Decreasing costs and favorable policies have resulted in increased penetration of solar photovoltaic(PV)power generation in distribution networks.As the PV systems penetration is likely to increase in the future,utili...Decreasing costs and favorable policies have resulted in increased penetration of solar photovoltaic(PV)power generation in distribution networks.As the PV systems penetration is likely to increase in the future,utilizing the reactive power capability of PV inverters to mitigate voltage deviations is being promoted.In recent years,droop control of inverter-based distributed energy resources has emerged as an essential tool for use in this study.The participation of PV systems in voltage regulation and its coordination with existing controllers,such as on-load tap changers,is paramount for controlling the voltage within specified limits.In this work,control strategies are presented that can be coordinated with the existing controls in a distributed manner.The effectiveness of the proposed method was demonstrated through simulation results on a distribution system.展开更多
To enhance machining efficiency,tool change time has to be reduced.Thus,for an automatic tool changer attached to a machining center,the tool change time is to be reduced.Also the automatic tool changer is a main part...To enhance machining efficiency,tool change time has to be reduced.Thus,for an automatic tool changer attached to a machining center,the tool change time is to be reduced.Also the automatic tool changer is a main part of the machining center as a driving source.The static attributes of the automatic tool changer using the commercial code,ANSYS Workbench V12,were tried to interpret.And the optimum design of automatic tool changer arm was proposed by performing the multi-stage optimum design.The shape optimization of the automatic tool changer was proposed and the result was verified to obtain acceptable improvements.It is possible to obtain an optimized model in which the maximum deformation,maximum stress,and mass are reduced by 10.46%,12.89% and 9.26%,respectively,compared with those of the initial model.Also,the results between conventional method by the design of experiments and proposed method by the multi-stage optimum design method were compared.展开更多
A relation between heat transferred and energy loss, for turbulent flow. In different tube arrangements, is made. The conditions are determined which decide the dimensions and velocities for a heat exchanger. Also, a ...A relation between heat transferred and energy loss, for turbulent flow. In different tube arrangements, is made. The conditions are determined which decide the dimensions and velocities for a heat exchanger. Also, a reference to the economic dimensioning of heat exchangers is presented. In this study, the conditions which a heat exchanger must satisfy represent the best balance between the amounts of material employed. The investigation is restricted to the case of turbulent flow.展开更多
全球广播和媒体行业的盛会——NAB2016刚刚在美国拉斯维加斯落下帷幕。来自全世界的广播和媒体的从业者汇聚在这里,展示和交流最新的技术、产品和解决方案,共谋未来业务发展。索贝公司与SONY公司合作,向全球客户展示了基于HIVE的全新新...全球广播和媒体行业的盛会——NAB2016刚刚在美国拉斯维加斯落下帷幕。来自全世界的广播和媒体的从业者汇聚在这里,展示和交流最新的技术、产品和解决方案,共谋未来业务发展。索贝公司与SONY公司合作,向全球客户展示了基于HIVE的全新新闻制播系统Media Backbone HIVE,并一举摘取IABM Game Changer大奖!展开更多
XuetangX, the leading Chinese Massive Open Online Courses （MOOCs） platform created by Beijing-based Tsinghua University, has broken new ground yet again. After having reached more than 7 million users worldwide in M...XuetangX, the leading Chinese Massive Open Online Courses （MOOCs） platform created by Beijing-based Tsinghua University, has broken new ground yet again. After having reached more than 7 million users worldwide in May, XuetangX has now become the first Chinese MOOC platform to offer its online education services in Africa.展开更多
China Pakistan Economic Corridor （CPEC） is dreamed to be the game changer not only for China and Pakistan but other 50 regional, Middle East, Central Asian Republics, and European countries too. It is one of its kin...China Pakistan Economic Corridor （CPEC） is dreamed to be the game changer not only for China and Pakistan but other 50 regional, Middle East, Central Asian Republics, and European countries too. It is one of its kind a huge project with billion US$ investment by China. Since its inception, the internal controversies and disputes in Pakistan on the sharing of benefits as well as interests and concerns of the regional and international players are posing threats to it. The review article aims to investigate and analyze the strengths and weakness and opportunities and threats （SWOT） for CPEC. To analyze the qualitative data, a computer based software program ATLAS.ti was used by employing multiple methods like discourse, hermeneutics, and heuristic by Moustakas. The schematic model of the theoretical framework elaborates the association and impact between and on the dependent, independent, and mediating variables of the study. It was found that if the security, political support, internal and external threats, coordination and cooperation and involvement of stakeholders are properly addressed, the CPEC will bear the fruits.展开更多
With the growing demand for precise voltage adjustment and reactive regulation,the frequent operation of on-load tap changers(OLTCs)in oil-immersed systems has led to increased erosion of switch contacts by arcs durin...With the growing demand for precise voltage adjustment and reactive regulation,the frequent operation of on-load tap changers(OLTCs)in oil-immersed systems has led to increased erosion of switch contacts by arcs during the switching process.This erosion causes significant wear on the contacts,thereby reducing their lifespan.Therefore,the present study aims to investigate the behavior and mechanism of arc erosion on contact surfaces in oil-immersed OLTCs.To achieve this,a self-designed friction and wear test device for OLTC contacts was utilized to conduct experiments at various sliding speeds and contact pressures.Additionally,finite element analysis was employed to validate the experimental results regarding the influence of sliding speed on arc energy.The surface morphology of the contacts was observed using an optical microscope.The findings revealed that as the sliding speed increased,the arc energy,arc initiation rate,and contact resistance initially exhibited an upward trend,then decreased,and eventually increased again.The minimum values were observed at a sliding speed of 90 mm/s.Moreover,the arc energy,arc initiation rate,and contact resistance decreased gradually as the contact pressure increased.After reaching a contact pressure of 1.5 N,the variation in the arc energy stabilized.At lower contact pressures,arc erosion dominated the wear on the contact surface.However,at higher contact pressures,the wear transitioned from predominantly arc erosion to a combination of mechanical wear and arc erosion.In summary,experimental and analytical investigations provided insights into the effects of sliding speed and contact pressure on the behavior of arc erosion,contact resistance,and surface damage of OLTC contacts in oil-immersed systems.展开更多
基金by a project under the scheme entitled“Developing Policies&Adaptation Strategies to Climate Change in the Baltic Sea Region”(ASTRA),Project No.ASTRA6-4(2014-2020.4.01.16-0032).
文摘Decreasing costs and favorable policies have resulted in increased penetration of solar photovoltaic(PV)power generation in distribution networks.As the PV systems penetration is likely to increase in the future,utilizing the reactive power capability of PV inverters to mitigate voltage deviations is being promoted.In recent years,droop control of inverter-based distributed energy resources has emerged as an essential tool for use in this study.The participation of PV systems in voltage regulation and its coordination with existing controllers,such as on-load tap changers,is paramount for controlling the voltage within specified limits.In this work,control strategies are presented that can be coordinated with the existing controls in a distributed manner.The effectiveness of the proposed method was demonstrated through simulation results on a distribution system.
基金Work(RTI04-01-03) supported by Grant from Regional Technology Innovation Program of the Ministry of Knowledge Economy (MKE),Korea
文摘To enhance machining efficiency,tool change time has to be reduced.Thus,for an automatic tool changer attached to a machining center,the tool change time is to be reduced.Also the automatic tool changer is a main part of the machining center as a driving source.The static attributes of the automatic tool changer using the commercial code,ANSYS Workbench V12,were tried to interpret.And the optimum design of automatic tool changer arm was proposed by performing the multi-stage optimum design.The shape optimization of the automatic tool changer was proposed and the result was verified to obtain acceptable improvements.It is possible to obtain an optimized model in which the maximum deformation,maximum stress,and mass are reduced by 10.46%,12.89% and 9.26%,respectively,compared with those of the initial model.Also,the results between conventional method by the design of experiments and proposed method by the multi-stage optimum design method were compared.
文摘A relation between heat transferred and energy loss, for turbulent flow. In different tube arrangements, is made. The conditions are determined which decide the dimensions and velocities for a heat exchanger. Also, a reference to the economic dimensioning of heat exchangers is presented. In this study, the conditions which a heat exchanger must satisfy represent the best balance between the amounts of material employed. The investigation is restricted to the case of turbulent flow.
文摘全球广播和媒体行业的盛会——NAB2016刚刚在美国拉斯维加斯落下帷幕。来自全世界的广播和媒体的从业者汇聚在这里,展示和交流最新的技术、产品和解决方案,共谋未来业务发展。索贝公司与SONY公司合作,向全球客户展示了基于HIVE的全新新闻制播系统Media Backbone HIVE,并一举摘取IABM Game Changer大奖!
文摘XuetangX, the leading Chinese Massive Open Online Courses （MOOCs） platform created by Beijing-based Tsinghua University, has broken new ground yet again. After having reached more than 7 million users worldwide in May, XuetangX has now become the first Chinese MOOC platform to offer its online education services in Africa.
文摘China Pakistan Economic Corridor （CPEC） is dreamed to be the game changer not only for China and Pakistan but other 50 regional, Middle East, Central Asian Republics, and European countries too. It is one of its kind a huge project with billion US$ investment by China. Since its inception, the internal controversies and disputes in Pakistan on the sharing of benefits as well as interests and concerns of the regional and international players are posing threats to it. The review article aims to investigate and analyze the strengths and weakness and opportunities and threats （SWOT） for CPEC. To analyze the qualitative data, a computer based software program ATLAS.ti was used by employing multiple methods like discourse, hermeneutics, and heuristic by Moustakas. The schematic model of the theoretical framework elaborates the association and impact between and on the dependent, independent, and mediating variables of the study. It was found that if the security, political support, internal and external threats, coordination and cooperation and involvement of stakeholders are properly addressed, the CPEC will bear the fruits.
文摘With the growing demand for precise voltage adjustment and reactive regulation,the frequent operation of on-load tap changers(OLTCs)in oil-immersed systems has led to increased erosion of switch contacts by arcs during the switching process.This erosion causes significant wear on the contacts,thereby reducing their lifespan.Therefore,the present study aims to investigate the behavior and mechanism of arc erosion on contact surfaces in oil-immersed OLTCs.To achieve this,a self-designed friction and wear test device for OLTC contacts was utilized to conduct experiments at various sliding speeds and contact pressures.Additionally,finite element analysis was employed to validate the experimental results regarding the influence of sliding speed on arc energy.The surface morphology of the contacts was observed using an optical microscope.The findings revealed that as the sliding speed increased,the arc energy,arc initiation rate,and contact resistance initially exhibited an upward trend,then decreased,and eventually increased again.The minimum values were observed at a sliding speed of 90 mm/s.Moreover,the arc energy,arc initiation rate,and contact resistance decreased gradually as the contact pressure increased.After reaching a contact pressure of 1.5 N,the variation in the arc energy stabilized.At lower contact pressures,arc erosion dominated the wear on the contact surface.However,at higher contact pressures,the wear transitioned from predominantly arc erosion to a combination of mechanical wear and arc erosion.In summary,experimental and analytical investigations provided insights into the effects of sliding speed and contact pressure on the behavior of arc erosion,contact resistance,and surface damage of OLTC contacts in oil-immersed systems.
文摘随着配电网中分布式光伏(distributed photovoltaic,DPV)大量并网,电压越限和电压波动越来越严重,考虑新型电能质量治理装置的电压无功优化协调控制方法需要进一步完善,以适应电网的新变化。该文考虑了新型柔性有载调压变压器(on-load tap changer,OLTC)的电能质量调节作用,提出一种两阶段电压无功优化协调控制方法,其中一阶段为日前小时级调度阶段,根据分布式光伏和负荷的预测数据,通过潮流计算和迭代优化,获取DPV的有功出力结果、柔性OLTC分接头和电容器组的投切结果;二阶段为分钟级无功优化阶段,在第一阶段的基础上,考虑柔性OLTC和DPV的无功出力特性,调节装备无功出力的同时修正第一阶段电容器组投切组合,进一步降低各个节点最大电压偏差,使配电网电压分布更合理。搭建了IEEE33节点配电系统仿真模型,所提出的考虑柔性OLTC的两阶段电压无功优化协调控制方法能够在常规经济性最优目标下的88.07%DPV消纳水平基础上提高9.29%,同时满足全节点全时段电压偏差小于0.1pu,综合经济性提高7.8%,结果证明了所提方法的合理性和有效性。
