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The presence of a substantial short‐circuit current generates a large electromagnetic repulsive force. The energy of such a short‐circuit current increases the likelihood of equipment damage. Furthermore, the occurrence of short‐circuits disrupts the stable supply of electric power. When a short‐circuit occurs in a distribution line, short‐circuit point identification is realized based on information such as overcurrent indicators and equipment damage caused by the short‐circuit. However, there is no established method for promptly pinpointing the short‐circuit location. Therefore, this study proposes a short‐circuit point estimation method for distribution lines using smart‐meters; whose performance is anticipated to improve in the future. The proposed method involved using smart‐meter voltage measurements to measure and determine the changes in the voltage drop slope, caused by the distribution‐substation short‐circuit currents and load currents, from the short‐circuit location to the end point. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

In order to improve the electrical performance of the inverter system and make its output waveform close to a sinusoidal waveform, an inverter based on a linear phase‐shifting transformer is proposed, which can eliminate the low harmonics with opposite phase by the effect of phase shift and superposition. Firstly, the components and working process of the multiple superposition inverter system are introduced, and the working principle and winding structure of the linear phase‐shifting transformer are analyzed; Secondly, the Fourier decomposition of the inverter output voltage is carried out to obtain the harmonic currents at the same frequency as it, and it is demonstrated that the inverter is capable of eliminating most of the harmonics below the 23rd order by calculating the magneto‐dynamic potential synthesized in the air gap; Again, in order to overcome the harmonic electric potential caused by the edge‐end effect and the tooth slot structure of the linear phase‐shifting transformer, the secondary side winding of the linear phase‐shifting transformer adopts a short pitch structure, and it is proved that this structure has a significant suppression effect on the 5th and 7th harmonics without reducing the fundamental wave amplitude; Then, the model of multiple superposition inverter system is built based on Maxwell simulation software, and the effectiveness of the inverter device and winding structure on harmonic suppression is proved through spectral analysis of voltage waveforms with different load types and power factors; Finally, its reasonableness and accuracy are verified by experiments. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper presents a novel frequency compensation scheme for the stability of low dropout regulator (LDO). The proposed compensation scheme introduces a zero in the voltage regulation loop to enlarge gain and phase margin at high‐frequencies. As a result, high open‐loop‐gain and improved load regulation performances are achieved, and a particular resistor is introduced in the compensation structure to cancel the voltage drop originating from cable resistances at the output to further improve the load regulation performance. The proposed LDO with wide input/output range and high‐power supply rejection is designed and implemented in a 180 nm CMOS process. The LDO operates with an input voltage range of 4–16 V, an output voltage range of 1.5–5 V and an output current range of 0–1000 mA. High open loop gain and high bandwidth are achieved, and the simulated performances of load regulation and line regulation are less than 32 μV/mA and less than 3 mV/V over the whole operation range, respectively. The on‐chip compensation capacitor required by the compensation module is only 1.8 pF. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Owing to the large number of power distribution equipment, the supply voltage is managed independently in 6.6‐kV medium‐voltage (MV) and 100‐V low‐voltage (LV) systems in Japanese distribution systems. Both systems have their respective independent allowable voltage range. We have studied the optimum allowable voltage range for MV and LV systems in order to reduce the equipment cost. In this study, we analyze the relationship between the maximum voltage drop and system configuration in an LV systems from the viewpoint of investment costs. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

At present, intermittent control is a main method to solve the problem of pumping output voltage with light load of LLC resonant converter, which can not only solve the problem of high pumping output voltage, but also, to a certain extent, improve the efficiency of light load to a certain extent when converter is operating. However, in extremely light‐loading, especially in no‐ loading, with the intermittent cycle increasing and the low‐frequency ripple being introduced, which cannot meet the demand of high‐quality output voltage, and is not conducive to the converter's stable operation. Due to the extremely small power transferred by the converter, in this case, efficiency is not the main factor considered. In this paper, a voltage regulation strategy based on energy feedback is proposed for LLC resonant converter in extremely light‐loading. The output voltage is controlled by adjusting the feedback energy to the source. Compared with the uncontrollable burst off mode of the intermittent control, the proposed control method can effectively improve the output voltage quality due to the controllability in voltage drop mode and the independence from the load. It also can eliminate low frequency ripple and extend battery charging life. The output voltage ripple is minimized by optimizing the duty cycle and the phase shift angle. The correctness and feasibility of the proposed method are verified by experiments. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

An interleaved parallel high step‐up DC‐DC converter with cross‐coupled inductors for low current/voltage ripple and auto‐current sharing was proposed in this paper. This converter applies interleaved parallel input which decreases the input current ripple significantly. Due to the interleaved coupling effect of three coils of the cross‐coupled inductors, this converter can realize automatic current sharing under asymmetric distribution of duty ratio of switch control signal or coupled inductors. By using the leakage inductance of coupled inductors, the proposed DC‐DC converter has high voltage gains and small voltage stress of the main switches and output diodes. Moreover, the proposed converter solves the reverse recovery problem of the output diodes at the minimum loss. In addition, its power switches realize zero‐current turn on. In this paper, working principle is analyzed thoroughly and performance of this topological circuit is verified through a prototype with 1 kW output. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper reports analytical evaluation for minimum reverse recovery loss and turn‐off loss of PiN diodes and IGBTs, respectively. In this evaluation, we take account of structural parameters and current continuity at the both ends of the i‐layer, and we calculate switching losses (E) from energy dissipation on the i‐layer during switching action by using position integration instead of time integration. In the case of IGBT, we assume that depletion layer spreads from the i‐layer and n+ layer interface of the PiN diode that corresponds to bottom p type layer ‐ n− layer ‐ p type backgate region of IGBT cells. We evaluate optimum structure for minimum energy dissipation of these switching actions and conduction states by newly employed index RE consists of R calculated by voltage drop at the i‐layer and both ends of the i‐layer and E. We clarify that ideal carrier profile for minimum RE, and we also evaluate structural parameters for that condition. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Railway transportation is of safety, convenience, economy, and environmental friendliness. However, with energy issues becoming increasingly important in this century, it is important to assess the situation in the transportation sector. When the superconducting cable is used as a feeder of the railway electrification system, the voltage drop can be significantly reduced. Therefore, the superconducting feeder has many effects, for example, the reduction transmission losses, the improvement of the regeneration factor, and the reduction of substations. We designed superconducting feeder and introduced to the Izuhakone Railway Sunzu line in Japan. After the system was checked from the aspect of cooling and current properties, the train running test was conducted. From the result of switching notch tests, it was found that the current flows continuously via the superconducting cable according to the notch operation. Furthermore, to inspect the influence of superconducting material, a large pulse current test was performed using the transmission equipment of a railway. It can be confirmed that superconductor can be used as railway feeder because the materials can cope with the current change peculiar to railway required for practical use. [ABSTRACT FROM AUTHOR]

Selection of current transformers (CTs) must be done carefully to ensure protection, control, and measuring systems function correctly. Some of the conventional CTs on medium voltage (MV) switchgear in nuclear power plants (NPPs) perform poorly due to accuracy errors and saturation. This paper suggests the use of electronic current transformers (ECTs) as a solution. Simulations were done on a 13.8 kV switchgear using electromagnetic transient program restructured version (EMTP‐RV) software to compare the performance of conventional CTs and ECTs under high fault currents. It was found that ECTs show significant improvement in performance with the secondary current output of 97.37% and eliminate saturation even in systems with high symmetrical and asymmetrical short‐circuit currents. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

A new type of DC electric field sensor has been developed. It is not mill type electric field sensor whose principle is to measure electric potentials in the atmosphere. The new type DC sensor can directly detect electric fields in all spaces. For minimizing disturbances of electric field configuration in the space, the new type sensor uses a simple linear dipole antenna. The key point in the detection method is to measure a potential difference between only two equipotential lines connecting to each dipole element. The validity of the configuration of equipotential lines around the dipole elements was confirmed by numerical analysis. It has been confirmed that angular dependence of the DC electric field intensities measured by a prototype of the new sensor was consistent with theoretical one. Then we began to observe natural DC electric fields in electrically quiet environment, installing its practical three antennas (5 m tip‐to‐tip) orthogonal with each other. We have found, from the measured electric fields, that behaviors of the measured electric fields suggest those of ionosphere Sq (solar quiet) electric fields. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Calcium sulfate and other slightly soluble salts in the natural pollution of catenary insulators could result in differences in flashover voltages between artificially and naturally polluted insulators at the same salt deposition density. Based on the insulator pollution characteristics in saline‐alkali areas and the saturated water absorption of polluted insulators, the equivalent salt deposit density and nonsoluble deposit density of insulators are corrected according to the influence of other coexisting soluble salts on the solubility of calcium sulfate. The correction formula of the insulator flashover voltage is proposed, which considers the equivalent salt deposit density, nonsoluble deposit density and pollution components. The results from the correction formula are compared with the experimental data from the artificial pollution test of the ceramic cap and pin insulator. The results show that salt‐alkali areas are more easy to flashover than other areas. The remaining pollutants can change the conductivity of the pollutant layer by inhibiting or promoting the dissolution of calcium sulfate. Moreover, its effect on the flashover voltage cannot be ignored. The error between the calculated value based on the correction formula and the experimental data is below 6%. A pollution flashover warning mechanism based on relevant meteorological data is proposed. The results can be used as an important reference for the operation and maintenance of catenary insulators in saline‐alkali areas. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In recent years, a rapid spread of residential photovoltaic power systems (PVs) causes voltage imbalance in distribution systems. For this reason, it has become difficult to control voltage in distribution systems to within the allowable range. Therefore, the authors have proposed a system for suppressing the voltage unbalance using single‐phase static capacitors (SCs). The purpose of the system (SC system) is to suppress voltage imbalance by controlling single‐phase SCs in each phase, and its effect has been confirmed by the previous authors' study. On the other hand, as a result of analyzing the voltage measured on some distribution lines, the authors found that it is not necessary to control single‐phase SCs in each phase because the voltage imbalance hardly changes throughout a day. In this paper, an alternative method for suppressing the voltage imbalance by constantly installing single‐phase SCs on distribution lines is proposed in order to realize at a lower cost than the previous SC system. In addition, the authors verify the effect of the method on the actual distribution lines. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In recent years, measurement of transformer vibration is being carried out as a means of detecting the looseness and deformation of its windings. Conventionally, the vibration components of even multiples of the power supply frequency (electrically generated vibration) were analyzed to diagnose the transformer. On the other hand, the natural vibrational frequencies of the winding structures represent their conditions, and the changes of these frequencies must be representing the changes in their pre‐stress or displacement. We have measured the tank vibration of an extra‐high‐voltage transformer and investigated the dependence of load current, voltage, and temperature of the oil. As a result, although the electrically generated vibration has a complicated dependence, the winding's natural frequency is not affected by the current and voltage, and the influence of the oil temperature is not very large. It is considered that the natural vibrational frequencies of the windings are a suitable index for transformer diagnosis. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

This article discusses the breakdown voltage characteristics of gas‐filled transformers and reactors. To determine their insulation characteristics, this study has used models simulating their insulating elements: interturn and section‐to‐section insulation. The study measured 50% breakdown voltages in the section‐to‐section and interturn models under standard lightning impulse voltages that were 1.13 and 1.06 times higher than those under the standard switching impulse voltages, respectively. The mechanism of the above‐mentioned facts is discussed, in terms of the formative time lag of the discharge. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Aiming to achieve a superconducting feeder cable system applicable to Japan, France, and other countries, we summarize the required specifications created for prototyping of superconducting cables. Superconducting cables manufactured based on the required specifications were subjected to voltage, current, and other tests and then verification tests using train. The abovementioned test results have given us good prospects for superconducting feeder cables that can be applied to actual lines in Japan and France. Simulation was conducted to check the effect of these superconducting cables in actual lines. Analysis results were obtained to confirm that the introduction of a 310-m superconducting cable had an effect of compensating for voltage drops. [ABSTRACT FROM AUTHOR]

In recent years, the power quality problem has become more complicated in power grids because of the extensive usage of power electronics and multisource multitransformation features. The method, based on physical characteristics such as time domain, frequency domain and transform domain, is facing challenges in terms of adaptability, algorithm efficiency and accuracy for the recognition of complex disturbance recognition. The bidirectional long short‐term memory network is an algorithm in deep learning. It is based on data for characterization learning, which can effectively overcome the problem of information loss and generalization ability of physical methods. Moreover, it has the characteristics of memory, which can simultaneously consider historical information and future information and can better learn data features with time series characteristics. Aiming at the transient voltage sag time series data, this paper proposes a recognition method of the voltage sag causes based on the bidirectional long short‐term memory network's extraction eigenvalue, the full‐connection layer's high‐dimensional feature extraction and the Softmax network layer's classification. The experiment uses simulation data and measured data to prove that the model has good recognition ability and good antinoise performance in the recognition of voltage sag causes and can be reliably applied in practical engineering. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Series hybrid vehicles using free‐piston engine coupled with linear generator are expected for high‐efficiency energy conversion systems. Such engines do not have a crank mechanism, which greatly reduces the friction loss. In addition, the piston action can be controlled freely by the generation braking thrust by using an inverter control. In a conventional crank engine, past research has shown that delaying the piston motion after the combustion increases the maximum combustion pressure, and this delay brings a constant‐volume degree close to the Otto cycle. In the free‐piston system, a high braking thrust is needed at a low piston speed immediately after combustion. However, the highest braking thrust was limited in the low‐speed range because the back electromotive force of a permanent magnet synchronous generator was too small. This article shows the range that can be theoretically attained for a low‐speed generator. The delaying piston movement with only the braking thrust improved the effective work by 25% near the top dead center. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The line start permanent magnet synchronous motor (LSPMSM) can be used for direct‐on‐line (DOL) starting, so it is easily affected by voltage unbalance. Based on the finite element method (FEM) and analytical method, the influence of voltage unbalance on the steady‐state performance of LSPMSM is studied in this paper. A two‐dimensional finite element model is built, and the armature current, losses and torque ripple as a function of the phase voltage unbalance rate (PVUR) are obtained. The influence mechanism of voltage unbalance on the steady‐state performance of a motor is demonstrated. Finally, a prototype of LSPMSM is manufactured and tested. By comparing the experimental data with the simulation data, the accuracy of the calculation model is verified, and the correctness of the research is proved. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Discharge voltage prediction of engineering gap configurations is a great challenge for external insulation design in high‐voltage engineering. This paper presents an air gap discharge voltage prediction model based on the support vector regression (SVR). A series of features are defined on the shortest interelectrode path of an air gap, and they are extracted from the electric field calculation results using the finite element method. These electric field features are considered as the input parameters of the SVR‐based model, and the output is the air gap discharge voltage. The genetic algorithm is used for parameter optimization of the SVR model. Trained by a few experimental data of the Institute of Electrical and Electronics Engineers standard rod–rod gaps, this model is applied to predict the standard lightning impulse flashover voltages of parallel gaps for insulator strings under different gap configurations. The prediction results coincide well with the experimental data collected from previous publications. The mean absolute percentage error of the eight test samples is within 4.07%, which is acceptable for engineering applications. The SVR‐based model may be helpful to guide the structure design and insulation coordination of parallel gaps and insulator strings, thus reducing the required full‐scale tests. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In recent years, the AC‐DC‐AC electric locomotives have been wildly applied in electrified railways, deteriorating the current quality of network. Therefore, filters in electrified railways are essential. However, considering the volume and weight of filters, it is inappropriate to install them on locomotives. And resonance accident caused by high‐frequency harmonics is hard to suppress because of the low switching speed of high‐power Si‐based devices. In this article, a novel locomotive auxiliary converter control strategy with harmonic suppression function is proposed to filter harmonic currents injected into the traction supply network. By controlling the auxiliary converter, the strategy could complete the function of rectification and filtering, converting power for auxiliary equipment, filtering the harmonic current, and suppressing resonance accidents with the high‐frequency characteristics of SiC devices. For compensating high‐frequency harmonics, the parameters of main circuit and control scheme are analyzed to ensure a stable system. The feasibility of the scheme is verified by simulation and RT‐LAB hardware‐in‐loop experiment. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The basic design and characteristic analysis of the coreless axial flux permanent magnet synchronous generator (AFPMSG) for small wind power generation are carried out. The prototype is manufactured and tested to verify the designed generator. In addition, to reduce the voltage regulation rate and harmonic content of the generator, the optimal design is carried out on the basis of the original generator. The voltage regulation rate and THD of a coreless AFPMSG using the Halbach permanent magnet array are studied. The effects of different generator parameters such as pole arc coefficient, air gap length, permanent magnet thickness, and number of turns in series per phase on the voltage regulation rate and THD are analyzed when the generator is loaded with pure resistance. Because the various parameters of the generator are affected each other, the Taguchi algorithm was adopted for multi‐objective optimization. The influence proportion of different generator parameters on the voltage regulation rate and THD was analyzed. According to the results, the parameters are reasonably selected to design the generator and improve the performance of the generator. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Remanence and coercivity are important parameters to characterize the magnetic properties of permanent magnetic (PM) materials. The variation of PM parameters will lead to the variation of generator output performance. To find out the key PM parameter affecting generator output performance, a 117‐kW, 60 000‐rpm high‐speed permanent‐magnet generator is taken as an example and a 2D finite element model is established. By comparing the calculation results and the test data, the accuracy of the model is verified. By using the field‐circuit coupling method, the mechanism of nonlinear variation of output voltage with the change of load is revealed when the variation degree of remanence and coercivity is consistent. The sensitivities of no‐load electromotive force (EMF), output voltage at rated power, voltage regulation, and overload capability to the variations of PM parameters are studied. Furthermore, the mechanism of PM parameters affecting generator output performance is revealed. The results show that the sensitivity of generator output performance to different PM parameters is different and the influence degree of PM parameters on the generator output performance depends on the permeance of the main magnetic circuit. Finally, the basis for selecting PM parameters is given. The research can assist generator designers to select PM in the design stage. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In this article, water tree degradation was detected and was located by applying the method entitled 'Charge Radar method'. We studied the reduction of charge depending on the number of pulse voltages and the time interval between each pulse (5 µs or 1 s). It was revealed that the charge amount remained stable at 5 µs of the time interval and decayed significantly at 1 s of the time interval. This tendency suggested that the number of pulses did not provide a significant change to the reduction of charge amount. We investigated the space charge behavior of a thin crosslinked polyethylene (XLPE) film sample using the Pulse Electro‐Acoustic (PEA) method. The result suggested that the shallowly trapped charge was released shortly after the film sample had been short‐circuited, and the residual charge would stay for a long time depending on the depth of the trapping layer. It was also revealed that the residual charge was not disturbed by a short pulse voltage. It was suggested that the reduction in charge amount depended on the short‐circuiting time after polarization. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

This article introduces a new method for optimizing the placement of a multiple of D‐Statcoms for voltage sag mitigation in distribution systems. The D‐Statcom's placement is optimally selected not only for improving system voltage sag caused by a single fault event but also for all possible fault events in the system of interest. Therefore, D‐Statcom's placement is optimized in a problem of optimization where the objective function is to minimize the system voltage sag index—SARFIx. D‐Statcom's effectiveness for voltage sag mitigation is modeled based on the method of Thevenin's superimposition for the problem of short‐circuit calculation in distribution systems. This article considers the case of using a multiple of D‐Statcoms with a proposed voltage compensating principle that can be practical for large‐size distribution systems. This article uses the IEEE 33‐buses distribution feeder as the test system for voltage sag simulation and influential parameters to the outcomes of the problem of optimization are considered and discussed. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

To solve the problems of high cost and high waveform deviation factor of the electromotive force (EMF) of the rare earth permanent magnet (REPM) generator for extended‐range electric vehicle (EREV), a consequent‐pole REPM generator is proposed. Based on the model of the conventional 18‐slot/12‐pole REPM generator for the range extender, three models are proposed, and the optimized model of REPM generator is obtained by optimizing the rotor structure. Finite element software is used for simulation analysis. The results show that the amplitude of the fundamental wave of EMF of the optimized REPM generator model accounts for 93.7% of that of the conventional model, the waveform deviation factor of EMF accounts for 35.8% of that of the conventional model, and the amount of REPM materials accounts for merely 55.2% of that of the conventional model. Finally, the rationality of the design of the consequent‐pole REPM generator for the range extender is verified by experiments. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

With the object of reducing CO2 emission and the reliance on fossil fuels, solar power generation has received special support and is being deployed rapidly in many distribution networks. Battery energy storage system (BESS), an effective voltage management solution for low‐voltage (LV) networks to deal with the high penetration of rooftop photovoltaic (PV) systems, is investigated in this paper considering the degradation of BESS due to aging. Two optimal strategies of BESS cost minimization are proposed for long‐term planning and operation planning, where the utility is the BESS owner. As for the long‐term planning, a strategy for siting and sizing of BESS is formulated based on the characteristics of the network, typical load, and PV generation profiles. Then, for the operation planning, schedules of BESSs and their cost estimation are provided based on the load and PV generation forecasts of 1 day ahead. The effectiveness of the proposed methods is demonstrated on the simplified network of the Metropolitan Electricity Authority, Thailand, using MATLAB (Natick, Mssachusetts, USA) 2016a and MATPOWER 6.0. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In general, an autotransformer (AT) is used to improve the voltage sag and inductive interference in power lines and communication lines in the Korean ac electric railway feeding system. In particular, the Korean AT feeding system has a different configuration compared to those of the other countries, such as Japan or France; therefore, it has certain distinctive characteristics. However, a fault locator imported from the other countries has been used in Korea, and the settings of these equipment should be modified and reflect the distinct characteristics of the Korean AT feeding system. Thus, the development of a novel fault-location scheme for the Korean railway system is required. Herein, we analyzed the fault current and developed a specific relationship for use in our new algorithm. We presented the current magnitude of each branch, expressed by the boosting current of the ATs; further, the novel fault-location scheme using this relationship is developed. The novel scheme performance is verified through power system computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) and the field measured data. [ABSTRACT FROM AUTHOR]

Due to the threshold voltage of diode switches, existing symmetrical voltage equalizers suffer from voltage drops across battery cells. To overcome this problem, this letter presents a novel voltage equalizer for series‐connected batteries. The proposed inductor‐less cross‐coupled topology allows the voltage of each battery cell to be balanced evenly without a threshold voltage drop, because no diode switch is required to design the proposed voltage equalizer. The effectiveness of the proposed voltage equalizer is confirmed through experiments. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Virtual synchronous generators composed of an inverter are affected by an over‐current caused by voltage dip and recovery. This letter addresses the current analysis under a symmetrical voltage dip and recovery. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper presents a new algorithm based on the sequential method for power flow calculation in integrated multi-terminal, high-voltage, direct current (HVDC) systems. Unlike similar studies in the literature, a real equivalent circuit model is considered for under-load tap changer (ULTC) transformers of the DC converters, for the first time. So, new DC equations are obtained. Thus, exact and accurate results can be obtained for practical applications by the proposed algorithm. Adjustment effects of the DC converters' ULTCs tap values are included in the Jacobian matrix instead of the bus admittance matrix in the sequential AC power flow algorithm as well as other ULTCs in AC system. To this aim, new equations for the calculation of power and Jacobian matrix elements are obtained for the AC system. The proposed approach is tested on the modified IEEE 17-bus AC-DC test system. Numerical results show that the proposed approach is accurate and reliable in convergence. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

This paper describes the detailed design of the quench protection circuits (QPCs) for the superconducting toroidal field (TF) and poloidal field (PF) magnets of the satellite tokamak JT-60SA, which will be installed in Naka, Japan. The nominal currents to be interrupted and the maximum reapplied voltages are 25.7 kA and 2.8 kV for the TF QPCs and 20 kA and 5 kV for the PF QPCs. The innovative solution proposed in the QPC design is based on a hybrid circuit breaker (CB) composed of a mechanical bypass switch for conducting the continuous current, in parallel to a static CB for current interruption. The main choices of the final design are presented and discussed, either to confirm or to update and complete the study performed at the conceptual design level. [ABSTRACT FROM PUBLISHER]

Abstract: The magnetic-field angle dependence of critical current densities Jc (H,θ) in commercial YBCO tapes grown by MOCVD and MOD was examined at liquid nitrogen temperatures. We first measured Jc (H,θ) in MOCVD-YBCO tapes at 70 and 77.3K in fields up to 2T using both transport and inductive (the third harmonic voltage) methods and compared the results. It was observed that, in low magnetic fields, the transport measurements gave higher Jc than the inductive ones; however, in high fields they agreed well, which is well explained by the effects of weak links due to low-angle grain boundaries. We then investigated Jc (H,θ) in MOCVD- and MOD-YBCO tapes at 77.3K in fields up to 2T. All the tapes exhibited peaks at H//ab in the shape of Mount Fuji, which shows that small random pinning plays a major role. However, an anisotropic scaling analysis showed that the flux pinning mechanisms in those tapes were different, resulting in distinctive angular behaviors of Jc (H,θ). It is suggested that the difference in the flux pinning mechanisms of the two types of tapes came from the different sizes of point defects originating from the growing processes. [Copyright &y& Elsevier]

A new ac-dc comparator system of 20-1000 V has been developed at the National Metrology Institute of Japan (NMLJ) for the calibration of ac-dc thermal voltage converters (TVCs), which are used as national ac-dc transfer standards. The ac-dc transfer differences of high-voltage transfer standards were evaluated by a traditional step-up procedure. The voltage dependence of the ac-dc transfer difference was observed in the earlier step-up procedures over 300 V, as reported by the latest international intercomparison. The experimental results for high- voltage TVCs with several different range resistors at the NMU suggest that the voltage dependence may primarily be caused by input connectors of range resistors and the change in the resistance value of the resistor and TVC modules due to heating from resistors. This paper describes the voltage dependence improvement of ac-dc transfer differences over 300 V at the NMLJ. [ABSTRACT FROM AUTHOR]

There is significant potential for an increase in the use of kilowatt-class small wind turbines (SWTs) in Japan due to reduced limitations with respect to installation, despite their high cost. At this stage, the Japanese grid code has not been considered sufficiently with respect to grid-connected SWTs, and the addition of fault ride-through (FRT) requirements for SWTs has been requested. Moreover, the FRT of SWTs is challenging to achieve owing to the low inertia constants when compared with those of large-scale wind turbines, which result in significant acceleration of the rotor speed and an increase in the input voltage of the power conditioning system (PCS) during FRT operation. In this study, FRT field tests were conducted on SWT systems against a voltage dip with a duration of ~ 1 s, and it was confirmed that the SWT systems satisfied the FRT requirements for photovoltaic (PV) systems connected to low-voltage distribution lines in Japan. The behaviors of the rotational speed of the SWTs and the PCS input voltage in an FRT operation were then analyzed, and it was noted that the increase in the PCS input voltage with the overspeed of the turbine can reach the upper limit and make the PCS cease operation, which indicates failure of the FRT. The overvoltage, therefore, requires restriction using a method such as pitch control, furling, and electrical and/or mechanical brakes. [ABSTRACT FROM AUTHOR]