New electrical shunt with two rectangular holes in a copper plate

A new concept of an electrical shunt with two rectangular holes in a copper plate (ESRP) has been developed to be used for measuring a large current with a short‐duration steep wave in a high‐voltage field. The ratio of the input current to the output current is 10⁶, as obtained from a DC voltage test circuit. The electrical shunt has a special configuration. To verify the shunt current ratio of ESRP in a real application, the shunt current was connected to a sphere‐to‐sphere electrode breakdown test circuit with a 10 mm gap to measure the large damping current (8.4 kA) of a DC breakdown voltage. The voltage signal from the shunt was transmitted to excite two light‐emitting diodes (max. 50 mA, 4 V), which were reverse‐connected in series. The light‐emitting diodes operated properly and were illuminated, which validated the capability of the newly designed electrical shunt. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Multiple operating points in a square‐root domain first‐order filter

In this paper novel corrective circuits to avoid multiple operating points in a square‐root domain first‐order filter are proposed. By employing a DC test it is demonstrated that the filter possesses three operating points (two stable and one unstable) and the corrective circuits enforce the proper operating mode. The corrective circuits and filter are able to operate with very low supply voltages (as low as V_GS+2V_DSsat). Moreover, a detailed analysis concerning the impact that produces the corrective circuits on the filter performance is discussed. Both measurement and simulation results are provided to validate the circuits and analysis employed. Copyright © 2006 John Wiley & Sons, Ltd.     

Characteristic measurement of discharge current injected by the air discharge of an ESD gun onto a ground

An immunity testing method for electrostatic discharge (ESD) is being specified in IEC 61000‐4‐2, in which the contact discharge of an ESD gun is being normally specified. Air discharge testing is known to be a severe immunity test compared to contact discharge testing, while the discharge current injected is not well reproduced. Grasping the behavior of the current injected by the air discharge would be helpful in establishing the worst‐case ESD immunity testing. We previously measured the discharge currents for air discharge testing onto the IEC‐recommended current transducer with a commercially available ESD gun, and showed that there exists a specific relationship of Ip·tr^ξ/V_c=constant (ξ=0.75), between rise time tr and current peak Ip. The current transducer, however, has a frequency‐dependent transfer impedance which should affect the measured current waveform. In this study, we investigated whether the above‐mentioned specific relationship can be obtained for air discharge of an ESD gun onto a ground that assumes a metal enclosure of electronic equipment under test. A method was presented for estimating the discharge current from simultaneously measured magnetic fields with two magnetic field probes regardless of the distance between the gun discharge‐point and the probe position. This method was validated for contact discharge of an ESD gun to an SMA connector. With this method, we estimated the discharge currents injected onto a ground for air discharge testing of an ESD gun with intentionally fast and slow approaches. As a result, we could confirm a specific relationship between rise time tr and current peak Ip of Ip·tr^ξ/V_c=constant with ξ=0.57 independent of charge voltages and gun approaches. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 51– 59, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20454     

碳化硅金属氧化物半导体场效应晶体管短路特性

器件的短路能力对整流器及其故障保护具有极其重要的意义。当器件故障运行时,为避免器件损坏,须在最短的时间内将故障予以切除,而此时器件的最大短路运行时间为系统保护装置提供了有力的时间支持。主要研究了碳化硅金属氧化物半导体场效应晶体管(Si C MOSFET)在短路条件下的运行能力,以Cree公司的1 200 V/19 A Si C MOSFET为模型,设计了硬件电路,测试其不同电压等级下的短路电流;并在直流电压等级为600 V的条件下,测试了不同栅极电压、不同温度工况下的短路电流。研究结果表明器件的短路峰值电流随着栅极电压的升高而增大,而其短路运行时间却大幅降低;温度对短路运行时间的影响则相对不甚明显;同时还给出了器件在不同工况下的最大短路运行时间Tsc(max)。     

Mapping duality as a means to allow finite βF compensation in bipolar log filters

Log-domain filters are a promising design paradigm for analog signal processing. They achieve tunability and operation up to high frequencies, with voltage and power requirements typically better than those of conventional filtering architectures. Implementation can be based only on capacitors, current sources and an exponential, differential V/I converter referred to as the E-cell. Non-idealities in the E-cell, like the presence of non-negligible input currents due to finite β_F, can reduce system performance. The aim of this paper is to investigate E-cell-based design strategies and to introduce a duality principle whose exploitation can allow finite β_F compensation. As a validation, HSPICE simulation results are illustrated for a second-order bandpass filter. Copyright © 2000 John Wiley & Sons, Ltd.     

CMOS Non‐tailed differential pair

A continuous‐time complementary metal–oxide–semiconductor differential pair that does not require the traditional tail current source as a way to control the direct current and common‐mode current is presented. Compared with a p‐channel long‐tailed pair, the proposed non‐tailed solution operates under a higher maximum input common‐mode voltage that includes (V_DD + V_SS)/2 even under low supply voltages. Experimental measurements on a prototype fabricated in a 0.35‐µm technology (with metal – oxide – semiconductor thresholds greater than 0.6 V) confirm this behavior for supply voltages as low as 1.2 V, whereas the long‐tailed pair with the same technology offers the same capability only for supplies higher than 1.6 V. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimation of breakdown voltages of surface flashovers initiated from triple junction in SF6 gas

In this paper, a method is proposed to estimate the minimum breakdown voltages of surface flashovers initiated from the triple junction at which a solid insulator, SF₆ gas, and a metal electrode come in contact. Using four kinds of test samples, the flashover voltages V_f are measured. The voltages V_f become lower than the theoretical voltages V_s of streamer inception in the case of the test sample with the large electrode area at the triple junction. To understand the phenomena quantitatively, we estimated the real partial discharge voltages V_c from the voltages V_f, and investigated the relationship between the voltages V_c and the theoretical values V_s. The values of V_s/V_c, which characterize the properties of the partial discharges, can be shown by the product λS_90%E_av P of the following parameters: (1) coefficient λ representing the surface roughness of electrode at the triple junction; (2) effective area S_90% of the electrode; (3) average field E_av at the area S_90%; and (4) gas pressure p. The minimum surface flashover voltages in the insulators for coaxial electrode systems can be estimated precisely, considering the properties of V_s/V_c.     

Reduction in Ripple Current and Self‐Inductance by Using Electromagnetic Coupling of Reactor

To produce DC current by using a multiphase reversible chopper, smoothing reactors are needed. When smoothing reactors are employed, the chopper device becomes large and heavy, especially if electromagnetic interference is avoided. The reduction in the ripple current by electromagnetic coupling contributes to making the chopper device smaller and lighter. We deduced the relationships among the ripple current amplitude, duty factor, and electromagnetic coupling coefficient. To determine the loss and gain, we introduced the ratio of the amplitude of the ripple current in each phase and in the total combined current of the multiphase chopper system to that of the ripple current in a one‐phase chopper, A_ph, A_sum, respectively. This value indicates the reduction not only in the ripple current amplitude but also in the self‐inductance. The minimum value of the above‐mentioned ratio obtained analytically is accurately determined. We derived the minimum values and obtained the range within which reduction of the ripple current amplitude for both each phase and total combined is achieved. Finally, we applied an optimal electromagnetic coupling coefficient to the design of on‐board reactors of electric railway vehicles. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(2): 68–82, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22480     

Interface potential barrier height and leakage current behavior of Pt/(Ba,Sr)TiO3/Pt capacitors fabricated by sputtering process

Abstract

Variations of the leakage current behaviors and interface potential barrier height (φ _B ) of rf-sputter deposited (Ba, Sr)TiO₃ (BST) thin films, with thickness ranging from 20nm to 150 nm are investigated as a function of the thickness and bias voltages. The top and bottom electrodes are dc-sputter-deposited Pt films. φ _B critically depends on the BST film deposition temperature, postannealing atmosphere and time after the annealing. The postannealing under N₂ atmosphere results in a high interface potential barrier height and low leakage current. Maintaining the BST capacitor in air for a long time reduces the φ _B from about 2.4 eV to 1.6eV due to the oxidation. φ _B is not so dependent on the film thickness in this experimental range. The leakage conduction mechanism is very dependent on the BST film thickness; the 20nm thick film shows tunneling current, 30 and 40 nm thick films show Schottky emission current and the thicker films show a mixed characteristics and bulk and interface limited currents although the mechanism is not clearly understood at this moment.     

Simulation of slow current transients and current collapse in GaN FETs

Two-dimensional transient simulations of GaN MESFETs are performed in which a three-level compensation model is adopted for a semi-insulating buffer layer, where a shallow donor, a deep donor and a deep acceptor are considered. When the drain voltage V _D is raised abruptly (while keeping the gate voltage V _G constant), the drain current I _D overshoots the steady-state value, and when V _D is lowered abruptly, I _D remains a low value for some periods, showing drain-lag behavior. These are explained by the deep donor’s electron capturing and electron emission processes. We also calculate a case when both V _D and V _G are changed abruptly from an off point, and quasi-pulsed I-V curves are derived from the transient characteristics. It is shown that the drain currents in the pulsed I-V curves are rather lower than those in the steady state, indicating that so-called current collapse could occur due to deep levels in the semi-insulating buffer layer. It is also shown that the current collapse is more pronounced when V _D is lowered from a higher voltage during turn-on, because the trapping effects become more significant.     

液流电池旁路电流的研究概况

大规模储能液流电池体系是由多个电池模块串并联构成,其中每个模块又由固定个数的串联单电池组成,其电解液通过输液总管统一供应,这种电解液供应方式会在电堆中引起旁路电流,削弱电池的性能.介绍了旁路电流产生的原因及其对液流电池系统的危害,并综述了旁路电流模型及预测旁路电流大小的数值计算方法,以及消除旁路电流可以采用的措施.     

ELECTROMAGNETIC FAULT CURRENT LIMITER (EMFCL)

ABSTRACT

Due to electrical power system expansion, the utility systems are faced with fault currents higher than the momentary and interrupting capabilities of the equipment installed. One method, to convert the problem, is to use a fault current limiter. The limiter must limit the peak current to a level below that of the momentary capabilities of the system components and limit the subsequent current peaks to a level which allows correct relay operation within the interrupting capabilities of the circuit breakers. This paper describe the design and modeling of a new device for limiting the fault currents. Tliis device is an electromagnetic circuit consisting of an iron core and armature with adjustable air gap. With load current, the device has minimum impedance at the supply frequency. During fault conditions, the fault current is used to give the operating force needed to change the device inductance to the maximum impedance. The fault current limiter is successfully modeled using a digital computer and validated in the laboratory.     

Self-rehealing characteristics of a sodium current limiter and its overcurrent coordination for low-voltage distribution system

The sodium current limiter developed and applied for low voltage use is not a current limiting fuse but a new type of reusable current limiting device that utilizes metallic sodium as a fusible element. Excellent current limiting performance and quick self-rehealing properties of the sodium limiter allowed highly reliable electric power systems to be obtained economically and compactly. Here we examine experimentally the rehealing properties of the sodium limiter after current limiting operation and discuss the overcurrent coordination of the sodium limiter for a low-voltage distribution system. The results are summarized here:

• 1 (1) The resistance of the sodium limiter, being between about one thousand and several thousand times its normal resistance r₀ at room temperature during a current limiting operation of short circuit fault currents, changes abruptly to 30 to 40 times its r_o value just after the disappearance of the fault current and falls steadily to r_o.
• 2 (2) The sodium limiter can recover current-carrying capability for an overload current even immediately after a current limiting operation and maintain its capability for the following normal load current. The upper limit of the recovery of the sodium limiter is given by its overcurrent against the time characteristics under the normal condition.
• 3 (3) The self-rehealing characteristics of the sodium limiter presented here give the ability to design a low-voltage motor control center using the sodium limiter which maintains maximum service continuity up to high fault currents.

     

Measurement method of plasma current and density in atmospheric pressure plasma jet

We present a measurement method of the plasma current and density in an atmospheric‐pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying a high RF voltage. The plasma in the form of a bullet is released as a plume or jet into the atmosphere. To study the characteristics of the atmospheric‐pressure plasma, the plasma current is measured using a current probe, and the drift velocity of plasma plume is measured using a photodetector. The current of the plasma plume is estimated by subtracting the ground line current from the power line current in the circuit. The density of plasma plume n is estimated from the plasma plume current I and the drift velocity v as I = envS, where S is the cross section of plasma plume. The density of the released plasma into the atmosphere is estimated as ∼10¹⁸ m⁻³ by the method. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Microstructural and electrical properties of multicomponent varistor ceramics with PbO–ZnO–B2O3 glass addition

Zinc oxide based ceramics are widely used materials in varistors because of their excellent nonlinearity. Traditionally these ceramics are sintered at high temperatures (about 1,100–1,300°C). In this work a novel zinc oxide-based material with a low sintering temperature (900–1,000°C) was investigated. This material can be used in varistors consisting of several ceramic layers with embedded silver/palladium thick-film electrodes. This paper explains the research procedure employed with this novel varistor material, including the effect of sintering aid addition on the final electrical properties and fired microstructure. The electrical properties achieved are compared to the values measured from the original zinc oxide composition without sintering aid addition. Especially the I–V characteristics, nonlinearity coefficient α, breakdown voltage V _bk and leakage current density J _L are investigated. The sintering properties are also reported. It was found that by adding 10 wt.% of glass and using a 900 °C sintering temperature, the material had good varistor characteristics, as V _bk = 378 V/mm, α = 33 and J _L  = 15 μA/cm². The investigated varistor material can be applied to protect electrical circuits against surges.     

高压并联电容器组的合闸涌流计算方法的研究

在实践中发现,高压并联电容器组实测的合闸涌流与现行规程的计算结果相互矛盾。鉴于合闸涌流的数值十分重要,直接影响到断路器触头不检修的电寿命和电容器组继电保护的整定计算,重新推导了投切电容器组的涌流计算公式,推荐了单组电容器合闸的涌流计算公式,电抗率相同、多组电容器组合闸的涌流计算公式,以及2种电抗率时、多组电容器组合闸的涌流计算公式,供工程技术人员参考。算例计算结果表明了这些计算公式的正确性。     

Relation between breakdown voltage and prebreakdown current in vacuum gap

Two different surface treatments (mechanical polishing, thin film deposition) were performed on cathode surfaces, and the field emission currents from the cathodes were measured with a microchannel plate. In order to discuss the relationship between the breakdown voltage and prebreakdown current in the vacuum gap, the breakdown voltage was measured after field emission measurement. The V–I characteristics of the field emission and breakdown voltage were influenced by surface treatment, and the breakdown voltages of mechanical polished cathodes were lower than those of the thin film deposited cathodes. It was found that the probability of breakdown increased when the field emission current reached 10^–11 A. Atomic force microscope (AFM) measurements showed numerous protrusions on the cathode surface in the case of thin film deposition treatment, but we estimated by the finite element method that these protrusions make the field enhancement effect low. It was inferred that the breakdown voltage in vacuum gaps could be increased by the thin film deposition method. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 11–18, 2000     

Computer Programs for Fault Studies Using Symmetrical Components in Undergraduate and Postgraduate Teaching

ABSTRACT

The paper first reviews development of a digitial fault studies program for use in undergraduate and postgraduate teaching, highlighting aspects of program design. System data details: arrays containing details of system data: fault data; positive-, negative-, and zero-sequence network data; voltage arrays which store node voltages before and after the fault; corresponding current arrays; in addition to the file editor; routines for printing system data on screen or on paper; modifying system data; together with line data; and diagnostics are discussed for various shunt and series faults.

Improved routines which employ complex impedances to represent generators, transformers and transmission lines on the more common PC's are explained. Phase voltages and currents for both shunt and series faults which illustrate the effect of the more common approximations such as neglecting system resistance or approximating complex impedance to constant angle impedance in shunt and series faults are made.     

基于稳健性设计理论的锰铜分流器优化设计

锰铜分流器作为单相智能电能表的电流采样装置,在工频外磁场干扰下会产生感应电流,影响电能表计量的准确性。提出了一种基于稳健设计理论的锰铜分流器结构优化设计方法,提高锰铜分流器抗磁场干扰能力。首先,理论分析了锰铜分流器在外加工频磁场干扰下产生感应电流的基本原理,并基于Flux软件建立了锰铜分流器感应电流仿真模型;进而,基于正交试验设计对影响感应电流大小的因素进行信噪比分析,确定显著因素作为后续优化目标,采用Taguchi稳健设计方法对锰铜分流器进行优化设计;最后通过蒙特卡洛仿真对优化前后感应电流大小一致性评价,验证了稳健设计方法在提高锰铜分流器抗磁场干扰能力的适用性。     

Silicon-Germanium Structure in Surrounding-Gate Strained Silicon Nanowire Field Effect Transistors

In this paper we numerically examine the electrical characteristics of surrounding-gate strained silicon nanowire field effect transistors (FETs) by changing the radius (R_SiGe) of silicon-germanium (SiGe) wire. Due to the higher electron mobility, the n-type FETs with strained silicon channel films do enhance driving capability (∼8% increment on the drain current) in comparison with the pure Si one. The leakage current and transfer characteristics, the threshold-voltage (V_t), the drain induced barrier height lowering (DIBL), and the gate capacitance (C_G) are estimated with respect to different gate length (L_G), gate bias (V_G), and R_SiGe. For short channel effects, such as V_t roll-off and DIBL, the surrounding-gate strained silicon nanowire FET sustains similar characteristics with the pure Si one.