Pub Date : 2014-04-24DOI: 10.1109/CPRE.2014.6799012
R. Hedding
This paper re-examined certain nuances of fundamental principles which are directly or indirectly related to protective relaying that were in the original paper. We've found that in most every case the previous conclusion reached was correct. In those instances filtering in microprocessor relaying was able to eliminate that harmonics that were applied to electromechanical relays. Current transformers still obey the laws of Physics. Fortescue's rules of Symmetrical Components still apply. Power line carrier modal analysis still applies, and Kirchoff's law still applies to transformer differential relays.
{"title":"False Applications of Reliable Relaying Principles revisited","authors":"R. Hedding","doi":"10.1109/CPRE.2014.6799012","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799012","url":null,"abstract":"This paper re-examined certain nuances of fundamental principles which are directly or indirectly related to protective relaying that were in the original paper. We've found that in most every case the previous conclusion reached was correct. In those instances filtering in microprocessor relaying was able to eliminate that harmonics that were applied to electromechanical relays. Current transformers still obey the laws of Physics. Fortescue's rules of Symmetrical Components still apply. Power line carrier modal analysis still applies, and Kirchoff's law still applies to transformer differential relays.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"58 1-4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131727185","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6799020
C. Mozina
As a result of the NERC analysis of the 2003 blackout, NERC has proposed “voltage ride through” criteria that have resulted in two standards. Transmission line protection loadability and low voltage “ride through” has been addressed in Standard PRC-023-2. NERC PRC-025-1 addresses loadability of power plant protection and is much more complicated to apply than the transmission loadability requirements outlined in PRC-023-2. PRC-025-1 addresses the effects of generator field forcing. As discussed in this paper, PRC-025-1 has many options and calculation methods to establish stress point limits. The adoption of PRC-025-1 will result in limiting generator remote backup protection for transmission system faults on lines exiting power plants. It will require that transmission line protection for lines exiting power plants to have delineated primary and backup protection and local breaker failure because in most cases remote backup will not be possible.
{"title":"NERC requirements for setting load-dependent power plant protection: PRC-025-1","authors":"C. Mozina","doi":"10.1109/CPRE.2014.6799020","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799020","url":null,"abstract":"As a result of the NERC analysis of the 2003 blackout, NERC has proposed “voltage ride through” criteria that have resulted in two standards. Transmission line protection loadability and low voltage “ride through” has been addressed in Standard PRC-023-2. NERC PRC-025-1 addresses loadability of power plant protection and is much more complicated to apply than the transmission loadability requirements outlined in PRC-023-2. PRC-025-1 addresses the effects of generator field forcing. As discussed in this paper, PRC-025-1 has many options and calculation methods to establish stress point limits. The adoption of PRC-025-1 will result in limiting generator remote backup protection for transmission system faults on lines exiting power plants. It will require that transmission line protection for lines exiting power plants to have delineated primary and backup protection and local breaker failure because in most cases remote backup will not be possible.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130926383","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6799018
N. Fischer, D. Finney, Douglas I. Taylor
Differential protection is often touted as being The protection for generator stator windings. In this paper, we examine the degree of protection afforded by the various types of differential elements (phase, negative, and zero sequence) for stator winding faults. To understand why and how windings fail, we need to know how a stator is constructed, how the winding coils are made, and how they are mounted into the stator core. This paper examines various types of winding configurations and the makeup of the winding insulation. We analyze how different winding failures can be detected using the various differential elements mentioned. Because protection elements are not only required to be sensitive but also secure, we contrast the dependability and security of each element. Security of any differential element must include the performance of the primary current transformers (CTs); therefore, we extend the discussion to setting recommendations and CT selection rules. Finally, the paper answers the question, How much protection does each type of differential element provide? Knowing the limits to performance will allow protection engineers to set the elements for realistic sensitivity without unnecessarily risking any security.
{"title":"How to determine the effectiveness of generator differential protection","authors":"N. Fischer, D. Finney, Douglas I. Taylor","doi":"10.1109/CPRE.2014.6799018","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799018","url":null,"abstract":"Differential protection is often touted as being The protection for generator stator windings. In this paper, we examine the degree of protection afforded by the various types of differential elements (phase, negative, and zero sequence) for stator winding faults. To understand why and how windings fail, we need to know how a stator is constructed, how the winding coils are made, and how they are mounted into the stator core. This paper examines various types of winding configurations and the makeup of the winding insulation. We analyze how different winding failures can be detected using the various differential elements mentioned. Because protection elements are not only required to be sensitive but also secure, we contrast the dependability and security of each element. Security of any differential element must include the performance of the primary current transformers (CTs); therefore, we extend the discussion to setting recommendations and CT selection rules. Finally, the paper answers the question, How much protection does each type of differential element provide? Knowing the limits to performance will allow protection engineers to set the elements for realistic sensitivity without unnecessarily risking any security.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125239367","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6798993
D. Tziouvaras, H. Altuve, F. Calero
This paper is a tutorial on the protection of mutually coupled transmission lines. It discusses how mutual coupling affects the polarizing quantities of ground directional elements, the reach of ground distance elements, and the accuracy of single-ended fault locating algorithms. The paper provides settings guidelines for instantaneous directional overcurrent and ground distance elements. It discusses in detail how transmission line mutual coupling causes overreaching or underreaching of ground distance elements. It also discusses the impact on these elements of grounding the mutually coupled line at both line ends during maintenance. The paper analyzes whether mutual coupling compensation offers any benefits to line protection. The ease and benefit of line current differential schemes are contrasted in the discussion. Lastly, the paper examines a case when a double-circuit transmission line is operated as a single circuit with jumpers placed across similar phases along the line. This situation typically arises when the utility company needs to free one of the bays to bring an additional line into the substation. The protection engineer needs to decide where to install jumpers to parallel the two circuits in order to avoid distance element underreaching. The paper provides an analysis of this problem and offers suggestions on how to address it.
{"title":"Protecting mutually coupled transmission lines: Challenges and solutions","authors":"D. Tziouvaras, H. Altuve, F. Calero","doi":"10.1109/CPRE.2014.6798993","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6798993","url":null,"abstract":"This paper is a tutorial on the protection of mutually coupled transmission lines. It discusses how mutual coupling affects the polarizing quantities of ground directional elements, the reach of ground distance elements, and the accuracy of single-ended fault locating algorithms. The paper provides settings guidelines for instantaneous directional overcurrent and ground distance elements. It discusses in detail how transmission line mutual coupling causes overreaching or underreaching of ground distance elements. It also discusses the impact on these elements of grounding the mutually coupled line at both line ends during maintenance. The paper analyzes whether mutual coupling compensation offers any benefits to line protection. The ease and benefit of line current differential schemes are contrasted in the discussion. Lastly, the paper examines a case when a double-circuit transmission line is operated as a single circuit with jumpers placed across similar phases along the line. This situation typically arises when the utility company needs to free one of the bays to bring an additional line into the substation. The protection engineer needs to decide where to install jumpers to parallel the two circuits in order to avoid distance element underreaching. The paper provides an analysis of this problem and offers suggestions on how to address it.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126926089","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6799041
Tobias Planert, Benno Hornischer, J. Jenkner, R. Eick, Antoni Furlani Rosa
Choosing the right number and configuration of test access points is a necessity for smooth maintenance and testing operations throughout the usage time of a panel. This process should begin when designing the panel, with a consideration of the type and amount of test access points needed. Secondly, a choice of hardware and the associated benefits can be made (e.g. knife-blade switches or a test block/test plug solution). Once a decision about the hardware has been made, the specific configuration of the access point needs to be determined. In this step, as well as already in the previous step, possible benefits of standardization should be taken into account. Finally, a lab setup of the chosen technology and configurations can be used for a test-run, as well as advance training of personnel. In some cases design can be done from the ground up, in others retrofit solutions are required for pre-existing installations. This paper looks at the process of designing panels with test access points from an international perspective, showcasing real-world best practice examples.
{"title":"Considerations for the implementation of test access points a best practice guide","authors":"Tobias Planert, Benno Hornischer, J. Jenkner, R. Eick, Antoni Furlani Rosa","doi":"10.1109/CPRE.2014.6799041","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799041","url":null,"abstract":"Choosing the right number and configuration of test access points is a necessity for smooth maintenance and testing operations throughout the usage time of a panel. This process should begin when designing the panel, with a consideration of the type and amount of test access points needed. Secondly, a choice of hardware and the associated benefits can be made (e.g. knife-blade switches or a test block/test plug solution). Once a decision about the hardware has been made, the specific configuration of the access point needs to be determined. In this step, as well as already in the previous step, possible benefits of standardization should be taken into account. Finally, a lab setup of the chosen technology and configurations can be used for a test-run, as well as advance training of personnel. In some cases design can be done from the ground up, in others retrofit solutions are required for pre-existing installations. This paper looks at the process of designing panels with test access points from an international perspective, showcasing real-world best practice examples.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116583949","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6799011
R. Aguilar, Joe Perez
These new test methods are a new tool that can be used to verify the stability of differential relays for external faults. By simulating real time events, one can discovered errors that were not possible using single phase test methods. As a result, it is encouraged that new microprocessor relays be tested as close to real system events as possible.
{"title":"Preventing transformer mis-operations for external faults","authors":"R. Aguilar, Joe Perez","doi":"10.1109/CPRE.2014.6799011","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799011","url":null,"abstract":"These new test methods are a new tool that can be used to verify the stability of differential relays for external faults. By simulating real time events, one can discovered errors that were not possible using single phase test methods. As a result, it is encouraged that new microprocessor relays be tested as close to real system events as possible.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"301 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114478877","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6799004
M. Feller, Bryan Fazzari, Robert Van Singel, William C. Edwards
The City of Wadsworth, Ohio, is upgrading and adding new capabilities to its protection and control (P&C) system. A cohesive set of ground-breaking new technologies is being deployed, leveraging an existing fiber-optic communications network. The integration of modern recloser controls, capacitors, regulators, and feeder circuits with a centralized automated fault detection, isolation, and restoration system is the focus of the new P&C system. In addition, the new P&C design provides a solution to a present challenge: engineering a centralized automated feeder voltage profile optimization solution that can remain fully functional alongside a fault detection and isolation system that is capable of automatically modifying the distribution system topology. The problem with many existing automated voltage profile optimization solutions is that they may need to be disabled when a distribution feeder is not in its normal configuration. These two technologies are being integrated into a single interdependent solution that provides the city with a volt/VAR control system that can automatically and appropriately adapt to constantly changing distribution system topology as faults, loss of potential, miscoordinations, or overloads occur and are automatically and immediately mitigated.
{"title":"Case study: Using distribution automation to build the next generation utility in the City of Wadsworth","authors":"M. Feller, Bryan Fazzari, Robert Van Singel, William C. Edwards","doi":"10.1109/CPRE.2014.6799004","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799004","url":null,"abstract":"The City of Wadsworth, Ohio, is upgrading and adding new capabilities to its protection and control (P&C) system. A cohesive set of ground-breaking new technologies is being deployed, leveraging an existing fiber-optic communications network. The integration of modern recloser controls, capacitors, regulators, and feeder circuits with a centralized automated fault detection, isolation, and restoration system is the focus of the new P&C system. In addition, the new P&C design provides a solution to a present challenge: engineering a centralized automated feeder voltage profile optimization solution that can remain fully functional alongside a fault detection and isolation system that is capable of automatically modifying the distribution system topology. The problem with many existing automated voltage profile optimization solutions is that they may need to be disabled when a distribution feeder is not in its normal configuration. These two technologies are being integrated into a single interdependent solution that provides the city with a volt/VAR control system that can automatically and appropriately adapt to constantly changing distribution system topology as faults, loss of potential, miscoordinations, or overloads occur and are automatically and immediately mitigated.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"254 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116880561","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6799016
D. J. Hansen
The application and connection of current transformers for electromechanical differential circuits creates vulnerability for mis-operation under rare but identified scenarios. As a lesson learned from a real-world incident, discovery of the vulnerability occurred during the investigation of a generating unit trip from a nearby switchyard fault immediately outside a generator step-up transformer (GSU) differential zone of protection. Problem resolution is correctable or minimized with the available features of microprocessor differential relays, with sufficient winding inputs, and the proper application of current transformer connections. However, shortcuts in the design and installation of new circuits and microprocessor relays can introduce similar vulnerabilities.
{"title":"GSU transformer - Current transformer connections and differential relay applications","authors":"D. J. Hansen","doi":"10.1109/CPRE.2014.6799016","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799016","url":null,"abstract":"The application and connection of current transformers for electromechanical differential circuits creates vulnerability for mis-operation under rare but identified scenarios. As a lesson learned from a real-world incident, discovery of the vulnerability occurred during the investigation of a generating unit trip from a nearby switchyard fault immediately outside a generator step-up transformer (GSU) differential zone of protection. Problem resolution is correctable or minimized with the available features of microprocessor differential relays, with sufficient winding inputs, and the proper application of current transformer connections. However, shortcuts in the design and installation of new circuits and microprocessor relays can introduce similar vulnerabilities.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"87 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133713694","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6799009
M. Proctor
When analyzing arc flash hazards in an electrical distribution system, it is not uncommon for equipment with high incident energy levels to be a great distance from the immediate upstream interrupting device. Adding more complexity to the problem is the fact that the immediate upstream interrupting device is at a higher voltage level, so the upstream protective device senses a small fraction of the actual arcing fault current. In some cases, this means that the arcing fault must be detected by a device at the low voltage equipment, and a trip signal must be sent several thousand feet to the upstream breaker. This paper analyzes the advantages and disadvantages of different media which can be used to transmit this transfer trip signal. The reader is advised of different methods of alarming to alert operations personnel that the protection scheme is not operational, either due to communications channel or protective device failure. Different design architecture concepts are explored to advise how to achieve maximum reliability, and different failure scenarios are examined to show how increased message delays for certain failures can dramatically increase incident energies.
{"title":"Considerations for sending a breaker trip command over great distances for the purpose of arc flash mitigation","authors":"M. Proctor","doi":"10.1109/CPRE.2014.6799009","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799009","url":null,"abstract":"When analyzing arc flash hazards in an electrical distribution system, it is not uncommon for equipment with high incident energy levels to be a great distance from the immediate upstream interrupting device. Adding more complexity to the problem is the fact that the immediate upstream interrupting device is at a higher voltage level, so the upstream protective device senses a small fraction of the actual arcing fault current. In some cases, this means that the arcing fault must be detected by a device at the low voltage equipment, and a trip signal must be sent several thousand feet to the upstream breaker. This paper analyzes the advantages and disadvantages of different media which can be used to transmit this transfer trip signal. The reader is advised of different methods of alarming to alert operations personnel that the protection scheme is not operational, either due to communications channel or protective device failure. Different design architecture concepts are explored to advise how to achieve maximum reliability, and different failure scenarios are examined to show how increased message delays for certain failures can dramatically increase incident energies.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123661577","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 : 2014-04-24DOI: 10.1109/CPRE.2014.6799026
Silvio Roesler, Ruben Lobo
Deploying line current differential protection over Ethernet packet switched transport is more than just making the connections, as the application demands certain deterministic characteristics from the communication channel. Packet switched traffic by its very nature of statistical multiplexing is subject to variances in propagation time due to queuing delays, which can impact the performance of line current differential schemes that are dependent on channel-based synchronization. This paper details the results of testing a line current differential system on a Multiprotocol Label Switching (MPLS) based Ethernet packet switched network. A variety of simulations were performed in order to determine if reliable protection could be achieved in such a network. Protection times were measured and reliability assessed. Impacts of a number of potential threats were established and overall protection performance was evaluated. Details on engineering the network to meet the Reliability, Selectivity, Coordination, Sensitivity, and Speed requirements of a line current differential system are provided.
{"title":"Proving viability of line current differential over packet switched networks","authors":"Silvio Roesler, Ruben Lobo","doi":"10.1109/CPRE.2014.6799026","DOIUrl":"https://doi.org/10.1109/CPRE.2014.6799026","url":null,"abstract":"Deploying line current differential protection over Ethernet packet switched transport is more than just making the connections, as the application demands certain deterministic characteristics from the communication channel. Packet switched traffic by its very nature of statistical multiplexing is subject to variances in propagation time due to queuing delays, which can impact the performance of line current differential schemes that are dependent on channel-based synchronization. This paper details the results of testing a line current differential system on a Multiprotocol Label Switching (MPLS) based Ethernet packet switched network. A variety of simulations were performed in order to determine if reliable protection could be achieved in such a network. Protection times were measured and reliability assessed. Impacts of a number of potential threats were established and overall protection performance was evaluated. Details on engineering the network to meet the Reliability, Selectivity, Coordination, Sensitivity, and Speed requirements of a line current differential system are provided.","PeriodicalId":285252,"journal":{"name":"2014 67th Annual Conference for Protective Relay Engineers","volume":"81 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122620938","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：