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< Page ,Total 540 >
New estimating techniques for multi-stress aging test of large generator stator winding insulation EI CPCI-S Scopus
会议论文 | 2000 , 951-956 | 6th Interantional Conference on Properties and Applications of Dielectric Materials
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Abstract :

The stator winding insulation of large generator suffers from combined stresses including thermal, mechanical, electrical and environmental stresses in the service, resulting in gradually deterioration. Much work has been done to propose model and reveal insulation degradation mechanism under single stress or double stresses. However, few attentions are paid to the synergy effect of multi-stresses. In the present investigation, aging test model of multi-stresses including electrical, thermal, mechanical vibration and thermal cycling factor is developed. According to the model, a multi-stress aging system is established and with it long-term aging tests of stator bar specimen in 780kW/6kV motor have been carried out. Several new diagnostic parameters, such as dynamic increase rate of loss tangent, the index of partial discharge magnitude, the second current rapid increase index, and so on, are put forward in this paper which appear to be correlated with the deterioration of generator stator insulation. It has been verified that these parameters can be used to estimate the aging degree of stator winding insulation for power plants.

Keyword :

test model multi-stress aging aging diagnosis stator winding insulation

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GB/T 7714 Song, Jiancheng , Yue, Bo , Xie, Hengkun . New estimating techniques for multi-stress aging test of large generator stator winding insulation [C] . 2000 : 951-956 .
MLA Song, Jiancheng 等. "New estimating techniques for multi-stress aging test of large generator stator winding insulation" . (2000) : 951-956 .
APA Song, Jiancheng , Yue, Bo , Xie, Hengkun . New estimating techniques for multi-stress aging test of large generator stator winding insulation . (2000) : 951-956 .
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Effect of reaction-induced phase separation on dielectric properties of epoxy resin modified with rubber EI CPCI-S Scopus
会议论文 | 2000 , 926-929 | 6th Interantional Conference on Properties and Applications of Dielectric Materials
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Abstract :

The phase separation and polymerization took place during the curing process of the epoxy resin system. which consisted of diglycidyl ether of bisphenol A and a novel liquid rubber QR. The phase structure development was investigated by scanning electron microscopy (SEM). SEM revealed that the spherical rubber domain was dispersed randomly in the cured epoxy resin matrix. The domain size was changed with the content of the modified rubber QR in the system. The higher QR content, the larger the spherical domain. Therefore dielectric loss (tan delta), dielectric constant (epsilon (r)) and volume resistivity (rho (v)) of the cured resin were changed by the different polarization, especially the interface polarization, which introduced by the second rubber phase The more elastic rubber phase, the larger size of the rubber phase, the higher values of tans and epsilon (r), but the rho (v) changed a little.

Keyword :

epoxy resin dielectric phase separation

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GB/T 7714 Wang, Desheng , Zhang, Guanghua , Zhang, Yajie et al. Effect of reaction-induced phase separation on dielectric properties of epoxy resin modified with rubber [C] . 2000 : 926-929 .
MLA Wang, Desheng et al. "Effect of reaction-induced phase separation on dielectric properties of epoxy resin modified with rubber" . (2000) : 926-929 .
APA Wang, Desheng , Zhang, Guanghua , Zhang, Yajie , Chen, Shoutian . Effect of reaction-induced phase separation on dielectric properties of epoxy resin modified with rubber . (2000) : 926-929 .
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The mechanism of PTC effect in polyethylene/carbon black composite CPCI-S
会议论文 | 2000 , 995-998 | 6th International Conference on Properties and Applications of Dielectric Materials
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Abstract :

Investigation on the positive temperature coefficient (PTC) effect in polyethylene/carbon black composite is reported in this paper. A model based on phase change in the polyethylene matrix is proposed. In this model, carbon black particles mainly reside in the amorphous phase in the composite, thus forming a conductive channel below the melting point. When temperature rises near to the melting point of the polyethylene, the crystalline phase starts to melt leading to formation of new amorphous regions. The volume of the new amorphous regions is larger than that of the previous crystalline region. Some portion of the new amorphous phase will extend into the previous amorphous regions. As the newly formed amorphous phase contains no carbon black, this extension can reduce and finally break up the conducting channel in the previous amorphous phase, resulting in rapid increase in resistivity of the composite. Thus this model can be used to explain the PTC effect in semicrystalline polymeric composite.

Keyword :

polyethylene crystalline carbon black phase change model PTC property

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GB/T 7714 Xi, B , Chen, G . The mechanism of PTC effect in polyethylene/carbon black composite [C] . 2000 : 995-998 .
MLA Xi, B et al. "The mechanism of PTC effect in polyethylene/carbon black composite" . (2000) : 995-998 .
APA Xi, B , Chen, G . The mechanism of PTC effect in polyethylene/carbon black composite . (2000) : 995-998 .
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Discussion on the relation between residual breakdown voltage and nondestructive parameters of stator insulation in generator EI CPCI-S Scopus
会议论文 | 2000 , 970-973 | 6th Interantional Conference on Properties and Applications of Dielectric Materials
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Abstract :

Long-term accelerated aging test of generator stator insulation in the laboratory was conducted. Nondestructive parameters, such as dissipation factor (tan delta), capacitance (C) and the voltage (U-i2) at which the current increases abruptly, were measured in the period of aging test. The breakdown test was performed to determine residual breakdown voltage (BDV). The correlation coefficients between BDV and nondestructive parameters were compared, The most effective parameter to describe the aging condition of the stator insulation was U-i2. In this paper, the relationship between BDV and nondestructive parameters was analyzed theoretically.

Keyword :

nondestructive parameters breakdown voltage correlation multi-stress aging stator insulation epoxy mica

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GB/T 7714 Jia, Zhidong , Jiang, Xiongwei , Xie, Hengkun et al. Discussion on the relation between residual breakdown voltage and nondestructive parameters of stator insulation in generator [C] . 2000 : 970-973 .
MLA Jia, Zhidong et al. "Discussion on the relation between residual breakdown voltage and nondestructive parameters of stator insulation in generator" . (2000) : 970-973 .
APA Jia, Zhidong , Jiang, Xiongwei , Xie, Hengkun , Wang, Ruijun . Discussion on the relation between residual breakdown voltage and nondestructive parameters of stator insulation in generator . (2000) : 970-973 .
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Testing for spatial autocorrelation among the residuals of the geographically weighted regression SSCI Scopus
期刊论文 | 2000 , 32 (5) , 871-890 | ENVIRONMENT AND PLANNING A | IF: 1.21
WoS CC Cited Count: 57
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Abstract :

Geographically weighted regression (GWR) is a useful technique for exploring spatial nonstationarity by calibrating, for example, a regression model which allows different relationships to exist at different points in space. In this line of research, many spatial data sets have been successfully analyzed and some statistical tests for spatial variation have been developed. However, an important assumption in these studies is that the disturbance terms of the GWR model are uncorrelated and of common variance. Similar to the case in the ordinary linear regression, spatial autocorrelation can invalidate the standard assumption of homoscedasticity of the disturbances and mislead the results of statistical inference. Therefore, developing some statistical methods to test for spatial autocorrelation is a very important issue. In this paper, two kinds of the statistical tests for spatial autocorrelation among the residuals of the GWR model are suggested. Also, an efficient approximation method for calculating the p-values of the test statistics is proposed. Some simulations are run to examine the performances of the proposed methods and the results are encouraging. The study not only makes it possible to test for spatial autocorrelation among the GWR residuals in a conventional statistical manner, but also provides a useful means for model validation.

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GB/T 7714 Leung, Y , Mei, CL , Zhang, WX . Testing for spatial autocorrelation among the residuals of the geographically weighted regression [J]. | ENVIRONMENT AND PLANNING A , 2000 , 32 (5) : 871-890 .
MLA Leung, Y et al. "Testing for spatial autocorrelation among the residuals of the geographically weighted regression" . | ENVIRONMENT AND PLANNING A 32 . 5 (2000) : 871-890 .
APA Leung, Y , Mei, CL , Zhang, WX . Testing for spatial autocorrelation among the residuals of the geographically weighted regression . | ENVIRONMENT AND PLANNING A , 2000 , 32 (5) , 871-890 .
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Statistical tests for spatial nonstationarity based on the geographically weighted regression model SSCI Scopus
期刊论文 | 2000 , 32 (1) , 9-32 | ENVIRONMENT AND PLANNING A | IF: 1.21
WoS CC Cited Count: 145
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Abstract :

Geographically weighted regression (GWR) is a way of exploring spatial nonstationarity by calibrating a multiple regression model which allows different relationships to exist at different points in space. Nevertheless, formal testing procedures for spatial nonstationarity have not been developed since the inception of the model. In this paper the authors focus mainly on the development of statistical testing methods relating to this model. Some appropriate statistics for testing the goodness of fit of the GWR model and for testing variation of the parameters in the model are proposed and their approximated distributions are investigated. The work makes it possible to test spatial nonstationarity in a conventional statistical manner. To substantiate the theoretical arguments, some simulations are run to examine the power of the statistics for exploring spatial nonstationarity and the results are encouraging. To streamline the model, a stepwise procedure for choosing important independent variables is also formulated. In the last section, a prediction problem based on the GWR model is studied, and a confidence interval for the true value of the dependent variable at a new location is also established. The study paves the path for formal analysis of spatial nonstationarity on the basis of the GWR model.

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GB/T 7714 Leung, Y , Mei, CL , Zhang, WX . Statistical tests for spatial nonstationarity based on the geographically weighted regression model [J]. | ENVIRONMENT AND PLANNING A , 2000 , 32 (1) : 9-32 .
MLA Leung, Y et al. "Statistical tests for spatial nonstationarity based on the geographically weighted regression model" . | ENVIRONMENT AND PLANNING A 32 . 1 (2000) : 9-32 .
APA Leung, Y , Mei, CL , Zhang, WX . Statistical tests for spatial nonstationarity based on the geographically weighted regression model . | ENVIRONMENT AND PLANNING A , 2000 , 32 (1) , 9-32 .
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Computer aided analysis and manufacture for engagement pair of single screw compressor CPCI-S
会议论文 | 2000 , 818-823 | 5th International Conference on Progress of Machining Technology (ICPMT 2000)
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Abstract :

Based on gearing theory and computing technology. the mathematical model of the engagement and manufacture for single screw compressor (SSC) is established, the space locations and section shapes of every teeth for worm (mainrotor) and gear (gaterotor) are given, contact lines at every instant are displayed. The relationship of two kinds of surfaces for gaterotor is discussed in this paper, one surface is shaped by the entering edge of the worm and the other is the enveloping surface of the worm, interference value between two kinds of surfaces is calculated. Possibility: to generate gear by flying tool and honing worm is analyzed. a hob which is very difficult for manufacturing is not used, it makes gear manufacturing very easy and gear tooth is accurate and smooth. For the nonmodified double enveloping worm gearing in SSC, besides the first and second instantaneous contact lines, another (the third) contact region is exist, equation, shape and existing condition of the third contact line are presented. The assembling condition of norm and gear is discussed.

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GB/T 7714 Liu, ZM , Hou, DH , Wang, XC et al. Computer aided analysis and manufacture for engagement pair of single screw compressor [C] . 2000 : 818-823 .
MLA Liu, ZM et al. "Computer aided analysis and manufacture for engagement pair of single screw compressor" . (2000) : 818-823 .
APA Liu, ZM , Hou, DH , Wang, XC , Zhang, XZ . Computer aided analysis and manufacture for engagement pair of single screw compressor . (2000) : 818-823 .
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Study on UWB frequency characteristics of partial discharge as a criterion of aging degree of stator winding insulation EI CPCI-S Scopus
会议论文 | 2000 , 181-184 | 6th Interantional Conference on Properties and Applications of Dielectric Materials
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Abstract :

Since the introduction of partial discharge (PD) detection, the majority of conventional electrical measurement of PD has been performed with detectors operating in narrow bandwidths from 10kHz to 1MHz for several decades. In the past decade, advances in electronic instrumentation have permitted the measurement of PD with bandwidths up to 1GHz. Since PD pulses are fundamentally events with duration as low as a few nanoseconds which have a very wide frequency spectrum, comparing with narrow band PD detection, PD measurement with such ultra-wideband (UWB) detection methods can provide more information on the deterioration of stator winding insulation subjected to combined stresses. A UWB PD measuring technique with bandwidths from 20kHz to 1GHz is presented, and some waveforms of UWB PD signals of stator bar specimens in different aging periods both in time domain and frequency domain are given in this paper. It has been found that the ultra high frequency components contained in PD pulse increase and the rise-time of the pulse decrease gradually with aging time. It would be suggested that the ultra high components of PD pulse may be used to characterize the aging degree of stater winding insulation.

Keyword :

large generator partial discharge detection stator winding insulation UWB

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GB/T 7714 Song, Jiancheng , Xie, Hengkun , Cheng, Yonghong . Study on UWB frequency characteristics of partial discharge as a criterion of aging degree of stator winding insulation [C] . 2000 : 181-184 .
MLA Song, Jiancheng et al. "Study on UWB frequency characteristics of partial discharge as a criterion of aging degree of stator winding insulation" . (2000) : 181-184 .
APA Song, Jiancheng , Xie, Hengkun , Cheng, Yonghong . Study on UWB frequency characteristics of partial discharge as a criterion of aging degree of stator winding insulation . (2000) : 181-184 .
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Space charge distribution, TSC and TSL spectra in polyethylene aged by electrical stress EI CPCI-S Scopus
会议论文 | 2000 , 46-50 | 6th Interantional Conference on Properties and Applications of Dielectric Materials
WoS CC Cited Count: 1
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Abstract :

PE samples were aged under an ac stress of 50 kV/mm for 100, 300, 700, 1000 and 1200hrs respectively The space charge distribution in the samples was measured by pulsed electro-acoustic (PEA) method. Thermally stimulated current and luminescence spectra were simultaneously detected by a United Spectrum Instrument. The test results show that the space charges in samples were mainly negative charges from dissociated impurities. The space charges in the samples increased with aging time. An increase of hetero-charges promotes the electrodes to emit home-charges and separate charge peaks in the aged samples. Aging increases the densities of traps and luminescence centers (LC), but does not change their energy level in gamma relaxation region of PE sample. However, aging not only increases the density of traps in beta and alpha relaxation range or structure defects, but also increases their energy level. Space charges in short circuited aged sample may be an indication of change in densities of trap and luminescence center.

Keyword :

polyethylene space charge TSC TSL

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GB/T 7714 Tu, Demin , Yin, Yi , Wang, Xuan et al. Space charge distribution, TSC and TSL spectra in polyethylene aged by electrical stress [C] . 2000 : 46-50 .
MLA Tu, Demin et al. "Space charge distribution, TSC and TSL spectra in polyethylene aged by electrical stress" . (2000) : 46-50 .
APA Tu, Demin , Yin, Yi , Wang, Xuan , Fan, Yong , Wang, Jinqiao , Lei, Qingquan . Space charge distribution, TSC and TSL spectra in polyethylene aged by electrical stress . (2000) : 46-50 .
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Space charge distribution and capacitance-voltage characteristics of metal/polyimide Langmuir-Blodgett film/metal structure CPCI-S
会议论文 | 2000 , 112-115 | 6th International Conference on Properties and Applications of Dielectric Materials
WoS CC Cited Count: 1
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Abstract :

The capacitance-voltage (C-V) characteristics of the metal/polyimide (PI) Langmuir-Blodgett (LB) film/metal structure are analyzed, taking into account the interfacial electrostatic phenomena and the presence of the interfacial electronic states. The capacitance (C) and the additional relative capacitance [(C-C-0)/C-0] at various applied external voltages (V-ex) are calculated, under the assumption that the electron acceptor density of states (DOS) at the interfaces has a Gaussian profile centered at the energy level of the lowest unoccupied molecular orbital (LUMO). The results reveal that when a positive bias (V-ex>0) is applied to a metal/insulator (PI LB film)/metal (MIM) element, the capacitance and the additional relative capacitance decrease as the thickness of PI LB film increases, while a negative bias (V-ex<0) gives rise to slight changes of the capacitance and the additional relative capacitance. In addition, it is found that the density of space charge also experiences slight changes as the applied external bias increases. The calculated results of the C-V characteristics of the MIM element show good agreement with the experimental results.

Keyword :

interface MIM element density of electronic states capacitance-voltage characteristic LB film

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GB/T 7714 Li, CQ , Wu, CX , Iwamoto, M . Space charge distribution and capacitance-voltage characteristics of metal/polyimide Langmuir-Blodgett film/metal structure [C] . 2000 : 112-115 .
MLA Li, CQ et al. "Space charge distribution and capacitance-voltage characteristics of metal/polyimide Langmuir-Blodgett film/metal structure" . (2000) : 112-115 .
APA Li, CQ , Wu, CX , Iwamoto, M . Space charge distribution and capacitance-voltage characteristics of metal/polyimide Langmuir-Blodgett film/metal structure . (2000) : 112-115 .
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