Bipolar blocking and commutation failure in the renewable energy transmission system through ultra-high voltage direct current will produce significant temporary overvoltage.This paper analyzes the physical process of...Bipolar blocking and commutation failure in the renewable energy transmission system through ultra-high voltage direct current will produce significant temporary overvoltage.This paper analyzes the physical process of sending end grid overvoltage caused by two types of DC faults and establishes a DC overvoltage model considering renewable energy sources.According to characteristics of the sending end grid,the influence of the system equivalent impedance,the proportion of renewable energy output,the active and reactive power coefficients of the renewable energy sources during the low voltage ride through process on the overvoltage is analyzed respectively,and the relationship between the proportion of renewable energy output and the short-circuit ratio under the overvoltage constraint is constructed.The validity and practicality of the model and analysis method proposed in this paper are verified by combining the typical transmission system at the sending end of the actual power grid and regional power grid systems.展开更多
High-voltage direct current(HVDC) transmission is a crucial way to solve the reverse distribution of clean energy and loads. The line commutated converter-based HVDC(LCCHVDC) has become a vital structure for HVDC due ...High-voltage direct current(HVDC) transmission is a crucial way to solve the reverse distribution of clean energy and loads. The line commutated converter-based HVDC(LCCHVDC) has become a vital structure for HVDC due to its high technological maturity and economic advantages. During the DC fault of LCC-HVDC, such as commutation failure, the reactive power regulation of the AC grid always lags the DC control process, causing overvoltage in the AC sending grid, which brings off-grid risk to the wind power generation based on power electronic devices. Nevertheless, considering that wind turbine generators have fast and flexible reactive power control capability, optimizing the reactive power control of wind turbines to participate in the transient overvoltage suppression of the sending grid not only improves the operational safety at the equipment level but also enhances the voltage stability of the system. This paper firstly analyses the impact of wind turbine's reactive power on AC transient overvoltage. Then, it proposes an improved voltage-reactive power control strategy, which contains a reactive power control delay compensation and a power command optimization based on the voltage time series prediction. The delay compensation is used to reduce the contribution of the untimely reactive power of wind turbines on transient overvoltage, and the power command optimization enables wind turbines to have the ability to regulate transient overvoltage, leading to the variation of AC voltage, thus suppressing the transient overvoltage. Finally, the effectiveness and feasibility of the proposed method are verified in a ±800kV/5000MW LCC-HVDC sending grid model based on MATLAB/Simulink.展开更多
Gas pressurized closing switches are one of the most important elements in FLTD-based systems. Improving the trigger performance of gas switches is useful for optimizing the output parameters and the reliability of th...Gas pressurized closing switches are one of the most important elements in FLTD-based systems. Improving the trigger performance of gas switches is useful for optimizing the output parameters and the reliability of the FLTD. In this paper, the breakdown characteristics of the trigger gap and the overvoltage gap are studied experimentally. The reasons for the different breakdown performance of the two gaps are also investigated. The results show that the breakdown delay of the trigger gap is more influenced by the trigger voltage, while the breakdown delay of the overvoltage gap is more influenced by the working coefficient and always higher than that of the trigger gap. The jitter of the trigger gap is more influenced by the trigger voltage and accounts more than 60% of the total switch jitter, while the jitter of the overvoltage gap is hardly changed with the trigger voltage as well as the working coefficient and maintains less than 1.4 ns. It is proved that the discharging product from the trigger gap can effectively reduce the breakdown delay and jitter of the overvoltage gap. Based on that, the effect and improvement of pre-ionization on the two gaps are also studied. It is concluded that the jitter of the trigger gap reduces obviously when the pre-ionization is added, while the pre-ionization almost has no effect on the jitter of the overvoltage gap. The jitter of the overvoltage gap is about two times higher than the trigger gap in the pre-ionizing switch.展开更多
The anodic overvoltage of neodymium electrolysis was determined by slow scanning oscillograrn. The effects of some factors, i.e. the temperature, the anodic current density, the concentration of Nd2O3 and the componen...The anodic overvoltage of neodymium electrolysis was determined by slow scanning oscillograrn. The effects of some factors, i.e. the temperature, the anodic current density, the concentration of Nd2O3 and the components of the electrolyte were investigated and the approaches to decrease the anodic overvoltage were also discussed. The results show that the anodic overvoltage increases with the anodic current density and decreases with the increasing temperature. The linear relation between the anodic overvoltage and the current density corresponding to Tafel equation is determined to some extent. The anodic overvoltage decreases with the increasing concentrations of LiF and NdF3. It also decreases by controlling the anodic current density properly, increasing the temperature or the concentrations of LiF and NdF3 and the reducing polar distance.展开更多
The overvoltage phenomena of ultra high voltage (UHV) transmission lines are analyzed and verified by EMTDC/PSCAD simulation. Referring to the theoretical analyses and operating experiences of extra high voltage (EHV)...The overvoltage phenomena of ultra high voltage (UHV) transmission lines are analyzed and verified by EMTDC/PSCAD simulation. Referring to the theoretical analyses and operating experiences of extra high voltage (EHV) transmission lines in China and UHV transmission lines in Russia and Japan, the methods to suppress the internal overvoltage in UHV transmission lines by protection and control strategies are discussed. Through the cooperation among the recloser, shunt reactor, tripping and closing resistance, and metal oxide varistor(MOV), the overvoltage can be restrained within an acceptable level.展开更多
Analyzes the mechanism of overvoltage when contactless tap changer switch which is applied in distributing transformer converted directly.When the device convert the tap off,it employs the way that the SSR is switche...Analyzes the mechanism of overvoltage when contactless tap changer switch which is applied in distributing transformer converted directly.When the device convert the tap off,it employs the way that the SSR is switched on when voltage through zero and switched off when current through zero.But in the experiment we found that overvoltage will occur in the process of changing tap changer.The paper illustrates the mechanism of overvoltage in theory by analyzing the equivalent circuit and using analytic method of transition process.展开更多
This paper researches the voltage transfer characteristics when one-phase ground fault occurred in the resistance grounding system, by using the theory of the asymmetric variable characteristics and the sequence netwo...This paper researches the voltage transfer characteristics when one-phase ground fault occurred in the resistance grounding system, by using the theory of the asymmetric variable characteristics and the sequence network analysis of the -11 transformer, and concludes the scope of voltage sag and swell and the degree of power frequency overvoltage and their influencing factors in the 110 kV resistance grounding system. Accordingly this paper puts forward the resistance choosing principle: the resistance grounding coefficient must be equal to or greater than 10. So it can not only wipe out the voltage sag and voltage swell but also make sure the overvoltage is limited to electrical equipment allowing range. The method mentioned above is verified by simulation results of a 110 kV power system in ATP.展开更多
With the application of the articulated phase insulator, and the speed of electric locomotive rising, it is inevitable for the electric locomotive to adopt the technology automatic passing through the electric phase s...With the application of the articulated phase insulator, and the speed of electric locomotive rising, it is inevitable for the electric locomotive to adopt the technology automatic passing through the electric phase separation. However, when the locomotive passes the electric phase separation, a variety of overvoltages will be generated, such as the cut-off overvoltage and the closing overvoltage. In this paper, the causes of the two overvoltages above are analyzed theoretically and simulated in Simulink. Then this paper discusses the suppression effects on the cut-off overvoltage and the closing overvoltage by paralleling the nonlinear resistance and the main breaker, or parallelling the nonlinear resistance and the locomotive transformer. The simulation results show that parallelling the nonlinear resistance and the locomotive transformer has suppressive effects on the two overvoltages mentioned above.展开更多
This paper presents the results of the simulations and their respective analyses corresponding to the power frequency overvoltages resulting from various fault types occurring inside a microgrid. During the islanded m...This paper presents the results of the simulations and their respective analyses corresponding to the power frequency overvoltages resulting from various fault types occurring inside a microgrid. During the islanded mode of operation, the analysed microgrid can be simultaneously fed by a diesel generator, a 1 MW wind power turbine, a small solar system and a 1 MW hydroelectric scheme. The operating voltage of the microgrid is 2.4 kV. During a fault in the system, the overvoltages normally occur in two remarkable instants. The first one occurs at the beginning of the fault itself. The second one occurs at the instant when the fault is cleared. The major concern here is the overvoltage during the fault period. Due to the travelling wave effect along cables and overhead lines composing the microgrid system, these overvoltages can be amplified, thus jeopardizing the insulation level of the microgrid transmission system and related equipment. Much of the work available now is dedicated to overvoltages present in high-voltage systems leaving a gap for the study and behaviour on low voltage microgrid systems. The overvoltage stress is characterized by the maximum low-frequency, short-duration (crest value) of the overvoltage. Both cables and overhead lines that constitute the microgrid transmission system are characterized by their R-L-C parameters. The simulations of the microgrid system are conducted using the ATP program. According to the international ANSI and IEEE standards, the minimum BIL (Basic Impulse Insulation Level) and BSL (Basic Impulse Switching Level) for the 2.4 kV voltage level are 20 kV and 10 kV, respectively;thus, care should be taken so that the healthy phases upon which commonly appear such overvoltages are not exceeded in their insulation level.展开更多
This paper describes the statistical study of important factors that influences transient over voltages resulting from three-phase reclosing of shunt compensated transmission lines. These factors include the model use...This paper describes the statistical study of important factors that influences transient over voltages resulting from three-phase reclosing of shunt compensated transmission lines. These factors include the model used for transmission line representation and the influence of line transposition. Additionally, the over voltages reduction to proper levels depending on the type of control technique are illustrated and analyzed in statistical terms. The evaluation covers three shunt compensation degrees. The digital simulations were performed using the PSCAD/EMTDC software.展开更多
Present-day small hydropower plants (SHPs) have a large development potential because of the increasing interest in renewable resources and distributed energy generation, therefore, there are many SHPs in places of Ch...Present-day small hydropower plants (SHPs) have a large development potential because of the increasing interest in renewable resources and distributed energy generation, therefore, there are many SHPs in places of China where are rich in water resources. However, it has caused overvoltages in the distribution network, and which is even worse for the switching overvoltage such as isolated network operation, changing power supply path. The simple network model is used to analyze the reasons of the switching overvoltage, and the simulation software DIgSILENT/PowerFactory is used to check out the results of the theoretical analysis.展开更多
The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which ...The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which is the so-called Baihetan-Jiangsu HVDC(BJ-HVDC)project of China.In one LCC and two MMCs(1+2)operation mode,the sub-module(SM)capacitors suffer the most rigorous overvoltage induced by three-phase-to-ground fault at grid-side MMC and valve-side single-phase-to-ground fault in internal MMC.In order to suppress such huge overvoltage,this paper demonstrates a novel alternative by employing the MMC-based embedded battery energy storage system(MMC-BESS).Firstly,the inducements of SM overvoltage are analyzed.Then,coordinated with MMC-BESS,new fault ride-through(FRT)strategies are proposed to suppress the overvoltage and improve the FRT capability.Finally,several simulation scenarios are carried out on PSCAD/EMTDC.The overvoltage suppression is verified against auxiliary device used in the BJ-HVDC project in a monopolar BJ-HVDC system.Further,the proposed FRT strategies are validated in the southern Jiangsu power grid of China based on the planning data in the summer of 2025.Simulation results show that the MMC-BESS and proposed FRT strategies could effectively suppress the overvoltage and improve the FRT capability.展开更多
We present the ferroresonance overvoltage mitigation concerning the power systems of the grid-connectcd wind energy conversion systems(WECSs).WECS is considered based on a doubly-fed induction generator(DFIG).Ferrores...We present the ferroresonance overvoltage mitigation concerning the power systems of the grid-connectcd wind energy conversion systems(WECSs).WECS is considered based on a doubly-fed induction generator(DFIG).Ferroresonance overvoltage associated with a single-pole outage of the line breaker is mitigated by fast regulating the reactive power using the static compensator(STATCOM).STATCOM controller is introduced,in which t>\o incorporated proportional-integral(PI)controllers are optimally tuned using a modified flow-er pollination algorithm(MFPA)as an optimization technique.To show the capability of the proposed STATCOM controller in mitigating the ferroresonance overvoltage,two test cases are introduced,which are based on the interconnection status of the power transformer used with the grid-connected DFIGs.The results show that the ferroresonance disturbance can occur for the power transformers installed in the wind farms although the transformer terminals are interconnected,and neither side of the transformer is isolated.Furthermore,as a mitigation method of ferroresonance overvoltage,the proposed STATCOM controller succeeds in improving the system voltage profile and speed profile of the wind turbine as well as protecting the system components against the ferroresonance overvoltage.展开更多
The ability of a structure in the form of a photovoltaic element with a built-in posistor layer based on a polymer nanocomposite with carbon filler being in direct thermal contact to protect against overvoltages was s...The ability of a structure in the form of a photovoltaic element with a built-in posistor layer based on a polymer nanocomposite with carbon filler being in direct thermal contact to protect against overvoltages was studied experimentally and by simulation.It was shown that the current and voltage on the reverse-biased p-n junction of the photovoltaic layer are limited and decrease from the moment when the temperature of this structure reaches values close to the tripping temperature of the posistor nano-composite to the low-conductivity state.The temperature of the photovoltaic layer has a value close to the tripping temperature of the posistor layer,which is equal to~125°C.The possibility of realizing protection against reverse electrical overvoltages and thermal breakdown of photovoltaic systems based on photovoltaic elements with built-in layers of posistor polymer nano-composites with carbon fillers was established.展开更多
The increasing applications of net-zero energy buildings (NZEBs) will lead to more frequent and larger energy interactions with the connected power grid, thereby being able to result in severe grid overvoltage risks. ...The increasing applications of net-zero energy buildings (NZEBs) will lead to more frequent and larger energy interactions with the connected power grid, thereby being able to result in severe grid overvoltage risks. Control optimization has been proven effective to reduce such risks. Existing controls have oversimplified the overvoltage quantification by simply using the aggregated power exchanges to represent the connected grid overvoltages. Ignoring the complex voltage influences among the grid nodes, such oversimplification can easily result in low-accuracy impact evaluations of the NZEB-grid energy interactions, thereby causing non-optimal/unsatisfying overvoltage mitigations. Therefore, this study proposes a novel coordinated control method in which a power-distribution-network model has been adopted for more accurate overvoltage quantification. Meanwhile, the battery operations of individual NZEBs are iteratively coordinated using a sequential optimization approach for achieving the global optimum with substantially reduced computation complexity. For verifications, the proposed coordinated control has been systematically compared with an uncoordinated control and a conventional coordinated control in grid overvoltage minimization. The study results show that the overvoltage improvements can reach 23.5% and 12.3% compared with the uncoordinated control and the conventional coordinated control, respectively. The reasons behind the improvements have also been analyzed in detail. The proposed coordinated control can be used in practice to improve NZEB-clusters’ grid friendliness.展开更多
The amplitude of switching overvoltages is a key factor for designing the insulation of UHV equipment. The effect of different arresters needs to be studied, since installing arresters is an important way to suppress ...The amplitude of switching overvoltages is a key factor for designing the insulation of UHV equipment. The effect of different arresters needs to be studied, since installing arresters is an important way to suppress switching overvoltages in UHV transmission lines. Switching overvoltages on the 1000 kV Huainan-Huxi double-circuit transmission line were simulated for different operating modes and different arrester designs using the electromagnetic transient program PSCAD/EMTDC. With parallel resistors, the switching overvoltages are less than 1.70 p.u. （1.0 p.u.=1100×√ 2 /√3 kV）. If the arrestors are better, the switching overvoltages can be reduced even lower to 1.55 p.u. Without parallel resistors, the arresters can reduce three-phase energizing overvoltages to 1.70 p.u, while the single-phase reclosing overvoltages still exceed the limit. The results show that the parallel resistors cannot be eliminated if the arresters are only installed at each end of the transmission line. Also, better quality arresters significantly lower the switching overvoltages.展开更多
Rechargeable lithium-oxygen(Li-O_(2))batteries have attracted wide attention due to their high energy density.However,the sluggish cathode kinetics results in high overvoltage and poor cycling performance.Ruthenium(Ru...Rechargeable lithium-oxygen(Li-O_(2))batteries have attracted wide attention due to their high energy density.However,the sluggish cathode kinetics results in high overvoltage and poor cycling performance.Ruthenium(Ru)-based electrocatalysts have been demonstrated to be promising cathode catalysts to promote oxygen evolution reaction(OER).It facilitates decomposition of lithium peroxide(Li_(2)O_(2))by adjusting Li_(2)O_(2) morphologies,which is due to the strong interaction between Ru-based catalyst and superoxide anion(O_(2))intermediate.In this review,the design strategies of Ru-based electrocatalysts are introduced to enhance their OER catalytic kinetics in Li-O_(2) batteries.Different configurations of Ru-based catalysts,including metal particles(Ru metal and alloys),single-atom catalysts,and Ru-loaded compounds with various substrates(carbon materials,metal oxides/sulfides),have been summarized to regulate the electronic structure and the matrix architecture of the Ru-based electrocatalysts.The structure-property relationship of Ru-based catalysts is discussed for a better understanding of the Li_(2)O_(2) decomposition mechanism at the cathode interface.Finally,the challenges of Ru-based electrocatalysts are proposed for the future development of Li-O_(2) batteries.展开更多
基金supported by the National Key R&D Program of China(2022YFB2403100).
文摘Bipolar blocking and commutation failure in the renewable energy transmission system through ultra-high voltage direct current will produce significant temporary overvoltage.This paper analyzes the physical process of sending end grid overvoltage caused by two types of DC faults and establishes a DC overvoltage model considering renewable energy sources.According to characteristics of the sending end grid,the influence of the system equivalent impedance,the proportion of renewable energy output,the active and reactive power coefficients of the renewable energy sources during the low voltage ride through process on the overvoltage is analyzed respectively,and the relationship between the proportion of renewable energy output and the short-circuit ratio under the overvoltage constraint is constructed.The validity and practicality of the model and analysis method proposed in this paper are verified by combining the typical transmission system at the sending end of the actual power grid and regional power grid systems.
基金supported in part by the National Natural Science Foundation of China under Grant 52307141, Grant 52237005 and Grant 52177117in part by Sichuan Science and Technology Program 2021JDTD0016。
文摘High-voltage direct current(HVDC) transmission is a crucial way to solve the reverse distribution of clean energy and loads. The line commutated converter-based HVDC(LCCHVDC) has become a vital structure for HVDC due to its high technological maturity and economic advantages. During the DC fault of LCC-HVDC, such as commutation failure, the reactive power regulation of the AC grid always lags the DC control process, causing overvoltage in the AC sending grid, which brings off-grid risk to the wind power generation based on power electronic devices. Nevertheless, considering that wind turbine generators have fast and flexible reactive power control capability, optimizing the reactive power control of wind turbines to participate in the transient overvoltage suppression of the sending grid not only improves the operational safety at the equipment level but also enhances the voltage stability of the system. This paper firstly analyses the impact of wind turbine's reactive power on AC transient overvoltage. Then, it proposes an improved voltage-reactive power control strategy, which contains a reactive power control delay compensation and a power command optimization based on the voltage time series prediction. The delay compensation is used to reduce the contribution of the untimely reactive power of wind turbines on transient overvoltage, and the power command optimization enables wind turbines to have the ability to regulate transient overvoltage, leading to the variation of AC voltage, thus suppressing the transient overvoltage. Finally, the effectiveness and feasibility of the proposed method are verified in a ±800kV/5000MW LCC-HVDC sending grid model based on MATLAB/Simulink.
基金supported by the Foundation of State Key Laboratory of Intense Pulsed Radiation Simulation and Effect (No. SKLIPR1601)
文摘Gas pressurized closing switches are one of the most important elements in FLTD-based systems. Improving the trigger performance of gas switches is useful for optimizing the output parameters and the reliability of the FLTD. In this paper, the breakdown characteristics of the trigger gap and the overvoltage gap are studied experimentally. The reasons for the different breakdown performance of the two gaps are also investigated. The results show that the breakdown delay of the trigger gap is more influenced by the trigger voltage, while the breakdown delay of the overvoltage gap is more influenced by the working coefficient and always higher than that of the trigger gap. The jitter of the trigger gap is more influenced by the trigger voltage and accounts more than 60% of the total switch jitter, while the jitter of the overvoltage gap is hardly changed with the trigger voltage as well as the working coefficient and maintains less than 1.4 ns. It is proved that the discharging product from the trigger gap can effectively reduce the breakdown delay and jitter of the overvoltage gap. Based on that, the effect and improvement of pre-ionization on the two gaps are also studied. It is concluded that the jitter of the trigger gap reduces obviously when the pre-ionization is added, while the pre-ionization almost has no effect on the jitter of the overvoltage gap. The jitter of the overvoltage gap is about two times higher than the trigger gap in the pre-ionizing switch.
文摘The anodic overvoltage of neodymium electrolysis was determined by slow scanning oscillograrn. The effects of some factors, i.e. the temperature, the anodic current density, the concentration of Nd2O3 and the components of the electrolyte were investigated and the approaches to decrease the anodic overvoltage were also discussed. The results show that the anodic overvoltage increases with the anodic current density and decreases with the increasing temperature. The linear relation between the anodic overvoltage and the current density corresponding to Tafel equation is determined to some extent. The anodic overvoltage decreases with the increasing concentrations of LiF and NdF3. It also decreases by controlling the anodic current density properly, increasing the temperature or the concentrations of LiF and NdF3 and the reducing polar distance.
基金ABB (China) Research Ltd. and National Natural Science Foundation of China(No.50477037)
文摘The overvoltage phenomena of ultra high voltage (UHV) transmission lines are analyzed and verified by EMTDC/PSCAD simulation. Referring to the theoretical analyses and operating experiences of extra high voltage (EHV) transmission lines in China and UHV transmission lines in Russia and Japan, the methods to suppress the internal overvoltage in UHV transmission lines by protection and control strategies are discussed. Through the cooperation among the recloser, shunt reactor, tripping and closing resistance, and metal oxide varistor(MOV), the overvoltage can be restrained within an acceptable level.
基金Harbin science an technology officecontract num ber is 0 0 112 110 98
文摘Analyzes the mechanism of overvoltage when contactless tap changer switch which is applied in distributing transformer converted directly.When the device convert the tap off,it employs the way that the SSR is switched on when voltage through zero and switched off when current through zero.But in the experiment we found that overvoltage will occur in the process of changing tap changer.The paper illustrates the mechanism of overvoltage in theory by analyzing the equivalent circuit and using analytic method of transition process.
文摘This paper researches the voltage transfer characteristics when one-phase ground fault occurred in the resistance grounding system, by using the theory of the asymmetric variable characteristics and the sequence network analysis of the -11 transformer, and concludes the scope of voltage sag and swell and the degree of power frequency overvoltage and their influencing factors in the 110 kV resistance grounding system. Accordingly this paper puts forward the resistance choosing principle: the resistance grounding coefficient must be equal to or greater than 10. So it can not only wipe out the voltage sag and voltage swell but also make sure the overvoltage is limited to electrical equipment allowing range. The method mentioned above is verified by simulation results of a 110 kV power system in ATP.
文摘With the application of the articulated phase insulator, and the speed of electric locomotive rising, it is inevitable for the electric locomotive to adopt the technology automatic passing through the electric phase separation. However, when the locomotive passes the electric phase separation, a variety of overvoltages will be generated, such as the cut-off overvoltage and the closing overvoltage. In this paper, the causes of the two overvoltages above are analyzed theoretically and simulated in Simulink. Then this paper discusses the suppression effects on the cut-off overvoltage and the closing overvoltage by paralleling the nonlinear resistance and the main breaker, or parallelling the nonlinear resistance and the locomotive transformer. The simulation results show that parallelling the nonlinear resistance and the locomotive transformer has suppressive effects on the two overvoltages mentioned above.
文摘This paper presents the results of the simulations and their respective analyses corresponding to the power frequency overvoltages resulting from various fault types occurring inside a microgrid. During the islanded mode of operation, the analysed microgrid can be simultaneously fed by a diesel generator, a 1 MW wind power turbine, a small solar system and a 1 MW hydroelectric scheme. The operating voltage of the microgrid is 2.4 kV. During a fault in the system, the overvoltages normally occur in two remarkable instants. The first one occurs at the beginning of the fault itself. The second one occurs at the instant when the fault is cleared. The major concern here is the overvoltage during the fault period. Due to the travelling wave effect along cables and overhead lines composing the microgrid system, these overvoltages can be amplified, thus jeopardizing the insulation level of the microgrid transmission system and related equipment. Much of the work available now is dedicated to overvoltages present in high-voltage systems leaving a gap for the study and behaviour on low voltage microgrid systems. The overvoltage stress is characterized by the maximum low-frequency, short-duration (crest value) of the overvoltage. Both cables and overhead lines that constitute the microgrid transmission system are characterized by their R-L-C parameters. The simulations of the microgrid system are conducted using the ATP program. According to the international ANSI and IEEE standards, the minimum BIL (Basic Impulse Insulation Level) and BSL (Basic Impulse Switching Level) for the 2.4 kV voltage level are 20 kV and 10 kV, respectively;thus, care should be taken so that the healthy phases upon which commonly appear such overvoltages are not exceeded in their insulation level.
文摘This paper describes the statistical study of important factors that influences transient over voltages resulting from three-phase reclosing of shunt compensated transmission lines. These factors include the model used for transmission line representation and the influence of line transposition. Additionally, the over voltages reduction to proper levels depending on the type of control technique are illustrated and analyzed in statistical terms. The evaluation covers three shunt compensation degrees. The digital simulations were performed using the PSCAD/EMTDC software.
文摘Present-day small hydropower plants (SHPs) have a large development potential because of the increasing interest in renewable resources and distributed energy generation, therefore, there are many SHPs in places of China where are rich in water resources. However, it has caused overvoltages in the distribution network, and which is even worse for the switching overvoltage such as isolated network operation, changing power supply path. The simple network model is used to analyze the reasons of the switching overvoltage, and the simulation software DIgSILENT/PowerFactory is used to check out the results of the theoretical analysis.
文摘The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which is the so-called Baihetan-Jiangsu HVDC(BJ-HVDC)project of China.In one LCC and two MMCs(1+2)operation mode,the sub-module(SM)capacitors suffer the most rigorous overvoltage induced by three-phase-to-ground fault at grid-side MMC and valve-side single-phase-to-ground fault in internal MMC.In order to suppress such huge overvoltage,this paper demonstrates a novel alternative by employing the MMC-based embedded battery energy storage system(MMC-BESS).Firstly,the inducements of SM overvoltage are analyzed.Then,coordinated with MMC-BESS,new fault ride-through(FRT)strategies are proposed to suppress the overvoltage and improve the FRT capability.Finally,several simulation scenarios are carried out on PSCAD/EMTDC.The overvoltage suppression is verified against auxiliary device used in the BJ-HVDC project in a monopolar BJ-HVDC system.Further,the proposed FRT strategies are validated in the southern Jiangsu power grid of China based on the planning data in the summer of 2025.Simulation results show that the MMC-BESS and proposed FRT strategies could effectively suppress the overvoltage and improve the FRT capability.
文摘We present the ferroresonance overvoltage mitigation concerning the power systems of the grid-connectcd wind energy conversion systems(WECSs).WECS is considered based on a doubly-fed induction generator(DFIG).Ferroresonance overvoltage associated with a single-pole outage of the line breaker is mitigated by fast regulating the reactive power using the static compensator(STATCOM).STATCOM controller is introduced,in which t>\o incorporated proportional-integral(PI)controllers are optimally tuned using a modified flow-er pollination algorithm(MFPA)as an optimization technique.To show the capability of the proposed STATCOM controller in mitigating the ferroresonance overvoltage,two test cases are introduced,which are based on the interconnection status of the power transformer used with the grid-connected DFIGs.The results show that the ferroresonance disturbance can occur for the power transformers installed in the wind farms although the transformer terminals are interconnected,and neither side of the transformer is isolated.Furthermore,as a mitigation method of ferroresonance overvoltage,the proposed STATCOM controller succeeds in improving the system voltage profile and speed profile of the wind turbine as well as protecting the system components against the ferroresonance overvoltage.
文摘The ability of a structure in the form of a photovoltaic element with a built-in posistor layer based on a polymer nanocomposite with carbon filler being in direct thermal contact to protect against overvoltages was studied experimentally and by simulation.It was shown that the current and voltage on the reverse-biased p-n junction of the photovoltaic layer are limited and decrease from the moment when the temperature of this structure reaches values close to the tripping temperature of the posistor nano-composite to the low-conductivity state.The temperature of the photovoltaic layer has a value close to the tripping temperature of the posistor layer,which is equal to~125°C.The possibility of realizing protection against reverse electrical overvoltages and thermal breakdown of photovoltaic systems based on photovoltaic elements with built-in layers of posistor polymer nano-composites with carbon fillers was established.
文摘The increasing applications of net-zero energy buildings (NZEBs) will lead to more frequent and larger energy interactions with the connected power grid, thereby being able to result in severe grid overvoltage risks. Control optimization has been proven effective to reduce such risks. Existing controls have oversimplified the overvoltage quantification by simply using the aggregated power exchanges to represent the connected grid overvoltages. Ignoring the complex voltage influences among the grid nodes, such oversimplification can easily result in low-accuracy impact evaluations of the NZEB-grid energy interactions, thereby causing non-optimal/unsatisfying overvoltage mitigations. Therefore, this study proposes a novel coordinated control method in which a power-distribution-network model has been adopted for more accurate overvoltage quantification. Meanwhile, the battery operations of individual NZEBs are iteratively coordinated using a sequential optimization approach for achieving the global optimum with substantially reduced computation complexity. For verifications, the proposed coordinated control has been systematically compared with an uncoordinated control and a conventional coordinated control in grid overvoltage minimization. The study results show that the overvoltage improvements can reach 23.5% and 12.3% compared with the uncoordinated control and the conventional coordinated control, respectively. The reasons behind the improvements have also been analyzed in detail. The proposed coordinated control can be used in practice to improve NZEB-clusters’ grid friendliness.
基金Supported by the National Natural Science Foundation of China(No. 50737001)
文摘The amplitude of switching overvoltages is a key factor for designing the insulation of UHV equipment. The effect of different arresters needs to be studied, since installing arresters is an important way to suppress switching overvoltages in UHV transmission lines. Switching overvoltages on the 1000 kV Huainan-Huxi double-circuit transmission line were simulated for different operating modes and different arrester designs using the electromagnetic transient program PSCAD/EMTDC. With parallel resistors, the switching overvoltages are less than 1.70 p.u. （1.0 p.u.=1100×√ 2 /√3 kV）. If the arrestors are better, the switching overvoltages can be reduced even lower to 1.55 p.u. Without parallel resistors, the arresters can reduce three-phase energizing overvoltages to 1.70 p.u, while the single-phase reclosing overvoltages still exceed the limit. The results show that the parallel resistors cannot be eliminated if the arresters are only installed at each end of the transmission line. Also, better quality arresters significantly lower the switching overvoltages.
基金the National Natural Science Foundation of China(22325902 and 51671107)Haihe Laboratory of Sustainable Chemical Transformations.
文摘Rechargeable lithium-oxygen(Li-O_(2))batteries have attracted wide attention due to their high energy density.However,the sluggish cathode kinetics results in high overvoltage and poor cycling performance.Ruthenium(Ru)-based electrocatalysts have been demonstrated to be promising cathode catalysts to promote oxygen evolution reaction(OER).It facilitates decomposition of lithium peroxide(Li_(2)O_(2))by adjusting Li_(2)O_(2) morphologies,which is due to the strong interaction between Ru-based catalyst and superoxide anion(O_(2))intermediate.In this review,the design strategies of Ru-based electrocatalysts are introduced to enhance their OER catalytic kinetics in Li-O_(2) batteries.Different configurations of Ru-based catalysts,including metal particles(Ru metal and alloys),single-atom catalysts,and Ru-loaded compounds with various substrates(carbon materials,metal oxides/sulfides),have been summarized to regulate the electronic structure and the matrix architecture of the Ru-based electrocatalysts.The structure-property relationship of Ru-based catalysts is discussed for a better understanding of the Li_(2)O_(2) decomposition mechanism at the cathode interface.Finally,the challenges of Ru-based electrocatalysts are proposed for the future development of Li-O_(2) batteries.
