Project Subjects
Lightning Protection for an ICT Oriented Society
Background and Objective
Recently highly sophisticated society systems have been constructed using information and communication technologies (ICTs). These systems, however, are vulnerable against external disturbances such as lightning.
Once social infrastructures such as information networks and power supply systems will stop, extraordinary
confusion may occur in society.
In this project, we will further develop lightning protection methods constructed so far and will establish
novel lightning protection technologies to construct robust power supply systems in society with information andcommunication technologies, taking the concept of the lightning risk management into consideration.

Main results
1. Enhancement of the lightning database
We have constructed an enhanced lightning database based on the data for 17 years obtained with lightning
location systems in cooperation with electric power companies in Japan. Using the database, we have clariﬁed
lightning characteristics such as annual, seasonal and regional variations in lightning occurrence, the relationshipbetween lightning occurrence and climate conditions [Fig. 1].
2. Development of lightning risk assessment method for an ICT oriented society
We have constructed lightning risk assessment program to evaluate various lightning risks such as theoccurrence of instantaneous voltage drops [Fig. 2]. In the program, the concept of lightning hazard, which is anindex of severity determined by not only the number of lightning ﬂashes but other factors such as the distributionof lightning current peaks and striking characteristics, is used.
3. Development of technologies of lightning protection and EMC for control, information and communication equipment in power systems
We have been carrying out basic research into the effects of lightning surges on low-voltage circuits ofsubstations both experimentally and theoretically [H08004, H08017]. Using a model GIS circuit which simulates
actual substation equipments [Fig. 3 (a)], we have measured voltages induced in the control circuits by surge
currents ﬂowing into the bus of the model GIS. The experiments clariﬁed several important characteristics asfollows.
1) Capacitors set at the entrance of the relay system effectively reduce the induced voltage.
2) The peak values of induced voltages do not depend on grounding methods of the sheath of control lines. This
characteristic is different from a case where a surge current ﬂows into the grounding mesh of a substation.
These results will be used as fundamental data to establish a calculation method to predict induced voltages.

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Stable Power Supply Technology
1,000,000

WinterSummer

900,000

Number of flashes

800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
01992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Fiscal Year

Fig. 1 Annual variation of the number of lightning ﬂashes in Japan
Numbers of lightning ﬂashes all over Japan are shown for summer (Apr. to Oct.) and winter (Nov. to Mar.) About 0.7
million of cloud-to-ground ﬂashes have recently occurred.

Lightning
database
Facility
data

Calculation of outage rate
for transmission lines

Lightning risk
assessment

Calculation of outage rate
for distribution lines
Calculation of damage rate
for wind turbines
Calculation of damage rate
for low-voltage circuits

・・・

Geologicaldata

Evaluation of
economical losses

Calculation modules

Lightning risk map (Image)

単位電流あたりInduced
voltage [V/A]の発生電圧 [V]Fig. 2 Concept of lightning risk assessment program

両端非接地
保護継電装置側接地
両端接地

0.020.01
0–0.010(a) Experimental arrangement

10時間 [ μs]20(b) Effects of grounding position of thesheath on the induced voltage

Fig. 3 Voltage induced on a control circuit when a surge current ﬂows into the bus of a GIS
Voltage waveforms shown in Fig.3 (b) are obtained when a surge current ﬂows into the bus of the model GIS (Gas Insulated Switchgear) shown in Fig.3 (a). The voltage waveforms are almost the same and it indicates that effects of grounding
method on induced voltages are negligible.

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