The coupled dynamic characteristics of the conical electromagnetic bearing are presented and their definitions are given. On the basis of the analyses of the characteristics, the dynamic model of five degrees of freed...The coupled dynamic characteristics of the conical electromagnetic bearing are presented and their definitions are given. On the basis of the analyses of the characteristics, the dynamic model of five degrees of freedom (five-DOF) rotor-conical electromagnetic bearing system is made, and the influence of the coupled characteristics on the system optimal controller is analyzed.展开更多
Substations have a large number of signal transmission cables beneath the ground.Both the insulation safety and signal reliability of the cables are affected severely by the electromagnetic field.Under high-amplitude ...Substations have a large number of signal transmission cables beneath the ground.Both the insulation safety and signal reliability of the cables are affected severely by the electromagnetic field.Under high-amplitude impulsive currents,the dispersion of currents can cause soil discharge and thus cause unexpected distortions in an electromagnetic field.This paper focuses on the distortions of the electric field.In general,soil discharge channels occur in the vicinity of the independent rod.Closer development of the channel might enhance the electric field distribution and the potential surrounding the outer insulation of the cables(i.e.the surface potential on the cable).Therefore,this paper establishes a platform for observing the soil discharge channel and measuring the surface potential.Direction characteristic of the channel is extracted from the captured image of soil discharge channels and the surface potential is obtained by the measured coupling capacitive current on the shield experimentally.This paper also presents an improved model considering a dynamic growing discharge channel for the transient analysis of the grounding electrode.Study results show the surface potential increases as the discharge channel approaches the cable.To quantify this enhancement effect,the ratio of the highest to the lowest value of surface potential in different directions is taken as the multiple of the surface potential increase.The calculated multiples of the surface potential increase are in the range of 1 to 1.64 times under different conditions by the improved model.Therefore,taking the soil discharge channel into account is helpful to accurately analyze the impulsive interference of buried cables.展开更多
This paper introduces a novel hybrid FEM-BEM method for calculating 3D eddy cur-rent field. In the eddy current region, the eddy current density J is solved by the finite element method (FEM) which is discretized by b...This paper introduces a novel hybrid FEM-BEM method for calculating 3D eddy cur-rent field. In the eddy current region, the eddy current density J is solved by the finite element method (FEM) which is discretized by brick finite element mesh, while in the eddy current free re-gion, the magnetic field intensity H is solved by the boundary element method (BEM) which is dis-cretized by rectangular boundary element mesh. Under the boundary conditions, an algebraic equation group is obtained that only includes J by eliminating H. This method has many advan-tages over traditional ones, such as fewer variables, more convenient coupling between the FEM and the BEM and wider application to multiply-connected regions. The calculated values of two models are in good agreement with experimental results. This shows the validity of our method.展开更多
The parallel-wound technique is an effective method for reducing charging delay and enhancing electromagnetic margin of no-insulation high-temperature superconducting(NI HTS)coils,as demonstrated by both experiments a...The parallel-wound technique is an effective method for reducing charging delay and enhancing electromagnetic margin of no-insulation high-temperature superconducting(NI HTS)coils,as demonstrated by both experiments and numerical simulations.From an engineering standpoint,the parallel-wound design also mitigates the constraint of individual conductor length,which is a significant limitation in large-scale coils requiring a single continuous conductor of the same specifications.However,traditional electromagnetic modeling of parallel-wound no-insulation(PWNI)HTS coils relies on equivalent circuit models,and a combined finite element model is required to capture the screening current characteristics of HTS coated conductors.The mutual invo-cation between circuit models and finite element models increases the technical demands on simulation engi-neers and complicates the analysis of electromagnetic interactions with other physical fields.To address these challenges,we first propose an axisymmetric distributed equivalent circuit model for PWNI HTS double pancake(DP)coils.The equivalent circuit model is then integrated directly into the finite element framework of T-A formulation,resulting in a streamlined electromagnetic finite element model.The validity of this model is confirmed through the charging and discharging experiments with a dual-wound NI HTS coil.Utilizing this model,we further investigate the effects of joint resistance and turn-to-turn contact resistivity on the electro-magnetic characteristics of PWNI HTS coils.Additionally,the excitation loss and stress of multiple PWNI HTS DP coils in a 35 T all-superconducting high field magnet are also analyzed.The results indicate that both the lower turn-to-turn contact resistivity and joint resistance may lead to significant non-uniform currents within the coil.The joint resistance has a significant impact on the critical current of PWNI HTS coils,and the optimization of energization methodology increased the critical current of the experimental coil by 12 A.Enhancing the equivalent radial resistance between bundled turns proves more effective for reducing charging delay of PWNI coil than increasing that within bundled turns.Multiple PWNI coils in high field magnet exhibit elevated losses relative to single-tape equivalents due to coupling currents,particularly during the initial excitation.However,their peak strain accumulation is marginally lower than that of single-wound configuration.展开更多
文摘The coupled dynamic characteristics of the conical electromagnetic bearing are presented and their definitions are given. On the basis of the analyses of the characteristics, the dynamic model of five degrees of freedom (five-DOF) rotor-conical electromagnetic bearing system is made, and the influence of the coupled characteristics on the system optimal controller is analyzed.
基金supported by the National Natural Science Foundation of China(51777020)supported by the Science and Technology Project of State Grid Corporation of China(“Study on the Transient Characteristics of Grounding System and the Test and Evaluation Method of Current Dispersion Performance Under the Successive Impulse Current”,5500-202026088A-0-0-00)。
文摘Substations have a large number of signal transmission cables beneath the ground.Both the insulation safety and signal reliability of the cables are affected severely by the electromagnetic field.Under high-amplitude impulsive currents,the dispersion of currents can cause soil discharge and thus cause unexpected distortions in an electromagnetic field.This paper focuses on the distortions of the electric field.In general,soil discharge channels occur in the vicinity of the independent rod.Closer development of the channel might enhance the electric field distribution and the potential surrounding the outer insulation of the cables(i.e.the surface potential on the cable).Therefore,this paper establishes a platform for observing the soil discharge channel and measuring the surface potential.Direction characteristic of the channel is extracted from the captured image of soil discharge channels and the surface potential is obtained by the measured coupling capacitive current on the shield experimentally.This paper also presents an improved model considering a dynamic growing discharge channel for the transient analysis of the grounding electrode.Study results show the surface potential increases as the discharge channel approaches the cable.To quantify this enhancement effect,the ratio of the highest to the lowest value of surface potential in different directions is taken as the multiple of the surface potential increase.The calculated multiples of the surface potential increase are in the range of 1 to 1.64 times under different conditions by the improved model.Therefore,taking the soil discharge channel into account is helpful to accurately analyze the impulsive interference of buried cables.
文摘This paper introduces a novel hybrid FEM-BEM method for calculating 3D eddy cur-rent field. In the eddy current region, the eddy current density J is solved by the finite element method (FEM) which is discretized by brick finite element mesh, while in the eddy current free re-gion, the magnetic field intensity H is solved by the boundary element method (BEM) which is dis-cretized by rectangular boundary element mesh. Under the boundary conditions, an algebraic equation group is obtained that only includes J by eliminating H. This method has many advan-tages over traditional ones, such as fewer variables, more convenient coupling between the FEM and the BEM and wider application to multiply-connected regions. The calculated values of two models are in good agreement with experimental results. This shows the validity of our method.
基金supported by the Natural Science Foundation of China(Grant No.52325701,52293421,52293422,52277032)Beijing Nova Program(20220484102).
文摘The parallel-wound technique is an effective method for reducing charging delay and enhancing electromagnetic margin of no-insulation high-temperature superconducting(NI HTS)coils,as demonstrated by both experiments and numerical simulations.From an engineering standpoint,the parallel-wound design also mitigates the constraint of individual conductor length,which is a significant limitation in large-scale coils requiring a single continuous conductor of the same specifications.However,traditional electromagnetic modeling of parallel-wound no-insulation(PWNI)HTS coils relies on equivalent circuit models,and a combined finite element model is required to capture the screening current characteristics of HTS coated conductors.The mutual invo-cation between circuit models and finite element models increases the technical demands on simulation engi-neers and complicates the analysis of electromagnetic interactions with other physical fields.To address these challenges,we first propose an axisymmetric distributed equivalent circuit model for PWNI HTS double pancake(DP)coils.The equivalent circuit model is then integrated directly into the finite element framework of T-A formulation,resulting in a streamlined electromagnetic finite element model.The validity of this model is confirmed through the charging and discharging experiments with a dual-wound NI HTS coil.Utilizing this model,we further investigate the effects of joint resistance and turn-to-turn contact resistivity on the electro-magnetic characteristics of PWNI HTS coils.Additionally,the excitation loss and stress of multiple PWNI HTS DP coils in a 35 T all-superconducting high field magnet are also analyzed.The results indicate that both the lower turn-to-turn contact resistivity and joint resistance may lead to significant non-uniform currents within the coil.The joint resistance has a significant impact on the critical current of PWNI HTS coils,and the optimization of energization methodology increased the critical current of the experimental coil by 12 A.Enhancing the equivalent radial resistance between bundled turns proves more effective for reducing charging delay of PWNI coil than increasing that within bundled turns.Multiple PWNI coils in high field magnet exhibit elevated losses relative to single-tape equivalents due to coupling currents,particularly during the initial excitation.However,their peak strain accumulation is marginally lower than that of single-wound configuration.
