This study investigated the feasibility of distance protection in extra-high voltage(EHV) networks. In long-distance transmission lines, the distributed parameter characteristic of the EHV network is obvious. When a f...This study investigated the feasibility of distance protection in extra-high voltage(EHV) networks. In long-distance transmission lines, the distributed parameter characteristic of the EHV network is obvious. When a fault occurs far away from the measurement site, the measured impedance might not be directly proportional to the fault distance, and the protection domain of distance protection will be decreased. The detailed theory inferred and proven in this paper reveals that this phenomenon is widespread in EHV transmission lines. The results indicate that the protection domain error is greatly reduced by the application of the shunt reactor. Overall, simulation results show that the proposed method is effective for impedance relay, considering different characteristics, different lengths of lines, and compensation degrees.展开更多
To observe the inner operating process of distance protection,a Matlab/Simulink based dynamic simulation system for microprocessor-based distance protection is designed in this paper.As a modularized design,the simula...To observe the inner operating process of distance protection,a Matlab/Simulink based dynamic simulation system for microprocessor-based distance protection is designed in this paper.As a modularized design,the simulation system is composed of several modules such as fault transient calculation,startup,Fourier algorithm,phase selection,impedance computing and impedance comparison etc.Some typical simulation cases,which focus on the main factors affecting distance relay's operation,have been simulated with the system.Simulation results show that the system is able to demonstrate the dynamic behaviors of distance protection under different operating conditions.展开更多
Saving the electrical power system in stable condition is considered as one of important challenges to avoid any failure of high voltage equipment. Additionally, with the increasing off the critical loads, it’s very ...Saving the electrical power system in stable condition is considered as one of important challenges to avoid any failure of high voltage equipment. Additionally, with the increasing off the critical loads, it’s very important to use the accurate protection system that can deal with any abnormal condition. This paper studies one of critical cases that can effect on the coordination of the protection system with the faults during fuse fail condition. Over Head transmission line (OHTL) is the most part in the power system that faces the disturbances, which can be protected by multi-protection functions as line differential function, distance protection function, over current, earth fault, over/under voltage etc. The distance protection function is depending on the line voltage and the load current to calculate the load zone. This paper aims to prevent the falls operation of distance protection function during voltage transformer fuse failure condition.展开更多
In an offshore wind farm connected with a high-voltage direct current(HVDC)transmission system based on modular multilevel converter(MMC),a symmetric fault on the outgoing line at the sending end(SFOLSE)exhibits compl...In an offshore wind farm connected with a high-voltage direct current(HVDC)transmission system based on modular multilevel converter(MMC),a symmetric fault on the outgoing line at the sending end(SFOLSE)exhibits complex controlled characteristics in the fault current,which can undermine the reliability of relay protection.Detailed analysis of the control interaction between the wind farm and the MMC sending station(MMCSS)is conducted to ascertain the fault current characteristics.Considering the constraints imposed by the existence of a stable operating point(SOP)during SFOLSE,the phase angle difference distribution law for short-circuit currents sourced from both the wind farm and MMCSS is analyzed.Furthermore,the influence of control interaction on the reliability of distance protection is discussed.The results show that the additional impedance exhibits specific distribution characteristics under the influence of control interaction.In addition,the setting ratio of the dq-axis current reference for wind farm distance protection is analyzed,and the impact of wind farm control on the adaptability of distance protection under the constraints of the grid-connected guideline is evaluated.The main risk scenarios of misoperation are clarified,and the correctness of the analytical results is validated through PSCAD time-domain simulations.展开更多
The distributed capacitance of the line becomes larger as the scale of wind farms,the transmission voltage level,and the transmission distance increase.Hence,the error of the traditional time-domain distance protectio...The distributed capacitance of the line becomes larger as the scale of wind farms,the transmission voltage level,and the transmission distance increase.Hence,the error of the traditional time-domain distance protection scheme based on the R-L model,which ignores the distributed capacitance of the line,becomes unacceptable.Therefore,the error of the time-domain fault location method based on the R-L model,especially the maximum error range,is theoretically analyzed in this paper.On this basis,a novel fault location method based on the RL and Bergeron models is proposed.Then,a fast time-domain distance protection scheme is designed.In the proposed scheme,the error in the fitting calculation is used to construct a weight matrix,and an algorithm for solving the time-domain differential equations is designed to improve the calculation speed and stability.Compared with the traditional frequency-domain distance protection scheme,the proposed scheme is independent of the power supply characteristics;thus,it is suitable for wind farm transmission lines.In addition,compared with the traditional method based on the R-L model,the proposed scheme effectively avoids the negative influence of the distributed capacitance of the line,which significantly improves the operating speed.Different types of faults are simulated by PSCAD/EMTDC to verify the effectiveness and superiority of the proposed scheme.展开更多
Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer(CT) saturation for the typically employed breaker-and-a-half configuration. This...Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer(CT) saturation for the typically employed breaker-and-a-half configuration. This paper addresses this issue by proposing a new distance protection approach that combines the blocking and unblocking criteria of distance protection based on the values of incomplete differential current,operation voltage, and current harmonic content. The proposed approach is verified by theoretical analysis, dynamic simulation testing, and field operation to ensure that the obtained distance protection is reliable and refrains from operating unnecessarily under reverse fault-induced CT saturation in the breaker-and-ahalf configuration. Meanwhile, the proposed approach is demonstrated can operate reliably when forward faults occur or various reverse faults are converted to forward faults.展开更多
The active saturated iron-core superconductive fault current limiter(SISFCL)is a good choice to decrease fault current.This paper introduced the principles and impedance characteristic of the active SISFCL.Then,it sho...The active saturated iron-core superconductive fault current limiter(SISFCL)is a good choice to decrease fault current.This paper introduced the principles and impedance characteristic of the active SISFCL.Then,it shows the current-limiting effects of the SISFCL.Besides,the impact of the active SISFCL on the distance protection of the EHV transmission line is evaluated.Based on that,the coordination scheme of the distance protections is proposed.A 500 kV double-circuit transmission system with SISFCLs is simulated by Electro-Magnetic Transients Program including DC(EMTDC).Simulation tests demonstrate the correctness and validity of theoretical analyses.展开更多
The impedance element in distance protection equipment in the outgoing line of a wind park(WP)may be heavily affected by the fault response of the WP.During resistive grid faults,relay over-reach(or under-reach)may ma...The impedance element in distance protection equipment in the outgoing line of a wind park(WP)may be heavily affected by the fault response of the WP.During resistive grid faults,relay over-reach(or under-reach)may manifest,depending on the fault current regulating requirements in the specific grid code deployed in WP and the fault conditions.Aiming at potential solution,i.e.the existing zone 1(fast tripping zone,non-delayed)top-line tilting(Z-1-TLT)function in modern numerical relays,this paper first assesses its adaptability under the WP integrated background.Combining the principle of Z-1-TLT itself and fault modeling to the WP,an improved Z-1-TLT scheme is developed,which can actively compensate for the possible relay overreach or under-reach during resistive faults,utilizing relay side fault quantities only.Aiming at the needless action of the new Z-1-TLT scheme against certain faults,malfunction risk area detection and dead zone detection are introduced as auxiliary criteria to optimize protective efficiency.Simulation results prove the improved Z-1-TLT scheme can effectively improve reliability of distance protection deployed in the WP outgoing line.展开更多
Protection distance of surge protective devices (SPDs) is an important problem in designing a good location scheme of SPDs in low voltage distribution systems for protecting electrical equipments against over- voltage...Protection distance of surge protective devices (SPDs) is an important problem in designing a good location scheme of SPDs in low voltage distribution systems for protecting electrical equipments against over- voltage caused by lightning stroke. The simplified lumped-parameter circuit model and the circuit method were used to study the protection distance problem of SPDs. The analytical solutions of the load voltage and general equations of the protection distance of SPDs under different load conditions were given. Simulation results of examples proved the validity of the proposed analytical method.展开更多
Based on the characteristics of wind-sand movement in the gravel desert area along the GolmudKorla Railway,this study employs numerical simulation,wind tunnel and field measurement methods to investigate the wind-sand...Based on the characteristics of wind-sand movement in the gravel desert area along the GolmudKorla Railway,this study employs numerical simulation,wind tunnel and field measurement methods to investigate the wind-sand protection mechanisms and effectiveness of various sand control measures for the Golmud-Korla Railway.Results reveal that wind-sand flow is significantly influenced by sand barrier with notable fluctuations in wind speed observed around these barriers.In the region of 0H to 5H(H is the height of the sand barrier model)downstream the barrier,where turbulent flow disturbances are particularly intense,substantial modifications to the airflow patterns were observed.Among the three types of sand barriers tested,the horizontal wind speed fluctuations on the leeward side of the reed bundle sand barrier are the most pronounced,with the lowest wind speed attenuation coefficient reaching 0.29.Within a specific range of wind speeds,the effective protective width of a sand barrier is negatively correlated with the upstream wind speed.The reed bundle sand barrier demonstrates the largest average protection width,followed by the highdensity polyethylene(HDPE)board sand barrier,while the metal mesh sand barrier provides the smallest protection.In the gravel desert area of southern Xinjiang,the sand trapping efficiency of the reed bundle and HDPE board barriers reaches 93.85%and 96.42%,respectively,with annual maximum accumulated sand volume of 3.342 m3/m and 3.73 m3/m.Both barriers demonstrate excellent wind-sand protection effects.From an environmental sustainability and operating lifetime perspective,a three-dimensional wind-sand control system composed of two or three reed bundle sand barriers is recommended for the Golmud-Korla Railway area.This endeavor would provide valuable insights and guidance for wind-sand disaster prevention and control in the gravel desert areas.展开更多
When a single-phase to ground fault(SPGF)occurs near the main power source in an active distribution network,distance protection sectionⅡ(DPS-Ⅱ)lo-cated at the distributed generator(DG)side operates with a delay.In ...When a single-phase to ground fault(SPGF)occurs near the main power source in an active distribution network,distance protection sectionⅡ(DPS-Ⅱ)lo-cated at the distributed generator(DG)side operates with a delay.In gap-grounded transformers,this delay can lead to gap breakdown due to neutral-point overvoltage,which adversely affects the operation of DPS-Ⅱon the DG side.To address this issue,this paper proposes an improved DPS designed for active distribution networks with gap-grounded transformers.First,the factors influencing the additional impedance are analyzed after gap breakdown.To mitigate the effects of the additional impedance on DPS performance,an improved DPS based on real short-circuit impedances is introduced for active distribution networks.This scheme utilizes the negative-sequence current distribution factor on the DG side to accurately calculate the additional impedance angle,ensuring reliable protection.Simulation results demonstrate that the proposed scheme effectively operates under forward faults across various DG capacities,fault locations,local loads,and fault transition resistances.In addition,it avoids tripping under reverse faults,thereby confirming its reliability and superiority.展开更多
The paper has presented the impact on the line protection performance with the introduction of MUs （merging units） in the process bus level. The paper begins with the introduction on modem digital substation structu...The paper has presented the impact on the line protection performance with the introduction of MUs （merging units） in the process bus level. The paper begins with the introduction on modem digital substation structure and process bus. Then, the paper describes the performances of different sensors such as CTs （current transformers）, CVTs （capacitive voltage transformers）, FOCS （fiber optical current transducers） and FOVS （fiber optical voltage transducers）. With the use of above transducers together with MUs, the performance of distance protection function and line differential protection function have been investigated and presented. Finally, conclusions based on the study are presented in the paper.展开更多
To ensure the mining safety of working face in the protective seam and meanwhile extract pressure-relief gas of the lower protected seam and eliminate its outburst risk,the present study researched into fracture devel...To ensure the mining safety of working face in the protective seam and meanwhile extract pressure-relief gas of the lower protected seam and eliminate its outburst risk,the present study researched into fracture development of floor coal-rock mass of the protective seam and migration rule of pressure-relief gas from a protected seam so as to obtain an effective pressure- relief gas extraction method.The results show that after the upper protective seam was mined,mining-induced fracturing floor coal-rock mas...展开更多
The introduction of new mobile services,mainly UMTS(Universal Mobile Telecommunications System)and LTE(Long Term Evolution),in the digital dividend portion of the UHF spectrum(from 790 MHz to 862 MHz),resulting from t...The introduction of new mobile services,mainly UMTS(Universal Mobile Telecommunications System)and LTE(Long Term Evolution),in the digital dividend portion of the UHF spectrum(from 790 MHz to 862 MHz),resulting from the digital switchover process,makes necessary the assessment of how much the interference of these signals impacts on QoS of existing DVB-T services,in particular when operating on adjacent bands.To this aim,in this paper an analysis of coexistence between broadcast television services and broadband mobile communication systems is carried out.It is based on the computation of specific parameters,such as the Protection Distance,evaluated in some specific operative scenarios.The goal of this analysis is to provide valuable inputs to operators,in deploying new mobile cellular networks in the above mentioned frequency band.展开更多
Among different sources of alternate energy,wind and solar are two prominent and promising alternatives to meet the future electricity needs for mankind.Generally,these sources are integrated at the distribution utili...Among different sources of alternate energy,wind and solar are two prominent and promising alternatives to meet the future electricity needs for mankind.Generally,these sources are integrated at the distribution utilities to supply the local distribution customers.If the power generated by these sources is bulk,then they are either integrated at the distribution/transmission level or may be operated in an island mode if feasible.The integration of these renewables in the power network will change the fault level and network topologies.These fault levels are intermittent in nature and existing protection schemes may fail to operate because of their pre-set condition.Therefore,the design and selection of a proper protection scheme is very much essential for reliable control and operation of renewable integrated power systems.Depending upon the level of infeed and location of the renewable integration,the protection requirements are different.For low renewable infeed at the distribution level,the existing relay settings are immune from any small change in the network fault current from new incoming renewables.However,bulk renewable infeed requires modification in the existing protection schemes to accommodate the fault current variation from the incoming renewables.For bulk penetration of the renewable,the requirement of modified/additional protection schemes is unavoidable.Adaptive relaying and non-adaptive relaying schemes are discussed in the literature for protection of power networks,which are experiencing dynamic fault currents and frequent changing network topologies.This article presents a detailed review of protection schemes for renewable integrated power networks which includes distribution,transmission and microgrid systems.The merits and demerits of these protection schemes are also identified in this article for the added interest of the readers.The visible scope of advance protection schemes which may be suitable for providing reliable protection for dynamic fault current networks is also explored.展开更多
In order to rapidly clear a fault in all-parallel autotransformer(AT)railway system,the existing protection scheme trips both faulted line and healthy line.To solve this problem,a novel unit protection scheme is propo...In order to rapidly clear a fault in all-parallel autotransformer(AT)railway system,the existing protection scheme trips both faulted line and healthy line.To solve this problem,a novel unit protection scheme is proposed in this paper.From fault characteristics measured at substation(SS),AT station(ATS)and section post(SP),we can observe that SS protective relays can detect all the faults but could not be selective,and ATS or SP relays can discriminate the faulted line but not sensitively enough;therefore,we make full use of the fault characteristics and propose a novel unit protection scheme.We employ directional distance protections at SS,ATS and SP,and unify them with networked inter-tripping signals and interlocking signals.When a forward distance protection detects a fault and does not receive inter-locking signals from reverse distance protections of other relays in a short setting time,it will trip the relevant circuit breaker and send an inter-tripping signal to other relays in the same protection unit.Field test results show the proposed scheme trips only the faulted line rapidly and never interrupts the power supply of healthy lines;therefore,the proposed protection scheme obtains both selectivity and speed.展开更多
文摘This study investigated the feasibility of distance protection in extra-high voltage(EHV) networks. In long-distance transmission lines, the distributed parameter characteristic of the EHV network is obvious. When a fault occurs far away from the measurement site, the measured impedance might not be directly proportional to the fault distance, and the protection domain of distance protection will be decreased. The detailed theory inferred and proven in this paper reveals that this phenomenon is widespread in EHV transmission lines. The results indicate that the protection domain error is greatly reduced by the application of the shunt reactor. Overall, simulation results show that the proposed method is effective for impedance relay, considering different characteristics, different lengths of lines, and compensation degrees.
基金National Natural Science Foundation of China(No.50777040)
文摘To observe the inner operating process of distance protection,a Matlab/Simulink based dynamic simulation system for microprocessor-based distance protection is designed in this paper.As a modularized design,the simulation system is composed of several modules such as fault transient calculation,startup,Fourier algorithm,phase selection,impedance computing and impedance comparison etc.Some typical simulation cases,which focus on the main factors affecting distance relay's operation,have been simulated with the system.Simulation results show that the system is able to demonstrate the dynamic behaviors of distance protection under different operating conditions.
文摘Saving the electrical power system in stable condition is considered as one of important challenges to avoid any failure of high voltage equipment. Additionally, with the increasing off the critical loads, it’s very important to use the accurate protection system that can deal with any abnormal condition. This paper studies one of critical cases that can effect on the coordination of the protection system with the faults during fuse fail condition. Over Head transmission line (OHTL) is the most part in the power system that faces the disturbances, which can be protected by multi-protection functions as line differential function, distance protection function, over current, earth fault, over/under voltage etc. The distance protection function is depending on the line voltage and the load current to calculate the load zone. This paper aims to prevent the falls operation of distance protection function during voltage transformer fuse failure condition.
基金supported by the National Natural Science Foundation of China(No.51977019).
文摘In an offshore wind farm connected with a high-voltage direct current(HVDC)transmission system based on modular multilevel converter(MMC),a symmetric fault on the outgoing line at the sending end(SFOLSE)exhibits complex controlled characteristics in the fault current,which can undermine the reliability of relay protection.Detailed analysis of the control interaction between the wind farm and the MMC sending station(MMCSS)is conducted to ascertain the fault current characteristics.Considering the constraints imposed by the existence of a stable operating point(SOP)during SFOLSE,the phase angle difference distribution law for short-circuit currents sourced from both the wind farm and MMCSS is analyzed.Furthermore,the influence of control interaction on the reliability of distance protection is discussed.The results show that the additional impedance exhibits specific distribution characteristics under the influence of control interaction.In addition,the setting ratio of the dq-axis current reference for wind farm distance protection is analyzed,and the impact of wind farm control on the adaptability of distance protection under the constraints of the grid-connected guideline is evaluated.The main risk scenarios of misoperation are clarified,and the correctness of the analytical results is validated through PSCAD time-domain simulations.
基金supported by the Science and Technology Program of State Grid Corporation of China“Research on the Principle of Fast Protection in Time-frequency Domain with Single-ended Quantities of High-proportion New Energy Grid Lines”(No.5100-202040327A-0-0-00).
文摘The distributed capacitance of the line becomes larger as the scale of wind farms,the transmission voltage level,and the transmission distance increase.Hence,the error of the traditional time-domain distance protection scheme based on the R-L model,which ignores the distributed capacitance of the line,becomes unacceptable.Therefore,the error of the time-domain fault location method based on the R-L model,especially the maximum error range,is theoretically analyzed in this paper.On this basis,a novel fault location method based on the RL and Bergeron models is proposed.Then,a fast time-domain distance protection scheme is designed.In the proposed scheme,the error in the fitting calculation is used to construct a weight matrix,and an algorithm for solving the time-domain differential equations is designed to improve the calculation speed and stability.Compared with the traditional frequency-domain distance protection scheme,the proposed scheme is independent of the power supply characteristics;thus,it is suitable for wind farm transmission lines.In addition,compared with the traditional method based on the R-L model,the proposed scheme effectively avoids the negative influence of the distributed capacitance of the line,which significantly improves the operating speed.Different types of faults are simulated by PSCAD/EMTDC to verify the effectiveness and superiority of the proposed scheme.
基金supported by Science and Technology Program of State Grid Corporation of China “Research on Fault Coupling Characteristics and New Protection Principle of AC/DC Hybrid Power Grid”。
文摘Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer(CT) saturation for the typically employed breaker-and-a-half configuration. This paper addresses this issue by proposing a new distance protection approach that combines the blocking and unblocking criteria of distance protection based on the values of incomplete differential current,operation voltage, and current harmonic content. The proposed approach is verified by theoretical analysis, dynamic simulation testing, and field operation to ensure that the obtained distance protection is reliable and refrains from operating unnecessarily under reverse fault-induced CT saturation in the breaker-and-ahalf configuration. Meanwhile, the proposed approach is demonstrated can operate reliably when forward faults occur or various reverse faults are converted to forward faults.
文摘The active saturated iron-core superconductive fault current limiter(SISFCL)is a good choice to decrease fault current.This paper introduced the principles and impedance characteristic of the active SISFCL.Then,it shows the current-limiting effects of the SISFCL.Besides,the impact of the active SISFCL on the distance protection of the EHV transmission line is evaluated.Based on that,the coordination scheme of the distance protections is proposed.A 500 kV double-circuit transmission system with SISFCLs is simulated by Electro-Magnetic Transients Program including DC(EMTDC).Simulation tests demonstrate the correctness and validity of theoretical analyses.
基金This work was supported by the EUDP Project‘Voltage Control and Protection for a Grid towards 100%Power Electronics and Cable Network(COPE)’(EUDP17-I:12561)。
文摘The impedance element in distance protection equipment in the outgoing line of a wind park(WP)may be heavily affected by the fault response of the WP.During resistive grid faults,relay over-reach(or under-reach)may manifest,depending on the fault current regulating requirements in the specific grid code deployed in WP and the fault conditions.Aiming at potential solution,i.e.the existing zone 1(fast tripping zone,non-delayed)top-line tilting(Z-1-TLT)function in modern numerical relays,this paper first assesses its adaptability under the WP integrated background.Combining the principle of Z-1-TLT itself and fault modeling to the WP,an improved Z-1-TLT scheme is developed,which can actively compensate for the possible relay overreach or under-reach during resistive faults,utilizing relay side fault quantities only.Aiming at the needless action of the new Z-1-TLT scheme against certain faults,malfunction risk area detection and dead zone detection are introduced as auxiliary criteria to optimize protective efficiency.Simulation results prove the improved Z-1-TLT scheme can effectively improve reliability of distance protection deployed in the WP outgoing line.
文摘Protection distance of surge protective devices (SPDs) is an important problem in designing a good location scheme of SPDs in low voltage distribution systems for protecting electrical equipments against over- voltage caused by lightning stroke. The simplified lumped-parameter circuit model and the circuit method were used to study the protection distance problem of SPDs. The analytical solutions of the load voltage and general equations of the protection distance of SPDs under different load conditions were given. Simulation results of examples proved the validity of the proposed analytical method.
基金financially supported by Gansu Province Science and Technology Program Funding(25YFFA005)the Science and Technology Research and Development Program of China Railway Corporation(2017G004-E)the Natural Science Foundation of Gansu Province,China(23JRRE0741)。
文摘Based on the characteristics of wind-sand movement in the gravel desert area along the GolmudKorla Railway,this study employs numerical simulation,wind tunnel and field measurement methods to investigate the wind-sand protection mechanisms and effectiveness of various sand control measures for the Golmud-Korla Railway.Results reveal that wind-sand flow is significantly influenced by sand barrier with notable fluctuations in wind speed observed around these barriers.In the region of 0H to 5H(H is the height of the sand barrier model)downstream the barrier,where turbulent flow disturbances are particularly intense,substantial modifications to the airflow patterns were observed.Among the three types of sand barriers tested,the horizontal wind speed fluctuations on the leeward side of the reed bundle sand barrier are the most pronounced,with the lowest wind speed attenuation coefficient reaching 0.29.Within a specific range of wind speeds,the effective protective width of a sand barrier is negatively correlated with the upstream wind speed.The reed bundle sand barrier demonstrates the largest average protection width,followed by the highdensity polyethylene(HDPE)board sand barrier,while the metal mesh sand barrier provides the smallest protection.In the gravel desert area of southern Xinjiang,the sand trapping efficiency of the reed bundle and HDPE board barriers reaches 93.85%and 96.42%,respectively,with annual maximum accumulated sand volume of 3.342 m3/m and 3.73 m3/m.Both barriers demonstrate excellent wind-sand protection effects.From an environmental sustainability and operating lifetime perspective,a three-dimensional wind-sand control system composed of two or three reed bundle sand barriers is recommended for the Golmud-Korla Railway area.This endeavor would provide valuable insights and guidance for wind-sand disaster prevention and control in the gravel desert areas.
基金supported by the Science and Technology Project of China Southern Power Grid(No.030108KK52222003).
文摘When a single-phase to ground fault(SPGF)occurs near the main power source in an active distribution network,distance protection sectionⅡ(DPS-Ⅱ)lo-cated at the distributed generator(DG)side operates with a delay.In gap-grounded transformers,this delay can lead to gap breakdown due to neutral-point overvoltage,which adversely affects the operation of DPS-Ⅱon the DG side.To address this issue,this paper proposes an improved DPS designed for active distribution networks with gap-grounded transformers.First,the factors influencing the additional impedance are analyzed after gap breakdown.To mitigate the effects of the additional impedance on DPS performance,an improved DPS based on real short-circuit impedances is introduced for active distribution networks.This scheme utilizes the negative-sequence current distribution factor on the DG side to accurately calculate the additional impedance angle,ensuring reliable protection.Simulation results demonstrate that the proposed scheme effectively operates under forward faults across various DG capacities,fault locations,local loads,and fault transition resistances.In addition,it avoids tripping under reverse faults,thereby confirming its reliability and superiority.
文摘The paper has presented the impact on the line protection performance with the introduction of MUs （merging units） in the process bus level. The paper begins with the introduction on modem digital substation structure and process bus. Then, the paper describes the performances of different sensors such as CTs （current transformers）, CVTs （capacitive voltage transformers）, FOCS （fiber optical current transducers） and FOVS （fiber optical voltage transducers）. With the use of above transducers together with MUs, the performance of distance protection function and line differential protection function have been investigated and presented. Finally, conclusions based on the study are presented in the paper.
基金Funded by the Major State Basic Research Development Program of China(No.2005CB221503)the Key Program of the Natural Science Foundation of China(No.70533050,50904068 and 50674089)
文摘To ensure the mining safety of working face in the protective seam and meanwhile extract pressure-relief gas of the lower protected seam and eliminate its outburst risk,the present study researched into fracture development of floor coal-rock mass of the protective seam and migration rule of pressure-relief gas from a protected seam so as to obtain an effective pressure- relief gas extraction method.The results show that after the upper protective seam was mined,mining-induced fracturing floor coal-rock mas...
文摘The introduction of new mobile services,mainly UMTS(Universal Mobile Telecommunications System)and LTE(Long Term Evolution),in the digital dividend portion of the UHF spectrum(from 790 MHz to 862 MHz),resulting from the digital switchover process,makes necessary the assessment of how much the interference of these signals impacts on QoS of existing DVB-T services,in particular when operating on adjacent bands.To this aim,in this paper an analysis of coexistence between broadcast television services and broadband mobile communication systems is carried out.It is based on the computation of specific parameters,such as the Protection Distance,evaluated in some specific operative scenarios.The goal of this analysis is to provide valuable inputs to operators,in deploying new mobile cellular networks in the above mentioned frequency band.
文摘Among different sources of alternate energy,wind and solar are two prominent and promising alternatives to meet the future electricity needs for mankind.Generally,these sources are integrated at the distribution utilities to supply the local distribution customers.If the power generated by these sources is bulk,then they are either integrated at the distribution/transmission level or may be operated in an island mode if feasible.The integration of these renewables in the power network will change the fault level and network topologies.These fault levels are intermittent in nature and existing protection schemes may fail to operate because of their pre-set condition.Therefore,the design and selection of a proper protection scheme is very much essential for reliable control and operation of renewable integrated power systems.Depending upon the level of infeed and location of the renewable integration,the protection requirements are different.For low renewable infeed at the distribution level,the existing relay settings are immune from any small change in the network fault current from new incoming renewables.However,bulk renewable infeed requires modification in the existing protection schemes to accommodate the fault current variation from the incoming renewables.For bulk penetration of the renewable,the requirement of modified/additional protection schemes is unavoidable.Adaptive relaying and non-adaptive relaying schemes are discussed in the literature for protection of power networks,which are experiencing dynamic fault currents and frequent changing network topologies.This article presents a detailed review of protection schemes for renewable integrated power networks which includes distribution,transmission and microgrid systems.The merits and demerits of these protection schemes are also identified in this article for the added interest of the readers.The visible scope of advance protection schemes which may be suitable for providing reliable protection for dynamic fault current networks is also explored.
基金supported in part by the National Natural Science Foundation of China under Grant No.52177116,51777174in part by the Sichuan Science and Technology Program under Grant No.2023JDRC0002.
文摘In order to rapidly clear a fault in all-parallel autotransformer(AT)railway system,the existing protection scheme trips both faulted line and healthy line.To solve this problem,a novel unit protection scheme is proposed in this paper.From fault characteristics measured at substation(SS),AT station(ATS)and section post(SP),we can observe that SS protective relays can detect all the faults but could not be selective,and ATS or SP relays can discriminate the faulted line but not sensitively enough;therefore,we make full use of the fault characteristics and propose a novel unit protection scheme.We employ directional distance protections at SS,ATS and SP,and unify them with networked inter-tripping signals and interlocking signals.When a forward distance protection detects a fault and does not receive inter-locking signals from reverse distance protections of other relays in a short setting time,it will trip the relevant circuit breaker and send an inter-tripping signal to other relays in the same protection unit.Field test results show the proposed scheme trips only the faulted line rapidly and never interrupts the power supply of healthy lines;therefore,the proposed protection scheme obtains both selectivity and speed.
