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
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.
