Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to thei...Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs.展开更多
We demonstrate high-performance In0.23 Ga0.77 As channel metal-oxide-semiconductor field-effect transistors （ MOS- FETs） with high on-current to off-current （Ion/Ioff） ratio grown on semi-insulating GaAs wafers by...We demonstrate high-performance In0.23 Ga0.77 As channel metal-oxide-semiconductor field-effect transistors （ MOS- FETs） with high on-current to off-current （Ion/Ioff） ratio grown on semi-insulating GaAs wafers by metal-organic chemical vapor deposition （MOCVD）. The 2μm channel-length devices exhibit a peak extrinsic transeonductance of 150 mS/mm and a drain current up to 500 mA/mm. The maximum effective mobility is 1680 cm2/Vs extracted by the split C-V method. Furthermore, the Ion/Ioff ratio is significantly improved from approximately 4.5 × 10^3 up to approximately 4.32 × 10^4 by controlling the etch thickness of In0.49Ga0.51P, The high drain current and high Ion/Ioff ratio of the In0.23Ga0.77As channel MOSFETs are achieved due to the high effective mobility and the low gate leakage current density.展开更多
A new line protection for HVDC systems using the ratio of currents of a DC filter and smoothing reactor is presented.Characteristic analysis on a DC filter shows that it behaves like an inductor at a high frequency ba...A new line protection for HVDC systems using the ratio of currents of a DC filter and smoothing reactor is presented.Characteristic analysis on a DC filter shows that it behaves like an inductor at a high frequency band whose inductance is far less than the sum of smoothing reactor inductance plus converter equivalent inductance.Based on this characteristic,fault analysis shows that during high-frequency DC line faults(on either side),the DC filter current amplitude significantly exceeds that of the smoothing reactor,with a current ratio much greater than 1.Whereas for external faults,near faulty end,DC filter current amplitude is less than the one of a smoothing reactor and current ratio at this end is smaller than 1,while the current ratio at the distance faulty end is still far greater than 1.The effectiveness of the protection is verified by a large number of simulation experiments.It does not need synchronization of signals at both ends.In addition,it has high sensitivity for high-resistance faults,and is insensitive to the length of DC transmission line and power flow change.展开更多
Amorphous Ga_(2)O_(3)(a-Ga_(2)O_(3))has been attracting more and more attention due to its unique merits such as wide bandgap(∼4.9 eV),low growth temperature,large-scale uniformity,low cost and energy efficient,makin...Amorphous Ga_(2)O_(3)(a-Ga_(2)O_(3))has been attracting more and more attention due to its unique merits such as wide bandgap(∼4.9 eV),low growth temperature,large-scale uniformity,low cost and energy efficient,making it a powerful competitor in flexible deep ultraviolet(UV)photodetection.Although the responsivity of the ever-reported a-Ga_(2)O_(3)UV photodetectors(PDs)is usually in the level of hundreds of A/W,it is often accompanied by a large dark current due to the presence of abundant oxygen vacancy(VO)defects,which severely limits the possibility to detect weak signals and achieve versatile applications.In this work,the VO defects in a-Ga_(2)O_(3)thin films are successfully passivated by in-situ hydrogen doping during the magnetron sputtering process.As a result,the dark current of a-Ga_(2)O_(3)UV PD is remarkably suppressed to 5.17×10^(-11) A at a bias of 5 V.Importantly,the photocurrent of the corresponding device is still as high as 1.37×10^(-3)A,leading to a high photo-to-dark current ratio of 2.65×107 and the capability to detect the UV light with the intensity below 10 nW cm^(-2).Moreover,the H-doped a-Ga_(2)O_(3)thin films have also been deposited on polyethylene naphtholate substrates to construct flexible UV PDs,which exhibit no great degradation in bending states and fatigue tests.These results demonstrate that hydrogen doping can effectively improve the performance of a-Ga_(2)O_(3)UV PDs,further promoting its practical application in various areas.展开更多
Sparse measurements challenge fault location in distribution networks.This paper proposes a method for asymmetric ground fault location in distribution networks with limited measurements.A virtual injected current vec...Sparse measurements challenge fault location in distribution networks.This paper proposes a method for asymmetric ground fault location in distribution networks with limited measurements.A virtual injected current vector is formulated to estimate the fault line,which can be reconstructed from voltage sags measured at a few buses using compressive sensing(CS).The relationship between the virtual injected current ratio(VICR)and fault position is deduced from circuit analysis to pinpoint the fault.Furthermore,a two-stage recovery strategy is proposed for improving reconstruction accuracy of the current vector,where two different sensing matrixes are utilized to improve the incoherence.The proposed method is validated in IEEE 34 node test feeder.Simulation results show asymmetric ground fault type,resistance,fault position and access of distributed generators(DGs)do not significantly influence performance of our method.In addition,it works effectively under various scenarios of noisy measurement and line parameter error.Validations on 134 node test feeders prove the proposed method is also suitable for systems with more complex structure.展开更多
In this work,the incorporation of tantalum(Ta)into p-type metal-oxide(SnO_(x))semiconductor film is investigated to improve the electrical characteristics and suppress the fringe effect of thin film transistors(TFTs)....In this work,the incorporation of tantalum(Ta)into p-type metal-oxide(SnO_(x))semiconductor film is investigated to improve the electrical characteristics and suppress the fringe effect of thin film transistors(TFTs).The Ta-doped SnO_(x)(SnO_(x):Ta)film is deposited by radio-frequency(RF)magnetron sputtering with a Sn:Ta(3 at.%)target and thermally annealed at 270℃ for 30 min.Here,we observe that the SnO_(x):Ta film presents increased crystallinity,reduced defect density(3.25×10^(12)cm^(−2)·eV^(−1)),and widened bandgap(1.98 eV),in comparison with the undoped SnO_(x)film.As a result,the SnO_(x):Ta TFTs exhibit a lower off-state current(Ioff),an improved on/off current ratio(2.17×10^(4)),a remarkably decreased subthreshold swing(SS)by 41%,and enhanced device stability.Additionally,by introducing Ta dopants,the fringe effect as well as the impact of channel width-to-length ratio(W/L)on electrical performances of the p-type oxide TFTs can be effectively suppressed.These results shall contribute to further exploration and development of p-type SnO_(x)TFTs.展开更多
An In0.53Ga0.47As/AlAs resonant tunneling diode （RTD） with a high doping emitter is designed and fabricated using air bridge technology. The RTD exhibits a high peak-to-valley current ratio （PVCR） of more than 40 ...An In0.53Ga0.47As/AlAs resonant tunneling diode （RTD） with a high doping emitter is designed and fabricated using air bridge technology. The RTD exhibits a high peak-to-valley current ratio （PVCR） of more than 40 at room temperature, with a peak current density of 24 kA/cm2. The extraction of device parameters from DC and microwave measurements is presented together with an RTD equivalent circuit. The high PVCR RTD with small intrinsic capacitance is favorable for microwave/THz applications.展开更多
Background: While public municipal hospitals in Japan are supported by public financing and are less likely to fail than private hospitals, more than half are in financial deficit. Hospitals running at a deficit may h...Background: While public municipal hospitals in Japan are supported by public financing and are less likely to fail than private hospitals, more than half are in financial deficit. Hospitals running at a deficit may have poorer outcomes and less investment in maintenance of human or physical capital, as well as increased rates of patient adverse events. We sought to clarify the relationship between municipal hospital surpluses or deficits and salary expenditures. Methods: We extracted financial data for 253 general hospitals of 300 beds or more from financial statements for the 2013 fiscal year available in the Yearbook of Public Firms, Edition for Hospital. From these data, we calculated account balance ratios and compared the average value of the ratio of labor to the output (salary ratio) for each group using analysis of variance (ANOVA). Results: The salary ratios of hospitals in the surplus group were significantly lower than the salary ratios of hospitals in the deficit group (55.5% vs. 49.4%;p p = 0.342). In the surplus group, the average value of salary ratios was different among the three-bed count groups (mean salary ratio: 53.0% vs. 48.5% vs. 47.4%;ANOVA p = 0.012). In addition, there was a significant difference in mean value between the 300-bed group and ≥500 beds group (mean salary ratio: 53.0% vs. 47.4%;p = 0.002). Conclusion: This study suggests that maintaining a favorable salary ratio to the current account balance is a useful proxy of fiscal health, and interventions to improve the salary ratio may be effective in improving municipal hospital management. Furthermore, among well-managed municipal hospitals, larger hospital size may confer some advantage in purchasing power.展开更多
Five generalized physical models of different distortion ratios were built according to DOU Guo-ren's similarity theory of total sediment transport modeling for estuarine and coastal regions. Experiments on local ...Five generalized physical models of different distortion ratios were built according to DOU Guo-ren's similarity theory of total sediment transport modeling for estuarine and coastal regions. Experiments on local scour in front of groins were made under the actions of tidal currents and waves with clear and sediment entraining water. The scour depths under different dynamic actions are compared. The effect of the distortion ratio on the depth of scour hole is discussed. A relationship between scour depths for distorted and undistorted models is given.展开更多
AlAs/GaAs/In0.1Ga0.9As/GaAs/AlAs double-barrier resonant tunneling diodes （DBRTDs） grown on a semi-insulated GaAs substrate with molecular beam epitaxy is demonstrated. By sandwiching the In0.1 Ga0.9 As layer betwee...AlAs/GaAs/In0.1Ga0.9As/GaAs/AlAs double-barrier resonant tunneling diodes （DBRTDs） grown on a semi-insulated GaAs substrate with molecular beam epitaxy is demonstrated. By sandwiching the In0.1 Ga0.9 As layer between GaAs layers, potential wells beside the two sides of barrier are deepened, resulting in an increase of the peak-to-valley current ratio （PVCR） and a peak current density. A special shape of collector is designed in order to reduce contact resistance and non-uniformity of the current;as a result the total chrrent density in the device is increased. The use of thin barriers is also helpful for the improvement of the PVCR and the peak current density in DBRTDs. The devices exhibit a maximum PVCR of 13.98 and a peak current density of 89kA/cm^2 at room temperature.展开更多
零序电流互感器(current transformer,CT)测量精度问题一直是限制配电网故障选线准确率的关键性问题,现有研究方法在理论层面已较为成熟,但在现场使用中受限于零序CT测量精度,耐过渡电阻能力往往不佳。灵活接地系统是一种新型接地方式,...零序电流互感器(current transformer,CT)测量精度问题一直是限制配电网故障选线准确率的关键性问题,现有研究方法在理论层面已较为成熟,但在现场使用中受限于零序CT测量精度,耐过渡电阻能力往往不佳。灵活接地系统是一种新型接地方式,系统感知永久性接地故障后,于中性点投入并联小电阻,使得配电网接地方式发生转变,从而导致同一电气信号量呈现两种完全不同的故障特征,故障信息量增加了一倍,综合利用两阶段故障特征有望突破现有故障选线装置性能极限,摆脱选线装置对零序CT测量精度的依赖。为此,该文首先分析了灵活接地系统不同阶段各电气量的故障特征,之后结合灵活接地系统特点提出了一种基于零序电流幅值比的高阻接地故障选线方法,最后通过合理设计选线算法,剔除误差较大数据,最大程度降低保护对零序CT测量精度的依赖。实时数字仿真系统(real time digital simulation system,RTDS)以及低压实验平台实验结果表明,该方法不受零序CT极性反接与相位测量误差影响,且无需故障信息间的横向比较,具有耐过渡电阻能力强、可靠性高、对零序CT测量精度要求低、易实现等优点。展开更多
An experimental investigation of the saturation ion current densities （Jions） in hydrogen inductively coupled plasma （ICP） produced by a large-power （2-32 kW） radio frequency （RF） generator is reported, then s...An experimental investigation of the saturation ion current densities （Jions） in hydrogen inductively coupled plasma （ICP） produced by a large-power （2-32 kW） radio frequency （RF） generator is reported, then some reasonable explanations are given out. With the increase of RF power, the experimental results show three stages： in the first stage （2-14 kW）, the electron temperature will rise with the increase of RF power in the ICP, thus, the Jions increases continually as the electron temperature rises in the ICP. In the second stage （14 20 kW）, as some H- ions lead to the mutual neutralization （MN）, the slope of Jio^s variation firstly decreases then increases. In the third stage （20-32 kW）, both the electronic detachment （ED） and the associative detachment （AD） in the ICP result in the destruction of H- ions, therefore, the increased amplitude of the Jions in the third stage is weaker than the one in the first stage. In addition, with the equivalent transformer model, we successfully Explain that the Jions at different radial locations in ICP has the same rule. Finally, it is found that the Jions has nothing to do with the outer/inner puffing gas pressure ratio, which is attributed to the high-speed movement of hydrogen molecules.展开更多
运行数据显示全光纤电流互感器(fiber optic current transformer,FOCT)在极端环境下(温度为–45~85℃、振动加速度>15 m/s^(2))故障概率明显偏高,因此研究极端环境对FOCT性能的影响十分必要。在分析FOCT工作原理基础上,重点讨论了F...运行数据显示全光纤电流互感器(fiber optic current transformer,FOCT)在极端环境下(温度为–45~85℃、振动加速度>15 m/s^(2))故障概率明显偏高,因此研究极端环境对FOCT性能的影响十分必要。在分析FOCT工作原理基础上,重点讨论了FOCT核心模块的结构特征及极端环境的影响,并建立FOCT传变模型。根据FOCT真实工作环境,分析了极端环境对其测量准确性的影响。结果表明:温度的升高、光纤长度的增加、振动加速度的变大,都会使FOCT比差增大,测量精度下降。特别是在极端环境下,测量误差较大,无法满足0.2S级测量准确度的要求。为验证模型的可靠性,开展了温度和振动影响试验。针对现有试验缺乏对极端环境的考核,提出增加测点的温度试验方法和增加振动响应试验及振动耐久试验的振动试验方法。试验结果与仿真结果对比表明:两者结果具有一致性,偏差电流波形变化趋势比较一致。该研究为FOCT可靠性问题提供有益参考。展开更多
基金supported in part by National Key Research and Development Program of China(2016YFB0900603)Technology Projects of State Grid Corporation of China(52094017000W).
文摘Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs.
文摘We demonstrate high-performance In0.23 Ga0.77 As channel metal-oxide-semiconductor field-effect transistors （ MOS- FETs） with high on-current to off-current （Ion/Ioff） ratio grown on semi-insulating GaAs wafers by metal-organic chemical vapor deposition （MOCVD）. The 2μm channel-length devices exhibit a peak extrinsic transeonductance of 150 mS/mm and a drain current up to 500 mA/mm. The maximum effective mobility is 1680 cm2/Vs extracted by the split C-V method. Furthermore, the Ion/Ioff ratio is significantly improved from approximately 4.5 × 10^3 up to approximately 4.32 × 10^4 by controlling the etch thickness of In0.49Ga0.51P, The high drain current and high Ion/Ioff ratio of the In0.23Ga0.77As channel MOSFETs are achieved due to the high effective mobility and the low gate leakage current density.
基金supported in part by the National Natural Science Foundation of China under Grant(U2066210).
文摘A new line protection for HVDC systems using the ratio of currents of a DC filter and smoothing reactor is presented.Characteristic analysis on a DC filter shows that it behaves like an inductor at a high frequency band whose inductance is far less than the sum of smoothing reactor inductance plus converter equivalent inductance.Based on this characteristic,fault analysis shows that during high-frequency DC line faults(on either side),the DC filter current amplitude significantly exceeds that of the smoothing reactor,with a current ratio much greater than 1.Whereas for external faults,near faulty end,DC filter current amplitude is less than the one of a smoothing reactor and current ratio at this end is smaller than 1,while the current ratio at the distance faulty end is still far greater than 1.The effectiveness of the protection is verified by a large number of simulation experiments.It does not need synchronization of signals at both ends.In addition,it has high sensitivity for high-resistance faults,and is insensitive to the length of DC transmission line and power flow change.
基金supported by Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2022A1515110607 and 2019B1515120057)the National Natural Science Foundation of China(Grant Nos.62174113,12174275,61874139,61904201 and 11875088).
文摘Amorphous Ga_(2)O_(3)(a-Ga_(2)O_(3))has been attracting more and more attention due to its unique merits such as wide bandgap(∼4.9 eV),low growth temperature,large-scale uniformity,low cost and energy efficient,making it a powerful competitor in flexible deep ultraviolet(UV)photodetection.Although the responsivity of the ever-reported a-Ga_(2)O_(3)UV photodetectors(PDs)is usually in the level of hundreds of A/W,it is often accompanied by a large dark current due to the presence of abundant oxygen vacancy(VO)defects,which severely limits the possibility to detect weak signals and achieve versatile applications.In this work,the VO defects in a-Ga_(2)O_(3)thin films are successfully passivated by in-situ hydrogen doping during the magnetron sputtering process.As a result,the dark current of a-Ga_(2)O_(3)UV PD is remarkably suppressed to 5.17×10^(-11) A at a bias of 5 V.Importantly,the photocurrent of the corresponding device is still as high as 1.37×10^(-3)A,leading to a high photo-to-dark current ratio of 2.65×107 and the capability to detect the UV light with the intensity below 10 nW cm^(-2).Moreover,the H-doped a-Ga_(2)O_(3)thin films have also been deposited on polyethylene naphtholate substrates to construct flexible UV PDs,which exhibit no great degradation in bending states and fatigue tests.These results demonstrate that hydrogen doping can effectively improve the performance of a-Ga_(2)O_(3)UV PDs,further promoting its practical application in various areas.
基金supported in part by Key-Area Research and Development Program of Guangdong Province(No.2020B010166004)State Key Program of National Natural Science Foundation of China under Grant(No.U1866210)Natural Science Foundation of Guangdong Province(No.2022A1515011587).
文摘Sparse measurements challenge fault location in distribution networks.This paper proposes a method for asymmetric ground fault location in distribution networks with limited measurements.A virtual injected current vector is formulated to estimate the fault line,which can be reconstructed from voltage sags measured at a few buses using compressive sensing(CS).The relationship between the virtual injected current ratio(VICR)and fault position is deduced from circuit analysis to pinpoint the fault.Furthermore,a two-stage recovery strategy is proposed for improving reconstruction accuracy of the current vector,where two different sensing matrixes are utilized to improve the incoherence.The proposed method is validated in IEEE 34 node test feeder.Simulation results show asymmetric ground fault type,resistance,fault position and access of distributed generators(DGs)do not significantly influence performance of our method.In addition,it works effectively under various scenarios of noisy measurement and line parameter error.Validations on 134 node test feeders prove the proposed method is also suitable for systems with more complex structure.
基金supported in part by National Key R&D Program of China(Grant No.2022YFE0141500)National Natural Science Foundation of China(Grant Nos.62004065 and 62274059).
文摘In this work,the incorporation of tantalum(Ta)into p-type metal-oxide(SnO_(x))semiconductor film is investigated to improve the electrical characteristics and suppress the fringe effect of thin film transistors(TFTs).The Ta-doped SnO_(x)(SnO_(x):Ta)film is deposited by radio-frequency(RF)magnetron sputtering with a Sn:Ta(3 at.%)target and thermally annealed at 270℃ for 30 min.Here,we observe that the SnO_(x):Ta film presents increased crystallinity,reduced defect density(3.25×10^(12)cm^(−2)·eV^(−1)),and widened bandgap(1.98 eV),in comparison with the undoped SnO_(x)film.As a result,the SnO_(x):Ta TFTs exhibit a lower off-state current(Ioff),an improved on/off current ratio(2.17×10^(4)),a remarkably decreased subthreshold swing(SS)by 41%,and enhanced device stability.Additionally,by introducing Ta dopants,the fringe effect as well as the impact of channel width-to-length ratio(W/L)on electrical performances of the p-type oxide TFTs can be effectively suppressed.These results shall contribute to further exploration and development of p-type SnO_(x)TFTs.
基金Project supported by the National Fundamental Research Program of China(No.2009CB320207)
文摘An In0.53Ga0.47As/AlAs resonant tunneling diode （RTD） with a high doping emitter is designed and fabricated using air bridge technology. The RTD exhibits a high peak-to-valley current ratio （PVCR） of more than 40 at room temperature, with a peak current density of 24 kA/cm2. The extraction of device parameters from DC and microwave measurements is presented together with an RTD equivalent circuit. The high PVCR RTD with small intrinsic capacitance is favorable for microwave/THz applications.
文摘Background: While public municipal hospitals in Japan are supported by public financing and are less likely to fail than private hospitals, more than half are in financial deficit. Hospitals running at a deficit may have poorer outcomes and less investment in maintenance of human or physical capital, as well as increased rates of patient adverse events. We sought to clarify the relationship between municipal hospital surpluses or deficits and salary expenditures. Methods: We extracted financial data for 253 general hospitals of 300 beds or more from financial statements for the 2013 fiscal year available in the Yearbook of Public Firms, Edition for Hospital. From these data, we calculated account balance ratios and compared the average value of the ratio of labor to the output (salary ratio) for each group using analysis of variance (ANOVA). Results: The salary ratios of hospitals in the surplus group were significantly lower than the salary ratios of hospitals in the deficit group (55.5% vs. 49.4%;p p = 0.342). In the surplus group, the average value of salary ratios was different among the three-bed count groups (mean salary ratio: 53.0% vs. 48.5% vs. 47.4%;ANOVA p = 0.012). In addition, there was a significant difference in mean value between the 300-bed group and ≥500 beds group (mean salary ratio: 53.0% vs. 47.4%;p = 0.002). Conclusion: This study suggests that maintaining a favorable salary ratio to the current account balance is a useful proxy of fiscal health, and interventions to improve the salary ratio may be effective in improving municipal hospital management. Furthermore, among well-managed municipal hospitals, larger hospital size may confer some advantage in purchasing power.
文摘Five generalized physical models of different distortion ratios were built according to DOU Guo-ren's similarity theory of total sediment transport modeling for estuarine and coastal regions. Experiments on local scour in front of groins were made under the actions of tidal currents and waves with clear and sediment entraining water. The scour depths under different dynamic actions are compared. The effect of the distortion ratio on the depth of scour hole is discussed. A relationship between scour depths for distorted and undistorted models is given.
文摘AlAs/GaAs/In0.1Ga0.9As/GaAs/AlAs double-barrier resonant tunneling diodes （DBRTDs） grown on a semi-insulated GaAs substrate with molecular beam epitaxy is demonstrated. By sandwiching the In0.1 Ga0.9 As layer between GaAs layers, potential wells beside the two sides of barrier are deepened, resulting in an increase of the peak-to-valley current ratio （PVCR） and a peak current density. A special shape of collector is designed in order to reduce contact resistance and non-uniformity of the current;as a result the total chrrent density in the device is increased. The use of thin barriers is also helpful for the improvement of the PVCR and the peak current density in DBRTDs. The devices exhibit a maximum PVCR of 13.98 and a peak current density of 89kA/cm^2 at room temperature.
文摘零序电流互感器(current transformer,CT)测量精度问题一直是限制配电网故障选线准确率的关键性问题,现有研究方法在理论层面已较为成熟,但在现场使用中受限于零序CT测量精度,耐过渡电阻能力往往不佳。灵活接地系统是一种新型接地方式,系统感知永久性接地故障后,于中性点投入并联小电阻,使得配电网接地方式发生转变,从而导致同一电气信号量呈现两种完全不同的故障特征,故障信息量增加了一倍,综合利用两阶段故障特征有望突破现有故障选线装置性能极限,摆脱选线装置对零序CT测量精度的依赖。为此,该文首先分析了灵活接地系统不同阶段各电气量的故障特征,之后结合灵活接地系统特点提出了一种基于零序电流幅值比的高阻接地故障选线方法,最后通过合理设计选线算法,剔除误差较大数据,最大程度降低保护对零序CT测量精度的依赖。实时数字仿真系统(real time digital simulation system,RTDS)以及低压实验平台实验结果表明,该方法不受零序CT极性反接与相位测量误差影响,且无需故障信息间的横向比较,具有耐过渡电阻能力强、可靠性高、对零序CT测量精度要求低、易实现等优点。
基金supported by the National Magnetic Confinement Fusion Science Program of China(Nos.2011GB108011 and 2010GB103001)the Major International(Regional)Project Cooperation and Exchanges of China(No.11320101005)the Startup Fund from Fuzhou University(No.510071)
文摘An experimental investigation of the saturation ion current densities （Jions） in hydrogen inductively coupled plasma （ICP） produced by a large-power （2-32 kW） radio frequency （RF） generator is reported, then some reasonable explanations are given out. With the increase of RF power, the experimental results show three stages： in the first stage （2-14 kW）, the electron temperature will rise with the increase of RF power in the ICP, thus, the Jions increases continually as the electron temperature rises in the ICP. In the second stage （14 20 kW）, as some H- ions lead to the mutual neutralization （MN）, the slope of Jio^s variation firstly decreases then increases. In the third stage （20-32 kW）, both the electronic detachment （ED） and the associative detachment （AD） in the ICP result in the destruction of H- ions, therefore, the increased amplitude of the Jions in the third stage is weaker than the one in the first stage. In addition, with the equivalent transformer model, we successfully Explain that the Jions at different radial locations in ICP has the same rule. Finally, it is found that the Jions has nothing to do with the outer/inner puffing gas pressure ratio, which is attributed to the high-speed movement of hydrogen molecules.
文摘运行数据显示全光纤电流互感器(fiber optic current transformer,FOCT)在极端环境下(温度为–45~85℃、振动加速度>15 m/s^(2))故障概率明显偏高,因此研究极端环境对FOCT性能的影响十分必要。在分析FOCT工作原理基础上,重点讨论了FOCT核心模块的结构特征及极端环境的影响,并建立FOCT传变模型。根据FOCT真实工作环境,分析了极端环境对其测量准确性的影响。结果表明:温度的升高、光纤长度的增加、振动加速度的变大,都会使FOCT比差增大,测量精度下降。特别是在极端环境下,测量误差较大,无法满足0.2S级测量准确度的要求。为验证模型的可靠性,开展了温度和振动影响试验。针对现有试验缺乏对极端环境的考核,提出增加测点的温度试验方法和增加振动响应试验及振动耐久试验的振动试验方法。试验结果与仿真结果对比表明:两者结果具有一致性,偏差电流波形变化趋势比较一致。该研究为FOCT可靠性问题提供有益参考。
