Based on simple analytical equations, short circuit current density （Jsc） of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important r...Based on simple analytical equations, short circuit current density （Jsc） of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important role in the determination of Jsc; and obvious oscillatory behaviour of Jsc was observed as a function of thickness. At the same time, the influence of the carrier lifetime on Jsc also cannot be neglected. When the carrier lifetime is relatively short, Jsc only increases at the initial stage and then decreases rapidly with the increase of active layer thickness. However, for a relatively long carrier lifetime, the exciton dissociation probability must be considered, and Jsc behaves wave-like with the increase of active layer thickness. The validity of this model is confirmed by the experimental results.展开更多
With the development of power system, the level of short circuit current will increase accordingly. In general, the influence of the HVDC system and the new energy source is not considered in the calculation of the sh...With the development of power system, the level of short circuit current will increase accordingly. In general, the influence of the HVDC system and the new energy source is not considered in the calculation of the short circuit current. For the power grid that short circuit current level closes to the interrupting capacity of circuit breaker, it’s necessary to fully consider all kinds of influence factors, careful checking, so as to obtain more accurate calculation results of short circuit current. In 2018, two ±800 kV high-power Ultra High Voltage Direct Current (UHVDC) transmission projects will be connected with Shaanxi power grid, accompanied by a lot of concomitant fossil-fuel generating plants as power resource, and also a large number of new energy source, includes wind power generation and photovoltaic power generation. Around one of the UHVDC converter stations, short circuit current may exceed the withstand limit of some certain circuit breakers. In order to get more accurate short circuit current calculation results, three measures are used: 1) contrastive calculation and analysis by algorithm based on schemes and algorithm based on power flow;2) analysis the influence of UHVDC by electromagnetic transient and electromechanical transient hybrid simulation;3) considered a detailed model of Doubly Fed Induction Generator (DFIG) with low voltage ride through characteristics. The calculation results shows that: in the typical operation mode of Shaanxi power grid of 2018, the original calculation results by conventional calculation method are coincident with the results by considering the influence of algorithms, UHVDC and DFIG in large, in which: the results of the algorithm based on power flow are smaller than that of the algorithm based on schemes about 2 - 8 kA;the steady values of the short circuit current provided by UHVDC converterstation (includes rectifiers and smoothing capacitors) are about 0 - 3 kA;the steady values of the short circuit current provided by DFIG are about 0 - 5 kA. The calculation results can provide reference for the selection of the circuit breaker, and it can be verified by fault recording data in the future.展开更多
Objective To investigate the property of the endometrium ion transport in the normal estruation and ovariectomize rats. Methods The basic electrophysiological property of the endometrium was carried out by mean of the...Objective To investigate the property of the endometrium ion transport in the normal estruation and ovariectomize rats. Methods The basic electrophysiological property of the endometrium was carried out by mean of the short circuit current （Isc） recording with the rats. Results The baseline Lsc and the transepithelial resistance （Rte） were different between the estruation and ovariectomized groups. Apical application of Na＋ channel blocker, amiloride （10 μmol/L）, or CFTR Cl- channel agonist, forskolin （10 μmol/L） did not significantly affect the Lc in the two groups. However, the 1sc in the model group was more sensitive to the CFTR Cl- channel blocker （glibenclamide, 1 mmol/L, apical） decreased about 27.0% （P〈0.05, n=6）, no remarkably changes in the estruation rats. While apical application CA CC CI-channel blocker, DIDS （4, 4 ＇-diisothiocyanostilbene- 2,2 ＇-disulfonic, 100 μmol/L）, the Isc was much more sensitive, percentage almost to 36.52% （P〈0.01） in the model group than that in the control Furthermore, basolateral application of bumetanide （100μmol/L）, a blocker of Na＋-K＋-2Cl- cotransport, didn＇t significantly reduce the Lc in the two groups. Conclusion The baseline Lsc and membrane resistance in the ovariectomize group is much higher than that in the normal estruation group, and the endometrial epithelium CI- secretion may be mediated by predominantly calcium-dependent CI- channels （CACC） and activating adenylate cyclase and apical cAMP-dependent Cl- channels （CFTR） in the model group with minor contributions in the control. Furthermore, the endometrial epithelium responses to different stimulants exists difference in the control and model group a likely mechanism for the ovary hormone.展开更多
The commissioning of Southern Hami-Zhengzhou ±800 kV UHVDC transmission project has important significance to heighten operation reliability, transfer capability and supply electric ability of Henan power grid. H...The commissioning of Southern Hami-Zhengzhou ±800 kV UHVDC transmission project has important significance to heighten operation reliability, transfer capability and supply electric ability of Henan power grid. However, short circuit currents of 500 kV buses in the Center of Henan are almost close to the operation upper limitation. In order to decrease the short circuit currents effectively, it’s necessary to strengthen the network structure of Center of Henan power grid and calculate short circuit currents. Two schemes of strengthening the network structure of Center of Henan power grid are studied. The calculated values of short circuit currents of some important 500 kV buses in the two schemes are still bigger than excepted. According to the latest Plan of State Grid, Yubei UHV substation and Zhumadian UHV substation located in Henan power grid. The calculated values of short circuit currents of some important 500 kV buses with the commissioning of Yubei UHV and Zhumadian UHV are qualified. So, reasonable network structure with UHV is suitable to heighten transfer capability and supply electric ability of Henan power grid.展开更多
With the rapid development of economy, strengthen the continuous construction of national infrastructure, etc., many industry demand for steel, steel enterprise capacity expands, at the same time, the steel enterprise...With the rapid development of economy, strengthen the continuous construction of national infrastructure, etc., many industry demand for steel, steel enterprise capacity expands, at the same time, the steel enterprises to positive response to the call of national energy conservation and emission reduction, using plant waste heat green development is the only way to realize the transformation and upgrading of the steel industry. This paper will be mainly for the domestic steel enterprise 6kV system short circuit current exceeds the limit and take the restrictive measures for detailed analysis and discussion for the industry reference.展开更多
Due to increased penetration of renewable energies,DC links and other emerging technologies,power system operation and planning have to cope with various uncertainties and risks.In order to solve the problems of excee...Due to increased penetration of renewable energies,DC links and other emerging technologies,power system operation and planning have to cope with various uncertainties and risks.In order to solve the problems of exceeding short circuit current and multi-infeed DC interaction,a coordinated optimization method is presented in this paper.Firstly,a branch selection strategy is proposed by analyzing the sensitivity relationship between current limiting measures and the impedance matrix.Secondly,the impact of network structure changes on the multi-infeed DC system is derived.Then the coordinated optimization model is established,which considers the cost and effect of current limiting measures,the tightness of network structure and the voltage support capability of AC system to multiple DCs.Finally,the non-dominated sorting genetic algorithm II combining with the branch selection strategy,is used to find the Pareto optimal schemes.Case studies on a planning power system demonstrated the feasibility and speediness of this method.展开更多
An approach of transmission network expan-sion planning with embedded constraints of short circuit currents and N-1 security is proposed in this paper.The problem brought on by the strong nonlinearity property of shor...An approach of transmission network expan-sion planning with embedded constraints of short circuit currents and N-1 security is proposed in this paper.The problem brought on by the strong nonlinearity property of short circuit currents is solved with a linearization method based on the DC power flow.The model can be converted to a mixed-integer linear programming problem,realizing the optimization of planning model that considers the constraints of linearized short circuit currents and N-1 security.To compensate the error caused by the assump-tions of DC power flow,the compensation factor is pro-posed.With this factor,an iterative algorithm that can compensate the linearization error is then presented.The case study based on the IEEE 118-bus system shows that the proposed model and approach can be utilized to:opti-mize the construction strategy of transmission lines;ensure the N-1 security of the network;and effectively limit the short circuit currents of the system.展开更多
Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been...Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.展开更多
Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a signifi...Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a significant issue.However,the traditional calculation methods aiming at synchronous generators cannot be directly applied to the DFIG wind turbines.A new method is needed to calculate the short-circuit current required by the planning,protection and control of the power grid.The short-circuit transition of DFIG under symmetrical and asymmetric short-circuit conditions are mathematically deduced,and the short-circuit characteristics of DFIG are analyzed.A new method is proposed to calculate the steady-state short-circuit current of DFIG based on the derived expressions.The time-domain simulations are conducted to verify the accuracy of the proposed method.展开更多
To study the effects of wind generators on distribution system protection,the short-circuit current(SCC) characteristics of wind generators is important.Although there are many researches on the issue,a clear agreemen...To study the effects of wind generators on distribution system protection,the short-circuit current(SCC) characteristics of wind generators is important.Although there are many researches on the issue,a clear agreement has not been reached so far.The SCC characteristics for different wind generators are studied.PSCAD simulation is performed in the same system integrated with different kinds of wind generators,and their results are compared with those reported in IEEE papers.The detection possibility by overcurrent relay(OCR)is discussed based on the simulation results.展开更多
The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination o...The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.展开更多
It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and ...It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and short-circuit impedance model of axial dual-low-voltage split-winding transformer is established, and then the 2D and 3D leakage magnetic field are analyzed. Secondly, the short-circuit impedance and split parallel branch current distribution in different working conditions are calculated, which is based on field-circuit coupled method. At last, effectiveness and feasibility of the proposed model is verified by comparison between experiment, analysis and simulation. The results showed that the 3D analysis method is a better approach to calculate the short-circuit impedance, since its analytical value is more closer to the experimental value compared with the 2D analysis results, the finite element method calculation error is less than 2%, while the leakage flux method maximum error is 7.2%.展开更多
For the past decades,practical calculation method of short circuit current(SCC)contributed by doubly fed induction generator(DFIG)under asymmetrical short circuit fault is deficient due to its control strategies and u...For the past decades,practical calculation method of short circuit current(SCC)contributed by doubly fed induction generator(DFIG)under asymmetrical short circuit fault is deficient due to its control strategies and unlinear equipment.Asymmetrical SCC of DFIG is much more complicated and may be higher than that of a symmetrical fault in some situations.To address the problem,analytical derivations of SCC under asymmetrical faults are presented by establishing current equations between DFIG windings and converter controller or crowbar protection.Each frequency component could be directly extracted from time-domain expressions.Furthermore,clear mathematical models of asymmetrical peak and steady-state SCC used for practical calculation of power systems are proposed.Simulation results verify the effectiveness and robustness to different parameters and fault conditions of the proposed method.Finally,the influences of possible parameters on characteristics of asymmetrical SCC are summarized based on the proposed method.展开更多
文摘Based on simple analytical equations, short circuit current density （Jsc） of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important role in the determination of Jsc; and obvious oscillatory behaviour of Jsc was observed as a function of thickness. At the same time, the influence of the carrier lifetime on Jsc also cannot be neglected. When the carrier lifetime is relatively short, Jsc only increases at the initial stage and then decreases rapidly with the increase of active layer thickness. However, for a relatively long carrier lifetime, the exciton dissociation probability must be considered, and Jsc behaves wave-like with the increase of active layer thickness. The validity of this model is confirmed by the experimental results.
文摘With the development of power system, the level of short circuit current will increase accordingly. In general, the influence of the HVDC system and the new energy source is not considered in the calculation of the short circuit current. For the power grid that short circuit current level closes to the interrupting capacity of circuit breaker, it’s necessary to fully consider all kinds of influence factors, careful checking, so as to obtain more accurate calculation results of short circuit current. In 2018, two ±800 kV high-power Ultra High Voltage Direct Current (UHVDC) transmission projects will be connected with Shaanxi power grid, accompanied by a lot of concomitant fossil-fuel generating plants as power resource, and also a large number of new energy source, includes wind power generation and photovoltaic power generation. Around one of the UHVDC converter stations, short circuit current may exceed the withstand limit of some certain circuit breakers. In order to get more accurate short circuit current calculation results, three measures are used: 1) contrastive calculation and analysis by algorithm based on schemes and algorithm based on power flow;2) analysis the influence of UHVDC by electromagnetic transient and electromechanical transient hybrid simulation;3) considered a detailed model of Doubly Fed Induction Generator (DFIG) with low voltage ride through characteristics. The calculation results shows that: in the typical operation mode of Shaanxi power grid of 2018, the original calculation results by conventional calculation method are coincident with the results by considering the influence of algorithms, UHVDC and DFIG in large, in which: the results of the algorithm based on power flow are smaller than that of the algorithm based on schemes about 2 - 8 kA;the steady values of the short circuit current provided by UHVDC converterstation (includes rectifiers and smoothing capacitors) are about 0 - 3 kA;the steady values of the short circuit current provided by DFIG are about 0 - 5 kA. The calculation results can provide reference for the selection of the circuit breaker, and it can be verified by fault recording data in the future.
基金Beijing Municipal Project for Developing Advanced Human Resources for Higher Education(PHR201008384)Foundation Clinic Research Program of Capital Medical University(10JL31 and 10JL-L05)
文摘Objective To investigate the property of the endometrium ion transport in the normal estruation and ovariectomize rats. Methods The basic electrophysiological property of the endometrium was carried out by mean of the short circuit current （Isc） recording with the rats. Results The baseline Lsc and the transepithelial resistance （Rte） were different between the estruation and ovariectomized groups. Apical application of Na＋ channel blocker, amiloride （10 μmol/L）, or CFTR Cl- channel agonist, forskolin （10 μmol/L） did not significantly affect the Lc in the two groups. However, the 1sc in the model group was more sensitive to the CFTR Cl- channel blocker （glibenclamide, 1 mmol/L, apical） decreased about 27.0% （P〈0.05, n=6）, no remarkably changes in the estruation rats. While apical application CA CC CI-channel blocker, DIDS （4, 4 ＇-diisothiocyanostilbene- 2,2 ＇-disulfonic, 100 μmol/L）, the Isc was much more sensitive, percentage almost to 36.52% （P〈0.01） in the model group than that in the control Furthermore, basolateral application of bumetanide （100μmol/L）, a blocker of Na＋-K＋-2Cl- cotransport, didn＇t significantly reduce the Lc in the two groups. Conclusion The baseline Lsc and membrane resistance in the ovariectomize group is much higher than that in the normal estruation group, and the endometrial epithelium CI- secretion may be mediated by predominantly calcium-dependent CI- channels （CACC） and activating adenylate cyclase and apical cAMP-dependent Cl- channels （CFTR） in the model group with minor contributions in the control. Furthermore, the endometrial epithelium responses to different stimulants exists difference in the control and model group a likely mechanism for the ovary hormone.
文摘The commissioning of Southern Hami-Zhengzhou ±800 kV UHVDC transmission project has important significance to heighten operation reliability, transfer capability and supply electric ability of Henan power grid. However, short circuit currents of 500 kV buses in the Center of Henan are almost close to the operation upper limitation. In order to decrease the short circuit currents effectively, it’s necessary to strengthen the network structure of Center of Henan power grid and calculate short circuit currents. Two schemes of strengthening the network structure of Center of Henan power grid are studied. The calculated values of short circuit currents of some important 500 kV buses in the two schemes are still bigger than excepted. According to the latest Plan of State Grid, Yubei UHV substation and Zhumadian UHV substation located in Henan power grid. The calculated values of short circuit currents of some important 500 kV buses with the commissioning of Yubei UHV and Zhumadian UHV are qualified. So, reasonable network structure with UHV is suitable to heighten transfer capability and supply electric ability of Henan power grid.
文摘With the rapid development of economy, strengthen the continuous construction of national infrastructure, etc., many industry demand for steel, steel enterprise capacity expands, at the same time, the steel enterprises to positive response to the call of national energy conservation and emission reduction, using plant waste heat green development is the only way to realize the transformation and upgrading of the steel industry. This paper will be mainly for the domestic steel enterprise 6kV system short circuit current exceeds the limit and take the restrictive measures for detailed analysis and discussion for the industry reference.
基金This work was supported by State Grid Corporation of China,Major Projects on Planning and Operation Control of Large Scale Grid under Grant SGCC-MPLG020-2012.
文摘Due to increased penetration of renewable energies,DC links and other emerging technologies,power system operation and planning have to cope with various uncertainties and risks.In order to solve the problems of exceeding short circuit current and multi-infeed DC interaction,a coordinated optimization method is presented in this paper.Firstly,a branch selection strategy is proposed by analyzing the sensitivity relationship between current limiting measures and the impedance matrix.Secondly,the impact of network structure changes on the multi-infeed DC system is derived.Then the coordinated optimization model is established,which considers the cost and effect of current limiting measures,the tightness of network structure and the voltage support capability of AC system to multiple DCs.Finally,the non-dominated sorting genetic algorithm II combining with the branch selection strategy,is used to find the Pareto optimal schemes.Case studies on a planning power system demonstrated the feasibility and speediness of this method.
基金This work was supported by National Key Technology R&D Program of China(No.2013BAA01B02)National Natural Science Foundation of China(Nos.51325702,51407100).
文摘An approach of transmission network expan-sion planning with embedded constraints of short circuit currents and N-1 security is proposed in this paper.The problem brought on by the strong nonlinearity property of short circuit currents is solved with a linearization method based on the DC power flow.The model can be converted to a mixed-integer linear programming problem,realizing the optimization of planning model that considers the constraints of linearized short circuit currents and N-1 security.To compensate the error caused by the assump-tions of DC power flow,the compensation factor is pro-posed.With this factor,an iterative algorithm that can compensate the linearization error is then presented.The case study based on the IEEE 118-bus system shows that the proposed model and approach can be utilized to:opti-mize the construction strategy of transmission lines;ensure the N-1 security of the network;and effectively limit the short circuit currents of the system.
文摘Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.
基金supported by State Key Laboratory of Power Transmission Equipment and System Security(No.2007DA10512711102,No.2007DA10512709202)Program of Introducing Talents of Discipline to Universities("111"Program)(No.B08036)the Fundamental Research Funds for the Central Universities(No.CDJXS11150026)
文摘Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a significant issue.However,the traditional calculation methods aiming at synchronous generators cannot be directly applied to the DFIG wind turbines.A new method is needed to calculate the short-circuit current required by the planning,protection and control of the power grid.The short-circuit transition of DFIG under symmetrical and asymmetric short-circuit conditions are mathematically deduced,and the short-circuit characteristics of DFIG are analyzed.A new method is proposed to calculate the steady-state short-circuit current of DFIG based on the derived expressions.The time-domain simulations are conducted to verify the accuracy of the proposed method.
基金supported by the Power Generation & Electricity Delivery of the Korea Institute of Energy Technology and Planning(KETEP)grant funded by the Korea Government Ministry of Knowledge Economy(No.2009T100200067)
文摘To study the effects of wind generators on distribution system protection,the short-circuit current(SCC) characteristics of wind generators is important.Although there are many researches on the issue,a clear agreement has not been reached so far.The SCC characteristics for different wind generators are studied.PSCAD simulation is performed in the same system integrated with different kinds of wind generators,and their results are compared with those reported in IEEE papers.The detection possibility by overcurrent relay(OCR)is discussed based on the simulation results.
文摘The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.
文摘It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and short-circuit impedance model of axial dual-low-voltage split-winding transformer is established, and then the 2D and 3D leakage magnetic field are analyzed. Secondly, the short-circuit impedance and split parallel branch current distribution in different working conditions are calculated, which is based on field-circuit coupled method. At last, effectiveness and feasibility of the proposed model is verified by comparison between experiment, analysis and simulation. The results showed that the 3D analysis method is a better approach to calculate the short-circuit impedance, since its analytical value is more closer to the experimental value compared with the 2D analysis results, the finite element method calculation error is less than 2%, while the leakage flux method maximum error is 7.2%.
基金supported by the Science and Technology Project of State Grid Corporation of China:Deepening Research and Application of Short-circuit Current Calculation Method in Power Electronics Dominated Power Systems(5100-202055439A-0-0-00)。
文摘For the past decades,practical calculation method of short circuit current(SCC)contributed by doubly fed induction generator(DFIG)under asymmetrical short circuit fault is deficient due to its control strategies and unlinear equipment.Asymmetrical SCC of DFIG is much more complicated and may be higher than that of a symmetrical fault in some situations.To address the problem,analytical derivations of SCC under asymmetrical faults are presented by establishing current equations between DFIG windings and converter controller or crowbar protection.Each frequency component could be directly extracted from time-domain expressions.Furthermore,clear mathematical models of asymmetrical peak and steady-state SCC used for practical calculation of power systems are proposed.Simulation results verify the effectiveness and robustness to different parameters and fault conditions of the proposed method.Finally,the influences of possible parameters on characteristics of asymmetrical SCC are summarized based on the proposed method.
