Discovery of new upward lightning phenomenon in winter

Back-flashover at double-circuit 500 kV transmission tower by winter lightning

Photo.1 Back-flashover at double-circuit 500 kV transmission tower by winter lightning

High current upward lightning discharge in winter and its current waveform

Photo.2 High current upward lightning discharge in winter and its current waveform

 Winter lightning in Japan had been reported to the scientific community since 1960s; however, it had not drawn attention of engineers until late 1970s when much higher fault rates than expected were experienced in winter at newly constructed 500 kV double circuit lines in the coastal area of the Sea of Japan. By intensive study jointly conducted by the electric power industry and universities, it was concluded that lightning presumably was the cause. Thus countermeasures to improve lightning performance of transmission lines had been taken, and they worked. Later in 1990s, a multiple-line back-flashover phenomenon at a 500 kV double-circuit line was photographed in winter by an automatic camera for the first time in the world, and the presumption of the cause of high fault rate of transmission lines in winter was proved to be correct. But the reason of the high fault rate in winter remained unsolved from the lightning data then available.
A new relaying system was introduced in the power system in this century, and the time of a line fault has become known with the precision of a millisecond. This improvement made it possible to rigorously compare the record of line faults with GPS-timed records of lightning electromagnetic pulses (LEMP) radiated by lightning discharges. Then the cause of multiple line faults in winter was identified to be back-flashovers caused by high-current upward lightning discharges. Especially, the high-current upward discharge in the negative polarity was a newly discovered phenomenon to the scientific community, and this phenomenon is now known to the world through an invited paper published in the transactions of IEEE.
New phenomena of lightning discharges discovered after 1990s include optical phenomena in the mesosphere, represented by red sprite, and compact intracloud discharges (CID) in high altitude. They attract intention of scientific community and have been intensively studied, however, they are not threatening to the activity of human. The newly discovered phenomenon of winter lightning is hazardous to modern infrastructure, so it is a much more important subject of research than sprites or CID from the engineering point of view. Because the new phenomenon, the negative high-current upward lightning discharge in winter, rarely occurs, it had not been discovered by observation of lightning current at instrumented towers. The investigators discovered it through observation of LEMP, thus clarified the enigma why winter lightning, which is considerably less active than summer lightning, causes more number of severe lightning faults than by summer lightning.
The lightning performance of transmission lines in winter can now be estimated like that in summer without introducing an adjustment factor, which used to be indispensable in comparing the estimated value with actual performance.


[1] M. Ishii, M.Sato, A. Sugita, and N. Itamoto, “High current upward lightning flashes in winter”,13th International Conference on Atmospheric Electricity, Beijing,2007
[2] M.Saito, M. Ishii, M. Matsui, and N.Itamoto, “Spatial distributions of high current lightning discharges in Hokuriku area in winter”,IEEJ Transactions on Power and Energy, Vol.127, N0.12,pp1325-1329,2007[3] M. Ishii, M. Saito, F. Fujii, M. Matsui, and N. Itamoto, “High-Current Lightning Discharges in Winter”,IEEJ Transactions on Power and Energy, Vol.128, N0.1,pp291-297,2008
[4] M. Saito, M. Ishii, F. Fujii, M. Matsui, H. Kawamura, and N. Itamoto, “Evaluation of Lightning Fault Rate of Transmission Line on the Coastal Area of the Sea of Japan in Winter”,IEEJ Transactions on Power and Energy, Vol.129, N0.1,pp157-164,2009
[5]M. Ishii, and M. Saito, “Lightning electric field characteristics associated with transmission-line faults in winter”,IEEE Transactions on Electromagnetic compatibility, Vol. 51, No. 3, pp. 459-465,2009

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