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Summary: Many electrical systems are expressed as a complex ladder network consisting of combinations of resistances, inductances, and capacitances. Computation of electrical characteristics, such as voltages, currents, and equivalent impedances of these ladder networks require the solution of complicated differential‐algebraic equations that are quite tedious and cumbersome. The earlier works have given particular attention to purely resistive ladder networks ignoring the inductance and capacitance parameters. Moreover, there are no direct expressions available to quickly compute these characteristics. This paper derives generalized analytical expressions that can be directly used to obtain the electrical characteristics of a finite as well as semi‐infinite homogenous ladder network by simply plugging the values of its constituent parameters. Expressions are deduced for excitation source applied to the input terminal and across 2 arbitrary nodes, respectively. Kirchhoff mesh and node laws along with ordinary algebra and trigonometric theorems are applied to derive these expressions. Boundary‐value technique is used to circuit equations to determine unknown coefficients of the expressions. The derivation given in these paper would surely help the readers to quickly compute the electrical characteristics without solving recursive circuit equations and avoiding complex state‐space matrices. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents an experimental discussion on modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC). Hereinafter, a single MMCC-DSCC is referred to simply as a 'DSCC'. A couple of DSCCs are used to form a front-to-front (FTF) system capable of dc voltage matching and galvanic isolation between two dc grids. The FTF system can be considered as a dc-ac-dc power conversion system including an ac-link high-power transformer. The higher the ac-link frequency, the smaller and lighter are the ac-link transformer and dc capacitors. When the so-called 'phase-shifted-carrier PWM' is applied to the DSCC, theoretical analysis and computer simulation have confirmed that a ratio of the carrier frequency with respect to the ac-link frequency can be reduced to 5/2. This paper designs, constructs, and tests a 400-Vdc 10-kW downscaled FTF system with a carrier frequency of 450 Hz and an ac-link frequency of 180 Hz, where their ratio is 5/2. Experimental waveforms obtained from the downscaled system are compared with simulated ones obtained from a software package, PSCAD/EMTDC, under the same operating and circuit conditions. They agree well each other not only under steady states but also under transient states. [ABSTRACT FROM AUTHOR]

The impulse voltage wave invading a transformer is not the double exponential impulse wave (DEIW) specified by the IEC but a non-standard waveform with oscillation attenuation characteristics, and this fact leads to doubts about the scientificity and optimality of insulation coordination. A key solution for this issue is the establishment of an equivalent relationship between the measured non-standard impulse voltage wave and the DEIW. In this study, a test platform of multiparameter impulse voltage was set up. Then, the authors obtained the 50% breakdown voltage (U50%) of the oil-impregnated paper (OIP) for transformer under the bipolar oscillatory attenuated impulse wave (BOAIW) and the DEIW with different waveform parameters. The effects of waveform parameters on the breakdown characteristics of the OIP were finally revealed. On the basis of experimental data and several mathematical methods, the authors established the U50% prediction mathematical models for the OIP under the BOAIW and DEIW. Based on the prediction models and the microfluctuation characteristics of measured overvoltage's waveform parameters, the authors proposed a method for evaluating the waveform equivalence. The characteristics of voltage amplitude and change rate were regarded as the two key factors for the waveform equivalence of this method. [ABSTRACT FROM AUTHOR]

In this paper, a comprehensive analytical design methodology for a single-phase axial rotary transformer (RT) is presented. The proposed procedure is designed to yield the minimum RT volume or size while at the same time offer adequate efficiency. Furthermore, the proposed methodology is used in the design and evaluation of a 1.2-kVA single-phase axial RT. The developed prototype proved that the methodology leads to a significant reduction in size as compared to a prototype designed using standard methods. The measured efficiency of this transformer is found to be 91.4%. The presented design methodology can be easily extended to a three-phase RT that can be applied in place of slip rings in brushless doubly fed induction generators (DFIGs). This could reduce maintenance downtime in the operation life of the DFIG. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a high-frequency isolated ac/dc converter using the soft switching technique. The ac/dc converter consists of a matrix converter for transforming three-phase ac voltage to high-frequency ac voltage, a high-frequency transformer, and an ac/dc rectifier. In order to reduce the switching loss, soft switching at every commutation of the matrix converter and ac/dc converter is achieved. The effectiveness of the proposed converter and the control scheme was verified by experiments. [ABSTRACT FROM AUTHOR]

SUMMARY The kHz band power line communication (PLC) is one of the convincing mediums of the communication system for smart meter reading. Data transmission between medium-voltage (MV) and low-voltage (LV) points to pass the transformer by PLC is interested. In this paper, the PLC signal propagation characteristics between points of MV at substation and LV at customer are calculated and analyzed. The results show that direct communication between points on MV distribution line and most LV customers is impossible due to large propagation losses at MV-LV transformer and on LV distribution line. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, values of the electric field in the pressboard and oil during the polarity reversal test of the converter transformer were calculated with transient analysis. First, we confirmed the accuracy of the nonlinear analysis in the model test. Next, we carried out nonlinear transient electric field analysis for polarity reversal test of the converter transformer. In the results, when the applied time of dc voltage before the polarity reversal is 360 min, the values of the electric field of oil area are the same as when it is 90 min. Although, the electric field in the pressboard becomes higher in response to the applied time dc voltage, it does not cause a problem on the insulation. Because withstand voltage of pressboard is very high. In the results, the correlation between the applied time of dc voltage before the polarity reversal and the withstand voltage of transformer is considered low. This result can be applied to the design of the converter transformer. [ABSTRACT FROM AUTHOR]

SUMMARY This paper describes an improvement to the control method of a boost-type matrix converter (MC) for a three-phase four-wire system. The system is intended for use in a stand-alone power source with a constant voltage and frequency. However, the conventional method is not able to control the output voltage with a low power-factor load. To resolve this problem, we propose a new control method by using a MC and revising the conventional control method. [ABSTRACT FROM AUTHOR]

SUMMARY This paper discusses nontheoretical harmonics on the dc-side of a 12-pulse rectifier in dc railway systems. These harmonics are the commercial frequency component and the doubled component. The causes of these harmonics are (a) diode forward voltage drop difference, (b) transformer secondary inductance difference, (c) voltage harmonics at the ac-side of the rectifier, and (d) effects of the voltage induced by adjacent high-voltage power transmission lines. We evaluated cases (a), (b), and (c), as case (d) has been previously studied . The results of the evaluation were as follows: · The effects of both the transformer secondary inductance difference and the voltage harmonics inside the electric power system are not negligible in some cases in the discussion of the EMC problem among railway equipments. · If there are several traction circuits in parallel, each of which consists of an input filter, an inverter, and several traction motors, the harmonic reduction effect of the filters weakens significantly. [ABSTRACT FROM AUTHOR]

This paper studies the sympathetic interaction between transformers. The influencing factors of the sympathetic inrush current, including the system impedance, closing angle and the initial remnant flux of the added transformer, the system voltage, and the neutral grounding mode of the transformers, are analyzed in detail through dynamic simulation. Based on this, a method for identifying the sympathetic inrush current is proposed based on the essential curve feature of the magnetizing currents of the transformers during the sympathetic interaction, taking advantage of the information sharing between substations. The results from dynamic simulation and field-recorded data show the validity of the proposed method. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Hidden failures as potential faults in relay protection are lethal for power systems. Multi-grounding fault in the secondary circuit of a potential transformer (PT) is a typical hidden failure. When this hidden fault happens, zero-sequence voltage of computer relaying will shift. Then it will result in the mis-operation of zero-sequence directional protection, which may cause a cascading failure. In this paper, we analyze the impact on zero-sequence directional protection caused by multi-grounding fault first. Then in order to solve the problem, we analyze the characteristic of the affected voltage and current. We find that the zero-sequence voltage of the special phase is in phase with its negative sequence voltage under normal circumstance, but this is not true in this hidden failure. As a consequence, we propose an identification method of multi-grounding fault in a PT and a new zero-sequence direction algorithm that can avoid the mis-operation of the zero-sequence directional protection. Finally, the results of simulation prove the correctness of the theoretical analysis and the effectiveness of the identification method and the new zero-sequence direction algorithm. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

SUMMARY A contactless outlet for dc distribution systems is proposed. It uses an inductive contactless power transfer circuit with a series/parallel compensation circuit to prevent voltage fluctuation. However, the output voltage of the circuit rises in light load conditions. In this paper, the main circuit and control method for reducing the rise in output voltage and a method of estimating the output voltage are presented. The proposed circuit and methods were verified and evaluated experimentally using feedback control. [ABSTRACT FROM AUTHOR]