and these data,rntogether with the information of location and currentrnmagnitude of lightning strokes, were compared withrnEMTP calculations. The calculated surge voltages atrnsubstations well agree with observations.rnSome applications of lightning locationrnsystems to improvement of insulation design ofrntransmission lines are also presented.