Toyo Sekkei

Tokyo, Japan

Toyo Sekkei

Tokyo, Japan
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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.


Shindo T.,Japan Central Research Institute of Electric Power Industry | Sekioka S.,Shonan Institute of Technology | Ishii M.,University of Tokyo | Shiraishi H.,NEDO | Natsuno D.,Toyo Sekkei
44th International Conference on Large High Voltage Electric Systems 2012 | Year: 2012

Recently, wind power generation systems have drastically increased in Japan. As the increase of the wind power generation systems, outages of these systems by lightning have also increased and establishment of effective protection methods is strongly required. New Energy and Industrial Technology Development Organization (NEDO) in Japan has published a guideline for lightning protection of wind power generation systems based on the field observations and model experiments. Furthermore, many researchers in Japan have studied effective methods to reduce lightning damages of wind power generation systems. The results of these studies are summarized as follows. 1) Most of damage of wind turbine blades has been caused by lightning that occurs in the coastal area of the Sea of Japan in winter season, what we call 'winter lightning'. 2) In the case of the winter lightning, charge transfer exceeding the value of 300 C, which is the maximum value shown in an IEC Technical Report on lightning protection of wind turbines, often occurs. 3) Model experiments of lightning attachment shows that though the disc-type receptor is one of effective methods to prevent the damage of wind turbine blades by lightning, discharges cannot be always intercepted by receptors. On some conditions, lightning hits the blade and causes damage. The breakage characteristics of wind turbine blades are also clarified from the large current experiment. 4) Surge analysis shows overvoltage characteristics inside the wind power generation systems when lightning strikes a wind turbine and effective protection methods and grounding systems to reduce the overvoltages are proposed. 5) A hazard map for wind power generation systems in Japan has been constructed and a cost-effective protection scheme has been proposed based on the concept of lightning risk management.


Saito M.,Keio University | Ishii M.,Keio University | Ohnishi A.,Keio University | Fujii F.,Keio University | And 2 more authors.
Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi) | Year: 2015

In recent years, frequent damage to wind turbines by winter lightning has been reported in the region along the Sea of Japan. It is a serious finding that lightning hits concentrate on wind turbines in this region. The authors investigated the increase rate of the frequency of lightning hits on wind turbines due to wind turbine construction by using LLS (lightning location system) data. As a result, an experimental formula to estimate the increase rate of the frequency of lightning hits on wind turbines as a function of parameters related to the construction conditions, namely the height of wind turbines, the height above sea level, and the latitude, is proposed. © 2014 Wiley Periodicals, Inc.


Ishii M.,University of Tokyo | Saito M.,University of Tokyo | Fujii F.,University of Tokyo | Matsui M.,Franklin Japan Co. | Natsuno D.,Toyo Sekkei
2011 7th Asia-Pacific International Conference on Lightning, APL2011 | Year: 2011

In Japan, transmission lines or wind turbines in the coastal area of the Sea of Japan have suffered from higher frequencies of serious troubles by lightning in winter than those in summer. The thunderstorm days in this area are comparable in winter to those of summer; however, the number of lightning strokes observed by lightning location systems (LLS) in winter is much smaller. In winter, concentration of lightning hits to tall structures is observed by LLS in the coastal area of the Sea of Japan. Out of the observation by LLS, the authors propose an experimental formula to estimate the frequency of upward lightning occurring on tall structures in winter in Japan. © 2011 IEEE.


Fujii F.,University of Tokyo | Ishii M.,University of Tokyo | Saito M.,University of Tokyo | Matsui M.,Franklin Japan Co. | 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.


Ishii M.,University of Tokyo | Saito M.,University of Tokyo | Natsuno D.,Toyo Sekkei | Sugita A.,Franklin Japan Co.
2014 International Conference on Lightning Protection, ICLP 2014 | Year: 2014

In Japan, transmission lines or wind turbines in the coastal area of the Sea of Japan have suffered from higher frequencies of serious troubles due to lightning in winter than those in summer. Lightning which hits tall structures in winter in Japan has turned out to be mostly upward lightning, and the number of lightning hits to such structures is far more than that in summer although lightning flash density in winter is much lower. To evaluate lightning risk to tall structures in such an area, an experimental formula to estimate the frequency of lightning hits on wind turbines in winter in Japan is proposed. From 2008 to 2013, lightning hits to wind turbines were observed at 27 sites in Japan under a research project of NEDO (New Energy and Industrial Technology Development Organization). The aspects of attachment of upward lightning observed in this project are also reported on. © 2014 IEEE.


Ishii M.,University of Tokyo | Fujii F.,University of Tokyo | Saito M.,University of Tokyo | Natsuno D.,Toyo Sekkei | Sugita A.,Franklin Japan Co
IEEJ Transactions on Power and Energy | Year: 2013

In winter of 2010 and 2011, 65 return stroke currents were observed by Rogowski coils at 14 wind turbines in the coastal area of the Sea of Japan. Performance of JLDN, a large-scale lightning location system (LLS), in lightning detection is evaluated by comparison with the ground-truth data. Detection efficiency of JLDN highly depended on the peak current of return strokes, and strokes more than 15 kA in their peak values were all detected by JLDN irrespective of the polarity of the current. Absolute values of the peak current estimated by JLDN were on the average about 20% smaller than the directly measured values. © 2013 The Institute of Electrical Engineers of Japan.


Saito M.,University of Tokyo | Ishii M.,University of Tokyo | Sugita A.,Franklin Japan Co. | Natuno D.,Toyo Sekkei
2012 31st International Conference on Lightning Protection, ICLP 2012 | Year: 2012

Hot spots, where lightning strokes located by LLS (Lightning location system) concentrate, are formed almost in winter only in Japan in the coastal area of the Sea of Japan. The lightning strokes forming a hot spot are inferred to be related to upward lightning strokes which frequently damage wind turbines and electrical facilities in winter. Characteristics of lightning strokes forming a hot spot are investigated by using directly ob-served current, electric field waveforms and LLS data. © 2012 IEEE.


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.


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.

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