高频磁场环境下热电偶测温研究

在高频磁场环境下采用热电偶测温时,会存在很大的误差.本文分析了误差产生的机理,指出测温误差是由于高频磁场环境下热电偶金属端部的涡流效应产生较大的损耗密度所引起.在电磁场理论分析的基础上,搭建了热电偶高频磁场环境测温平台,结合测量结果,采用多元非线性回归算法建立了正弦波磁场环境下的K型热电偶温升模型,以修正高频磁场涡流效应的影响.利用加权平均等效正弦频率的方法,将正弦波磁场激励下的热电偶温升模型应用于方波电压激励下的三角波磁场测温环境.实验验证了本文建立的模型在正弦波与三角波高频磁场下具有很高的测温精度.     

DC-probes for electric field distribution measurements

The principles of how DC fields can be measured using an isolated probe coupled by fiber optics to a separate receiver are discussed. The construction of some practical systems is described, with attention given to induced current, voltage, power, and dipole systems. The electric fields around a full size wall bushing energized to 600 kV in rain were measured. The results of this measurement and other measurements are presented, demonstrating the usefulness of isolated DC field measurements     

Determination of the field source distribution based on field measurements

Contents The paper describes a method for the determination of a field source distribution in the conducting region when it is possible to measure the temperature distribution somewhere inside the conductor, or the heat flux distribution at a part of its boundary. The proposed algorithm is based on the application of a regularization method for solving an ill-conditioned, underdetermined system of equations. Numerical calculations performed in examples demonstrate all features of this method.

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Berechnung der Anregungsverteilung aus der gemessenen Feldverteilung

Übersicht Diese Arbeit beschreibt eine Methode zur Berechnung der Größe und Verteilung einer Feldanregung, wenn die Feldverteilung im Gebiet oder auf seinem Rand z. B. aufgrund von Messungen bekannt ist. Dieses wird am Beispiel einer zweidimensionalen Temperaturverteilung demonstriert. Der Algorithmus basiert auf einer Regularisierungsmethode zum Lösen von schlecht konditionierten und unterbestimmten Gleichungssystemen. Die in der Arbeit dargestellten numerischen Berechnungen zeigen die Anwendbarkeit der vorgestellten Methode.

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This paper was carried out at the Institut für elektrische Maschinen, Antriebe und Bahnen, TU Braunschweig, West Germany and the author would like to thank Prof. H. Weh, the Head of the Institute, for his support of this work. The financial support by the Alexander von Humboldt-Foundation is also gratefully acknowledged     

High field performance of thin-wall spacers in a vacuum gap

This paper reports the electrical conduction and breakdown characteristics of thin-wall ceramic spacers for a field emission display (FED). These spacers bridge two thin-film electrodes, which represent the FED cathode and the phosphor anode in a FED. Techniques to set up a high aspect-ratio thin-wall spacer without glue were developed. An extra-low light detection 3D-imaging system using an intensified CCD camera was developed which was able to identify the location of low-level light activity in the stressed vacuum-gap, indicative of imminent device failure. Thin wall spacers made of various ceramics were investigated extensively. The scanning electron microscopy (SEM) surface investigation showed that zirconia spacers exhibited a smoother surface morphology compared to all other materials studied; however, their breakdown voltages were rather low. The breakdown voltages of alumina spacers were severely limited by triple junction effects. At HV, breakdown at the edge of the thin-film electrode was observed. This edge breakdown can be used to explain the saturation of the breakdown voltage vs. vacuum gap spacing. The results of this work are highly encouraging in that an ~1000 μm tall spacer can support ~18 kV dc, at least 80% above the expected operational voltage of HV FED. The spacer breakdown voltage is expected to improve through surface treatment and elimination of the electrode edge-breakdown and triple junction effects     

Lightning return stroke current identification via field measurements

 An inverse procedure is presented for identifying and reconstructing the waveform of the lightning return stroke current. It is based only on the acquisition of the electromagnetic field radiated by the discharge channel in various locations on the ground and at various frequencies, and requires no information about the channel base current. The fundamental idea is shown to come from an electrostatic problem in which the linear charge density of a vertical thin wire is determined starting from the measured field. Three versions of this procedure have been developed: in the first, the identification is carried out by means of the measurement of the electric field at various distances from the lightning channel at a given frequency; in the second, only two sensors for the electric field are necessary, but various sampling frequencies; in the third, only one observation point is needed, for the measurement of both the electric and the magnetic field. A simulated validation of all the approaches is provided as well as a detailed analysis of their numerical accuracy. Received: 4 April 2001/Accepted: 30 April 2001     

High voltage AC resistive current measurements using a computerbased digital watts technique

A computer-based technique is described which can accurately determine high-voltage AC resistive currents by obtaining the watts loss of the test specimen and dividing by the true r.m.s. (t.r.m.s.) value of the applied voltage Therefore, the normal concern for guarding against stray capacitive currents and for the exact repetition of test setup geometry on successive testing are not required for accurate measurements of AC resistive current. The watts loss calculation is based on the general formula for average watts so that the resistive current can be measured accurately with some harmonics of the fundamental present in both the test current and the supply voltage. A digital oscilloscope is used to acquire the test voltage and current so that special-purpose amplifiers are not required. The overall system accuracy is verified to less than ±1.21% of full-scale current. A microprocessor was used to compute the following parameters: average power, t.r.m.s. voltage, t.r.m.s. resistive current, t.r.m.s. capacitive current, total t.r.m.s. current, and the magnitude of calculated measurement error. The waveforms displayed are volt-ampere, voltage, and total current. An EHV aerial lift boom, a 115 kV station post insulator, and a metal-oxide surge arrester are evaluated using this technique to illustrate the measurement advantages     

High field effects in solid dielectrics

High voltage solid dielectrics are employed in a wide range of electrotechnology, from video flyback transformers to transmission-class solid dielectric cables. The design criteria for the application of such dielectrics are well developed, and failure is primarily the result of unanticipated defects. In this context, a defect is anything that causes an electric field that is substantially greater than the design field. Thus the reliability of high voltage dielectrics is tied closely to high field effects, typically in microscopic volumes around defects such as asperities on a conductor or small cavities     

前后串列布置的吸水管周围流场PIV实验研究

水泵进水池中沿来流方向前后串列布置多根吸水管时,其周围流场具有复杂的三维、不稳定、强紊动的特性.本文在玻璃水槽内对不同管间距条件下的吸水管周围进行了大量的PIV流场量测实验,通过流场分析显示,上游吸水管的尾流作用加剧了下游吸水口的水流紊动强度,流场多处出现表面旋涡和水内旋涡,其运动形态复杂多变.同时,随着吸水管设置间距的缩短,吸水口附近流速分布趋于不均匀,旋涡涡量逐渐增强.     

Electrostatic fluctuation measurements in the periphery of reversed field pinch plasma

In this paper, the authors study the magnetic and electric properties of ferromagnetic substance/semimetal (Fe/Bi) system multilayered thin films prepared by ion beam sputtering. The multilayered thin film was prepared with 99.6% Fe and 99.99% Bi. The experimental results are summarized as follows. From XRD in the small‐degree region (2θ = 2 to 4^°), Fe/Bi system thin films for N = 3,4, and 5 Fe layers have formed multilayer structures. Coercive force H_c increased with increasing number of Fe layers. The maximum value was 4.522 kA/m at N = 6 Fe layers. The coercive force then decreased and its value was constant at more than 15 layers. Electrical resistivity, ρ, of Fe/Bi system multilayered thin films changed from conductivity to semiconductivity at temperatures in the range for T = 380 to 400 K. Magneto‐resistance (MR) ratio decreased with increasing applied field H when the current was parallel to an applied magnetic field (I‖H). MR ratio reached a maximum of 0.154% at N = 4 Fe layers at room temperature. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 1–8, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20068     

Superconducting transformer with a rotating magnetic field

The results of investigations into the physical model of a superconducting transformer with a rotating magnetic field with separate excitation winding are presented.     

High field insulation relevant to vacuum microelectronic devices

This paper briefly introduces our recent results on high field vacuum insulation relevant to vacuum microelectronics. It addresses the key factors that contribute to the failure of the vacuum gap insulation. Approaches to the development of specific solutions to improve the vacuum gap breakdown voltages are presented. Solutions to alleviate the edge breakdown effect in the thin-film vacuum gap and to inhibit the formation of electrical activity in the spacer triple junction area were proven to be very effective in improving the vacuum insulation performance of vacuum microelectronics. The influence of the presence of an electron beam on the plain-vacuum-gap insulation is also reported.     

High field emission efficiency surface conduction electron emitters

Two different surface conduction electron-emitter (SCE) structures with the nanogap of 90 nm wide fabricated by hydrogen embrittlement (HE) and focused ion beam techniques are simulated for the first time. We employ a three-dimensional particle-in-cell method coupling with finite-difference time-domain scheme to simulate the property of electron emission in these SCEs. Our calibrated simulation predicts high emission efficiency of the SCE structure which is fabricated by HE. Compared with the other SCE structure, it is observed that the proposed structure possesses low power consumption at the fixed emission current when the width of nanogap becomes narrower. The current-voltage characteristics including conducting mechanisms are investigated and explained.     

High resolution measurements of surface charge densities on insulator surfaces

The uses and limitations of the electrostatic probe for the measurement of charge densities on insulating surfaces are discussed. A development of the technique is described in which two important limitations have together been overcome: (i) The effects on the probe signal of charges on all points of the surface have been taken into account by means of a matrix inversion procedure; (ii) A robotic control system has been developed which enables the probe to follow and scan a wide range of axi-symmetric insulator profiles. The degree of resolution achieved enables the probe system to display and measure charge densities in individual streamer channels of a corona discharge on a polytetrafluoroethylene (PTFE) surface. An example is given and comparison made with a dust figure of the same event.     

采用高温超导线圈的电子高电压发生器

研究了应用高温超导（ＨＴＳ）线圈，通过Ｌ－Ｃ串联谐振电路从低压直流电源产生高电压的新方法。为了产生高电压，低压直流电源的极性需在电子开关的控制下每半个谐振周期切换一次。谐振电路中电阻的存在限制了它所能产生的高电压幅值。通过用ＨＴＳ线圈制成的电感取代铜线圈电感，该电路所能产生的高电压的幅度会明显增大，在本文中，（Ｂｉ，Ｐｂ）２Ｓｒ２Ｃａ２Ｃｕ３Ｏ１０＋ｘ套银多股ＨＴＳ线材被用来制造超导电感。虽然用此谐振方式产生的高电压不能给低阻抗负荷供电，但它可能用于电气设备局部放电测试或其他电气绝缘性能的检测等方面作为另一个应用该方法还可用于超导体自身电性能的测量。     

Electrical field measurements on an EPRI two-pole, 20-hp WrittenPole motor

The recent introduction of the Electric Power Research Institute (EPRI) single-phase Written Pole soft-start motor may open new possibilities and marketing opportunities for rural electric cooperatives. The new single-phase high-efficiency AC motor technology promises soft-start capabilities that allow designs and application of up to 60 hp 240 V motors. This paper summarizes some of the technical aspects of the new single-phase motor technology. An actual field test and application of a Written Pole motor is also be used to compare motor starting currents and line flicker with manufacturer's literature and specifications     

High field conduction and prebreakdown phenomena in dielectric liquids

The present paper is mainly devoted to phenomena occurring in point-plane electrode geometry, where breakdown is the result of the initiation and propagation of prebreakdown phenomena called "streamers". In this configuration, an investigative study of the streamer initiation processes, requiring very high electric field strengths (/spl sim/ MV/cm), and of propagation (requiring low electric field, /spl sim/ kV/cm) can easily be carried out for negative streamer development as well as for the positive case. From analysis of experimental results in pure liquids the physical processes connected with streamer initiation and propagation, particularly the electronic ones, are presented and discussed. Estimations of the main parameters of slower subsonic streamers and of the faster filamentary ones (such as field strength at the streamer tip, field inside the channel, charge density, etc.) have been obtained from qualitative considerations and compared to experimental data.     

Parameter estimation of a transformer with saturation using inrush measurements

This paper presents a method to compute the parameters of a transformer model with saturation using the voltage and current waveforms of an inrush test and a no-load test. The transformer is modeled with their electric and magnetic equivalent circuits and a single-valued function that characterizes its non-linear magnetic behavior. A 3-kVA single-phase transformer and a 5-kVA three-phase three-legged transformer have been tested in the laboratory. The method to obtain the parameters of the non-linear flux–current relation that characterize the saturation has been described in the paper. The analytical function used to adjust the experimental measurements fits them very well.     

建(构)筑物对大气电场测量影响的有限元分析

地面电场仪安装场地常常无法达到开阔要求,受附近建(构)筑物的影响,大气电场测量数据偏离实际值,直接影响测量数据在研究大气电学和雷电预警预报中的应用价值。针对这一问题,利用电磁场有限元分析软件Maxwell 3D进行了仿真模拟,通过讨论晴天天气条件下,不同形状、高度建筑物对地面大气电场测量的影响,以及细杆周围地面大气电场的分布,得到了建(构)筑物的影响范围,并提出了已有安装要求的不足之处,所得结论对电场仪的安装环境选择和误差修正有一定参考价值。