Pub Date : 2014-11-24DOI: 10.1109/NAPS.2014.6965457
Qiang Zhang, V. Venkatasubramanian
The most critical part of the synchrophasor technology is the availability of accurate UTC time. Usually an external GPS clock device feeds PMU with 1 pulse per second time signals. During the second, PMU's internal clock keeps the pace until the next time signal arrives. Because of various reasons, time skews have been observed in some real life synchrophasor data. Two fundamental types of time skews are identified in this paper. Synchrophasor time skew problem is fundamentally different from that in SCADA system, because time shift is translated into error in phase angle measurements and subsequent errors in frequency and rate of change of frequency measurements. Algorithms are developed to automatically detect time skews online and to estimate the time errors. A correction method is also provided. Both simulated data and real life data are used to verify that the proposed methods are effective and accurate.
{"title":"Synchrophasor time skew: Formulation, detection and correction","authors":"Qiang Zhang, V. Venkatasubramanian","doi":"10.1109/NAPS.2014.6965457","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965457","url":null,"abstract":"The most critical part of the synchrophasor technology is the availability of accurate UTC time. Usually an external GPS clock device feeds PMU with 1 pulse per second time signals. During the second, PMU's internal clock keeps the pace until the next time signal arrives. Because of various reasons, time skews have been observed in some real life synchrophasor data. Two fundamental types of time skews are identified in this paper. Synchrophasor time skew problem is fundamentally different from that in SCADA system, because time shift is translated into error in phase angle measurements and subsequent errors in frequency and rate of change of frequency measurements. Algorithms are developed to automatically detect time skews online and to estimate the time errors. A correction method is also provided. Both simulated data and real life data are used to verify that the proposed methods are effective and accurate.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115743355","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965452
L. Mathew, S. Chatterji
Pilot installations of STATCOM and UPFC have been built, commissioned and installed in the recent years. The high cost of these Voltage Source Converters (VSC) based FACTS controllers is found to be the major hindrance to their widespread use. Novel and cost effective FACTS topologies have been proposed which are built upon existing equipment which makes use of static converters. The different HPFC configurations devised by the investigator have been implemented on an SMIB system and simulated using MATLAB/ SIMULINK. The comparison of simulation results show that HPFC is a better option for damping power system oscillations and thus enhancing the stability of the system.
{"title":"Modeling and simulation of hybrid power flow controller implemented on SMIB system","authors":"L. Mathew, S. Chatterji","doi":"10.1109/NAPS.2014.6965452","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965452","url":null,"abstract":"Pilot installations of STATCOM and UPFC have been built, commissioned and installed in the recent years. The high cost of these Voltage Source Converters (VSC) based FACTS controllers is found to be the major hindrance to their widespread use. Novel and cost effective FACTS topologies have been proposed which are built upon existing equipment which makes use of static converters. The different HPFC configurations devised by the investigator have been implemented on an SMIB system and simulated using MATLAB/ SIMULINK. The comparison of simulation results show that HPFC is a better option for damping power system oscillations and thus enhancing the stability of the system.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"284 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114942926","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965395
Byungkwon Park, C. DeMarco
This paper revisits active and reactive power decomposition techniques as applied to the optimal power flow problem. The full nonlinear AC optimal power flow problem is decoupled into two lower dimensional nonlinear subproblems (active and reactive), seeking to characterize and exploit the well recognized property of the power flow Jacobian matrix: that the off-diagonal submatrix blocks are in some sense “small,” reflecting the fact that network flow of active power is relatively weakly dependent on bus voltage magnitudes, while reactive power flow is relatively weakly dependent on bus voltage phase angles. We further exploit the fact that the standard objective function of the optimal power flow depends directly on active powers (of generators) only, and different, loss-related objective functions may be used for the reactive subproblem. These formulations are examined in a number of numerical examples, evaluating speed of convergence, and how close decoupled P-Q OPF solution is to that of the full AC OPF. While the improvements in computation time are modest, use of decoupled solutions as initial guesses to a full AC OPF is shown to be promising. In addition to the solution algorithms themselves, a method to characterize the magnitude of off-diagonal coupling terms in the power flow Jacobian is examined.
{"title":"Active/reactive power decomposition approaches to the AC optimal power flow problem","authors":"Byungkwon Park, C. DeMarco","doi":"10.1109/NAPS.2014.6965395","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965395","url":null,"abstract":"This paper revisits active and reactive power decomposition techniques as applied to the optimal power flow problem. The full nonlinear AC optimal power flow problem is decoupled into two lower dimensional nonlinear subproblems (active and reactive), seeking to characterize and exploit the well recognized property of the power flow Jacobian matrix: that the off-diagonal submatrix blocks are in some sense “small,” reflecting the fact that network flow of active power is relatively weakly dependent on bus voltage magnitudes, while reactive power flow is relatively weakly dependent on bus voltage phase angles. We further exploit the fact that the standard objective function of the optimal power flow depends directly on active powers (of generators) only, and different, loss-related objective functions may be used for the reactive subproblem. These formulations are examined in a number of numerical examples, evaluating speed of convergence, and how close decoupled P-Q OPF solution is to that of the full AC OPF. While the improvements in computation time are modest, use of decoupled solutions as initial guesses to a full AC OPF is shown to be promising. In addition to the solution algorithms themselves, a method to characterize the magnitude of off-diagonal coupling terms in the power flow Jacobian is examined.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126863427","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965362
M. Cervantes, A. Ramirez
This paper presents a frequency-domain (FD) approach for calculating the maximum overvoltage along an underground cable (UC) due to lightning. It is considered that the UC is protected by surge arresters at both ends. In the proposed method, the UC is spatially subdivided and direct FD algebraic relations are used to calculate the voltage at each subdivision. Surge arresters are piece-wised represented in the FD and resolved based on the superposition principle. Flashovers are assessed and resolved also in the FD using the superposition principle. The proposed FD approach can be utilized to validate time domain (TD) methods based on the traveling wave concept or on constant-parameter line representation. The proposed method is applied to a 300 kV system with different cable lengths and compared with the results given by the PSCAD software.
{"title":"Frequency-domain computation of maximum lightning overvoltage along a cable protected by surge arresters","authors":"M. Cervantes, A. Ramirez","doi":"10.1109/NAPS.2014.6965362","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965362","url":null,"abstract":"This paper presents a frequency-domain (FD) approach for calculating the maximum overvoltage along an underground cable (UC) due to lightning. It is considered that the UC is protected by surge arresters at both ends. In the proposed method, the UC is spatially subdivided and direct FD algebraic relations are used to calculate the voltage at each subdivision. Surge arresters are piece-wised represented in the FD and resolved based on the superposition principle. Flashovers are assessed and resolved also in the FD using the superposition principle. The proposed FD approach can be utilized to validate time domain (TD) methods based on the traveling wave concept or on constant-parameter line representation. The proposed method is applied to a 300 kV system with different cable lengths and compared with the results given by the PSCAD software.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"106 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124097575","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965397
F. R. Alonso, D. Q. Oliveira, A. D. De Souza, B. Lopes
Power losses minimization is a goal for electricity utilities and distribution system reconfiguration is one of the available tools to accomplish it. Reconfiguring the network means altering its topology by changing the status of normally opened and normally closed switches. Besides power losses minimization, network reconfiguration also helps on load balance and service restoration. This paper proposes the use of artificial immune systems to optimize the distribution system reconfiguration by minimizing the switching operations and active power losses, considering as constraints the radial characteristics of the distribution networks and feeders' ampacity. The proposed algorithm is tested on a sample system, 14-Bus Test System, and on a Paraguayan real feeder.
{"title":"Distribution system reconfiguration using artificial immune systems","authors":"F. R. Alonso, D. Q. Oliveira, A. D. De Souza, B. Lopes","doi":"10.1109/NAPS.2014.6965397","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965397","url":null,"abstract":"Power losses minimization is a goal for electricity utilities and distribution system reconfiguration is one of the available tools to accomplish it. Reconfiguring the network means altering its topology by changing the status of normally opened and normally closed switches. Besides power losses minimization, network reconfiguration also helps on load balance and service restoration. This paper proposes the use of artificial immune systems to optimize the distribution system reconfiguration by minimizing the switching operations and active power losses, considering as constraints the radial characteristics of the distribution networks and feeders' ampacity. The proposed algorithm is tested on a sample system, 14-Bus Test System, and on a Paraguayan real feeder.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131759210","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965390
M. Lauby, J. Bian, S. Ekisheva, M. Varghese
With higher penetrations of renewable energy resources, assessing frequency response trends becomes extremely important. It is a critical component to the reliable operation of the bulk power system, particularly during disturbances and restoration. This paper presents a new and comprehensive statistical method to evaluate the trends for the Eastern and Western Interconnections of the North American electric grid. The statistical analysis tests whether observable decreases or increases between four annual data points constitute a statistically significant trend. The probability distribution of frequency response and contributing factors to it changes over the years are also examined. The statistical significance tests and studies have indicated a stable general trend for the Eastern and Western Interconnections over time.
{"title":"Frequency response assessment of Eastern and Western Interconnections","authors":"M. Lauby, J. Bian, S. Ekisheva, M. Varghese","doi":"10.1109/NAPS.2014.6965390","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965390","url":null,"abstract":"With higher penetrations of renewable energy resources, assessing frequency response trends becomes extremely important. It is a critical component to the reliable operation of the bulk power system, particularly during disturbances and restoration. This paper presents a new and comprehensive statistical method to evaluate the trends for the Eastern and Western Interconnections of the North American electric grid. The statistical analysis tests whether observable decreases or increases between four annual data points constitute a statistically significant trend. The probability distribution of frequency response and contributing factors to it changes over the years are also examined. The statistical significance tests and studies have indicated a stable general trend for the Eastern and Western Interconnections over time.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130228623","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965361
Po-Chen Chen, V. Malbasa, T. Dokic, M. Kezunovic, Yimai Dong
Single-phase-to-ground sub-cycle faults in the distribution network can be located using voltage sag fault location. This paper illustrates how a sensitivity study of measurement imperfections can be used to quantify the impact of sub-cycle faults on voltage sag based fault location. Our results suggest that there is a complex relationship between factors influencing error in fault location because the design of the study covered a wide range of conditions. The more complicated, higher order interactions have a stronger influence on error than any particular input factor alone.
{"title":"Sensitivity of voltage sag based fault location in distribution network to sub-cycle faults","authors":"Po-Chen Chen, V. Malbasa, T. Dokic, M. Kezunovic, Yimai Dong","doi":"10.1109/NAPS.2014.6965361","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965361","url":null,"abstract":"Single-phase-to-ground sub-cycle faults in the distribution network can be located using voltage sag fault location. This paper illustrates how a sensitivity study of measurement imperfections can be used to quantify the impact of sub-cycle faults on voltage sag based fault location. Our results suggest that there is a complex relationship between factors influencing error in fault location because the design of the study covered a wide range of conditions. The more complicated, higher order interactions have a stronger influence on error than any particular input factor alone.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133271698","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965373
Jiang Li, Peng Zhang, Yiwei Wang, Chao Wei
The loosely coupled transformer (also called separable transformer) is the key component of inductive coupled power transfer (ICPT) system. Its coupling coefficient is very low which limits transmission efficiency of ICPT system. This paper describes the principle of ICPT system, and utilizes ANSYS software to simulate magnetic field of loosely coupled transformer. Three-dimensional simulation can show the core structure more clearly, and makes the results of analysis more accurate. Through quantitative analyzing the distributions of magnetic field intensity, magnetic flux density of loosely coupled transformer and the secondary-side load electromotive force, the paper draws a conclusion that the key technical parameters, such as operating frequency, air gap, core thickness and magnetic core position shift etc have significant impact on the coupling coefficient of the loosely coupled transformer. Furthermore, the transmission efficiency is improved during the resonance after adding capacitors to primary side in the circuit. The simulation analysis of the relationship between the key parameters and the coupling coefficient will be very helpful for the development of loosely coupled transformer and subsequent experiments.
{"title":"The three-dimensional electromagnetic simulation analysis of power transmission of loosely coupled transformer based on ANSYS","authors":"Jiang Li, Peng Zhang, Yiwei Wang, Chao Wei","doi":"10.1109/NAPS.2014.6965373","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965373","url":null,"abstract":"The loosely coupled transformer (also called separable transformer) is the key component of inductive coupled power transfer (ICPT) system. Its coupling coefficient is very low which limits transmission efficiency of ICPT system. This paper describes the principle of ICPT system, and utilizes ANSYS software to simulate magnetic field of loosely coupled transformer. Three-dimensional simulation can show the core structure more clearly, and makes the results of analysis more accurate. Through quantitative analyzing the distributions of magnetic field intensity, magnetic flux density of loosely coupled transformer and the secondary-side load electromotive force, the paper draws a conclusion that the key technical parameters, such as operating frequency, air gap, core thickness and magnetic core position shift etc have significant impact on the coupling coefficient of the loosely coupled transformer. Furthermore, the transmission efficiency is improved during the resonance after adding capacitors to primary side in the circuit. The simulation analysis of the relationship between the key parameters and the coupling coefficient will be very helpful for the development of loosely coupled transformer and subsequent experiments.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123354233","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965462
Abosalah ElMehdi, Ahmed Momen, B. Johnson
Line commutated current source converter-based (LCC) HVDC systems are being considered for the transfer of power from remote wind resources to existing ac transmission systems. The rectifier terminals of these systems are connected to weak ac systems. A modified CIGRE HVDC benchmark model implemented in the PSCAD/EMTDC program is used to study the impact of varying amounts of dynamic reactive compensation on performance during rectifier operation. Determination of the amount of dynamic reactive compensation needed at the rectifier terminal is based on the following dynamic parameters: the magnitude of the first peak of the temporary overvoltages (TOVs) of the rectifier ac voltage following disturbance and time for the dc system to reach 80% of pre-disturbance dc power transfer after the clearing an ac fault. An effective short circuit ratio (ESCR) for best operation will be calculated based on the selected value of the dynamic reactive power compensation rating.
{"title":"Dynamic reactive compensation requirements at the rectifier end of an LCC HVDC link connected to a weak AC system","authors":"Abosalah ElMehdi, Ahmed Momen, B. Johnson","doi":"10.1109/NAPS.2014.6965462","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965462","url":null,"abstract":"Line commutated current source converter-based (LCC) HVDC systems are being considered for the transfer of power from remote wind resources to existing ac transmission systems. The rectifier terminals of these systems are connected to weak ac systems. A modified CIGRE HVDC benchmark model implemented in the PSCAD/EMTDC program is used to study the impact of varying amounts of dynamic reactive compensation on performance during rectifier operation. Determination of the amount of dynamic reactive compensation needed at the rectifier terminal is based on the following dynamic parameters: the magnitude of the first peak of the temporary overvoltages (TOVs) of the rectifier ac voltage following disturbance and time for the dc system to reach 80% of pre-disturbance dc power transfer after the clearing an ac fault. An effective short circuit ratio (ESCR) for best operation will be calculated based on the selected value of the dynamic reactive power compensation rating.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126185673","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 : 2014-11-24DOI: 10.1109/NAPS.2014.6965393
Witcha Kate-singnoy, S. Premrudeepreechacharn
This paper presents age estimation and optimal cost preventive maintenance of carbon brush in slip ring using Weibull distribution in statistical analysis. Carbon brush is used in Sirikit hydro power plant which is electrographite brush type. Weibull distribution can find mean time to failure, failure rate, reliability with few number of the length measurement of carbon brush. It has been applied to find optimal cost preventive maintenance which reduces unnecessary planned maintenance and also increases reliability of system. These results are assessed, analyzed and compared to carbon brush maintenance guide line of Sirikit hydro power plant in Electricity Generating Authority of Thailand (EGAT) which also can apply with other power plants of EGAT.
{"title":"Age estimation of electrographite brush in generator system for optimized maintenance planning of Sirikit hydro power plant","authors":"Witcha Kate-singnoy, S. Premrudeepreechacharn","doi":"10.1109/NAPS.2014.6965393","DOIUrl":"https://doi.org/10.1109/NAPS.2014.6965393","url":null,"abstract":"This paper presents age estimation and optimal cost preventive maintenance of carbon brush in slip ring using Weibull distribution in statistical analysis. Carbon brush is used in Sirikit hydro power plant which is electrographite brush type. Weibull distribution can find mean time to failure, failure rate, reliability with few number of the length measurement of carbon brush. It has been applied to find optimal cost preventive maintenance which reduces unnecessary planned maintenance and also increases reliability of system. These results are assessed, analyzed and compared to carbon brush maintenance guide line of Sirikit hydro power plant in Electricity Generating Authority of Thailand (EGAT) which also can apply with other power plants of EGAT.","PeriodicalId":421766,"journal":{"name":"2014 North American Power Symposium (NAPS)","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128846620","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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