Design Optimization of High Temperature Superconducting Magnets and Null-Flux Coils for Electrodynamic Suspension Train

Self Cite

The no-insulation (NI) winding technique is promising to be applied in the persistent-current mode (PCM) operation of high-temperature superconducting (HTS) coils to provide those advantages. To apply the NI PCM coil, its demagnetization behaviour (i.e., decay of persistent DC current) by external AC field, which occurs in maglev trains, electric machines, and other dynamic magnet systems, is essential to be understood. For this purpose, a 3D FEM model, capturing the full electromagnetic properties of NI HTS coils, is established. This work has studied three kinds of AC fields, observing the impact of turn-to-turn contact resistivity on demagnetization rates, which is attributed to current distribution modulations. Under transverse AC field, the lower contact resistivity attracts more transport current to flow in the radial pathway to bypass the ‘dynamic resistance’ generated in the superconductor, leading to slower demagnetization. Under axial AC field, the demagnetization rate exhibits a non-monotonic relation with the contact resistivity: (1) the initial decrease of contact resistivity leads to concentration of induced AC current on the outer turns, which accelerates the demagnetization; (2) the further decrease of contact resistivity makes the current smartly redistribute to avoid to flow through the loss-concentrated outer turns, thus slowing down the demagnetization. Under the rotating DC field, a hybrid of the transverse and axial fields, the impact of contact resistivity on the demagnetization rate exhibits combined characteristics of the transverse and axial components. Besides, quantitative prediction on the demagnetization rate of NI PCM coil under external AC field is instructive for practical designs and operations, which is tried by this 3D FEM model, and a comparison with experimental result is conducted.

Section: Introductionmentioning

confidence: 98%

Study of the demagnetization behavior of no-insulation persistent-current mode HTS coils under external AC fields by 3D FEM simulation

Zhong,

Wu,

et al. 2024

Self Cite

“…superconducting magnetic energy storage (SMES) [21][22][23], and superconducting maglev [24][25][26][27]. However, HTS magnets wound from CCs suffer from more severe quench problems than their LTS counterparts, due to the relatively low quench zone propagation velocity of CCs [1,2,28].…”

Section: Introductionmentioning

confidence: 99%

A quench detection method for parallel co-wound HTS coils based on current redistribution

Hu,

Lin,

Tan

et al. 2024

High-temperature superconducting (HTS) coated conductors (CCs) have become the preferred material for superconducting magnet applications due to their high engineering current density and high mechanical strength. However, due to low quench zone propagation velocity of CCs, magnets wound with CCs suffered from severe quench risks. Therefore, a rapid, sensitive, and reliable quench detection method is crucial for the safe operation of such HTS magnets. In this paper, we propose a quench detection method based on current redistribution, in which two pieces of HTS CCs are soldered together at each end and insulated in the middle part. then parallel co-wound into a double-pancake coil. The two tightly coupled windings and low resistance joints form a very low inductance current loop, resulting in fast current redistribution between the two co-windings even at at inception of quench ( with still low quench voltage ). We deducted analytical solutions of the current redistribution process under different magnet operational scenarios, including constant current operation, charging and discharging, and proposed quench detection criteria. Corresponding quench tests were done on a small scale co-wound HTS coil, and results well verified the analytical solutions and the effectiveness of the quench detection method. The work may be useful for lowering the risk of HTS magnet quench in various applications.

“…HTS magnets can experience considerable transverse (also referred to as 'crossed' in some publications) AC fields in some applications [9,[30][31][32][33][34][35]. In synchronous machines, the transverse AC field in the moving direction of the rotor and the axial AC field are the two principal components felt by the HTS coil [36,37]. Figure 3 shows HTS coils experiencing transverse AC fields in an axial-flux-type rotating machine (see the upper part) [29,38], and in a linear synchronous machine or maglev train (see the lower part) [36,37].…”

Section: Introductionmentioning

confidence: 99%

“…In synchronous machines, the transverse AC field in the moving direction of the rotor and the axial AC field are the two principal components felt by the HTS coil [36,37]. Figure 3 shows HTS coils experiencing transverse AC fields in an axial-flux-type rotating machine (see the upper part) [29,38], and in a linear synchronous machine or maglev train (see the lower part) [36,37]. Otherwise, the axial AC field effect has been studied in a recent publication [25].…”

Section: Introductionmentioning

confidence: 99%

Time-variant magnetic field, voltage, and loss of no-insulation (NI) HTS magnet induced by dynamic resistance generation from external AC fields

Zhong

et al. 2023

High-temperature superconducting (HTS) coils serving as DC magnets can be operated under non-negligible AC fields, like in synchronous machines of maglev trains and wind turbines. In these conditions, dynamic resistance generates in HTS tapes, causing redistribution/bypassing of the transport current inside the no-insulation (NI) coil and its unique operational features. This issue was studied by experiments on an NI coil with DC current supply put into external AC fields. Due to the current redistribution induced by dynamic resistance, the central magnetic field and voltage of the NI magnet initially undergo various transient processes, and eventually exhibit a stable central magnetic field reduction and a DC voltage. These time evolutions have implications for a time-varying torque and loss of an HTS machine. These time evolutions are strongly affected by the contact resistivity distribution, and whether it is the first time of the NI magnet being exposed to the AC field, showing several qualitatively different waveforms (e.g., some are even non-monotonic with time). The magnitudes of the stable central field reductions, and their observed linear correlation with the DC voltages are found to be decided by the local contact resistivity of the innermost and outermost several turns. It is also noted that the non-insulated turn-to-turn contact help lessening the loss induced by the dynamic resistance. A numerical model is established to analyse/explain those experimental results by observing the microscopic current distribution. Two risks of quench are noticed: (i) azimuthal current of the middle part turns increases as the AC field is applied; (ii) a concentration of radial current is observed near the terminals of the NI coil.