Showing papers in "Electrical Engineering in Japan in 2013"

A grid-connected inverter with virtual synchronous generator model of algebraic type

Abstract: Summary This paper presents experimental results on a grid-connected inverter. The control of the inverter is based on a virtual synchronous generator model of algebraic type. When using the virtual synchronous generator model of algebraic type, there is no evidence for satisfactory operation with unbalanced load and nonlinear load, because the generator models are constructed under the assumption that the load is linear and balanced. By choosing the feedback control loop gain appropriately, satisfactory operation is achieved even if an unbalanced and nonlinear load is connected. Experimental results show that the power controls, active and reactive, are achieved preferably in grid-connecting mode. Smooth transitions are also achieved from the connected mode to the island mode. The inverter can operate satisfactorily when the unbalanced load is connected. Harmonic analysis is performed with a three-phase full-wave rectifier connected as a nonlinear load. The harmonic current is supplied by the inverter and its output LC filter. It is shown that the harmonic current is supplied mainly by the inverter and that the voltage waveform is acceptable for practical use. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(4): 10–21, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22428

Global variation of ULF geomagnetic fields and detection of anomalous changes at a certain observatory using reference data

Abstract: By using multiple reference stations, we have developed a method to get reliable ULF global geomagnetic variations. This background is extremely useful for detecting local anomalous behaviors. In this paper we report on variable tools developed to identify the anomalies in two frequency ranges: daily variations and variations of 10- to 1000-second span. For estimating background daily variations, the periodical model has been applied for data observed at three reference stations and a study station. Comparison between the first principal component of the periodical data from the reference stations and the periodical data derived from the target station generally provides high correlation. For data with 100-second periods after wavelet filtering, the nighttime energy variations have been investigated among three reference stations and a study station. Similar principal component analysis as the diurnal variation has been performed and results also show high correlation between the variation at the target and the global background. These tendencies suggest that the two proposed methods are effective in automatically identifying the anomalous patterns. Examining the original data, we can obtain details of waveforms and distinguish whether the anomalies are related to underground activities or simply to some artificial noises. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(3): 9–18, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22299

Frequency control with dead band characteristic of battery energy storage system for power system including large amount of wind power generation

Abstract: Summary This paper proposes a method for frequency control of a battery energy storage system applied for frequency deviation suppression in a power system including a large amount of wind power generation. A 5000-MW power system capacity with governor control and load frequency control is assumed for the study, and 500 MW of wind power generation capacity is assumed. The battery energy storage system is assumed to be added for frequency control in the power system. Suitable frequency control functions of the battery energy storage system and suitable capacity of the battery energy storage system which coordinate with conventional frequency controllers in the power system are reported.

Location feasibility of degradation in cable through Fourier transform analysis of broadband impedance spectra

Abstract: Since electric cables play important roles such as power supply and information transmission, their degradation may cause serious problems. We have been trying to monitor the degradation of cable insulation by measuring the magnitude and phase angle of the impedance as a function of frequency in a very wide frequency range. The cables tested were insulated with flame-retardant ethylene propylene rubber or special heat-resistant polyvinyl chloride. They were partially damaged by peeling off their insulation layers, or partially aged by heat and γ-rays. The impedance and phase angle were measured from a terminal of the cable. The difference in impedance between the damaged and sound cables is made clear by fast Fourier transform analyses, from which the damaged portion can be located. It can be clearly shown that this method has the potential ability to detect the degradation of cable insulation induced by physical damage, γ-ray irradiation, and thermal aging. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(1): 1–8, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22384

Measurement of topcoat thickness of thermal barrier coating for gas turbines using terahertz waves

Abstract: The topcoat thickness of thermal barrier coating (TBC) samples was measured using terahertz (THz) waves. The index of refraction of yttria-stabilized zirconia (YSZ), which is the topcoat material, is necessary to obtain the topcoat thickness from time domain reflectometry. Time domain THz spectroscopy was applied to YSZ samples, and the index of refraction was measured to be 4.8 in the frequency region 0.1 to 1.2 THz. The topcoat thickness of six different TBC samples, which varied from 300 to 600 µm, was measured using THz waves. The results were in agreement with microscope observation results to within measurement error. In addition, the topcoat thickness profile of a turbine blade sample was measured with a resolution of 2.4 µm. The profile showed a standard deviation of 4 µm, which reflects the actual variation in the topcoat thickness. The results showed that THz waves are effective for high-resolution measurement of the topcoat thickness. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 1–9, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22385

Mega‐solar optimal allocation using data envelopment analysis

Abstract: In this paper, the optimal allocation of mega-solar is examined using data envelopment analysis (DEA). A great deal of attention is paid to photovoltaic power generation in Japan. Because such power generation can be freely used, it is attractive in Japan, which has few natural resources. The allocation of mega-solar, a large-scale photovoltaic power generation method, is an important problem for meeting the hope of efficient operation. We tried to apply DEA in Shizuoka Prefecture and to solve this issue. In this type of DEA application, some analyses often result in zero weighting factors in the parameters of some items to be studied, which implies that the corresponding items are not appropriately evaluated. The existing studies do not give special consideration to this situation. In this study, a new calculation scheme is proposed, the above-stated problems are successfully resolved, and the optimal candidate sites have been selected for the mega-solar allocation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 24–32, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22322

Magnetic properties and domain structure of nonoriented electrical steel under stress

Abstract: The influence of stresses on the magnetic properties of nonoriented electrical steels was studied. The dependence of iron loss on compressive stress was affected by grain size. The magnetic polarization J in strong magnetic fields such as 5000 and 10,000 A/m increased due to compressive stresses and decreased due to tensile stresses in samples with low Si content. Using Kerr-effect domain observation, it was found that the reduction in J caused by tensile stresses was attributable to residual striped domains. Magnetostriction measurements in strong magnetic fields indicated that the increase in J under compressive stresses originated from the Villari effect (inverse magnetostrictive effect) due to negative magnetostriction in low-Si materials. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(4): 10–18, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22320

Estimation model for magnetic properties of stamped electrical steel sheet

Abstract: Less deterioration in the magnetic properties of electrical steel sheets in the process of stamping out the iron core is necessary in order to maintain performance. First, the influence of plastic strain and stress on the magnetic properties is studied using test pieces, in which plastic strain is added uniformly and residual stress is not induced. Because the influence of plastic strain is expressed using the equivalent plastic strain, at each equivalent plastic strain state the influence of the load stress is investigated. Second, the elastic limit is determined to be about 60% of the macroscopic yield point (MYP), and this agrees with the stress limit inducing irreversible deterioration in the magnetic properties. Therefore, simulation models, in which excess elastic limit plastic deformation begins and the magnetic properties deteriorate sharply, are proposed. Additional points taken into consideration in the deformation analysis are the strain rate sensitivity of flow stress, the anisotropy under deformation, and the influence of stress triaxiality on fracture. Finally, the proposed models are shown to be valid because the magnetic properties of rectangular sheets 5 mm wide stamped out from a nonoriented electrical steel sheet (35A250 JIS grade) can be estimated with good accuracy. It is concluded that the elastic limit must be taken into account in both the stamping process simulation and magnetic field calculation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(2): 1–11, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22269

Forecasting of solar irradiance with just-in-time modeling

Abstract: PV power output mainly depends on solar irradiance, which is affected by various meteorological factors. Thus, it is required to predict solar irradiance in the future for the efficient operation of PV systems. In this paper we develop a novel approach for solar irradiance forecasting, in which we combine the black–box model (JIT modeling) with the physical model (GPV data). We investigate the predictive accuracy of solar irradiance over a wide controlled area of each electric power company by utilizing measured data from 44 observation points throughout Japan provided by JMA and 64 points around Kanto provided by NEDO. Finally, we propose an applied forecasting method of solar irradiance to deal with difficulties in compiling databases. We also consider the influence of different GPV default times on solar irradiance prediction. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(4): 19–28, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22338

Assessment of Japan's Optimal Power Generation Mix Considering Massive Deployment of Variable Renewable Power Generation

Abstract: Summary This paper analyzes Japan's optimal power generation mix considering massive deployment of solar photovoltaic (PV) systems and wind power generation. The extensive introduction of PV systems and wind power system is expected to play an important role in addressing energy security and climate change concerns in Japan. Considering this expected large-scale deployment of PV systems in the electric power system, it is necessary to investigate the optimal power generation mix which is technologically capable of controlling and accommodating the intermittent output-power fluctuations inherent in PV and wind energy systems. Against these backgrounds, we develop an optimal power generation mix model, explicitly analyzing the impact of output fluctuation in variable renewables in the detailed resolution of time intervals like 10 minutes for 365 consecutive days, with the role of stationary battery technology incorporated. Simulation results reveal that considerable deployment of those variable renewables does not necessarily require a scale of battery capacity similar to that of the variable renewable capacity, due to quick load-following treatment by thermal power plants, pumped-storage hydropower, and battery technology over renewable output fluctuation.

Analysis of possible introduction of PV systems considering output power fluctuations and battery technology, employing an optimal power generation mix model

Abstract: This paper presents an evaluation of the impact of extensive introduction of photovoltaic (PV) systems and stationary battery technology into the optimal power generation mix in the Kanto and Kinki regions. The introduction of solar PV systems is expected to be extensively deployed in the Japanese household sector and utility companies in order to address the concerns of energy security and climate change. Considering this expected large-scale deployment of PV systems in electric power systems, it is necessary to investigate the optimal power generation mix which is technologically capable of controlling and accommodating the intermittent output-power fluctuations inherent in PV systems. Against this background, we develop both a solar photovoltaic power generation model and an optimal power generation mix model, including stationary battery technology, which can be used to explicitly analyze the impact of PV output fluctuations at a detailed time interval resolution such as 10 minutes for 365 consecutive days. Simulation results reveal that PV introduction does not necessarily increase battery technology due to the cost competitiveness of thermal power plants in the load-following requirement caused by PV systems. Additionally, on the basis of sensitivity analysis on PV system cost, dramatic cost reduction proves to be indispensable for PV to supply bulk electricity similarly to thermal and nuclear power plants. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 9–19, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22329

Issues for power system operation for future renewable energy penetration: Robust power system security

Abstract: A large amount of PV penetration may introduce uncertainties in future power system planning and operations This paper proposes the concept of “Robust Security (RS)” and the “RS region” in order to investigate power system security in the presence of a large amount of uncertainties The RS region is defined as the region of power system operation where the system is secure under uncertainties It is shown that the region tends to shrink and disappear for a high degree of PV penetration Emerging problems concerned with security in future power systems are investigated © 2012 Wiley Periodicals, Inc Electr Eng Jpn, 182(1): 30–38, 2013; Published online in Wiley Online Library (wileyonlinelibrarycom) DOI 101002/eej22289

A method for compensating customer voltage drops due to nighttime simultaneous charging of evs utilizing reactive power injection from battery chargers

Abstract: When we consider global warming, the reduction of CO2 emissions is one of the most important issues which require urgent solutions. One option is to integrate low-CO2-emission generators to the grid as much as possible. Another option is to replace inefficient vehicles based on internal-combustion engines with electric ones (EVs). Due to the latter, we can easily predict that most consumers will charge EVs' batteries during nighttime. Thus, excessive voltage drops due to nighttime simultaneous charging are expected to be a possible future problem. This paper proposes a method for compensating the voltage drops by injecting reactive power from EV battery chargers. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(1): 19–29, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22390

Self-Tuning PI Control Using Adaptive PSO of a Web Transport System with Overlapping Decentralized Control

Abstract: SUMMARY Web transport systems for transporting films, textile material, paper, etc., are usually large-scale systems. The velocity and the tension of the web are controlled by dividing the systems into several subsystems in which strong coupling exists between the velocity and tension control. A self-tuning PI (STPI) controller with an estimator based on a novel adaptive particle swarm optimization method is constructed, and it is applied for controlling an actual web transport system. The controllers are designed on the basis of the methodology of the overlapping decentralized control by taking into consideration online executions performed by a general computer. The effectiveness of the constructed control system is verified on the basis of several experimental results obtained by using an actual experimental web transport system. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(1): 56–65, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22366

Robust design of vibration suppression control system for crane using sway angle observer considering friction disturbance

Abstract: It is desirable for a container crane to operate smoothly and quickly. For this purpose, the control system of a container crane should be capable of antisway control for suppressing vibrations. A vision sensor system is often used to detect the sway angle. However, since a control system with a vision sensor has a delay time when determining the angle, it sometimes leads to deterioration of control performance owing to the delay time. In order to overcome this problem, this paper proposes a new antisway crane control system based on a dual-state observer with sensor-delay correction. However, because of nonlinear friction in the crane, the estimation accuracy achieved by using the observer is poor. To overcome this problem, this paper proposes a disturbance observer considering friction disturbance. The control performance and effectiveness of the proposed robust control system based on the estimated information are shown to be satisfactory by experimental results. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(3): 36–46, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22412

Application of a modular multilevel cascade converter (MMCC-SDBC) to a STATCOM. Control of active power and negative-sequence reactive power

Abstract: This paper presents the application of a modular multilevel cascade converter based on single-delta bridge-cells (MMCC-SDBC) to a STATic synchronous COMpensator (STATCOM), particularly for negative-sequence reactive-power control. The SDBC is characterized by cascade connection of multiple single-phase H-bridge (or full-bridge) converter cells per leg, which facilitates flexible circuit design, low voltage steps, and low electromagnetic interference (EMI) emissions. However, there is no published report on such a STATCOM with experimental verification or a control strategy. This paper designs, constructs, and tests a 100-V 5-kVA PWM STATCOM based on the SDBC with focus on the operating principle and performance. Experimental results confirm that this converter can control not only the positive-sequence reactive power but also the negative-sequence reactive power and low-frequency active power intended for the flicker compensation of arc furnaces. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 33–44, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22365

A single‐switch equalization charger using multiple stacked buck‐boost converters for series‐connected energy‐storage modules

Abstract: Series connections of energy-storage modules such as electric double-layer capacitors (EDLCs) and lithium-ion batteries result in voltage imbalance because of the nonuniform properties of individual modules. Conventional voltage equalizers based on traditional DC-DC converters require numerous switches and/or transformers, and therefore their costs and complexity tend to increase. This paper proposes a novel single-switch equalization charger using multiple stacked buck-boost converters. The single-switch operation not only reduces the circuit complexity but also contributes to increasing the reliability. The fundamental operating principles and design procedures of key components are presented in detail. An experimental charge test using a 25-W prototype of the proposed equalization charger was performed for four series-connected EDLC modules whose initial voltages were intentionally imbalanced. The experimental results demonstrated that the proposed equalization charger could charge the series-connected modules preferentially in the order of increasing module voltage and that all the modules could be charged up to a uniform voltage level. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(3): 57–67, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22332

Analysis of Lightning Electromagnetic Field on Large‐Scale Terrain Model Using Three‐Dimensional MW‐FDTD Parallel Computation

Abstract: There have recently been analyses of lightning electromagnetic fields using the FDTD method. However, large-scale three-dimensional analyses of a real environment have not been considered, because the FDTD method has a huge computational cost in large-scale analysis. Thus, we have proposed a three-dimensional moving window FDTD (MW-FDTD) method with parallel computation. Our method has a lower computational cost than the conventional FDTD method and the original MW-FDTD method. In this paper, we study the computational performance of MW-FDTD parallel computation and large-scale three-dimensional analysis of lightning electromagnetic fields on a real terrain model using our MW-FDTD with parallel computation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 20–27, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22368

Position sensorless control of IPMSMs based on a novel flux model suitable for maximum torque control

Abstract: In this paper, a novel position sensorless control method for interior permanent magnet synchronous motors (IPMSMs) that is based on a novel flux model suitable for maximum torque control has been proposed. Maximum torque per ampere (MTPA) control is often utilized for driving IPMSMs with the maximum efficiency. In order to implement this control, generally, the accurate motor parameters are required. However, the inductance varies dramatically because of magnetic saturation, which has been one of the most important problems in recent years. Therefore, the conventional MTPA control method fails to achieve maximum efficiency for IPMSMs because of parameter mismatches. In this paper, first, a novel flux model has been proposed for realizing the position sensorless control of IPMSMs, which is insensitive to Lq. In addition, in this paper it is shown that the proposed flux model can approximately estimate the maximum torque control (MTC) frame, which is a new coordinate aligned with the current vector for MTPA control. Next, in this paper, a precise estimation method for the MTC frame has been proposed. By this method, highly accurate maximum torque control can be achieved. A decoupling control algorithm based on the proposed model is also addressed in this paper. Finally, some experimental results demonstrate the feasibility and effectiveness of the proposed method. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(3): 55–66, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22380

Study on the principle of contactless electric power transfer via electromagnetic coupling

Abstract: In recent years, contactless transfer of electric power has received worldwide attention. Among many contactless electric power transmission systems, an electromagnetic resonant system showed a remarkable ability to turn on a 60-watt light bulb located at a distance of 2 meters from a power source. Several papers that explain principles of the system have been published, but no analytical explanation of these principles has been provided. In this paper, the author provides an analytical explanation of the principle underlying the power transfer system. The analysis can facilitate the evaluation of the system characteristics, such as resonant frequencies, transferable power, efficiency, coil voltages, etc., and may be useful in the synthesis of contactless power transfer systems. Electr Eng Jpn, 182(2): 53–60, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21285 2

A Muscle Motion Solenoid Actuator

Abstract: It is one of our dreams to mechanically recover lost body capabilities for damaged humans. Realistic humanoid robots composed of such machines require muscle motion actuators controlled by all pulling actions. In particular, antagonistic pairs of bi-articular muscles are very important in animal motions. A system of actuators is proposed using the electromagnetic force of solenoids with a stroke length of over 10 cm and a strength of about 20 N, which are needed to move the real human arm. The devised actuators are based on the development of recent modern electromagnetic materials, where traditional materials cannot give such a possibility. Composite actuators are controlled by a high-capability computer and software to perform genuine motions. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 10–19, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22369

Deployment control of wireless multihop-relay mobile robots based on voronoi partition

Abstract: Summary This paper describes a new method for the deployment of wireless relay nodes. When using rescue robots in a building or underground city, radio signals are attenuated significantly, and therefore, multihop extension involving wireless communication relays is required. The goal of this research is to deploy wireless relay nodes to maintain connectivity between the base station and the leader robot that explores around the front line. To move the relay robot autonomously, a distributed algorithm is required. The proposed method is suitable when it is applied for wireless relay purposes. In this method, a virtual force drives a node to the centroid of Voronoi neighbors so that the connectivity of wireless communication is maintained. The proposed method is evaluated by conducting numerical simulations and experiments. In the simulation, one or two leader robots are assumed. In the experiment, a mobile robot equipped with omni-wheels is used. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(4): 42–51, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22413

Novel Core Structure and Iron-Loss Modeling for Contactless Power Transfer System of Electric Vehicle

Abstract: A contactless power transfer system for electric vehicles must have high efficiency, a large air gap, good tolerance to misalignment in the lateral direction, compactness, and light weight. In this paper, a new 1.5-kW transformer has been developed using a novel H-shaped core which is more efficient, more robust to misalignment, and lighter than previous rectangular cores, to satisfy these criteria, and its characteristics are described. An efficiency of 95% was achieved across a 70-mm mechanical gap. Iron-loss modeling of the equivalent circuit is also presented. The calculated efficiency using this model shows good agreement with experimental results. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 61–70, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22377

A General Analytical Method for a Three‐Phase Line‐Start Permanent‐Magnet Synchronous Motor

Abstract: Summary A line-start permanent-magnet synchronous motor (LSPMM) consists of a stator with symmetrical three-phase armature windings and a salient pole rotor with a permanent magnet for excitation and a starting winding similar to the squirrel-cage winding of an induction motor. In this paper, a general analytical method based on tensor analysis is proposed for practical performance calculation of a three-phase LSPMM. The general equation for the currents of the three-phase LSPMM is derived from the transient impedance tensor expressed in polyphase symmetry axes, and the general equation for vibratory and nonvibratory torques is derived from the current equation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(4): 60–68, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21284

Estimating Power Outage Costs Based on a Survey of Industrial Customers

Abstract: Summary Thousands of factories in Japan responded to a survey on power outage costs for industrial customers. From across the country, 5139 facilities designated as energy management factories answered questions about their power consumption and the loss of production value due to a hypothetical hour-long power outage on a summer weekday. Using their responses, we estimated the median unit cost of a power outage across all sectors to be 672 yen/kWh. The service sector of amusement and hobbies and the manufacturing sector that makes electronic information and communication equipment have relatively high unit costs for power outages. The direct cost of damage from a specified power outage across all sectors totaled 77 billion yen. Using input–output analysis, we estimated the indirect damage costs caused by the repercussions of halting production. Indirect damages across all sectors totaled 91 billion yen. The wholesale and retail trade sector had the largest direct damage costs, while the transportation equipment manufacturing sector has the largest indirect damage costs. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(4): 25–32, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22306

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

Abstract: 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

Thermal aging characteristics of insulation paper in mineral oil in overloaded operation of transformers

Abstract: A sudden capacity increase in demand during the summer peak, or in contingencies such as malfunctioning transformers, may cause an overload in normal transformers. In this paper, on the basis of overloaded transformer operation in distribution substations, thermal aging testing in oil was carried out under various overload patterns, such as short-term overload and long-term overload, but with the winding insulation paper's lifespan loss kept constant. From the results, various characteristics, such as the mean degree of polymerization and production of furfural and (CO2 +CO), and their effects on the lifespan loss of the insulation paper, were obtained. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 1–8, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21292

Comparison of partial discharge resistance of several nanocomposites

Abstract: Partial discharge (PD) resistance was evaluated for several kinds of nanocomposites. The following experimental results were obtained. Epoxy is stronger in PD resistance than is polypropylene. But the enhancement of PD resistance by nanofiller addition is higher for polypropylene than for epoxy. Silica and alumina nanofillers exhibit stronger PD resistance than does layered silicate when they are added to epoxy resins. Coupling agents or modifiers will help increase PD resistance. A similar level of this effect can be obtained for either epoxy with 5 wt% added nanofiller or epoxy loaded with 65 wt% microfiller. Nano–micro composites are the strongest of all tested specimens as regards PD resistance. Both of these experimental facts can be understood based on the concept that shortening of the interparticle distance is effective for reducing PD erosion. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(1): 1–9, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21291

Characteristics of Winter Lightning Threatening Wind Turbines in Coastal Area of the Sea of Japan

Abstract: 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 proves to be closely related to the temperature distribution at high altitudes. In this paper, the correlation between lightning hits of wind turbines and the height of the—10 °C layer is analyzed. When an upward lightning hits a wind turbine in winter, the height of the—10 °C layer is lower than 2000 m in most cases. Moreover, winter lightning is classified into two types, namely, the storm type and the inactive type, and it is found that the parameters of lightning currents observed by LLS differ depending on the type of lightning storm. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 44–50, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22357

A method for load frequency control using battery in power system with highly penetrated photovoltaic generation

Abstract: Summary It is generally believed that large battery systems will be needed to store surplus electric energy due to the high penetration of renewable energy (RE) such as photovoltaic generation (PV). Since the main objective of high penetration of RE is to reduce CO2 emissions, reducing kWh output of thermal generation that emits large amounts of CO2 in power systems should be sufficiently considered. However, thermal generation plays an important role in load frequency control (LFC) of power systems. Therefore, if LFC could be performed with batteries and hydropower generation, the kWh output of thermal generation could be reduced significantly. This paper presents a method of LFC using batteries in a power system with highly penetrated PVs. An assessment of the effect of the proposed method considering mutual smoothing effect of highly penetrated PVs is made. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(4): 22–31, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22425