共查询到20条相似文献,搜索用时 15 毫秒
1.
V. S. Vysotsky K. Funaki M. Takeo 《Physica C: Superconductivity and its Applications》1998,310(1-4):351-357
It is widely acknowledged that current non-uniformity is a major source of reduction of quench currents in superconducting multistrand cables at non-steady state conditions. Recently we performed several experimental studies on the current non-uniformity in CICC and AC cables. In this paper we present the summary of the experimental methods used. Indirect methods with use of local magnetic field sensors can provide general information about non-uniformity inside CICCs and other large size cables. Indirect methods may be used in real superconducting devices. Direct measurements of the current in each strand provide exact information about the current distribution, but they need special sample preparations. Because no method is perfect, the best idea is to use them as complementary to each other in the study of a certain type of a cable. The results obtained from the measurements of the current non-uniformity in CICC and AC cables by both methods are briefly discussed. 相似文献
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Based on a designed coaxial cylindrical corona discharge platform, this paper compares two methods for the measurement of corona current pulse, namely from cage side and conductor side both at low potential. It is found that the corona pulse can be obtained from both methods and the waveform of the current pulse is highly dependent on the sampling resistor. Then two simplified models are proposed to interpret the experimental results and the relationship between the two measurement methods. It shows that the key point in accurately measuring the corona current pulse is the selection of suitable sampling resistor. 相似文献
4.
Response characteristics of local vibrations in stay cables on an existing cable-stayed bridge 总被引:1,自引:0,他引:1
This paper examines local parametric vibrations in the stay cables of a cable-stayed bridge. The natural frequencies of the global modes are obtained by using a three-dimensional FE model. The global motions generated by (1) sinusoidal excitations using exciter, (2) a traffic loading, and (3) an earthquake are analyzed by using the modal analysis method or the direct integration method. The local vibration of stay cable is calculated by using a model in which inclined cable is subjected to time-varying displacement at one support during global motions. This paper describes the properties of the local vibrations in stay cables under these dynamic loadings by using an existing cable-stayed bridge. 相似文献
5.
A physical model of a self-sustaining reflective discharge is formulated based on the continuity equation for the electron
flux and the equation of energy balance on the hot cathode. The model allows one to calculate the current-voltage characteristic
of a high current reflective discharge with a hot cathode in a wide range of magnetic fields, discharge cell dimensions, and
cathode material work functions. An advantage of the model is that it is capable of describing the ordinary operating mode
of a reflective discharge with cold cathodes as a limiting case. The model predicts the existence of two discharge operating
modes with thermionic electron emission on the cathode: a low-voltage mode with a high current density and a high-voltage
mode with a significantly lower current density. It is shown that the low-voltage operating mode can occur in a wide range
of the discharge currents, while the discharge voltage can be substantially reduced by using a cathode material with a low
work function. 相似文献
6.
M.S. Triantafyllou 《Journal of sound and vibration》1985,103(2):171-182
The dynamics of a translating catenary are studied. The static and linearized dynamic governing equations are derived along the local tangential and normal directions and it is shown that in this form two simpler equations can be derived and solved asymptotically for both small and large sag cables, horizontal or inclined. For small sag cables the solutions of one of the asymptotic equations undergo fundamental changes for specific values of the elastic stiffness, inclination angle, sag-to-span ratio and speed of translation resulting in strong mode interactions. For horizontal cables this explains the phenomena of frequency coalescence and mode reversion [1], as well as the frequency crossover and modal changes of non-translating cables [2]. For inclined cables frequency coalescence never occurs, while mode reversion is partial and strongly dependent on the inclination angle. However, in all cases of mode interaction the dynamic tension is greatly amplified. For large sag cables the solution accounts for the significant tension and curvature variation. The solution reduces to previous results for non-translating cables horizontal [3, 4] or inclined [5]. 相似文献
7.
Karol Marton Jozef Balogh Jaroslav Džmura Jaroslav Petráš 《Journal of Electrostatics》2013,71(3):208-213
This paper deals with dust particle elimination on industry plastic foils in industry environment and with technical air cleaning for this environment. We describe electro-physical processes that are in progress during electric charge neutralization. These charges arise during foil manufacturing process. We describe a method for electric parameter measurement for such foils, surface charge measurement on foils and methods of their neutralization. We describe an unconventional type of contamination separator for various technical areas. The application of negative or positive unipolar discharge is used in area of air cleaning in medical and other environments. 相似文献
8.
Russian Physics Journal - A low-voltage low-pressure glow discharge with a hollow cathode is discussed. The discharge is ignited in a reflective discharge system with two symmetric peripheral... 相似文献
9.
N. Vogel 《JETP Letters》1998,67(9):647-654
The dynamics of x-ray emission from a low-voltage laser-induced discharge was studied with the aid of a picosecond x-ray streak
camera. Directed x-ray emission in the spectral range from 100 eV to 10 keV in the form of point sources and thin layers with
lifetimes ranging from 30 ps to 1 ns was observed in a low-voltage vacuum discharge (U=150 V) initiated by a picosecond laser beam. X-ray emission from a discharge was detected with a time delay (1–20 ns) relative
to ignition by the laser beam in order to prevent the radiation of the laser plasma from entering the detector. Detection
of directed x-ray emission in a low-voltage vacuum discharge is demonstrated.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 622–627 (10 May 1998) 相似文献
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Conditions for the electric breakdown of the accelerating gap of a plasma electron source are determined. It is shown that, depending on the gas pressure and the size of openings in the emission electrode, two types of breakdown can occur. One of them is due to the ignition of a low-voltage discharge between the electrodes of the accelerating system, and the other one is caused by switching of the main discharge from the anode to the accelerating electrode. 相似文献
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变压器中的一些放电和机械故障会产生异常声音,可用于故障检测。据此,本文提出基于可听声的变压器放电和机械故障诊断方法。针对机械故障声音与变压器本体噪声特征相似易混淆的问题提出改进小波包-BP神经网络算法,与传统小波包-BP神经网络算法相比声音的识别率提高了5.7%。为提高声音识别系统的泛化性,提出基于梅尔对数频谱和卷积神经网络的声音识别算法。两种算法相互验证,提高了系统的可靠性。在真实变压器油箱中模拟了不同类型放电和机械故障。试验结果表明,本文提出的两种方法能成功识别放电和机械故障的声音,声音识别率分别为99.6%和97.57%。 相似文献
13.
A. N. Dovbnya K. V. Korytchenko M. A. Krasnogolovets Yu. Ya. Volkolupov Yu. D. Tur S. M. Shkirida A. I. Kosoi 《Technical Physics》2003,48(12):1586-1589
The influence of the discharge conditions on the dynamics of energy release is considered for pulsed arcs in air at initial pressures from 105 to 8×105 Pa and a low-voltage capacitor voltage of up to 400 V. A novel method for determining the resistance of the discharge channel in the final stage of a spark discharge is proposed. The method is applied to estimating the discharge channel parameters. 相似文献
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I. A. Berezin 《Journal of Applied Spectroscopy》1965,3(6):376-379
The present paper concerns the effects of various impurities present in specimens on the conditions of sulfur, chlorine, and bromine spectrum excitation in a low-voltage discharge with graphite electrodes. The spectral line intensities of these elements increase with increasing atomic weights and decreasing ionization potentials of the impurities. The observed effect can be attributed to temperature changes, the influence of plasma composition on the excitation spectra by way of ionization processes, and the reduced rate of discharge channel expansion. 相似文献
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E. Cereda G. Coletta G. Crotti L. Gherardi G. Ottoboni S. Zannella 《Physica C: Superconductivity and its Applications》1998,310(1-4):231-235
High-Tc power cables based on Bi-2223 tapes are under development worldwide. An important parameter for design and cost optimization is the AC loss expected during 50/60 Hz operation. Its measurement can be affected by several experimental problems that may alter the results. For this purpose, the 50 Hz losses of a 1.5 m long conductor, made by helically winding four layers of Bi-2223 tapes, were measured simultaneously by electrical and calorimetric methods in a wide range of currents up to 2 kA in order to investigate the reasons for possible discrepancies. The present, specifically designed, calorimetric system is not based on temperature distribution analysis but on the measurement of the gas boil-off rate of the liquid nitrogen bath. 相似文献
17.
By means of statistical modelling and measurement, the triboelectric current noise spectral density is evaluated for shielded cables in body-borne wired network subjected to mechanical stresses. Assuming a shot noise model, an expression for the current spectral density of the noise is derived. The efficiency of the methodology is demonstrated by measuring the triboelectric current noise in two shielded cables subjected to bending. Thereafter the parameters of the noise pulses' waiting time and amplitude probability density functions are extracted from measurement, thus enabling the computation of the current spectral density of the noise induced mechanically in body-borne wired networks. 相似文献
18.
N. Jindapetch S. Plong-ngooluam K. Thongpull K. Chetpattananondh 《Journal of Electrostatics》2012,70(6):489-498
This paper presents a development of a low-voltage decay time analyzer to replace the charged plate monitor which works at the high-voltage level. The proposed low-voltage decay time analyzer is based on the measurement of the induced charges on a conductive plate via an ultra-high input impedance amplifier. A microcontroller with an Ethernet module is the central processing to control, calculate the decay time, and enable network communications. The test results show that the analyzed decay times correlate to the standard test method. 相似文献
19.
S. Bornholdt M. Wolter H. Kersten 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,60(3):653-660
In this paper, an experimental study is presented to characterize a commercially available atmospheric pressure plasma jet
(APPJ) kINPen which can be used for local surface modification, e.g. changing the wettability as well as for thin film deposition
with silicon-organic and metal-organic precursors to enhance scratch resistance or to lower the gas permeability. Characterization
of the jet discharge has been carried out by three methods: (i) measurement of the energy influx from the jet plasma to a
substrate by a calorimetric probe, (ii) spatial resolved investigation of the plasma beam by optical emission spectroscopy
(OES) and (iii) observation of the plasma jet by video imaging. The deposited SiO
x
and AlO
x
films were analyzed by XPS measurements. 相似文献
20.
Mechanical faults in the winding are often related to the changes in the vibro-acoustical response of the transformers with respect to the electromagnetic force in winding. Understanding of the effects of the faults on the vibration characteristics of transformer windings is useful when diagnosing winding faults using transformer’s vibration signature, and when predicting the environmental noise emission from transformers. In this paper, mechanical faults, such as failure of interlayer insulation pressboards and local winding deformations, of the disk-type windings in a 110-kV power transformer, and their effects on the vibration responses of the windings are presented. The disk-type windings are also experimentally modeled by a stack of coupled concentric rings with well-defined faults. A good qualitative agreement is found between measured responses of the power transformer and of the stack of coupled concentric rings. The dependence of the response of the stack on increasing degree of faults provides useful details for understanding the cumulative effect of the faults on the winding’s vibration characteristics. Methods for identifying the location and severity of the faults based on the measured vibration responses are also outlined. 相似文献