HTS Wind Power Generator: Electromagnetic Force Between No-Insulation and Insulation Coils Under Time-Varying Conditions (original) (raw)
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Dynamic Response of No-Insulation and Partial-Insulation Coils for HTS Wind Power Generator
IEEE Transactions on Applied Superconductivity, 2015
In this paper, we present results, experimental and numerical, of the electromagnetic interaction forces between pairs of racetrack coils under time-varying conditions. Three turn-toturn insulation designs were applied to wind three racetrack coils with GdBCO coated conductor: 1) no insulation (NI); 2) partial insulation (PI) of a polyimide layer every eight turns; and 3) insulation (INS) of a polyimide layer between each, i.e., NI, PI, and INS racetracks. Two racetrack pairs, namely, NI-INS and PI-INS, were tested for their interaction forces, measured with load cell under current-ramping conditions in a bath of liquid nitrogen at 77 K. Good experimental and simulation results validate our equivalent circuit model to compute interaction forces of PI-INS racetrack pair. Overcurrent test of NI and PI coils, where each racetrack coil was charged above critical current (I c), was also performed to compare coil stability. This result implies that, although the PI winding technique improves the dynamic response, stability will be somewhat compromised.
Effect of Winding Tension on Electrical Behaviors of a No-Insulation ReBCO Pancake Coil
IEEE Transactions on Applied Superconductivity, 2014
This paper presents a study on the effects of winding tension on the characteristic resistance of a no-insulation (NI) coil. Two ReBCO NI test pancake coils, having the same winding i.d. (60 mm), o.d. (67.6 mm) and number of turns (60), were sequentially prepared in a way that the first test coil was wound with a winding tension of 12-N, tested, and then rewound with a new winding tension of 20-N for the same tests. In each test, the test coil was energized at a target current, the power supply was "suddenly" disconnected, and then the temporal decay of the coil center field was measured, from which the time constant of the test coil and the consequent characteristic resistance were obtained. To check the reproducibility of experimental data, each test was repeated 4 times and each time the test coil was unwound and rewound with a given winding tension. The experimental results were analyzed with equivalent circuit analyses. Correlation between the winding tension and the characteristic resistance was discussed in detail.
Partial-Insulation Winding Technique for NbTi Coils
IEEE Transactions on Applied Superconductivity, 2014
In 2010, we reported, for the first time, the noinsulation (NI) winding technique for high-temperature superconducting (HTS) pancake coils. Based on our test results of small NbTi NI coils, reported in 2011, the key benefits, i.e., enhanced mechanical integrity, compactness, and thermal stability, of the NI winding technique, appear intact for lowtemperature superconducting (LTS) windings. However, the intrinsic charging delay observed in NI coils, caused by the lack of insulation, is more pronounced in LTS coils of a bare round wire than in HTS pancakes of thin, wide tape. Thus, to significantly reduce the charging delay in LTS coils of a bare round wire, we proposed a partial-insulation (PI) winding technique, a variation of the NI technique. In the PI winding of a bare round wire, a thin insulation sheet is introduced every few layers-note that in the PI winding, there are no turn-to-turn insulations. This paper reports results, experimental and analytical, of the PI winding technique in which bare-round-wire NI and PI coils were prepared to quantify the effects of PI winding technique. Three LTS coils of the identical dimension and magnet constant were wound with 0.4 mm diameter NbTi mono-filament wire and tested in a bath of liquid helium at 4.2 K, respectively, with three winding techniques: insulated (INS); NI; and PI. We analyzed the experimental results by applying an equivalent circuit model that had earlier been successfully applied to another set of experimental results. A graph model of resistance matrix was applied to estimate characteristic resistance of both NI and PI coils.
Superconductor Science and Technology, 2013
This paper presents experimental and analytical studies on the characteristic resistance of NI (noinsulation) ReBCO pancake coils, which are used in an equivalent circuit model to characterize 'radial as well as spiral' current paths within the NI coils. We identified turn-to-turn contact resistance as a major source of the characteristic resistance of an NI coil. In order to verify this, three single pancake NI HTS coils-60, 40, 20 turns-were fabricated with their winding tension carefully maintained constant. A sudden discharge test was performed on each coil to obtain its characteristic resistance, and the relation between the turn-to-turn contact and the characteristic resistance was investigated. Based on the characteristic resistance and the n-value model, an equivalent circuit model was proposed to characterize the time-varying response of the NI coils. Charging tests were performed on the three test coils and the experimental results were compared with the simulated ones to validate the proposed approach with the equivalent circuit model.
HTS Pancake Coils Without Turn-to-Turn Insulation
IEEE Transactions on Applied Superconductivity, 2011
This paper reports a study of HTS pancake coils without turn-to-turn insulation. Three noinsulation (NI) pancake coils were wound: each single and double pancake coil of Bi2223 conductor and one single pancake of ReBCO conductor. An equivalent electrical circuit for modeling NI coils was verified by two sets of test: 1) charge-discharge; and 2) sudden discharge. Also, an overcurrent test in which a current exceeding a coil's critical current by 2.3 times was performed, and analysed, to demonstrate that in terms of stability NI HTS coils outperform their counterparts. The new NI winding offers HTS coils enhanced performance in three key parameters: overall current density; thermal stability; and mechanical integrity.
Journal of Physics: Conference Series, 2018
Superconducting generators typically require a power supply, current lead (CL) and slip ring to deliver DC current to a high-temperature superconducting (HTS) coil, which causes a conduction heat load. On the other hand, a flux pump (FP) is possible to supply DC current to the HTS coils of the generator without the heat transfer loads. This paper deals with a structural design and heat load analysis of an FP-based HTS module coil for a 12 MW wind power generator. The structures such as HTS coil bobbins, coil supports, and the connection components between the FP and the HTS coils were designed. The conduction and radiation heat loads of the FP-based HTS module coils were analysed using a 3D finite element method program. The results of the HTS module coil of the generator were compared with a conventional CL-based HTS module coil. As a result, the total heat loads of the FP-based HTS module coil were lower than the conventional CL-based HTS module coil. The structural design and heat load analysis results of the FP-based HTS module coil can effectively be utilized to develop a large-scale HTS wind power generator.
IEEE Transactions on Applied Superconductivity, 2012
This paper presents the design of an AC loss experiment using nitrogen boil-off method. This experiment is aimed at exploring the AC loss of HTS double race-track coils which will be installed on the rotor of a wind turbine generator. The operating environment is simulated by designing a cryostat with rotating magnetic field windings. Apart from the fact that the alternating magnetic field causes most of AC loss on the HTS coils, we also believe that the DC background field would be another important factor causing AC loss if the HTS coil is experiencing by both alternating magnetic field in the perpendicular direction and DC background field in the parallel direction. In order to perform the boil-off measurement, we present the method to estimate the heat leakage in the cryostat which might cause errors to the measurement .
IEEE Transactions on Applied Superconductivity, 2014
This paper proposes a numerical approach to calculate the characteristic resistance (R c) of partial-insulation (PI) and no-insulation (NI) high-temperature superconductor pancake coils with the non-uniform current path in such coils taken into consideration. Recently, an analytic approach has been proposed to estimate R c of an NI coil, where the coil current is assumed to be "uniform" over the entire coil. This model, however, is not effective to explain the increase of R c when a coil is modified from NI to PI. In this paper, we firstly introduce our numerical approach based on a finite element analysis. Then, the charging characteristics of selected PI and NI coils that we had previously reported are analyzed by the proposed approach. Reasonable agreement between the measured and calculated data validates the proposed approach to estimate R c of a PI as well as an NI coil.
arXiv: Superconductivity, 2016
In this work we present a modeling tool designed to estimate the hysteretic losses in the coils of an electric generator with coils made of coated conductor tapes during transient operation. The model is based on a two-stage segregated model approach that allows simulating the electric generator and the current distribution in the superconducting coils using a one-way coupling from the generator to the HTS coils model. The model has two inputs: the rotational speed and the electric load signal. A homogeneous anisotropic bulk model for the coils allows computing the current distribution in the coils. From this distribution, the hysteretic losses are estimated. Beyond the interest on providing an estimate on the global energy dissipation in the machine, in this work we present a more detailed local analysis that allows addressing issues such as coil design, critical current ratting, electric load change rate limits, cryocooler design, identification of quench-prone regions and overall...
Journal of Physics: Conference Series, 2014
Axial Flux Electrical Machines (AFEM) with good power-to-weight and diameterto-length ratio and high efficiency are very attractive for most industrial and power applications. Investigations with both theoretical and experimental methods of ac losses are important for a reliable prediction of dissipation mechanisms in AFEM. In this paper, simulated and measured results for both critical current (I c ) and transport current losses (P loss ), obtained on HTS coils, are reported. To investigate shape effects, double pancake coils with variable turns and shapes have been manufacted. Commercial grade ReBa 2 Cu 3 O 7-x (Re = Y or rare earths, ReBCO) tape and epoxy resin has been used for coil winding. A magneto-static 2D finite element model (FEM) for the coils cross section, and a lumped model for AC losses estimations, have been implemented. The agreement among measured and simulated results are satisfactory.