Effects of stainless steel thickness and winding tension on electrical and thermal characteristics of metal insulation racetrack coils for 10-MW-class HTS wind generator

The double-layer metal-insulation method using the brass sheets as the double-layer insulators was proposed in this paper. It can enhance the contact resistivity while reserving greater thermal conductivity merit. The underlying mechanism of the contact resistivity enhancement is to increase the number of contact surfaces and to degrade the contact quality between the insulators. Then, we wound a single-layer brass-insulation coil and a double-layer brass-insulation coil to compare their contact resistivities and confirmed the effectiveness of the double-layer metal-insulation method. Besides, since the capacity withstanding the overcurrent is weakened with the increscent contact resistance of the metal-insulation coil, we further investigated the influence of the contact surface resistivity distribution on the coil performance under different scenarios to optimize the double-layer metal-insulation coil for receiving a superior thermal stability. Simulation results indicated that the coil possessed the dominated 2nd contact surface resistivity and minimum 1st and 3rd contact resistivity is the optimal design for the double-layer metal-insulation coil to receive the best thermal stability, irrespective of the cooling environment, contact resistivity magnitude, operating current and coil dimension. In addition, in regard to the thermal performance differences caused by the contact surface resistivity distribution, we found that the increment of contact surface resistivity and the overcurrent would enlarge the distinctions at different levels.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Performance enhancement of coated conductor magnet with double-layer metal insulation

Wang

Zhou

et al. 2023

“…It is concluded that the magnetic behaviors of REBCO magnets in the asynchronous operation should be considered to enhance the prediction accuracy in the I c , which is affected by external RMFs. [24,[37][38][39][40][41][42][43]. The equivalent circuit of the NI and MI magnets can be expressed by adding the parallel resistance (i.e., the characteristic resistance (R c )), in the equivalent circuit of the insulated magnet.…”

Section: Numerical Analysismentioning

confidence: 99%

“…Novel electrical insulation winding techniques, such as noinsulation (NI) and metal insulation (MI), in which an insulation material is completely removed between turns and electrically and thermally conductive metals are inserted between turns, respectively, have been proposed to improve the stability of REBCO magnets by solving the stability problem of insulation magnets [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. However, their behaviors under an unsynchronized magnetic field have not yet been studied and reported.…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic characteristic analysis of a REBCO magnet with a current bypass/distribution winding technique under an asynchronous rotating magnetic field

Chae¹,

Kim²,

Quach³

et al. 2022

Self Cite

Generally, high-temperature superconducting rotating machines (HTSRMs) are considered synchronous machines. If the output of the HTSRM fluctuates based on frequent changes in the electrical or mechanical loads, there is the concern that an asynchronous rotating magnetic field (RMF) is applied from the stationary copper armature winding to the high-temperature superconducting (HTS) field winding in the rotary. This may act as a magnetic disturbance to the HTS field magnet, resulting in permanent damage. To enhance the reliability of HTS magnets in wind power and electric propulsion applications, winding methods with current bypass/distribution characteristics, such as no-insulation (NI) and metal-insulation (MI), have attracted scholarly attention because of their high thermal and electrical stabilities, resulting in their self-stabilizing and protective performances. To verify the feasibility of the NI and MI winding techniques for wind power generators, the basic characteristics under a time-varying magnetic field must be studied, contrary to HTS magnet applications under a time-static magnetic field. Therefore, the electromagnetic characteristics of rare-earth barium copper oxide (REBCO) magnets applied with NI and MI winding technologies were compared and analyzed in this study, considering the magnetically transient situations in which an asynchronous RMF is applied to REBCO magnets. In addition, we developed a characteristic evaluation device similar to a synchronous rotating machine to generate the unsynchronized RMF. Moreover, various basic tests were performed to target the small racetrack-type field windings. The critical current, n-value, terminal voltage, and center magnetic field are investigated under various values of the frequency and current amplitude of the three-phase armature winding, and their behaviors are discussed in detail based on the characteristic resistances of the two test magnets.

“…Moreover, the metal-insulation coil with a thicker insulator possesses a larger critical current, could bring out a higher thermal margin accordingly, and thus promote the thermal stability, which is confirmed by the minimal temperature rise among these selected insulator thicknesses in the overcurrent process. Meanwhile, a thicker insulator can enhance its thermal capacity to absorb more energy from the hot spots as well and further improve the thermal stability of the coils [38]. All in all, for the scene emphasizing thermal stability primarily, a thicker insulator is preferable.…”

Section: The Influence Of Metallic Insulator Thicknessmentioning

confidence: 99%

Thermo-electromagnetic modeling of coated superconductor coils with metal insulation

Wang

Zhou

et al. 2021

The use of metallic sheets as the insulator in a coated superconductor coil is able to increase its turn-to-turn contact resistance for shortening the charging/discharging delay while preserving the self-protection ability. To theoretically understand and predict the properties of the metal-insulation coils, we developed a thermo-electromagnetic model, in which a modified equivalent circuit for electrically representing the metal-insulation coils is built to take the effect of insulator into account. The effectiveness and versatility of this model are verified by different experimental scenarios, e.g., charging, sudden-discharging, and overcurrent. Enabled by the validated model, we carried out a set of case studies and observed that, (a) the metal-insulation coil with a low resistivity and high thermal conductivity metallic insulator is preferable to achieve a better thermal stability; (b) there exists an optimal insulator thickness for realizing the shortest charging delay, but a thicker insulator is superior for realizing a stronger thermal stability; (c) contact resistivity of over 104 μΩ· cm2 can weaken the current sharing in the radial direction, which would deteriorate the thermal stability of the metal-insulation coils, although it can significantly suppress the charging delay, implying that a tradeoff is always needed to balance the charging delay and thermal stability when determining the contact resistivity. These findings, mostly being inaccessible from the experiments, provide guidance toward practical applications of metal-insulated coated superconductor coils.