As we all know, substation operation requires knowledge of different disciplines. In order to ensure the safety of substation operation and improve its operation efficiency, the negligence of details will cause seriou...As we all know, substation operation requires knowledge of different disciplines. In order to ensure the safety of substation operation and improve its operation efficiency, the negligence of details will cause serious potential safety hazards in a specific environment or at a specific time, which may lead to safety accidents. In order to improve the overall efficiency and quality of substation operation, the overcurrent protection in complex voltage direction of Substation operation is briefly discussed.展开更多
This paper summarizes some useful concepts about the coordination of directional overcurrent protections.The following key topics are described:the analysis of systems in a ring configuration and only one source of sh...This paper summarizes some useful concepts about the coordination of directional overcurrent protections.The following key topics are described:the analysis of systems in a ring configuration and only one source of short-circuit currents;the impossibility of obtaining selectivity for all the possible system configurations with multiple sources;the need for inverse functions in order to obtain selectivity in systems with multiple sources;the coordination with protections for radial loads;the coordination between instantaneous and delayed functions;the considerations to select the pickup values;the influence of contributions from motors to short circuit currents;the transient configurations due to sequential trips at both line ends;the influence of dynamic behavior of overcurrent functions;the influence of stability constraints;other specific considerations for ground functions;some specific considerations for systems with distributed generation.A summary of these points and their effect on the coordination of directional overcurrent protections is not available in the current literature.This novel description should facilitate the inclusion of these key points in research and coordination studies related to these protective functions.展开更多
This paper presents an integrated protection technique for power distribution systems. A novel integrated protection scheme based on overcurrent protection technique for distribution system is described, in which a sp...This paper presents an integrated protection technique for power distribution systems. A novel integrated protection scheme based on overcurrent protection technique for distribution system is described, in which a specially designed protection relay is installed at each substation of a network and responsible for the protection of every line sections connected to the substation busbar The conventional directional overcurrent and the new adaptive accelerated protection algorithms with multiple settings are implemented into the relay to cover all the protected line sections. The paper includes studies of a typical multi section distribution network to demonstrate the principle of the scheme. Studies show that the new scheme not only offer the new protection features for individual power line section, but also provide the characteristics of integrated protection.展开更多
Recent developments in agent-based systems provide an effective solution to many operational prob-lems of power systems.This paper proposes a protection scheme that uses agent-based relays in a cooperative multiagent ...Recent developments in agent-based systems provide an effective solution to many operational prob-lems of power systems.This paper proposes a protection scheme that uses agent-based relays in a cooperative multiagent structure.The relay primarily starts as an overcurrent relay to detect the fault.Then,it starts data exchange with one peer relay in case of line faults or few neighboring relays in case of busbar faults to confirm the fault location.At this later step,it acts as a differential relay that compares the current phasors at both line ends in the case of line faults and computes the net outgoing current in the case of busbar faults.The scheme design is presented,and the agent cooperation protocol is described.To enforce the scheme against false data injected by hackers via intruding communication facilities,an anom-aly detection device is prepared and integrated into each agent.The proposed tool is based on a one-class support vector machine and can firmly discriminate real fault data from injected false data.The tool also enables the relay to recognize the challenging high impedance fault.The proposed method is tested by dynamic simulation on the IEEE 9-and 39-bus systems under various conditions.The performance is evaluated by comparing it with that of other recent techniques.展开更多
The demand for PTC material for overcurrent protection application in automobile motors has been remarkably increasing. To meet the safety and reliability requirements in automobile system and communication equipment,...The demand for PTC material for overcurrent protection application in automobile motors has been remarkably increasing. To meet the safety and reliability requirements in automobile system and communication equipment, it is necessary to prepare PTC material with low resistivity and high performance. In this paper, the preparation and the properties of PTC material with a resistivity of approximately 12Ω. cm, especially its overcurrent protection are described.展开更多
Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks th...Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks the relay tripping during the transformer magnetizing inrush conditions. However, the backup overcurrent relay (SEL751A) applied to the transformer protection does not have harmonic restraint element and trip the overcurrent relay during the inrush conditions. Therefore, major contribution of this research work is the developed harmonic blocking scheme for transformer which uses element (87HB) of the transformer differential relay (SEL487E) to send an IEC61850 GOOSE-based harmonic blocking signal to the backup overcurrent relay (SEL751A) to inhibit from tripping during the transformer magnetizing inrush current conditions. The simulation results proved that IEC61850 standard-based protection scheme is faster than the hardwired signals. Therefore, the speed and reliability of the transformer scheme are improved using the IEC61850 standard-based GOOSE applications.展开更多
Transient stability of doubly-fed induction generators(DFIGs)is a major concern in both AC and DC grids,and DFIGs must stay connected for a time during grid faults according to the power grid requirements.For this pur...Transient stability of doubly-fed induction generators(DFIGs)is a major concern in both AC and DC grids,and DFIGs must stay connected for a time during grid faults according to the power grid requirements.For this purpose,this work proposes an overcurrent and overvoltage protective device(OCV-PD)to ensure that DCbased DFIG system can stay connected and operate well during the faults.Compared with a series dynamic braking resistor(SDBR),two aspects are improved.First,a twolevel control strategy and DC inductor circuit are used to ensure that the OCV-PD can limit the current impulse to protect DFIG system during an overcurrent fault.Second,the OCV-PD can protect system from overvoltage fault which a SDBR cannot do.Simulation results verify itsvalidity and feasibility,finding that for overcurrent protection the OCV-PD outperforms a SDBR with an average decreased index of 3.29%,and for overvoltage protection it achieves an average index of 1.02%.展开更多
文摘As we all know, substation operation requires knowledge of different disciplines. In order to ensure the safety of substation operation and improve its operation efficiency, the negligence of details will cause serious potential safety hazards in a specific environment or at a specific time, which may lead to safety accidents. In order to improve the overall efficiency and quality of substation operation, the overcurrent protection in complex voltage direction of Substation operation is briefly discussed.
文摘This paper summarizes some useful concepts about the coordination of directional overcurrent protections.The following key topics are described:the analysis of systems in a ring configuration and only one source of short-circuit currents;the impossibility of obtaining selectivity for all the possible system configurations with multiple sources;the need for inverse functions in order to obtain selectivity in systems with multiple sources;the coordination with protections for radial loads;the coordination between instantaneous and delayed functions;the considerations to select the pickup values;the influence of contributions from motors to short circuit currents;the transient configurations due to sequential trips at both line ends;the influence of dynamic behavior of overcurrent functions;the influence of stability constraints;other specific considerations for ground functions;some specific considerations for systems with distributed generation.A summary of these points and their effect on the coordination of directional overcurrent protections is not available in the current literature.This novel description should facilitate the inclusion of these key points in research and coordination studies related to these protective functions.
文摘This paper presents an integrated protection technique for power distribution systems. A novel integrated protection scheme based on overcurrent protection technique for distribution system is described, in which a specially designed protection relay is installed at each substation of a network and responsible for the protection of every line sections connected to the substation busbar The conventional directional overcurrent and the new adaptive accelerated protection algorithms with multiple settings are implemented into the relay to cover all the protected line sections. The paper includes studies of a typical multi section distribution network to demonstrate the principle of the scheme. Studies show that the new scheme not only offer the new protection features for individual power line section, but also provide the characteristics of integrated protection.
文摘Recent developments in agent-based systems provide an effective solution to many operational prob-lems of power systems.This paper proposes a protection scheme that uses agent-based relays in a cooperative multiagent structure.The relay primarily starts as an overcurrent relay to detect the fault.Then,it starts data exchange with one peer relay in case of line faults or few neighboring relays in case of busbar faults to confirm the fault location.At this later step,it acts as a differential relay that compares the current phasors at both line ends in the case of line faults and computes the net outgoing current in the case of busbar faults.The scheme design is presented,and the agent cooperation protocol is described.To enforce the scheme against false data injected by hackers via intruding communication facilities,an anom-aly detection device is prepared and integrated into each agent.The proposed tool is based on a one-class support vector machine and can firmly discriminate real fault data from injected false data.The tool also enables the relay to recognize the challenging high impedance fault.The proposed method is tested by dynamic simulation on the IEEE 9-and 39-bus systems under various conditions.The performance is evaluated by comparing it with that of other recent techniques.
基金Supported by a major project of the 8th Five-Year Plan of China.
文摘The demand for PTC material for overcurrent protection application in automobile motors has been remarkably increasing. To meet the safety and reliability requirements in automobile system and communication equipment, it is necessary to prepare PTC material with low resistivity and high performance. In this paper, the preparation and the properties of PTC material with a resistivity of approximately 12Ω. cm, especially its overcurrent protection are described.
基金funded by the National Research Foundation(NRF)THRIP grant TP2011061100004,ESKOM TESP(Capacitor Banks Placement)ESKOM Academy of Learning,ESKOM Power Plants Energy Institute(EPPEI)and CPUT(Prestigious Project)grant for the Centre of Substation Automation and Energy Management Systems(CSAEMS)development and growth.
文摘Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks the relay tripping during the transformer magnetizing inrush conditions. However, the backup overcurrent relay (SEL751A) applied to the transformer protection does not have harmonic restraint element and trip the overcurrent relay during the inrush conditions. Therefore, major contribution of this research work is the developed harmonic blocking scheme for transformer which uses element (87HB) of the transformer differential relay (SEL487E) to send an IEC61850 GOOSE-based harmonic blocking signal to the backup overcurrent relay (SEL751A) to inhibit from tripping during the transformer magnetizing inrush current conditions. The simulation results proved that IEC61850 standard-based protection scheme is faster than the hardwired signals. Therefore, the speed and reliability of the transformer scheme are improved using the IEC61850 standard-based GOOSE applications.
基金supported by Natural Science Foundation of China(No.61473170)Key R&D Plan Project of Shandong Province,PRC(No.2016GSF115018)
文摘Transient stability of doubly-fed induction generators(DFIGs)is a major concern in both AC and DC grids,and DFIGs must stay connected for a time during grid faults according to the power grid requirements.For this purpose,this work proposes an overcurrent and overvoltage protective device(OCV-PD)to ensure that DCbased DFIG system can stay connected and operate well during the faults.Compared with a series dynamic braking resistor(SDBR),two aspects are improved.First,a twolevel control strategy and DC inductor circuit are used to ensure that the OCV-PD can limit the current impulse to protect DFIG system during an overcurrent fault.Second,the OCV-PD can protect system from overvoltage fault which a SDBR cannot do.Simulation results verify itsvalidity and feasibility,finding that for overcurrent protection the OCV-PD outperforms a SDBR with an average decreased index of 3.29%,and for overvoltage protection it achieves an average index of 1.02%.
