The horizontal block stripe,as an image quality defect,was analyzed by means of output signals and bias voltage stress(BVS)test.The results showed that the defect was correlated with discharging efficiency.Further,two...The horizontal block stripe,as an image quality defect,was analyzed by means of output signals and bias voltage stress(BVS)test.The results showed that the defect was correlated with discharging efficiency.Further,two approaches were proposed,one was to improve TFT characteristic,the other was to add reset function.The combined experiments indicated that discharging promotion can improve the defect.Especially the latter is most optimal to eliminate the phenomenon.展开更多
为提高单相动态电压恢复器（dynamic voltage restorer,DVR）的补偿性能,提出一种基于等效基波及奇次谐波谐振器组的数字控制方法。采用可等效为一组谐振器的延时模块,能够有效抑制电网基波和谐波扰动。给出一种包含两个控制参数和一组...为提高单相动态电压恢复器（dynamic voltage restorer,DVR）的补偿性能,提出一种基于等效基波及奇次谐波谐振器组的数字控制方法。采用可等效为一组谐振器的延时模块,能够有效抑制电网基波和谐波扰动。给出一种包含两个控制参数和一组零相移陷波滤波器的结构及其设计方法,使系统在保证稳定性的同时,获得较大的谐振增益。其中,延时环节衰减系数可增加谐振器组鲁棒性;控制器比例增益可解决零相移陷波器中使用延时带来的问题;零相移陷波器组既能对消LC谐振峰,也能解决等效谐振器组高增益在高频处的稳定性问题。同时,引入电源电压和负载电流双前馈来保证响应速度,增加了对扰动的抑制能力。所提控制策略结构简单,谐波补偿能力强,动态响应快,易于实现。在2kW单相DVR实验装置上的实验结果验证了该控制方法的正确性。展开更多
Distribution transformers operating in modern system grids or in industrial networks are subjected to many switching transients,which may occur due to routine operations,network reconfigurations or as reaction on prot...Distribution transformers operating in modern system grids or in industrial networks are subjected to many switching transients,which may occur due to routine operations,network reconfigurations or as reaction on protection signals.Depending on the network configuration and parameters,such events may lead to external overvoltages and result in additional stresses on the insulation system.This paper presents the influence of a series choke on damping of switching transients in distribution transformers.The impact of the choke is assessed by both amplitude and rise time reduction.The suppression of the transient rise time is shown for a test configuration involving distribution transformers connected to low loss cable lines and a medium voltage breaker.Such phenomena are especially typical for industrial networks where switching operations are very frequent.Both simulation and experiment results are given.Simulation results as well as measurement results confirmed that switching events can lead to high dU/dt and in consequence,can have adverse impacts on insulation system.Voltage escalation during switching event is strongly related with system conditions.The results obtained for presented mitigation method are promising and indicate significant dU/dt reduction as well as number of ignitions and voltage peak value.The protection of distribution transformers with a series choke is a new approach dedicated to environments prone to the occurrence of transients with high steepness.Experimental results show that the application of serial choke with suitable parameters realizes the reduction of dU/dt at the machines terminal from 24 kV/μs to 5 kV/μs,as well as the reduction of voltage peak value from 10 kV to 5 kV.The number of ignitions is also reduced.展开更多
Electrical power transmission is dominated by overhead line systems at present.This is mainly based on more than hundred years of experience of utilities in running overhead lines.Furthermore,overhead lines have prove...Electrical power transmission is dominated by overhead line systems at present.This is mainly based on more than hundred years of experience of utilities in running overhead lines.Furthermore,overhead lines have proven their operational reliability and functional assurance.In the past,cables were used in distribution networks in urban areas for the most part with the exception of direct current submarine cables.New developments of high voltage XLPE cables make it possible to use this technology for EHV level applications in transmission networks.Within this paper,mixed network configurations,consisting of overhead lines and high voltage cables,are investigated.An exemplary EHV transmission line with a total length of about 100 km,which is quite typical for Central Europe,has been studied.Several different line combinations are discussed with varied rates between overhead line sections and cable sections length in practice.The length of the cable sections are ranging from several kilometers up to lengths of 100 km.In this paper the work focuses on the transient behavior of combined 400 kV overhead and cable lines during switching processes and lightning impacts.A number of calculations were carried out to get an overview of the transient stress in numerous network nodes along the transmission system.Numerical programs like ATP/EMTP have been used for these simulations.Peak values and wave shapes of the transient voltage stress have been evaluated,based on different systems and within possible combinations.In respect of the insulation coordination and transient stress at network nodes,the voltage-time trends are also analyzed.The combination of high voltage overhead and cable transmission systems,especially such with lengths of more than about 50 km,are making tightened and extended demands to the network design,to the operational management and of course to the network protection also.As an output of this investigations,the results might influence the strategy in running this new type of combined transmission systems.展开更多
文摘The horizontal block stripe,as an image quality defect,was analyzed by means of output signals and bias voltage stress(BVS)test.The results showed that the defect was correlated with discharging efficiency.Further,two approaches were proposed,one was to improve TFT characteristic,the other was to add reset function.The combined experiments indicated that discharging promotion can improve the defect.Especially the latter is most optimal to eliminate the phenomenon.
文摘为提高单相动态电压恢复器（dynamic voltage restorer,DVR）的补偿性能,提出一种基于等效基波及奇次谐波谐振器组的数字控制方法。采用可等效为一组谐振器的延时模块,能够有效抑制电网基波和谐波扰动。给出一种包含两个控制参数和一组零相移陷波滤波器的结构及其设计方法,使系统在保证稳定性的同时,获得较大的谐振增益。其中,延时环节衰减系数可增加谐振器组鲁棒性;控制器比例增益可解决零相移陷波器中使用延时带来的问题;零相移陷波器组既能对消LC谐振峰,也能解决等效谐振器组高增益在高频处的稳定性问题。同时,引入电源电压和负载电流双前馈来保证响应速度,增加了对扰动的抑制能力。所提控制策略结构简单,谐波补偿能力强,动态响应快,易于实现。在2kW单相DVR实验装置上的实验结果验证了该控制方法的正确性。
文摘Distribution transformers operating in modern system grids or in industrial networks are subjected to many switching transients,which may occur due to routine operations,network reconfigurations or as reaction on protection signals.Depending on the network configuration and parameters,such events may lead to external overvoltages and result in additional stresses on the insulation system.This paper presents the influence of a series choke on damping of switching transients in distribution transformers.The impact of the choke is assessed by both amplitude and rise time reduction.The suppression of the transient rise time is shown for a test configuration involving distribution transformers connected to low loss cable lines and a medium voltage breaker.Such phenomena are especially typical for industrial networks where switching operations are very frequent.Both simulation and experiment results are given.Simulation results as well as measurement results confirmed that switching events can lead to high dU/dt and in consequence,can have adverse impacts on insulation system.Voltage escalation during switching event is strongly related with system conditions.The results obtained for presented mitigation method are promising and indicate significant dU/dt reduction as well as number of ignitions and voltage peak value.The protection of distribution transformers with a series choke is a new approach dedicated to environments prone to the occurrence of transients with high steepness.Experimental results show that the application of serial choke with suitable parameters realizes the reduction of dU/dt at the machines terminal from 24 kV/μs to 5 kV/μs,as well as the reduction of voltage peak value from 10 kV to 5 kV.The number of ignitions is also reduced.
文摘Electrical power transmission is dominated by overhead line systems at present.This is mainly based on more than hundred years of experience of utilities in running overhead lines.Furthermore,overhead lines have proven their operational reliability and functional assurance.In the past,cables were used in distribution networks in urban areas for the most part with the exception of direct current submarine cables.New developments of high voltage XLPE cables make it possible to use this technology for EHV level applications in transmission networks.Within this paper,mixed network configurations,consisting of overhead lines and high voltage cables,are investigated.An exemplary EHV transmission line with a total length of about 100 km,which is quite typical for Central Europe,has been studied.Several different line combinations are discussed with varied rates between overhead line sections and cable sections length in practice.The length of the cable sections are ranging from several kilometers up to lengths of 100 km.In this paper the work focuses on the transient behavior of combined 400 kV overhead and cable lines during switching processes and lightning impacts.A number of calculations were carried out to get an overview of the transient stress in numerous network nodes along the transmission system.Numerical programs like ATP/EMTP have been used for these simulations.Peak values and wave shapes of the transient voltage stress have been evaluated,based on different systems and within possible combinations.In respect of the insulation coordination and transient stress at network nodes,the voltage-time trends are also analyzed.The combination of high voltage overhead and cable transmission systems,especially such with lengths of more than about 50 km,are making tightened and extended demands to the network design,to the operational management and of course to the network protection also.As an output of this investigations,the results might influence the strategy in running this new type of combined transmission systems.
