Frequency Dependence Of Ac Loss Research Articles

Effect of Core Materials on the Electrical Properties of Superconducting Conductor on Round Core Cable

High temperature superconducting (HTS) conductor on round core (CORC) cable is considered as a potential technology for power applications, because of its high current-carrying capacity, compactness, and strong mechanical properties. As the main component of CORC cable, center core is used to support the HTS conductors. However, for metal center core, eddy current induced in the core under alternating electromagnetic field is unneglectable, which will lead to extra AC loss in power applications. This paper focuses on the selection of center core of CORC cable. AC losses of CORC cable using different core materials are evaluated by both numerical and experimental methods, in which copper, stainless steel, fiberglass epoxy and nickel have been chosen as the core. Results illustrate that AC loss of CORC cable has a correspondingly increase with the conductivity of core material. Significant frequency dependence of AC loss indicates that for single layer CORC cable, proper core material should be chosen to minimize the eddy current loss. Besides, CORC cable with core of nickel shows a quite different AC performance due to its ferromagnetic characteristics. Conclusions obtained from this paper will provide essential data for future optimization on the design of CORC cables.

Frequency dependence of ac losses in a granular superconductor Lu2Fe3Si5

By using ac susceptibility measurements, the frequency dependence of ac losses was experimentally studied in a granular Lu2Fe3Si5 sample. Three types of temperature dependent ac loss peaks were observed which were attributed to the intergranular, intragranular and intrinsic bulk behaviors. It is found that the intergranular and intragranular peaks show clear frequency dependence while the intrinsic peak remains constant as the frequency changes. With increasing frequency the pinning difference between the intergranular and intragranular becomes small, and vanishes at high frequencies. The vortex glass temperature Tg was determined to be 5.97 K. The phase diagram was constructed by measuring the ac susceptibility under different magnetic fields.

AC Loss Measurement of High-Tc Superconducting Coils Wound With Stacked Conductors

In order to elucidate the ac loss characteristics of high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting coils wound with stacked conductors, we measured ac losses of Bi-2223 sample coils under the various electromagnetic conditions by a nitrogen boil-off method. The sample coils were wound with stacked conductors, which were composed of two Bi-2223 tapes. Each tape of stacked conductors was wrapped with polyimide tape, and the ends were made into the open circuit or short circuit. The coils with transposition and the coils without transposition were prepared as sample coils. We measured the magnetic amplitude dependence and the frequency dependence of ac losses of sample coils under external magnetic fields, and evaluated the magnetization losses and coupling current losses. Measured data were compared with theoretical values. Based on the obtained results, ac loss characteristics of high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting coils wound with stacked conductors under external magnetic fields were discussed.

Fabrication and characterization of Bi2223 tapes with Al 2O 3 barriers for reduction of AC losses

We fabricated and characterized the Bi2223 tape with Al 2O 3 as interfilamentary resistive barriers for the filament decoupling and also for the reduction of AC losses under AC external magnetic field. The tapes with thin Al 2O 3 barrier layers around the Bi2223 filaments were prepared by using a standard powder-in-tube (PIT) method. Al 2O 3 powders with mean grain size below 1 μm were used and they are coated with the slurry on the outside surface of hexagonal monocore rod before stacking. The phase formation inside the filament was evaluated by XRD measurement. The uniformity of transport properties ( J c) for Al 2O 3 barrier tapes was measured on the order of several metre lengths and compared with data for the tapes without barriers and with Ca 2CuO 3 + Bi2212 barriers. To evaluate the effect of introducing Al 2O 3 barriers on the filament decoupling, frequency dependence of AC losses under AC transverse magnetic field for barrier tapes were investigated.

バリア入りBi2223多芯線材の作製と交流損失特性

Synopsis: Bi2223 multifilamentary tapes with interfilamentary oxide barriers were fabricated and their AC loss properties were examined under AC external magnetic field. In order to avoid the side effect on Bi2223 phase formation during heat treatment, Ca2CuO3 and SrZrO3 with average grain sizes of 1-2 μm were selected as barrier materials. Furthermore, an additional Bi2212 powder corresponding to 20wt% were mixed with them to improve their deformation properties for cold working. The mixed oxide powders were introduced among the twisted Bi2223 filaments. The critical current densities (Jc) in the barrier tapes were 10-20% lower than those in the tapes without barriers. In a parallel field, the loss reduction in the SrZrO3/Bi2212 barrier tape is most remarkable because the continuity of the SrZrO3/Bi2212 barriers is far superior to the Ca2CuO3/Bi2212 barriers. At 50 mT around power-grid frequencies, parallel field losses in a twisted tape with SrZrO3/Bi2212 barriers are 80% lower than the non- twisted tape. From the frequency dependence of AC losses in a perpendicular field, it was confirmed that the transverse resistivity in the SrZrO3/Bi2212 barrier tape is 8-9 times higher than the tape without barriers. However, around the power-grid frequencies, the introduction of barrier reduces AC losses only slightly in a perpendicular field. The twist pitch of the present barrier tape (= 16 mm) is probably too long to decouple the filaments in a perpendicular field.

Temperature dependence of critical currents and ac transport losses in(Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Oy tapes

The critical currents and self-field ac losses ofYBa2Cu3Oy coatedconductors and (Bi,Pb)2Sr2Ca2Cu3Ox tapes were measured at several temperatures between 45 K and the respective criticaltemperature. The temperature dependence of ac losses was measured at 50 Hz using thelock-in method for a transport current. The frequency dependence of ac loss was measuredat 55 K for transport current frequencies from 25 to 400 Hz. The results showthat variation of ac transport loss as a function of normalized critical current isnearly the same at all temperatures in the measured temperature range for bothYBa2Cu3Oy and (Bi,Pb)2Sr2Ca2Cu3Ox tapes. The temperature dependence of the loss factor, however, is different for(Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Oy tapes because of the ferromagnetic loss in the NiW-based coated conductor substrate. Similaritiesand differences in the temperature and frequency dependence of ac transport losses between(Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Oy tapes are discussed.

Frequency dependent behavior of ac loss in high temperature superconductors

Influences of flux flow, flux creep, and temperature non-uniform distribution on ac loss in high temperature superconductors (HTS) are investigated. An asymptotic solutions of ac loss and temperature distribution are obtained in a form of power series of λ h, λ m, which are frequencies of the external ac magnetic field normalized to relaxation rates of thermal and magnetic field diffusions, respectively. Our results show that flux flow, flux creep, and thermal diffusion all contribute significantly to the frequency dependence of ac loss per cycle, although each of them affects the ac loss in a different way. Our calculation can well explain the frequency-dependent phenomena observed in HTS.

Thermal diffusion and ac loss in high- Tc superconductors

The influence of thermal diffusion and temperature nonuniform distribution on ac loss of high-temperature superconductors has been investigated. Asymptotic solutions of magnetic and electric fields and ac loss are presented in the form of power series of λ h, the normalized frequency of the external ac magnetic field. It reveals that influences of thermal diffusion on the ac loss behavior of high- T c superconductors include: (i) a weak frequency dependence of ac loss per cycle, i.e., ac loss per cycle increases with frequency in the incomplete field penetration, but decreases with frequency in the complete field penetration; (ii) nonuniform temperature distribution in the sample with the highest temperature located in the center; and (iii) existence of a critical frequency at which the superconductivity is destroyed at the hottest point in the sample.

Frequency dependence of AC loss in Bi(2223)Ag-sheathed tapes

The AC self-field loss in Bi(2223)Ag-sheathed tapes with different number of filaments has been measured between 59 and 2500 Hz by means of a dual lock-in amplifier. Due to the wide frequency range of the measurements, we have been able to dissociate quantitatively the different self-field loss contributions: hysteretic, eddy current and resistive loss (near I c). This is an important advantage compared to single frequency measurements where such loss dissociation is only qualitative. The hysteresis losses of the different tapes fall between Norris' predictions for elliptical and strip cross-section. The relative weight of eddy current loss is found to be inversely proportional to the current ratio—the higher the i, the less is their contribution. Frequency-independent resistive loss due to flux-creep is observed for high currents at low frequencies; this loss becomes quickly negligible with the increasing frequency.

Numerical analysis of AC losses in high T/sub c/ superconductors based on E-j characteristics represented with n-value

A numerical code for the electromagnetic analysis of high T/sub c/ superconductors by finite element method has been developed. The E-j characteristics of superconductor are represented with the n-value. The equivalent conductivity of superconductor is determined as a function of electric field, and Ohm's law is used as the constitutive equation. First, the current and magnetic flux distributions in the infinite slabs of superconductor exposed to a parallel external magnetic field are analyzed. The influence of n-value on AC loss and the frequency dependence of AC loss are studied. The AC loss in the infinitely-long superconductor tapes exposed to the external magnetic field is calculated numerically to study the influence of n-value.

AC losses in Y1Ba2Cu3O7??:Ag tapes

The frequency dependence of ac losses of a superconducting tape consisting of Y1Ba2Cu3O7-δ material in a silver sheath was measured from 50 Hz to 50 kHz using a four-probe technique developed and reported earlier. Contrary to expectation, the ac losses were found to have a frequency-independent regime in the loss spectrum. A tentative explanation has been offered to account for the frequency-independent loss.