It is well-known that winter lightning has many special characteristics, and the charge structure of winter thunderstorm has been under debate for tens of years. This paper reviews past studies on charge structure of winter thunderstorm and presents new results with the observation of lightning mapping array (LMA). The results show that compared to summer thunderstorm, winter thunderstorm can exhibit extremely complicated charge structures. Dipole and tripole structures of both positive and negative polarities have all been observed. Relatively large thunderstorms can exhibit different charge structures in different regions, and as a thunderstorm develops, its charge structure can also have significant changes. One common feature of the charge structures observed is that the charge regions are mainly around the -10°C and -20°C temperature level, in agreement with the non-inductive electrification mechanism. Another common feature of the charge structures is that its horizontal extension is usually much larger than its vertical extension. Besides, the vertical distance between the two charge layers in opposite polarity is usually small, around 1 or 2km. All these factors combined may conduce to the high percentage of positive CG, the high percentage of bipolar CG and the superbolts observed in the winter storms in Japan.

The three-dimensional finite difference time domain (3D-FDTD) method is employed to compute and to analyze the ground structure and conductivity effect on the lightning electromagnetic waveforms and their magnitudes. In this computation, the return-stroke current is represented by two electromagnetic models, namely: a vertical resistive wire having additional series distributed inductance and a vertical resistive wire coated by a fictitious material having a high relative permittivity and permeability. For validation needs, of the proposed calculating approach and the developed computation code, the obtained results are compared to those calculated by the achievement of analytical electromagnetic fields expressions taken from specialized literature. Against this comparison of these two approaches, a good agreement between results has been obtained validating thus our computation approach which has the advantage to take into account the real medium and ground geometry. At the end of this work we show that fields above a uniform or horizontally stratified ground near a vertical lightning return-stroke channel are not much influenced by the ground stratification, but the penetrating fields in the ground are influenced more by the presence of the stratified ground. It also appears that each electromagnetic model, tested in this work, yields reasonably accurate results of close electromagnetic fields.

This review covers selected results of recent observations of natural lightning and laboratory sparks performed using high-speed video cameras at the Lightning Observatory in Gainesville (LOG), Florida, and at the high-voltage research facility in Istra, Russia, respectively. The most important results include (a) the first high-speed video images of bidirectional leader that made contact with the ground and produced a return stroke, (b) the first speed profile of positive leader that developed in the channel of preceding negative stroke, (c) discovery of unusual plasma formations that coexist with “normal” discharges inside the artificially-charged cloud, and (d) the first two-frame record of the connection between negative and positive leaders after the common streamer zone has been formed.

This work provides insight in the attachment characteristics of upward initiated lightning discharges to wind turbines and their possible consequences for the lightning protection of wind turbine blades. All discharges were recorded at the Japanese coast of the Sea of Japan which is known for intense upward lightning activity. 172 video recordings of lightning discharges on rotating wind turbines are analysed and attachment angle, detachment angle, and the resulting angular displacement were determined. A classification between self-initiated and other-triggered upward lightning events is performed by means of video analysis. The results reveal that the majority of discharges are initiated when the wind turbine blade is aligned vertically; however, also lightning attachments to horizontal blades are reported. Horizontal attachment (or a slightly inclined blade state) is often related with a triggered lightning event prior to the discharge. There are about twice as many lightning attachments during the ascending blade movement compared to the descending blade movement. Furthermore, a comparison between current parameters of upward lightning flashes during stationary and rotating wind turbine operation reveal no substantial difference between the two operational states.

Recently, distribution surge arresters have been installed on Japanese distribution lines in high density for reducing lightning-related overvoltages. However, surge arresters are sometimes damaged by direct lightning strokes to the distribution lines, especially in winter. In order to prevent the damages of surge arresters, it is necessary to find out lightning protection performances of surge arresters sufficiently.

In Hokuriku Electric Power Company, the values of energy capability of surge arresters have been measured by experiments or observations. However, energy capability of a surge arrester after operations with lightning currents has not been measured in detail. In this paper, we present the values of energy capability of surge arresters after operations under several conditions of impulse currents.

ELF-band lightning electromagnetic pulses (ELF-LEMPs) have been used to retrieve lightning Charge Moment Change (CMC) and electric Current Waveform (CW). Since neither CMC nor CW can be measured by conventional Lightning Location System (LLS), it is advantageous to combine LLS and ELF measurements in order to monitor lightning geo-locations, CMC and CW simultaneously. To construct an accurate combined system of LLS and ELF measurements matching algorithms for associating lightning geo-locations and their corresponding ELF-LEMPs are important. This study developed three matching algorithms based on the time, the polarity and the direction of lightning discharges. Furthermore, we applied the newly developed algorithms to LLS and ELF measurements in Tohoku district and obtained a 30-70% Detection Efficiency (DE). The results also indicate that DE depends mainly on peak electric current (I_p). For example, DE exceeds 70% for lightning events with |I_p| ≥ 40kA while DE drops below 70% for lower I_p events.

We studied winter lightning current waveforms measured at the radar tower of Hokuriku Electric Power Company and estimated magnetic field waveforms from the lightning current waveforms using the Transmission Line (TL) model. A lightning current waveform, which is one of important parameters for surge simulations, can be estimated from the magnetic field waveform using the TL model for return strokes. It is necessary to study application of the model for estimation of current waveforms of winter lightning strokes.

Lightning currents were measured at the radar tower using a Rogowski coil and electromagnetic fields radiated from the lightning channels were measured at observation sites more than 12km away from the radar tower in Hokuriku area using an electric antenna and two cross loop antennas. 6 negative lightning currents were measured in winter from 2014 to 2016. The magnetic field waveforms were estimated from the lightning current waveforms using the TL model. The estimated waveforms agreed well with the waveforms measured at the observation sites when the velocities of the lightning current waves were set to 1 × 10⁸ m/s.

This study is concerned with an instability in DC arc channels that is analogous to a process called `avulsion' in river channels and which accordingly, is given the same name. The instability involves both an abrupt brightening of the arc channel and a straightening of its tortuosity. The evidence in the literature for this instability in the continuing current of lightning serves as motivation to suggest it as a mechanism for the M-component that is still poorly understood.

Abstract surge protective components (SPCs) such as metal oxide varistors (MOVs), avalanche breakdown diodes (ABDs), and thyristor surge suppressors (TSSs) have been widely used in low-voltage power distribution systems, in main AC power lines inside of appliances, electrical, and electronic systems, or signaling and telecommunication lines in ICT equipment to protect them against lightning surges. The maximum transient clamping voltage and surge-handling capability are important parameters to determine the ability of the SPCs. They are determined by the negative differential resistance, which depends on the steepness and wave-tail of the applied lightning surge waveform, especially characterized by winter lightning. The transient surge responses of SPCs were analyzed, and the mechanisms of negative differential resistance were clarified. Negative differential resistance was caused by the lead wire inductance in MOVs, the positive temperature coefficient of breakdown voltage in ABDs, the dependence on temperature of the Auger recombination, and the carrier mobility in TSSs. Clamping voltage and surge-handling capability designs considering inductance in the lead wire and the dependence on temperature during self-heating are important to apply to SPCs so that they can withstand high energy winter lightning with a long wave tail.

The literature on meteorological context, predominant microphysics, charge separation and lightning in winter storms in a wide variety of geographical locations is reviewed. Both similarities and differences between summer and winter conditions are discussed. Particular emphasis is given to a snow dipole, whose existence is clearly manifest in summer conditions in the End of Storm Oscillation and in the positive end of lightning `bipoles'. Outstanding problems in winter storm electrification are discussed.

Lightning observation has been carried out at Tokyo Skytree, which is a 634-m high freestanding broadcasting tower located in a flat terrain at 1m ASL. 25 downward and 37 upward flashes were observed at the tower during 2012 to 2016. This paper focuses on upward negative flashes initiated from the top of the tower. Of the 37 confirmed upward flashes, 35 current waveforms were recorded by Rogowski coils installed at 497-m height of the tower. One out of 35 upward flashes was a positive flash initiated by a negative upward leader, 7 out of 35 flashes were bipolar flashes initiated by positive upward leaders, and the rest were negative flashes initiated by positive upward leaders. The authors evaluated the lightning current parameters of subsequent strokes and initial continuous currents (ICC) of the upward negative flashes.

This paper develops a bottom-up energy system model, the power generation sector of which holds high temporal resolution so as to precisely analyze the massive deployment of intermittent renewables such as PV and wind, and to consider a number of technological features of power generation such as load following, minimum output and regular maintenance. The model has high inter-annual time resolution of ten minutes for 365 days, while most MARKAL/TIMES models have only two diurnal and three seasonal time-slices. The developed model is cast as linear programming model with ten million constraints and five million endogenous variables. Simulation analysis on CO₂ reduction toward 2030 in Japan reveals that decarbonization at power generation sector has a substantial role to mitigate the CO₂ emissions rather than improving energy efficiency at final energy demand sectors. Moreover, comparison analysis with low temporal resolution model finds out that the low resolution model would overestimate the optimal installation capacity of the PV systems because it cannot consider their intermittent feature well.

Recently, wind power generation are installed as a countermeasure for the environmental issue in Japan. However, wind power generation output is fluctuated due to wind condition. Moreover, it is some negative impact for system operation such as the economic load dispatching control and the load frequency control. In Japan, NEDO has started the project as a countermeasure for massive penetration of wind power generation in 2014, called “R&D Project on Grid Integration of Variable Renewable Energy”. In this paper, we proposed the output fluctuation suppression control method of wind power generation using the battery and forecast data of wind generation output. Specifically, the target value of wind power generation output is calculated to decrease the deviation output from fluctuation suppression code for ramp event using deterministic optimization method. The effectiveness of proposed method is evaluated through the computational simulation using forecast data and actual wind power generation output in Tohoku area.

SF₆ gas-insulated transformers (GITs) with a large capacity of 300MVA-275kV have applied to underground substations because of their big advantage in safety. The conventional GIT is consist of three single-phase transformers because of a limitation of transportation and an on-load tap changer (OLTC) is divided into two tanked parts such as a diverter switch and a tap selector to minimize room height of underground substations.

Unlike oil-immersed transformers (OITs), layout of GIT is not affected by requirements from the view point of fire protection because of its inflammable and non-explosive feature. This excellent feature is expected to contribute to space reduction not only for underground substations but also for outdoor substations. Therefore, we have developed the world's first three-phase 300MVA-275kV GIT with a built-in OLTC for outdoor EHV substations. This new GITs successfully reduced 40% or more of space of an EHV outdoor substation consisted of three transformers as compared with a case of applying OITs.

In this paper, we discuss some specific examples of effort to develop the new GIT such as optimization of specifications applied for the new GIT, achievement of significantly advanced insulation and cooling design of GIT windings, and results of a full-scale test using a prototype of the new GIT.