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Tokyo, Japan

Ishii M.,University of Tokyo | Saito M.,University of Tokyo | Natsuno D.,Toyo Sekkei
IEEJ Transactions on Power and Energy | Year: 2016

Upward lightning flashes in winter frequently damage wind turbines in the coastal area of the Sea of Japan. Aspects of initiation of upward leaders of such flashes of winter lightning were investigated by using optical images recorded by 30 fps digital video cameras at 12 wind turbines. Moving blades generate upward flashes more likely than stationary blades. Among the 252 analyzed upward flashes, only one flash was confirmed to be initiated not from the tip part of a blade. © 2016 The Institute of Electrical Engineers of Japan. Source


Yamamoto K.,Chuba University | Ueda N.,KEPCO E&C | Ametani A.,Doshisha University | Natsuno D.,Toyo Sekkei
Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi) | Year: 2012

A Rogowski coil, used for measuring lightning current through a wind turbine generator system, is generally set up at the foot of a tower. In most wind turbines, there is an entrance at the foot of the tower, which leads to a flight of stairs or a ladder. When lightning strikes the wind turbine, the lightning current flows to the ground through the blades, nacelle, and tower. The current is shunted to the tower and the stairs/ladder at the foot of the tower, from where it may flow into the foundation and the earth. A Rogowski coil is usually set up at only the foot of a tower. The lightning current shunted to the stairs/ladder cannot be measured using the Rogowski. The installation position of the Rogowski coil depends on the construction of the stairs/ladder. In this study, the lightning current distribution at the foot of a tower is calculated using the FDTD (Finite Difference Time Domain) method, which is one of the methods used for numerical analyses of electromagnetic fields. We also studied the effect that the setup of the stairs/ladder and the resistivity of the ground have on the lightning current distribution. The results of the current distribution are very important for predicting the total current that flows through an existing wind turbine generator system. © 2012 Wiley Periodicals, Inc. Source


Ishii M.,University of Tokyo | Saito M.,University of Tokyo | Chihara M.,Photoniks K.K. | Natsuno D.,Toyo Sekkei
IEEJ Transactions on Power and Energy | Year: 2012

Cumulative distributions of charge amount and specific energy of upward winter lightning flashes, observed by Rogowski coils instrumented on wind turbines in the coastal area of the Sea of Japan, were analyzed. Among 284 current data recorded at 16 measuring sites, the transferred charge of 13 lightning flashes exceeded 300 C, and the specific energy of 2 flashes exceeded 10 MJ/Ω. The medians of transferred charge are about 60% higher than those observed at Nikaho wind farm in winter for the three types of current, negative, positive and bipolar. Importance of observation at multiple sites is manifest. © 2012 The Institute of Electrical Engineers of Japan. Source


Yamamoto K.,Kobe City College of Technology | Ueda N.,Doshisha University | Ametani A.,Doshisha University | Natsuno D.,Toyo Sekkei
IEEJ Transactions on Power and Energy | Year: 2011

A Rogowski coil, used for measuring lightning current through a wind turbine generator system, is generally set up at the foot of a tower. In most wind turbines, there is an entrance at the foot of the tower, which leads to a flight of stairs or a ladder. When lightning strikes the wind turbine, the lightning current flows to the ground through the blades, nacelle, and tower. The current is shunted to the tower and the stairs/ladder at the foot of the tower, from where it may flow into the foundation and the earth. A Rogowski coil is usually set up at only the foot of a tower. The lightning current shunted to the stairs/ladder cannot be measured using the Rogowski. The installation position of the Rogowski coil depends on the construction of the stairs/ladder. In this study, the lightning current distribution at the foot of a tower is calculated using the FDTD (Finite Difference Time Domain) method, which is one of methods used for numerical analyses of electromagnetic fields. We also studied the effect that the setup of the stairs/ladder and the resistivity of the ground have on the lightning current distribution. The results of the current distribution are very important for predicting the total current that flows through an existing wind turbine generator system. © 2011 The Institute of Electrical Engineers of Japan. Source


Fujii F.,University of Tokyo | Ishii M.,University of Tokyo | Saito M.,University of Tokyo | Matsui M.,Franklin Japan Corporation | Natsuno D.,Toyo Sekkei
IEEJ Transactions on Power and Energy | Year: 2011

Wind turbines on the coast of the Sea of Japan have been damaged by lightning in winter. This is due to the frequent occurrence of upward lightning from wind turbines in winter. Occurrence of upward lightning turned out to be closely related to temperature distribution in high altitude. In this paper, correlation between lightning hits of wind turbines and the height of -10°C layer is analyzed. When an upward lightning hits a wind turbine in winter, the height of -10°C layer was lower than 2000 m in most of the cases. Moreover, winter lightning is classified into two types, namely storm type and inactive type, and it is found that parameters of lightning current observed by LLS differ depending on the type of lightning storms. © 2011 The Institute of Electrical Engineers of Japan. Source

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