Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995904
P. Werle, H. Borsi, E. Gockenbach
In this paper, an electrical partial discharge (PD) measurement technique for a dry type power transformer is presented. The method has been tested in the laboratory as well as on a transformer in a test bay using an automated partial discharge evaluation based on the comparison of quasi-simultaneously detected PD patterns at different decoupling points. Therefore a multiple sensor system is placed on the surface of the transformer coil, thus PD signals can be measured at various sites along the winding before they are processed and compared. The described technique enables, besides a localization of the PD source, a determination of the apparent charge, which can be more accurate than conventional narrowband PD measurements via a quadripole in parallel. A discussion of the results leads therefore to a proposal about improvements concerning the calibration for actual PD routine tests on dry type transformers.
{"title":"Diagnosing the insulation condition of dry type transformers using a multiple sensor partial-discharge-localization technique","authors":"P. Werle, H. Borsi, E. Gockenbach","doi":"10.1109/ELINSL.2002.995904","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995904","url":null,"abstract":"In this paper, an electrical partial discharge (PD) measurement technique for a dry type power transformer is presented. The method has been tested in the laboratory as well as on a transformer in a test bay using an automated partial discharge evaluation based on the comparison of quasi-simultaneously detected PD patterns at different decoupling points. Therefore a multiple sensor system is placed on the surface of the transformer coil, thus PD signals can be measured at various sites along the winding before they are processed and compared. The described technique enables, besides a localization of the PD source, a determination of the apparent charge, which can be more accurate than conventional narrowband PD measurements via a quadripole in parallel. A discussion of the results leads therefore to a proposal about improvements concerning the calibration for actual PD routine tests on dry type transformers.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"144 1","pages":"166-169"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77537664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995927
N. Hayashi, K. Kawahara, M. Sumikura, M. Hara, F. Endo
The authors have been probing the possibility of applying functionally graded materials to solid insulators in order to control the electric field profiles, and resultant improvement of insulation level. Investigated in the paper are the effects of the capacitive bulk-grading of the coaxial disc-type and post-type model spacers on the electric field along the insulator surface and on the corresponding surface breakdown voltage when the lightning impulse voltage is applied. It is obtained from the experimental work that the bulk-graded model spacers employed in the investigation stand for higher positive lightning impulse voltage by 10 to 25% than the ungraded model spacers, depending greatly on the manner of grading and model geometry.
{"title":"Electric field control by permittivity functionally graded materials and their lightning impulse withstand voltages for surface breakdown","authors":"N. Hayashi, K. Kawahara, M. Sumikura, M. Hara, F. Endo","doi":"10.1109/ELINSL.2002.995927","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995927","url":null,"abstract":"The authors have been probing the possibility of applying functionally graded materials to solid insulators in order to control the electric field profiles, and resultant improvement of insulation level. Investigated in the paper are the effects of the capacitive bulk-grading of the coaxial disc-type and post-type model spacers on the electric field along the insulator surface and on the corresponding surface breakdown voltage when the lightning impulse voltage is applied. It is obtained from the experimental work that the bulk-graded model spacers employed in the investigation stand for higher positive lightning impulse voltage by 10 to 25% than the ungraded model spacers, depending greatly on the manner of grading and model geometry.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"91 1","pages":"260-263"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79653894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995978
N. Amyot, É. David
Joints are generally known to be the weakest link of underground distribution lines. One of the most common failure modes is attributable to the occurrence of dielectric breakdown at the cable-joint interface. Interfacial pressure is known to be a key factor in the interfacial breakdown strength: a high interfacial pressure leads to good dielectric breakdown strength whereas a lower pressure leads to poor long-term-performance.The present work shows the behavior of two different types of distribution cable joints: ethylene-propylene rubber (EPR) based coldshrinkable cable joint and silicone rubber (SR) based coldshrinkable cable joint. Interfacial pressure was monitored for thermal cycles at three different temperatures: 75, 90 and 130/spl deg/C. The cycling protocol is based on an existing IEEE standard for cable joints for use with extruded dielectric cables rated 5-138 kV. A preliminary theoretical model has been developed and compared to the obtained data.
{"title":"A study of interfacial pressure behavior for two types of thermally cycled coldshrinkable joints","authors":"N. Amyot, É. David","doi":"10.1109/ELINSL.2002.995978","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995978","url":null,"abstract":"Joints are generally known to be the weakest link of underground distribution lines. One of the most common failure modes is attributable to the occurrence of dielectric breakdown at the cable-joint interface. Interfacial pressure is known to be a key factor in the interfacial breakdown strength: a high interfacial pressure leads to good dielectric breakdown strength whereas a lower pressure leads to poor long-term-performance.The present work shows the behavior of two different types of distribution cable joints: ethylene-propylene rubber (EPR) based coldshrinkable cable joint and silicone rubber (SR) based coldshrinkable cable joint. Interfacial pressure was monitored for thermal cycles at three different temperatures: 75, 90 and 130/spl deg/C. The cycling protocol is based on an existing IEEE standard for cable joints for use with extruded dielectric cables rated 5-138 kV. A preliminary theoretical model has been developed and compared to the obtained data.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"78 1","pages":"476-480"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86797486","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995970
S. Boggs, S. Nishiwaki, M. Toyoda, J. Kuang
A great deal of research related to high current contacts was reported by Holm through the 1960s, but most of this work was carried out using often ingenious analytical methods, before the practicability of computer-based numerical methods. As a result, the analysis does not include the effects of temperature-dependent material properties. We report computations of high current contact stability based on transient nonlinear finite element analysis which includes the effect of temperature-dependent material properties. These analyses indicate that if a Ag coating over Al is too thin and the surface is too rough, the Al can melt under the Ag, without the Ag melting, leading to premature contact instability.
{"title":"Effect of silver coating thickness on high current contact stability","authors":"S. Boggs, S. Nishiwaki, M. Toyoda, J. Kuang","doi":"10.1109/ELINSL.2002.995970","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995970","url":null,"abstract":"A great deal of research related to high current contacts was reported by Holm through the 1960s, but most of this work was carried out using often ingenious analytical methods, before the practicability of computer-based numerical methods. As a result, the analysis does not include the effects of temperature-dependent material properties. We report computations of high current contact stability based on transient nonlinear finite element analysis which includes the effect of temperature-dependent material properties. These analyses indicate that if a Ag coating over Al is too thin and the surface is too rough, the Al can melt under the Ag, without the Ag melting, leading to premature contact instability.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"61 1","pages":"444-448"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83619339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995893
S. Hvidsten, H. Faremo, R. Eriksson, Wei Min
The results show that the degree of water treeing in HV XLPE cables (36 kV and above) is strongly dependent upon the cable design and the service (system) voltage. The water trees are typically relatively short, but their density is similar to that observed in medium voltage cables with similar design. The results from the nondestructive diagnostic testing show that it can be possible to detect water treeing also in old high voltage cables extending diagnostic techniques developed for medium voltage cables.
{"title":"Water treeing and condition assessment of high voltage XLPE cables","authors":"S. Hvidsten, H. Faremo, R. Eriksson, Wei Min","doi":"10.1109/ELINSL.2002.995893","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995893","url":null,"abstract":"The results show that the degree of water treeing in HV XLPE cables (36 kV and above) is strongly dependent upon the cable design and the service (system) voltage. The water trees are typically relatively short, but their density is similar to that observed in medium voltage cables with similar design. The results from the nondestructive diagnostic testing show that it can be possible to detect water treeing also in old high voltage cables extending diagnostic techniques developed for medium voltage cables.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"83 1","pages":"112-115"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85602992","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995874
H. van Breen, E. Gulski, J. Smit, H. Verhaart, W. de Leeuw
This paper presents a method to perform online time domain partial discharge measurements in a high noise and disturbance environment. The method combines the sensitivity of an online VHF PD (very high frequency partial discharge) measurement with the power of a time domain measurement.. Two measurements on running turbogenerators are presented: one on an 150 MVA generator without disturbances and. one on an 650 MVA turbo generator in a high disturbance environment. The paper shows that it is possible to detect and record partial discharges in an environment with disturbance pulses over 1000 times their size. Using frequency analysis a signal to noise ratio can be obtained, which can be used to determine the optimum measuring frequencies for online VHF PD measurements. Using typical time and frequency wave shape parameter extraction it is possible to separate the recorded pulses into PDs and disturbances.
{"title":"Experience with on-line PD measurements on generators in frequency and time domain","authors":"H. van Breen, E. Gulski, J. Smit, H. Verhaart, W. de Leeuw","doi":"10.1109/ELINSL.2002.995874","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995874","url":null,"abstract":"This paper presents a method to perform online time domain partial discharge measurements in a high noise and disturbance environment. The method combines the sensitivity of an online VHF PD (very high frequency partial discharge) measurement with the power of a time domain measurement.. Two measurements on running turbogenerators are presented: one on an 150 MVA generator without disturbances and. one on an 650 MVA turbo generator in a high disturbance environment. The paper shows that it is possible to detect and record partial discharges in an environment with disturbance pulses over 1000 times their size. Using frequency analysis a signal to noise ratio can be obtained, which can be used to determine the optimum measuring frequencies for online VHF PD measurements. Using typical time and frequency wave shape parameter extraction it is possible to separate the recorded pulses into PDs and disturbances.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"110 1","pages":"31-35"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86882760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995905
T. Leibfried, A. Kachler
A lot of power transformers currently in operation have reached a critical age with an operating time of 30 years and more. Utilities have to make a decision either continuing to use these transformers or replacing them. As a basis for this decision, information about the condition of the currently operating power transformers is required. Ageing processes are caused by dielectric, chemical, thermal and electrodynamic stresses. They are of very complex nature. As an example, water in the solid insulation material acts as a catalyst and enforces the ageing processes. Due to variable load there is a complex temperature dependent moisture dynamic behaviour of the oil paper insulation system. Well-known methods like Karl-Fischer-Titration and dew point measurement cannot be applied on transformers in operation since it is risky and difficult to open the transformer for getting a material sample. New methods of dielectric spectroscopy have been developed to overcome this implication. The PDC-analysis (polarisation and depolarisation current analysis) is a nondestructive method for determining the moisture content in the solid insulation material of a power transformer. On the basis of this reliable analysis one can decide about further actions like an on-site drying of the active part. This paper presents the PDC technique and results of measurements on new and aged transformers.
{"title":"Insulation diagnostics on power transformers using the polarisation and depolarisation current (PDC) analysis","authors":"T. Leibfried, A. Kachler","doi":"10.1109/ELINSL.2002.995905","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995905","url":null,"abstract":"A lot of power transformers currently in operation have reached a critical age with an operating time of 30 years and more. Utilities have to make a decision either continuing to use these transformers or replacing them. As a basis for this decision, information about the condition of the currently operating power transformers is required. Ageing processes are caused by dielectric, chemical, thermal and electrodynamic stresses. They are of very complex nature. As an example, water in the solid insulation material acts as a catalyst and enforces the ageing processes. Due to variable load there is a complex temperature dependent moisture dynamic behaviour of the oil paper insulation system. Well-known methods like Karl-Fischer-Titration and dew point measurement cannot be applied on transformers in operation since it is risky and difficult to open the transformer for getting a material sample. New methods of dielectric spectroscopy have been developed to overcome this implication. The PDC-analysis (polarisation and depolarisation current analysis) is a nondestructive method for determining the moisture content in the solid insulation material of a power transformer. On the basis of this reliable analysis one can decide about further actions like an on-site drying of the active part. This paper presents the PDC technique and results of measurements on new and aged transformers.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"428 1","pages":"170-173"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86687294","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995876
Wei Wang, Wufeng Li, C.R. Li, L. Ding, Q. Su, C. Chang
The on-line monitoring of partial discharge on generators is more and more widely used to estimate the insulation condition of generator stator windings. In this paper a new detector for on-line monitoring of partial discharges of generators was introduced. The measurement of partial discharges was carried out on some generator model bars in a laboratory using the new detector. Features of different types of PD were analyzed using the spectrums of Hq(/spl phi/), Hn(/spl phi/) and Hn(q). Some primary results from field test are reported for a detector installed on a turbine generator in a power plant located in Shanxi Province of China.
{"title":"The estimation of insulation condition of generators by on-line monitoring of partial discharges using a new detector","authors":"Wei Wang, Wufeng Li, C.R. Li, L. Ding, Q. Su, C. Chang","doi":"10.1109/ELINSL.2002.995876","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995876","url":null,"abstract":"The on-line monitoring of partial discharge on generators is more and more widely used to estimate the insulation condition of generator stator windings. In this paper a new detector for on-line monitoring of partial discharges of generators was introduced. The measurement of partial discharges was carried out on some generator model bars in a laboratory using the new detector. Features of different types of PD were analyzed using the spectrums of Hq(/spl phi/), Hn(/spl phi/) and Hn(q). Some primary results from field test are reported for a detector installed on a turbine generator in a power plant located in Shanxi Province of China.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"23 1","pages":"40-43"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83568176","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.995989
F. Berton, R. Patsch
Pulse sequence analysis is a powerful tool to characterize defects that generate partial discharges. Usually, frequency distributions or scatter plots of sequence correlated parameters such as e.g. the external voltage differences /spl Delta/U between consecutive discharge events are used for diagnosis. In some cases, the analysis of the times of occurrence and especially the sequence of time-intervals /spl Delta/t between consecutive discharge pulses may even be more efficient to characterize a defect or to differentiate between different defects. In the case of only a few discharge events per cycle of the applied voltage, the parameter /spl Delta/U is very efficient and allows to distinguish clearly whether the partial discharge signals are generated by only one or more local defects, information that is very helpful for a reliable diagnosis. Even with only one type of defect, a small change in the height of the measuring voltage may significantly influence the discharge phenomenon, resp. the measured date set. The analysis of the frequency distributions of the time differences /spl Delta/t of consecutive discharge events and the elimination of 'multiple discharge pulses' together with the use of the parameter /spl Delta/U//spl Delta/t reveal very useful additional information.
{"title":"The use of time intervals between consecutive discharges to characterize PD-sources","authors":"F. Berton, R. Patsch","doi":"10.1109/ELINSL.2002.995989","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.995989","url":null,"abstract":"Pulse sequence analysis is a powerful tool to characterize defects that generate partial discharges. Usually, frequency distributions or scatter plots of sequence correlated parameters such as e.g. the external voltage differences /spl Delta/U between consecutive discharge events are used for diagnosis. In some cases, the analysis of the times of occurrence and especially the sequence of time-intervals /spl Delta/t between consecutive discharge pulses may even be more efficient to characterize a defect or to differentiate between different defects. In the case of only a few discharge events per cycle of the applied voltage, the parameter /spl Delta/U is very efficient and allows to distinguish clearly whether the partial discharge signals are generated by only one or more local defects, information that is very helpful for a reliable diagnosis. Even with only one type of defect, a small change in the height of the measuring voltage may significantly influence the discharge phenomenon, resp. the measured date set. The analysis of the frequency distributions of the time differences /spl Delta/t of consecutive discharge events and the elimination of 'multiple discharge pulses' together with the use of the parameter /spl Delta/U//spl Delta/t reveal very useful additional information.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"63 1","pages":"527-530"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83072476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-04-07DOI: 10.1109/ELINSL.2002.996005
G. Stone, V. Warren, M. Fenger
Online partial discharge testing has long been used to assess the condition of the high-voltage insulation in motor and generator stator windings. Past research has shown that motor and generator operating parameters such as voltage, power output, gas pressure, and stator winding temperature can have an important impact on the PD levels, and thus must be controlled if useful trends in PD activity over time are to be obtained. Over the years, results have been collected that indicate humidity may also be a factor that needs to be monitored. In addition, some simple laboratory experiments have been performed to verify that humidity can change the PD. When applying online PD testing to assess stator winding insulation condition, users must be aware of the influence of humidity on the measured PD activity to properly interpret the results.
{"title":"Case studies on the effect of humidity on stator winding partial discharge activity","authors":"G. Stone, V. Warren, M. Fenger","doi":"10.1109/ELINSL.2002.996005","DOIUrl":"https://doi.org/10.1109/ELINSL.2002.996005","url":null,"abstract":"Online partial discharge testing has long been used to assess the condition of the high-voltage insulation in motor and generator stator windings. Past research has shown that motor and generator operating parameters such as voltage, power output, gas pressure, and stator winding temperature can have an important impact on the PD levels, and thus must be controlled if useful trends in PD activity over time are to be obtained. Over the years, results have been collected that indicate humidity may also be a factor that needs to be monitored. In addition, some simple laboratory experiments have been performed to verify that humidity can change the PD. When applying online PD testing to assess stator winding insulation condition, users must be aware of the influence of humidity on the measured PD activity to properly interpret the results.","PeriodicalId":10532,"journal":{"name":"Conference Record of the the 2002 IEEE International Symposium on Electrical Insulation (Cat. No.02CH37316)","volume":"36 1","pages":"579-581"},"PeriodicalIF":0.0,"publicationDate":"2002-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89103284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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