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The increase in inverter-based resources associated with the increased installation of PV sources is a concern because it reduces the inertia of the power system during peak PV generation periods. As a countermeasure to reduce grid inertia, the addition of pseudo-inertia using virtual synchronous machines can be selected, and PV generation can cooperatively contribute to the stable operation of the power system by using the suppressed output as reserve power. However, few studies have analyzed VSMs that do not use batteries and use PV as a resource (PV-VSM) in simulations, including grid interconnection and solar radiation fluctuations, and it is necessary to clarify the issues and discuss countermeasures. In this study, electromagnetic transient response analysis was applied to a VSM connected to a two-generator system, simulations were performed, and the following findings were reported and countermeasure methods for the problem were proposed. When the PV capacity is insufficient for the output required by the VSM inverter, the PV-VSM control system may become unstable. This is caused by a drop in the capacitor voltage of the DC/DC converter due to insufficient PV output. The limiter control system is designed to address this problem by combining the headroom estimation system with the current limiting algorithm. The proposed limiter control system is validated on solar radiation ramp fluctuations as a test case and found that the system was effective in supressing PV-VSM instability. In our simulation case, the PV-VSM with our limiter control can continue to operate stably even if the PV available power is 0.03 [p.u.] short of the inverter's reference power by the solar power ramp fluctuation, as long as the inverter installation rate is less than 50%. [ABSTRACT FROM AUTHOR]

Field study of lightning stroke effects, particularly the mechanisms that produce distribution line faults, is essential for designing rational lightning protection for distribution lines. The Tokyo Electric Power Company has conducted photographic research and observed voltage and current waveforms due to lightning in actual distribution tines since 1996, obtaining 284 datasets, including 62 for direct hits to the tines. These results permit a comprehensive study of each lightning flash; the photographs show the precise location of the lightning, and the waveforms provide detailed analyses of flashovers in the distribution systems. This paper evaluates typical observed datasets, including surge insulator voltage waveforms. In some cases, the direct lightning strokes did not cause distribution line faults because the power follow current extinguished spontaneously after flashover generation. These results provide a solid basis for examining the mechanisms underlying the production of distribution line faults, and can lead to effective lightning protection practices. Index Terms--Direct lightning stroke, distribution line, flashover, indirect lightning stroke, lightning protection design.

The Tokyo Electric Power Company had conducted field research of voltages and currents in actual distribution lines due to lightning strokes between 1997 and 2001. These results confirm that the distribution line faults are mainly caused by direct lightning strokes to the line. Thus, it is important to simulate lightning performance for direct strokes to establish a lightning protection design of distribution lines. In this paper, statistical data of the observed voltages and currents are analyzed, and the validation of the observation results for the direct lightning strokes using a lightning surge analysis model is conducted. The observation results and the simulation model are useful in clarifying lightning performance in distribution lines. Index Terms--Direct lightning stroke, distribution line, lightning current, lightning protection design, lightning surge analysis model, soil ionization.

This paper describes the process of setting up an appropriate volt–var curve for the reactive power control of a photovoltaic (PV) inverter interconnected to a distribution line that is voltage controlled by a load ratio control transformer (LRT). Computer simulations with 360 patterns of volt–var curves applied to five actual distribution line models are presented. The number of patterns was narrowed down to 23 by using voltage, distribution-line loss, number of LRT tap operations, and a new evaluation index, the match ratio. When a power-factor constraint is imposed on the PV inverter, it may not output the reactive power according to the volt–var curve depending on the active power output. The match rate is an index to show the percentage of the operating points of the PV inverter that conform with the volt–var curve. By evaluating the match rate, it can be demonstrated if the PV inverter efficiently contributes to the voltage control, which greatly contributes to narrowing of the volt–var curve. It is demonstrated that the volt–var curve obtained using the proposed method is superior in terms of voltage controllability, distribution line losses, and the number of LRT tap controls. [ABSTRACT FROM AUTHOR]

Virtual inertia control is a methodology to make inverter-based resources (IBR) behave like a synchronous machine. However, an IBR cannot fully emulate the response of synchronous machine because of its low-current capacity. When the inertial response of an IBR is affected by the current limitation, the synchronization of the synchronous machine simulated virtually inside the IBR controller with the other synchronous generators in the grid is affected, which may cause step-out of the simulated generator. We propose a methodology which can keep the synchronization by modifying internal induced voltage of the simulated generator to follow the system voltage change. The proposal is validated by the simulation using a nine-bus transmission system model including two synchronous generators and a large-scale IBR. The result of the generator trip simulation shows that the proposed method suppresses the phase angle variation while the current is limited, and avoids the instability regarding the synchronism. Furthermore, the impact of the current limitation on frequency stability is also evaluated through the simulation study and it is found that as the amount of output suppression increases, the frequency nadir falls, but the rate-of-change of frequency is hardly affected. [ABSTRACT FROM AUTHOR]

Damage to home electric appliances due to lightning surges has recently become more common. The installation of SPDs (surge protective devices) in interior wiring is a countermeasure against damage and is also becoming more widespread after amendment of the regulation on indoor wires in 2005. Past study showed an effective method in which the earth line of the SPD is connected with that of home appliances and is grounded at one place in the home. However, because the methods of installing the distribution line in homes vary, it is difficult to estimate the effect of SPDs in every home, and high-precision analysis by EMTP for interior wiring and SPD in the home is required. In this study, experiments were conducted with interior wiring and varistors, which constitute SPDs, and this paper reports the results of those experiments and of EMTP analytical models. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(4): 24-33, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21062 [ABSTRACT FROM AUTHOR]

Electric supply reliability is an issue of wide importance to both an information-oriented society and electric power companies. This paper focuses on lightning effects on distribution lines. Field research is now underway in the northern part of the Kanto Plain in Japan, and voltage and current waveforms in distribution lines due to lightning hits have been observed since 1996. There are now 284 datasets; these include data on 62 direct flashes to lines. This research reveals that a distribution line can be protected from direct lightning strokes. In some cases, no power follow current was confirmed after a multiple phase flashover, and a statistical analysis was conducted to investigate factors affecting the generation of power follow current. These results can serve as a valuable resource to help clarify the mechanisms underlying the production of distribution-line faults caused by lightning effects. [ABSTRACT FROM AUTHOR]

As society becomes ever more dependent on electronics, interest in the patterns of lightning hazards in low-voltage distribution lines including residences is growing. However, there have been few studies on low-voltage distribution lines and many things remain unknown about the propagation patterns of lightning surges in the field, particularly the intrusion of lightning surges into residences. The Tokyo Electric Power Company has conducted field research of phenomena accompanying lightning flashes to actual distribution systems using lightning-activated cameras as well as lightning surge waveform detectors, obtaining invaluable 101 datasets of lightning flashes between 2002 and 2007. This paper analyzes typical observation examples and estimates the lightning surge propagation routes in low-voltage distribution lines. In some examples, it is inferred that a lightning current flowed in the reverse direction from the residence to the low-voltage distribution line caused by ground potential rise due to the nearby lightning to the ground. These results will be useful for clarifying lightning surge propagation patterns in low-voltage distribution lines. [ABSTRACT FROM AUTHOR]

Lightning overvoltages in low-voltage circuits in houses originating from a distribution line or an antenna have been actively studied. However, the mechanism by which damage is caused to home appliances due to a lightning strike to the ground near the house is still unclear. This paper discusses lightning overvoltages and currents in low-voltage circuits for various scenarios, such as a lightning strike to the ground, a direct strike to a distribution line, and a direct strike to an antenna. Simulations are carried out using the Electromagnetic Transients Program. From the simulation results, direct lightning strikes cause the most serious damage to home appliances, but nearby lightning strikes should also be considered when designing lightning protection schemes. [ABSTRACT FROM PUBLISHER]

Probability distribution of surge discharging current of arresters provided a basis for conventional theory of grounding systems. In order to rationalize the grounding systems, it is necessary to grasp the statistical data of lightning surges on distribution lines caused by direct lightning strokes and indirect lightning strokes. Lightning phenomena on TEPCO's distribution lines had been continuously observed for the rationalization of lightning protection design of distribution lines. The observation had been carried out with still cameras and monitoring sensors of lightning surges. This makes it possible to discover new interesting facts that can be useful for rationalization of lightning protection design of distribution lines. Cumulative frequency distribution of conventional data is close to that of ZnO discharging current in the case of direct strokes and indirect strokes through TEPCO's observation. Moreover, to verify the cumulative current distribution in concrete poles, the authors have compared the cumulative distribution of current through ground lines with that of current through ground lines and concrete poles. The results show that the distribution of current through ground lines and concrete poles is larger than that of current through only ground lines for high currents exceeding 1 kA. This fact suggests that lightning surge current flows not only in ground lines but also in concrete poles. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 36–44, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20468 [ABSTRACT FROM AUTHOR]

In order to rationalize the lightning protection design of distribution lines, lightning phenomena on TEPCO's distribution lines were continuously observed. The observations were carried out with still cameras and lightning surge monitoring sensors. The results elucidate the lightning performance of distribution lines. For example, direct lightning strokes are the major cause of the present distribution line faults. This fact suggests that it is important to investigate observation data on direct lightning strokes. The observation data were analyzed by means of a direct lightning analysis model. The calculated waveforms were compared with the measured waveforms on distribution lines. The probability distributions of the surge currents and voltages were calculated by the Monte Carlo method. These results provide new data on lightning performance. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 91(10): 28– 37, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10164 [ABSTRACT FROM AUTHOR]