AC Losses In HTS Coils Research Articles

Experimental and Numerical Study of AC Losses in HTS Coils of AC Electric Machines

Experimental and Numerical Study of AC Losses in HTS Coils of AC Electric Machines

Experimental and numerical study of AC losses in HTS coils of AC electrical machines

Experimental and numerical study of AC losses in HTS coils of AC electrical machines

Study on AC Loss Characteristics of 3-Phase HTS Coils With Iron Core and Its Reduction

Study on ac loss characteristics of HTS coils with an iron core to simulate an armature winding of ac rotational machine and a method to reduce ac losses in HTS coils combined with the iron core in 3-phase condition are reported in this paper. In this study, the 3-phase test model which combines 6 HTS coils wound by YBCO tapes and the iron core used for an armature of conventional induction motor is fabricated for the ac loss measurement. It is shown that the measured ac losses in the 3-phase condition coincides with the sum of the ac loss of each phase measured in the 1-phase condition. The effectiveness to suppress the perpendicular magnetic field applied to the tape in the coil by use of magnetic materials around the coil winding on the ac loss reduction in the 3-phase condition is investigated. The measured ac loss with placing the magnetic material around the coil winding in the slot of the iron core remarkably decreases. The results of the numerical magnetic field analysis confirmes that the perpendicular magnetic field significantly decreases by arranging the magnetic material and supportes the validity of the measurement results. The results obtained in this study demonstrates that the effectiveness to modify the magnetic field distribution by use of the magnetic material around the coil winding on the ac loss reduction in 3-phase HTS coil combined with the iron core.

AC losses in HTS coils for high-frequency and non-sinusoidal currents

AC losses in racetrack coils that are wound of YBCO tapes are measured for sinusoidal and non-sinusoidal transport currents with fundamental frequencies up to 1 kHz. An electrical method to measure losses for non-sinusoidal currents is developed for this purpose. The measured losses are compared to the losses calculated by 2D finite element models with power-law material models. The frequency and waveform-dependency of the measured losses are shown and compared to the results of the models over a wide range of frequencies and waveforms. Finally, it is shown that the finite element models can accurately predict AC losses resulting from non-sinusoidal transport currents as are present in highly dynamic motors with AC armature coils.

Total AC loss study of 2G HTS coils for fully HTS machine applications

The application of HTS coils for fully HTS machines has become a new research focus. In the stator of an electrical machine, HTS coils are subjected to a combination of an AC applied current and AC external magnetic field. There is a phase shift between the AC current and AC magnetic field. In order to understand and estimate the total AC loss of HTS coils for electrical machines, we designed and performed a calorimetric measurement for a 2G HTS racetrack coil. Our measurement indicates that the total AC loss is greatly influenced by the phase shift between the applied current and the external magnetic field when the magnetic field is perpendicular to the tape surface. When the applied current and the external magnetic field are in phase, the total AC loss is the highest. When there is a 90 degree phase difference, the total AC loss is the lowest. In order to explain this phenomenon, we employ H formulation and finite element method to model the 2G HTS racetrack coil. Our calculation agrees well with experimental measurements. Two parameters are defined to describe the modulation of the total AC loss in terms of phase difference. The calculation further reveals that the influence of phase difference varies with magnetic field direction. The greatest influence of phase difference is in the perpendicular direction. The study provides key information for large-scale 2G HTS applications, e.g. fully HTS machines and superconducting magnetic energy storage, where the total AC loss subjected to both applied currents and external magnetic fields is a critical parameter for the design.

The Nitrogen Boil-Off Method for Measuring AC Losses in HTS Coils

We have developed a novel apparatus for applying a nitrogen boil-off method as a mean of making calorimetric measurements and allowing for simple measuring and evaluating of AC losses in HTS coils at liquid nitrogen temperature. With the ability to measure AC loss generated in superconductors directly, this method produces more reliable data than that obtained by general, electro-magnetic measurements. A sensitivity of about 0.1 W was achieved by improving sensitivity in measuring gas evaporation via the following three steps: (1) use of nonmetallic vessel, heat-insulated housing in which the sample is located; (2) optimization for sample vessel thickness and tube size; and (3) stabilization of evaporating gas emitted by the heater. It is widely expected that the proposed apparatus may be used for individual measurement of the magnetization loss and the transport current loss in HTS coils, as well as their total losses, in addition to the AC loss in irregularly shaped samples.

Analysis of AC Loss Characteristics of High Temperature Superconducting Coil

This paper reports an analytical study on AC loss characteristics of a high temperature superconducting coil wound with a Bi2223/Ag tape. The electromagnetic AC loss in the high temperature superconducting coil made by stacking pancake coils wound with the Bi2223/Ag tape was numerically calculated by using the measured DC data of the HTS tape. The calculated AC loss was compared with measured AC losses in Bi2223 HTS coils obtained in a previous study. It had been found that the measured AC losses in the coils contained large mechanical loss. For the comparison of the measured and calculated losses, the mechanical loss was subtracted from the measured total loss data to estimate the electromagnetic loss. The calculated AC losses were compared with the measured electromagnetic losses in the coils, producing rather good agreement. A possible way to reduce the AC loss in the HTS coil was also presented and discussed.

AC loss measurement of HTS coils with ferromagnetic disks

Manufacturing techniques for low AC loss high-T/sub c/ superconducting coils are necessary to realize high efficiency superconducting power equipments. High-T/sub c/ superconducting tape conductors have anisotropic magnetic field dependence on critical current and AC magnetization loss. A magnetic field component perpendicular to the tape surface degrades HTS coil performance. We numerically investigated a magnetic field adjusting method and AC loss reduction effects by attaching ferromagnetic materials to both ends of HTS coils. We also measured total AC loss of an HTS coil comprising 10 HTS double pancake coils by the boil-off method. Total AC loss of the coil was dominated by mechanical loss due to vibration and movement of conductors and pancake coils. In this paper, methods to reduce total AC loss of HTS coils are discussed.