Lightning occurrence data observed with lightning location systems of electric power companies in Japan: 2009–2013

Nine electric power companies in Japan have been collecting lightning data with lightning location systems. Five years of the lightning data (2009–2013) are summarized and analyzed in this paper. The recent annual number of lightning flashes of which the current is more than 10 kA in Japan is around 1 million. The variations of lightning occurrence characteristics by areas, seasons, and so on, are clarified. Meteorological conditions that may affect lightning occurrence are also discussed. Furthermore, we show that there is a clear correlation between the number of lightning strikes and the outage rate of transmission lines. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Rocket‐triggered lightning current waveforms in winter and investigation of extra‐fast current change

Since 1986, the authors have been taking part in triggered lightning experiments in winter, at Okushishiku, Ishikawa, for the purpose of observing the entire lightning current waveforms with coaxial shunt resistors and an electro‐optical measuring system. Extra‐fast current changes of the order of 1,000 kA/μs were recognized by sharp pulse records superposed on the positive current waveform obtained by a shunt resistor of relatively high residual inductance. This was not the case with a resistor of lower inductance. Furthermore, a positive lightning current waveform which looks like the composite result of bi‐polar discharges has been observed by an advanced measuring system of high performance. This paper deals with these current‐related topics of triggered lightning discharges, which will be analyzed hereafter in detail. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 18–23, 1999     

Lightning occurrence characteristics in Japan for 17 years: observation results with lightning location systems of electric power utilities from 1992 to 2008

We summarize the lightning data for 17 years from 1992 to 2008 obtained with lightning location systems of nine electric power utilities in Japan and analyze them. The observed annual number of lightning flashes of which the current is more than 10 kA is 400 000–800 000 and the 50% value of the cumulative distribution of lightning peak currents is about 23 kA in recent times. The variation of lightning occurrence characteristics by areas, seasons, and so on, is clarified. Comparison of the obtained data with those obtained by another lightning location system is also made. The relationship between lightning occurrence and climate is discussed. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Study concerning production of lightning overvoltages on low‐voltage power distribution lines

In order to study lightning problems of low‐voltage power distribution lines, lightning overvoltage waveforms were observed inside the homes of customers. The cause of lightning overvoltages was examined from observation of striking points by still cameras. Lightning overvoltages of 62 waveforms were recorded by observation over a period of about 3 1/2 years. Observed waveforms can be classified into three types of single polarity (positive or negative), both polarities (which change from positive to negative or negative to positive), and pulsive waveform. The causes of these lightning overvoltages which were estimated from striking points are shown as follows: (1) Induced lightning overvoltages on low‐voltage distribution lines. (2)   Electric potential rise due to discharge of surge arresters or current of overhead ground wire. (3)   Shift of lightning overvoltages from high‐voltage side of transformer to low‐voltage side, which is due to electromagnetic induction. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 66–75, 2000     

Direct measurement of lightning current through a wind turbine generator structure

The development of a wind turbine generator system in Japan is regarded as a promising source of clean energy, and its popularization is rapidly increasing. In Japan, there are many wind turbine generator systems installed on the Sea of Japan coast, with large wind capacity. However, since the Sea of Japan coast is a region with abundant winter lightning, a phenomenon peculiar to Japan, the wind turbine generator systems are subject to damage from winter lightning. Thus, it is important to observe the lightning currents striking wind turbine generator systems in order to provide lightning protection. The authors therefore installed currents sensors (Rogowski coils) on wind turbine generators installed in Hokkaido and Kagoshima Prefectures, and performed waveform observation of lightning stroke current in the winter of 2002 and the summer of 2003. These observations yielded a few current waveforms for lightning striking wind turbine generators. This paper describes the investigation and presents the observation results. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 40– 47, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20250     

Lightning activity during winter thunderstorm and leader progression in thundercloud

We have been studying lightning discharges by means of a UHF interferometer, and we show a comparison between lightning during winter thunderstorms are those during summer. The main objective of the comparison is further understanding of features of lightning during winter storms, especially of positive cloud to ground flashes. For this purpose we compare negative and positive flashes on UHF radiation and pulse density, and perform two‐dimensional mappings of UHF radiation sources. Moreover we show the three‐dimensional imaging for a cloud flash, and discuss the relationship between the altitude of leader progressions and atmospheric temperature profiles as a function of height. We also show the estimated velocity of leader progressions and find no discrepancy with the earlier results obtained by Proctor. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 71–78, 2000     

Mechanism of pole‐mounted transformer damage by backflow lightning and measures against the damage on low‐voltage distribution line

Pole‐mounted transformers are especially vulnerable to lightning damage. The progress of the information society imposes increasingly stringent requirements for the reliability of electric power supply, and this in turn necessitates a reduction in lightning damage to pole‐mounted transformers. Lightning protective devices (surge arresters) are now being installed around the primary bushing of the transformers, which has decreased the number of disconnections around the primary bushing due to lightning. But surge arresters installed on the primary side of the transformer cannot protect it against backflow lightning entering the secondary side of the transformer. The characteristic of transformer damage by backflow lightning is that the electromagnetic force produced by the current flowing into the secondary side deforms the transformer windings. This paper elucidates the mechanism of transformer damage by lightning flowing into the secondary side by comparing actual lightning damage cases with the results of verification tests using a short‐circuit generator. Effective countermeasures against transformer damage by backflow lightning are examined by EMTP calculations, which indicate that neutral grounding on the low‐voltage distribution line is the most effective way of decreasing the current flowing into the transformer. The lower the grounding resistance, the less current flows into the transformer. In addition, decreasing the voltage on the secondary side is important in order to protect the secondary‐side bushing. The calculation results indicate that surge arresters installed around the secondary side of the transformer are effective in decreasing the voltage on the secondary side. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(2): 1–11, 2010; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20921     

A field study of lightning overvoltages in low‐voltage distribution lines

The number of home electric appliances, such as personal computers and telephones, has been rapidly increasing. Lightning damage to these home electric appliances has a great impact on a highly sophisticated information society. There are cases in which lightning overvoltages in low‐voltage distribution lines cause malfunctions in them, even though they are equipped with surge protective devices to protect against lightning overvoltages. Therefore, for lightning protection of low‐voltage equipment including home electric appliances, it is important to understand the phenomenon of lightning overvoltages in low‐voltage power distribution lines. However, many aspects of this problem are not entirely clear, in particular how they are generated. The Tokyo Electric Power Company carried out lightning observations on low‐voltage distribution lines. The observation results provide a statistical distribution of lightning overvoltages in low‐voltage distribution lines. A mechanism for generating lightning overvoltages in low‐voltage distribution lines is inferred from the observed waveforms and facilities data. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(2): 12–21, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21299     

Classification of lightning damage to wind turbine blades

Lightning damage to wind turbine blades is of great concern to wind power installations. We investigate various issues arising from lightning damage and assess the causes through actual lightning observations as well as from high‐voltage and large‐current experiments. Although installing lightning receptors and down conductors provide a good countermeasure, blade damage can still be caused by lightning still. New techniques are needed to better protect blades from lightning surges; these may include not only better performance and layout of receptors, but also independent lightning towers and new types of blade materials. This paper provides a classification of blade damage sustained in winter lightning, ranked in severity by analyzing the many incidents of damage that have actually occurred in Japan. Moreover, a list of possible causes of damage and relative countermeasures is also presented. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Results of lightning impulse tests for a 275‐kV full GIS substation

This paper describes the outline and results of the lightning impulse tests for a 275‐kV full GIS substation. The behavior of lightning surges is a very important factor for the rational design of substations and low‐voltage and control circuits inside the substations. For the above reason, we carried out lightning impulse tests for a new 275‐kV full GIS substation. In these tests, we measured voltage induced in low‐voltage and control circuits, transient characteristics of grounding grid, injected voltage and current waveforms, and so on. By investigating these data, we confirmed the behavior of lightning surges inside the substation. We also compared simulated waveforms by EMTP analysis with the measured waveforms. The simulated results agreed well with the measured results. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 46–58, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10230     

Lightning Observation in 3D Using a Multiple LF Sensor Network and Comparison with Radar Reflectivity

A three‐dimensional (3D) lightning mapper consisting of multiple low‐frequency (LF) sensors has been developed to monitor thunderstorms and to estimate their charge structure. We have been conducting an observation campaign using the 3D lightning mapper in Kansai, Japan, since October 2012. In this study, we determine 3D source locations of intracloud and cloud‐to‐ground flashes and compare them with the radar reflectivity estimated by phased‐array radar (PAR) with high temporal and spatial resolution. Most LF sources are located in high radar reflectivity regions, confirming that the 3D LF lightning mapper monitors thunderstorms. A lightning flash with heavy branches is clearly imaged. Based on the bidirectional leader theory that negative and positive ends of a lightning leader develop simultaneously, we estimate the positive and negative charge regions in a thundercloud from the LF source locations. The radar reflectivity estimated by PAR supports the charge structure estimated by LF source locations.     

Characteristics of creeping discharge along aerial insulated wire under impulse voltages with various wave front durations

When lightning occurs in the neighborhood of outdoor high‐voltage distribution lines, creeping discharges propagate along the wire surface from the binding wire tip just after insulator flashover. These discharges give rise to various faults on distribution lines, for instance, disconnection and melting of wire, punch‐through breakdown, and so on. We must clarify the creeping discharge characteristics associated with various inductive lightning surges from the viewpoint of safety in high‐voltage distribution systems. In our previous paper, it was reported that the lengths and aspects of the negative creeping discharges were influenced by the wave front durations of impulse voltages applied to the central line with a grounded binding wire. The present study was performed to obtain more information on such creeping discharges. This paper describes the distinctive characteristics of a creeping discharge along the insulated wire surface when impulse voltages with various wave front durations are applied to the binding wire. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 29–37, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20430     

A Verification of Estimation Accuracy of Lightning Current Waveform and Charge Transfer from Measured E‐Field Waveform

To establish effective countermeasures on power facilities against lightning damage, it is necessary to clarify the lightning characteristics such as current parameters at the area of interest. In order to collect lightning current parameters effectively, the authors have observed electric and magnetic field waveforms simultaneously at south Kyushu, where the lightning flash density in summer is high. Based on observed electric field waveforms, the lightning current parameters have been estimated by adopting the Diendorfer–Uman model (DU model) as the return‐stroke model. In this paper, the accuracy of the estimated return‐stroke current waveform is verified by comparison with directly measured return‐stroke current waveform, along with the accuracy of the estimated charge transfer from the electric field waveform measured with a slow antenna.     

The influence of wave front duration of impulse voltage on creeping discharges along aerial insulated wire

In high‐voltage aerial distribution systems, creeping discharges progress along the cable surface from the free end of the binding wire when overvoltages caused by a lightning surge have invaded the central line of an insulated cable. Consequently, various accidents such as punch‐through breakdown, melting, or snapping of a cable, often occur at these systems. In our previous studies, it has been clarified that the lengths and aspects of creeping discharges under a 1.2/50 µ s impulse voltage condition can be markedly affected by changes in the electric field strength on the cable surface. However, lightning impulse surges which may invade the central line of a cable have various wave front durations. This will further complicate creeping discharge phenomena due to lightning. In this paper, we report the influence of the wave front duration on both the lengths and the aspects of the creeping discharges which progress on the cable on application of lightning impulse voltages. It has been shown that the behavior of negative creeping discharges reveals pronounced changes in response to the duration of the wave front of the applied voltage. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(2): 30–38, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10263     

Breakdown characteristics of gas‐insulated switchgear for nonstandard lightning impulse waveforms under nonuniform electric field

To improve the insulation specification of gas‐insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF₆ gas during actual surges (called nonstandard lightning impulse waveforms) occurring at field substations. The authors observed the insulation characteristics of SF₆ gas gap under various types of nonstandard lightning impulse waveforms and compared them quantitatively with those obtained with standard lightning impulse waveforms. The experimental results were used to derive an evaluation method for real surges, which was applied to typical surges for various UHV and 500‐kV systems. In the preceding study, therefore, only the case of a quasi‐uniform electric field (with a typical range of field utilization factors in the bus of a GIS) was investigated. In the present investigation, the insulation characteristics of an SF₆ gas gap for a nonuniform electric field were observed experimentally and an evaluation method for converting nonstandard lightning impulse waveforms equivalently to the standard lightning impulse waveform was investigated. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(1): 11–18, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21144     

Evaluation of lightning fault rate of EHV transmission line based on lightning parameters derived from electromagnetic observation

Cloud-to-ground lightning flashes in the Niigata area in Japan have been observed for a few years by a magnetic direction-finder network. Data obtained so far are analyzed carefully taking into account the operating characteristics of the system. As a result, frequency distributions of return-stroke current for each polarity are produced, and their seasonal variations and the occurrence probabilities of high current exceeding 200 kA are clarified. Based on the estimated current distributions, back-flashover rates of 500-kV 2 cct transmission lines are calculated. It is known that the back-flashover caused by downward flashes can account for most of the line outages in the summer for both single- and multiple-line faults. However, this mechanism cannot explain the high outage rate in the winter experienced in the winter thunderstorm area in the late 1970s. In spite of the low lightning flash density in the winter, the multiple-line fault rate in the winter caused by back-flashovers is predicted to be comparable to that in the summer, because of the seasonal variation of the frequency distributions of return-stroke current.     

Study of lightning current by remanent magnetization

A study of remanent magnetization is made at the areas of lightning strikes. In the case of triggered lightning (Okushishiku, Hokuriku district), the magnetic direction of the specimens shows a clockwise rotation pattern around the point of lightning strike. At an archaeological site in Miyagi Prefecture, an anticlockwise pattern of the magnetic direction was detected. These results indicate that a stable remanent magnetization is acquired by the strong magnetic field induced surrounding the lightning current, both in negative and positive lightning flashes. Also, a detailed analysis of magnetization clarifies the electric current flow underground caused by the lightning. The study of remanent magnetization will become a useful method to elucidate the path of the lightning current. © 1998 Scripta Technica, Electr Eng Jpn, 123(4): 41–47, 1998     

Characteristics of mesospheric sprites in the Hokuriku area and their causative lightning discharges

Mesospheric optical phenomena (including sprites) are becoming an interesting subject from the standpoint of atmosphere–ionosphere coupling. This paper deals with our observation of sprites associated with winter thunderstorms in the Hokuriku area and we show the characteristics of those sprites and their parent lightning discharges. Although the scale of Japanese lightning in winter is very small compared with the MCS (Mesoscale Convective System) for the summer continental lightning, the essential quantities (polarity, charge transfer, and so on) are found to be nearly the same as those for the MCS. However, an additional factor might be required, such as the self‐organization of the lightning. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 9–17, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20178     

Experimental and analytical studies on lightning surge characteristics of ground mesh

Lightning surge characteristics of a ground mesh have an influence on electromagnetic transient behaviors in low‐voltage and control circuits. This paper describes experimental and analytical studies on lightning surge characteristics of a ground mesh. The experimental studies are carried out under various conditions. The experimental parameters considered in this measurement include earth resistances, current injection points, and injection current waveforms. These measured results are compared with calculated results based on the theoretical studies by Sunde. A comparison of the measured results with the calculated results shows good agreement. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 16– 23, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20559     

避雷针和半导体消雷器的火箭引雷试验分析

介绍了对普通避雷针和半导体消雷器进行的火箭引雷试验,列出了全部试验结果,包括用普通照相机的B门进行静态拍摄所得的典型照片以及用示波器记录的雷电流波形。讨论了雷击半导体消雷器和普通避雷针间的显著差别,说明半导体消雷器具有极大的限流能力。