VFDs （variable frequency drives） are an integral part of many industrial plants and stations. Reliable operation and maintenance of these drives is vital to ensure sustained plant operation and availability. Underst...VFDs （variable frequency drives） are an integral part of many industrial plants and stations. Reliable operation and maintenance of these drives is vital to ensure sustained plant operation and availability. Understanding of the principles of operation of VFD systems as well as knowledge about their required operating environment is necessary for all operating personnel. Many times the operating personnel do not get involved with different technical issues until a complete failure has occurred. Hence, the awareness of the most dominant failure causes has a significant impact on assisting operators to avoid catastrophic failures and tremendous economic losses due to VFD shutdown. Proper plant design, accurate monitoring and data logging, following manufacturer preventive maintenance schedule, and choosing qualified team of operators can be the key to an efficient operation and a long lifetime for any VFD system. In this paper, we have analyzed the electrical and non-electrical causes of VFD failures based on a case study of a typical medium voltage VFD pumping station. Finally, recommendations are given from field analysis and observations.展开更多
Non-electric welding is a novel efficient technique for emergency maintenance, which utilizes the heat released by self-propagating combustion to join metals without needing arty power supply or gas sources. Non-elect...Non-electric welding is a novel efficient technique for emergency maintenance, which utilizes the heat released by self-propagating combustion to join metals without needing arty power supply or gas sources. Non-electric welding material, named non-electric welding pen, was prepared by utilizing highly-exothermic thermit （ Cud ＋ Al） with other additive powders. The effects of reactant particle size and mixing uniformity on the combustion characteristic of the welding pen were investigated. The results show that the particle size of reactant powder has a significant effect on combustion velocity. With increasing the particle size of reactant powder, the combustion velocity decreases obviously. Moreover, mixing uniformity and particle size are shown to be main factors influencing heat produced in single time, and accordingly affect the combustion temperature. Welding experiments were performed with 45 steel as the base material, and results show that the joint is of a metallurgie bonding with the tensile strength above 280 MPa, which proves non-electric welding a fusion welding technique.展开更多
Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtai...Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.展开更多
The Jiaoshiba shale gasfield is located in the Fuling area of the Sichuan Basin,with the Upper Ordovician Wufeng-Lower Silurian Longmaxi Fm as the pay zone.At the bottom of the pay zone,a high-quality shale gas reserv...The Jiaoshiba shale gasfield is located in the Fuling area of the Sichuan Basin,with the Upper Ordovician Wufeng-Lower Silurian Longmaxi Fm as the pay zone.At the bottom of the pay zone,a high-quality shale gas reservoir about 20 m thick is generally developed with high organic contents and gas abundance,but its resistivity is relatively low.Accordingly,the gas saturation calculated by formulas(e.g.Archie)using electric logging data is often much lower than the experiment-derived value.In this paper,a new method was presented for calculating gas saturation more accurately based on non-electric logging data.Firstly,the causes for the low resistivity of shale gas reservoirs in this area were analyzed.Then,the limitation of traditional methods for calculating gas saturation based on electric logging data was diagnosed,and the feasibility of the neutronedensity porosity overlay method was illustrated.According to the response characteristics of neutron,density and other porosity logging in shale gas reservoirs,a model for calculating gas saturation of shale gas was established by core experimental calibration based on the density logging value,the density porosity and the difference between density porosity and neutron porosity,by means of multiple methods(e.g.the dual-porosity overlay method by optimizing the best overlay coefficient).This new method avoids the effect of low resistivity,and thus can provide normal calculated gas saturation of high-quality shale gas reservoirs.It works well in practical application.This new method provides a technical support for the calculation of shale gas reserves in this area.展开更多
In the field of power systems,insulating polymers have been found to have extensive applications due to their outstanding properties.However,these materials are susceptible to defects arising from various factors duri...In the field of power systems,insulating polymers have been found to have extensive applications due to their outstanding properties.However,these materials are susceptible to defects arising from various factors during production and operation,which may progress and potentially lead to safety incidents.This paper comprehensively reviews non-destructive testing(NDT)techniques for insulating polymers.Based on the physical principles underlying these methods,they are categorized into electrical testing methods,non-electrical passive testing methods,and non-electrical active testing methods.The paper offers a retrospective assessment of the applications of these methods in insulating polymers.Finally,evaluation of the applicability,advantages,and limitations of these diverse methods is systematically conducted,aiming to facilitate the targeted selection of the optimal NDT method in engineering applications.展开更多
文摘VFDs （variable frequency drives） are an integral part of many industrial plants and stations. Reliable operation and maintenance of these drives is vital to ensure sustained plant operation and availability. Understanding of the principles of operation of VFD systems as well as knowledge about their required operating environment is necessary for all operating personnel. Many times the operating personnel do not get involved with different technical issues until a complete failure has occurred. Hence, the awareness of the most dominant failure causes has a significant impact on assisting operators to avoid catastrophic failures and tremendous economic losses due to VFD shutdown. Proper plant design, accurate monitoring and data logging, following manufacturer preventive maintenance schedule, and choosing qualified team of operators can be the key to an efficient operation and a long lifetime for any VFD system. In this paper, we have analyzed the electrical and non-electrical causes of VFD failures based on a case study of a typical medium voltage VFD pumping station. Finally, recommendations are given from field analysis and observations.
文摘Non-electric welding is a novel efficient technique for emergency maintenance, which utilizes the heat released by self-propagating combustion to join metals without needing arty power supply or gas sources. Non-electric welding material, named non-electric welding pen, was prepared by utilizing highly-exothermic thermit （ Cud ＋ Al） with other additive powders. The effects of reactant particle size and mixing uniformity on the combustion characteristic of the welding pen were investigated. The results show that the particle size of reactant powder has a significant effect on combustion velocity. With increasing the particle size of reactant powder, the combustion velocity decreases obviously. Moreover, mixing uniformity and particle size are shown to be main factors influencing heat produced in single time, and accordingly affect the combustion temperature. Welding experiments were performed with 45 steel as the base material, and results show that the joint is of a metallurgie bonding with the tensile strength above 280 MPa, which proves non-electric welding a fusion welding technique.
基金Supported by the National Natural Science Foundation of China （No.20425619）.
文摘Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.
文摘The Jiaoshiba shale gasfield is located in the Fuling area of the Sichuan Basin,with the Upper Ordovician Wufeng-Lower Silurian Longmaxi Fm as the pay zone.At the bottom of the pay zone,a high-quality shale gas reservoir about 20 m thick is generally developed with high organic contents and gas abundance,but its resistivity is relatively low.Accordingly,the gas saturation calculated by formulas(e.g.Archie)using electric logging data is often much lower than the experiment-derived value.In this paper,a new method was presented for calculating gas saturation more accurately based on non-electric logging data.Firstly,the causes for the low resistivity of shale gas reservoirs in this area were analyzed.Then,the limitation of traditional methods for calculating gas saturation based on electric logging data was diagnosed,and the feasibility of the neutronedensity porosity overlay method was illustrated.According to the response characteristics of neutron,density and other porosity logging in shale gas reservoirs,a model for calculating gas saturation of shale gas was established by core experimental calibration based on the density logging value,the density porosity and the difference between density porosity and neutron porosity,by means of multiple methods(e.g.the dual-porosity overlay method by optimizing the best overlay coefficient).This new method avoids the effect of low resistivity,and thus can provide normal calculated gas saturation of high-quality shale gas reservoirs.It works well in practical application.This new method provides a technical support for the calculation of shale gas reserves in this area.
基金supported in part by the National Natural Science Foundation of China under Grant 51977117 and 51977118.
文摘In the field of power systems,insulating polymers have been found to have extensive applications due to their outstanding properties.However,these materials are susceptible to defects arising from various factors during production and operation,which may progress and potentially lead to safety incidents.This paper comprehensively reviews non-destructive testing(NDT)techniques for insulating polymers.Based on the physical principles underlying these methods,they are categorized into electrical testing methods,non-electrical passive testing methods,and non-electrical active testing methods.The paper offers a retrospective assessment of the applications of these methods in insulating polymers.Finally,evaluation of the applicability,advantages,and limitations of these diverse methods is systematically conducted,aiming to facilitate the targeted selection of the optimal NDT method in engineering applications.
