Tape Carrying AC Transport Current Research Articles

Total AC loss of Ag-Bi2223 tapes with various filament arrangements in parallel transverse magnetic field

In this paper, we experimentally investigated the total AC loss characteristics under AC parallel transverse field for Bi2223 tapes with various filament arrangements in their cross section. The tapes with different filament arrangements in final tape sections were prepared by standard powder-in-tube (PIT) process with drawing using round dice and rectangular deformation process using two-axial rolling (TAR) technique. Total AC losses in the tapes carrying AC transport current in AC parallel transverse field were measured by means of the electromagnetic method. The measured loss values in the tapes were compared with the several analytical models. Based on the experimental results, the influence of filament arrangements on total AC loss behaviors is discussed, under the different operating conditions with various amplitude of current and applied field.

Total AC loss of Ag-sheathed Bi2223 tapes with various filament arrangements carrying ACtransport current in AC parallel transverse magnetic field

For the applications of Bi2223 tapes as the strands to power cables with multilayerstructures, the tapes must carry the AC transport current in an AC parallel transverse fieldwith various field amplitudes depending on the layer positions. In this study, weexperimentally investigated the total AC loss characteristics under parallel transverse fieldfor Bi2223 tapes with various filament arrangements in their cross sections. The tapes withdifferent filament arrangements in the final tape sections were prepared by a conventionalpowder-in-tube (PIT) process with drawing using round dies and a rectangular deformationprocess using a two-axial rolling (TAR) technique. Total AC losses in the tapescarrying AC transport current in an AC parallel transverse field were measured bymeans of the electromagnetic method. The measured loss values in the tapes werecompared with several analytical models. Based on the experimental results, theinfluence of filament arrangements on total AC loss behaviour is discussed, under thedifferent operating conditions with various amplitudes of current and applied field.

Total AC loss in Bi2223/Ag tape carrying AC transport current in external AC magnetic field of various directions

Total AC loss characteristics of a high temperature superconducting tape carrying AC transport current in external AC magnetic field with various applied directions to tape surface was experimentally investigated. We measured the AC transport current loss and the AC magnetization loss in the Bi2223/Ag-seath tape carrying the AC transport current in AC magnetic field by changing the angle to the tape surface and obtained the total AC loss as the sum of these losses. Based on the measured data, the dependence of the AC losses on the direction of the external AC magnetic field was discussed.

FEM Analysis of AC Loss in Twisted Bi-2223 Multifilamentary Tapes Carrying AC Transport Current in AC Transverse Magnetic Field with Arbitrary Orientation

A new FEM code for electromagnetic field analysis of twisted multifilamentary superconductors was developed based on triangular element system and tensor equivalent conductivity. Finite element models of twisted Bi-2223 tapes exposed to an AC transverse magnetic field with various orientations were made, and the current distribution in these tapes was calculated. The calculated current distribution in a twisted tape carrying AC transport current in a parallel or nearly parallel AC transverse magnetic field shows that filaments are decoupled effectively to reduce the total AC loss, even if the transverse resistivity equals the resistivity of pure silver. However, in the perpendicular transverse magnetic field, only a little reduction of the total AC loss can be attained by twisting even if the transverse resistivity is increased to 100 times larger than the resistivity of pure silver.

AC Loss and Current Distribution Measurement for Superconducting Tapes

We made a co-axial copper tube measurement device in order to measure AC losses of HTS tapes. This device can minimize the external disturbance for high accuracy measurement. Also it is easy to fix the tape inside the copper tube. We used a linear amplifier in order to measure the voltage in high accuracy because the transport current was large. The voltage taps are located at the center and the edge of the tapes to measure the voltage drop on the samples. Our experimental data show that the inductive voltages are proportional to the frequency, and therefore this means that the main loss depends on hysteresis loss. In this study, the AC loss characteristics of twisted Bi-2223 tapes and untwisted tapes carrying AC transport current in self field is investigated. The magnetic flux generated by the transport current flowing in the HTS tape can be measured by using the same experimental setup. If the superconducting filament is twisted to reduce the AC losses, a relatively higher magnetic flux is induced at low frequencies, this is measured by winding the measuring wire around the tape - winding pick up method.

AC loss characteristics of twisted multifilament Bi2223/Ag sheathed tapes carrying ac transport currents in AC longitudinal magnetic fields

This paper reports on the total AC loss characteristics of a twisted multifilamentary Bi2223/Ag sheathed tape carrying AC transport current in longitudinal AC magnetic field in phase with the transport current. The tape was specially made for the experiment and had wider space between superconducting filaments than a usual multifilamentary Bi/Ag sheathed tape to suppress superconducting bridgings between the filaments. In our experiment the total losses were measured by the electric method. The losses supplied from the longitudinal magnetic field were measured by using a pick-up coil and the losses supplied from the power supply for the transport current by a four terminal method. The measurement results showed that the total losses depended on the direction of the longitudinal magnetic field. In the case that the combined magnetic field produced by the transport current and the external longitudinal magnetic field was nearly parallel to the filaments of the twisted wire, the losses were smaller than those in the case that the combined field was nearly perpendicular to the filaments. This was observed when the amplitude of the longitudinal magnetic field was larger than the full penetration magnetic field of the wire.

Total AC losses in twisted and untwisted multifilamentary Bi-2223 superconducting tapes carrying AC transport current in AC longitudinal magnetic field

In some electrical apparatuses, superconducting tapes are exposed to the longitudinal magnetic field. In this work, AC losses were measured in twisted and untwisted Bi-2223 tapes carrying AC transport current in the AC longitudinal magnetic field. In twisted tapes, the transport, magnetization and total losses depend on the relative direction of the longitudinal magnetic field to the direction of the transport current, while the field direction does not influence the AC loss characteristics in untwisted tapes. In the Z-twisted tapes, the total AC loss is larger in the longitudinal magnetic field that is anti-parallel to the transport current than in the longitudinal magnetic field of another direction. Numerical analysis shows that this field direction dependence of the total AC loss results from the change in the current distribution. In the longitudinal magnetic field that is anti-parallel to the transport current, the total AC loss in the Z-twisted tape is more than that in the untwisted tape. This dependence on the field direction is reversed in S-twisted tapes. It is to be noted that the twist increases the total AC loss in a longitudinal magnetic field of a certain direction, while it reduces the AC loss in the transverse magnetic field.

Computation of losses in a HTS tape carrying AC transport current in external AC magnetic field at temperatures of 20-40 K

In this paper losses in superconducting composite tapes carrying ac transport current in external ac magnetic field are studied by using a numerical model. The external field and the transport current are in phase, as usual in superconducting coils. The computational model is based on Maxwell's equations and a non-linear constitutive law between the current density and the electric field. By using the model ac loss behaviour between high temperature (HTS) and low temperature superconductors (LTS) is compared. Finally, the temperature dependence of losses in HTS tapes are studied at temperatures 20-40 K at constant amplitudes of the transport current and the external magnetic field. According to the results the ac losses decrease with temperature if the peak value of the current ramp is lower than the current which fully penetrates the conductor cross-section, i*. It is proposed, that frequency dependent i* is a more appropriate design parameter for HTS than a critical current defined by an electric field criterion.

Numerical analysis of AC loss in high T/sub c/ twisted tape carrying AC transport current in external AC magnetic field. Effect of twisting on loss reduction

The effect of twisting in BSCCO tapes on the loss reduction is discussed by a numerical analysis using the finite element method. The optimal twist pitch giving the lowest loss for the tape carrying the AC current under the AC magnetic field is presented. The numerical analysis takes the smooth E-j characteristics, the twisted structure and the dynamic resistivity into account, which allows more accurate loss estimations. For the BSCCO tape with a typical dimension of 3 mm/spl times/0.2 mm, the optimal twist pitch is around 10 mm, when it is carrying the AC transport current with normalized amplitude I/sub t//I/sub c/=0.8, under the parallel magnetic field to the tape face.

Finite element analysis of AC loss in non-twisted Bi-2223 tape carrying AC transport current and/or exposed to DC or AC external magnetic field

AC losses in Bi-2223 superconducting tapes carrying AC transport current and/or exposed to DC or AC magnetic field are calculated with a numerical model based on the finite element method. Superconducting property is given by the E– J characteristic represented by a power law using equivalent conductivity. First, transport loss and magnetization loss are calculated numerically and compared with measured values. The calculated losses almost agree with the measured losses. Frequency dependencies of calculated and measured transport losses are compared with each other. Next, the influence of DC external magnetic field on the transport loss is studied. DC external magnetic field reduces n that is an exponent in the power law connecting resistivity and current density. The numerically calculated transport loss increases with increasing DC magnetic field. Finally, the total loss of superconducting tape carrying AC transport current in AC magnetic field is calculated. In the perpendicular magnetic field, the calculated total loss is lager than the sum of the transport loss and the magnetization loss, while they almost agree with each other in the parallel magnetic field.

AC losses in multifilamentary Bi-2223/Ag superconducting tapes

In this study we examined AC losses in a multifilamentary Bi-2223/Ag superconducting tape carrying AC transport current. The tape consisting of 85 filaments was helically wound to a single-layer coil. The losses were measured at 77 K in the frequency range from 1 Hz up to 250 Hz. Current amplitudes I/sub p/ were ranging from l=I/sub p//I/sub c/=0.6 to 1.5, critical current I/sub c/=15.4 A determined by the standard 1 /spl mu/V/cm static electric field criterion. The roles of special loss components were considered: hysteresis, flux-creep, coupling and eddy current losses. Hysteresis losses due to the self-field of the AC transport current were found to dominate when l/spl les/1.1. Resistive losses dominated when l>1.2. In the hysteretic regime, the higher the frequency, the smaller the losses per cycle.

Electric field and losses in BSCCO-2223/Ag tapes carrying AC transport current

Electric field and losses in single layer coils wound of 0.75 m long multifilamentary BSCCO-2223/Ag tapes carrying AC transport current have been studied at both 4.2 K and 77 K in the frequency range from 0.01 Hz up to 100 Hz, with the main effort at 50 Hz. Current amplitudes (I/sub p/) ranged from i=I/sub p//I/sub c/=0.5 to 1.3, critical current (I/sub c/) determined by the standard 1 /spl mu/V/cm static electric field criterion. I/sub c/ of coil 1 was 15 A at 4.2 K and 3 A at 77 K. Losses due to the wide resistive transition of the coils were found to dominate over self-field losses even well below i=1. Therefore the total losses in the whole applicable i range could not be described well by equations based on the critical state model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>