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Each of the eight huge coils of the Barrel Toroid of the ATLAS detector consists of two double pancakes which are embedded in an aluminum alloy coil casing. The 57 mm times 12 mm sized conductor is a Rutherford cable with NbTi-Cu strands co-extruded with a high purity aluminum stabilizer. The race track coils have overall dimensions of 25 m times 5 m and the length of the conductor in the windings is 6.7 km. The coils are conduction cooled with forced flow helium. The nominal operating current is 20.5 kA and the nominal ramp rate is 4 A/s. During the test program of the individual coils the ramp losses are measured to confirm that they do not exceed the design cooling capacity of the ATLAS cryogenic system. The losses are determined from the amount of evaporated helium in the return flow. The ramp losses in the conductor consist of the hysteresis and coupling current losses in the Rutherford cable and eddy current loss in the pure aluminum stabilizer. Ohmic losses are generated in the coil casing which acts as a low resistive secondary of a transformer formed by the coil and the casing. In this paper the results of the loss measurements on the different coils, with different RRR (residual resistance ratio), are presented. Measurements are performed at various ramp rates. The results are in good agreement with the calculated losses, which are dominated by the loss in the coil casing

A method to calculate the AC loss of superconducting power devices from the measured AC loss of a short sample is developed. In coils and cables the magnetic field varies spatially. The position dependent field vector is calculated assuming a homogeneous current distribution. From this field profile and the transport current, the local AC loss is calculated. Integration over the conductor length yields the AC loss of the device. The total AC loss of the device is split up in different components. Magnetization loss, transport current loss and the loss due to the combined action of field and current all contribute to the AC loss of the device. Because ways to reduce the AC loss depend on the loss mechanism it is important to know the relative contribution of each component. The method is demonstrated on a prototype transformer coil wound from Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x//Ag superconducting tape. Differences between the model assumptions and devices are pointed out. Nevertheless, within the uncertainty margins the calculated AC loss is in agreement with the measured loss of the coil.

The magnetisation loss in multifilament HTS tape superconductors can be reduced by twisting the filaments and increasing the matrix resistivity. In this paper the influence of filament twist on the coupling current loss of the tape is studied. Magnetisation measurements on multifilament Bi2223 tape conductors with different twist pitches are performed at 77 K in magnetic field applied parallel and perpendicular to the wide face of the conductor. Both frequency and magnetic field amplitude are varied. In perpendicular magnetic field the filaments are fully coupled. In parallel magnetic field the twisted filaments are decoupled, even for twist pitches around 10 mm and a pure silver core. However, for increasing magnetic field >0.04 T, the influence of the coupling current loss increases. The transition to full coupling and the coupling current loss are analysed with an existing analytical model for a tape superconductor.

Bi2Sr2Ca2Cu3Ox/Ag tape superconductors are used in applications like power cables and transformers. In these applications the superconductor is exposed to an alternating magnetic field that has different orientations with respect to the tape surface. In this paper the angle dependency of the magnetisation loss is considered from two points of view. First the measurement technique with pickup coils is analysed theoretically. Measured magnetisation loss in uni-directional magnetic field with various orientations and rotating magnetic field are compared. When the orientation is changed from perpendicular (0°) to parallel (90°) applied magnetic fields, the contribution of the perpendicular field component to the magnetisation loss is dominant up to 60°. A new model to describe the angle dependency of the magnetisation loss, based on the measured loss in perpendicular and parallel magnetic field is developed. Deviations between models and the measured loss are explained with the help of the theoretical analysis of the measurement technique. The new model is not only applicable for the magnetisation loss but also for other AC loss components.

A high quality factor, superconducting resonator coil is developed in cooperation with the Dutch companies SMIT Transformers and SMIT DRAAD. The coil system is manufactured in industry, using industrial tooling. It has a design reactive power rating of 1 MVA at a frequency of 50 Hz and the operating temperature is 64 K. The system consists of four concentric but separate coils, made of 2 km of Bi-2223 conductors from two different manufacturers. The coils are optimized by shaping the magnetic field around the coil edges with ferro-magnetic C-cups to reach a design electrical quality factor of 1000. The system is operated in a glass-epoxy cryostat at 64 K and 77 K. The resonator coil design demonstrates all the superconducting elements that are essential for manufacturing superconducting transformers. A numerical model has been developed to predict the DC and AC behavior of the system based on measurements of short samples and test coils. A comparison is made between the experiment and model calculations.

Potentially, coils made with BSCCO-2223/Ag tape and operating in liquid nitrogen at 50-60 Hz are interesting for power related applications. The electrical characteristics of such a coil depend on the radial magnetic field in the windings. One way to suppress the radial field is by placing small iron pieces around coil edges. V-I curves of the 100 kVA coil are calculated and measured for two cases: coil edges without and with iron pieces. The coil is a solenoid with inner and outer diameters and a height of 470, 474 and 614 mm respectively. A numerical model adapted to the coil geometry is used to calculate the conductor losses. The loss voltage is also evaluated by measuring the coil temperature. The total loss of the coil is measured electromagnetically. Calculated and measured losses are in agreement. Finally, the loss V-I curves of the coil are simulated in the frequency range of 0 to 400 Hz. The results are applied to the design of a 1 MVA resonator coil.

An engineering function to describe the AC loss of BSCCO/Ag tape conductors is developed. For a wide range of transport currents and magnetic fields (with different orientation) the loss is described with an uncertainty of 10%. The equation is based on the analytical expressions available, BSCCO/Ag tapes used in power applications at liquid nitrogen temperature are fed with an AC transport current and exposed to an AC magnetic field. The magnetic field in a device has different orientations with respect to the position of the conductor in the device. In this contribution, AC loss measurements for simultaneously applied magnetic field (with different orientation) and transport current are presented for a high quality tape conductor that is used in a transformer coil. The results are separated into a magnetic and a transport current loss component.

Magnetisation loss is an important factor in the design of superconducting transformers and motors. In these devices the tapes are usually placed face-to-face. Then the magnetisation loss is influenced by the mutual magnetic shielding between adjacent tapes. The shielding is investigated by measuring the magnetisation loss in stacks with various numbers of Bi-2223 tapes, exposed to a 48-Hz perpendicular magnetic field at 77 K. In a stack the penetration field is increased and the magnetisation loss below penetration is greatly decreased, compared to the behaviour of a single tape. The loss at high magnetic-field amplitudes is unaffected. The measured loss is compared to the loss calculated with two different models. The effect of shielding is qualitatively well described with an analytical model. However, predictions made with a numerical model display a better quantitative agreement with the measurement results.

Characteristics of a circular superconducting coil made with BSCCO-2223/Ag tape depend on the amplitude and direction of the magnetic field in the windings. The effect can be estimated by studying a short sample of the same tape. However, the loss voltage-current and the frequency characteristics of a coil deviate considerably from those that are measured on a short sample. In order to estimate the deviation, the authors compared measured characteristics of a few small coils employing up to /spl sim/10 m of tape with those calculated from the short samples data. The comparison includes several arrangements of coils and field shaping elements around the coil edges and is performed in the frequency and temperature range typical for power applications (1-100 Hz and 64-78 K respectively). The results are applied to the design of a 100 kVA-50 Hz resonator coil with a high quality factor.

BSCCO/Ag tape superconductors are developed for electrical power applications at liquid nitrogen temperatures. In these applications, e.g., superconducting transformers and power cables, an AC transport current and an AC magnetic field are present at the same time. A set-up to measure the influence of external AC magnetic field on the transport current loss, i.e., the voltage drop across a sample supplied with an AC transport current, has been developed. The magnetic field can be applied both parallel and perpendicular to the broad side of the tape conductor. An increase of the transport current loss due to the external AC magnetic field is observed. When a DC external magnetic field is applied the increase of the self-field loss can be described well by the decrease of the critical current due to the magnetic field. In the case of an AC external magnetic field this is only a minor effect. For magnetic field amplitudes higher than a certain threshold value the transport current loss is described reasonably well by the self-field loss and a dynamic resistance contribution calculated from the DC voltage–current relation in AC magnetic field.

The self-field loss of BSCCOrAg tapes has been measured in combination with an external AC magnetic field. This situation occurs when conductors are used in applications such as coils or cables. An increase of the self-field loss due to external AC magnetic field is observed. An increase of the self-field loss caused by a decrease of the critical current is only a minor effect. For magnetic field amplitudes higher than 10 mT, the self-field loss is described reasonably well by the self-field loss and a dynamic resistance contribution calculated from the DC voltage–current relation in AC magnetic field. For magnetic field amplitudes smaller than 10 mT, the dynamic resistance contribution from the DC voltage–current relation only describes a small part of the increased self-field loss.

A high-quality superconducting resonator coil system has been developed in the Netherlands in cooperation with the companies SMIT Transformers and SMIT Draad. The coil system was manufactured in industry, using industrial tooling. It has a reactive power rating of 1 MVA at a frequency of 50 Hz and a temperature of 64 K. The system consists of four concentric solenoidal coils, including 2 km of Bi-2223 conductors from two manufacturers. The coil performance has been optimized by shaping the magnetic field around the coil edges with laminated ferro-magnetic C-cups to reduce the AC loss to about 1 kW at 1 MVA reactive power. The system is operated in a glass-epoxy cryostat at either 64 or 77 K. The resonator coil demonstrates all superconducting elements that are essential for manufacturing superconducting transformers. The construction of the system is finalized and the total system has been tested in various operational configurations. The results of the system test at full power are presented and analyzed.

Advanced ac loss measurement methods for superconducting tapes are described in detail and demonstrated on BSCCO/Ag (Bi2Sr2Ca2Cu3Ox with a Ag matrix) tapes in liquid nitrogen at 77 K. The aim of the measurements is to simulate the situation of a tape conductor in an electric power application like a transformer coil or a power cable. In this class of devices the conductor is fed with an alternating transport current and simultaneously exposed to an alternating magnetic field. In many devices the magnetic field vector points in a single direction but in some devices such as three-phase power cables and motors the magnetic field rotates around the conductor. In all cases described above an electromagnetic approach with pick-up coils and voltage taps is used to measure the ac loss. This method enables a separate study of magnetization loss and transport current loss when both the magnetic field and transport current are present simultaneously. The magnetization loss measurement setup for unidirectional and rotating magnetic field is described. The transport current loss measurement setup is described, focusing on the suppression of cross effects of ac transport current and ac magnetic field that disturb accurate measurements. Finally several relevant examples of the results obtained are shown.

In practical applications, BSCCO/Ag tapes are exposed to external AC magnetic field and fed with an AC transport current. The total AC loss can be separated in two contributions: first, the transport current loss influenced by an external AC magnetic field, and second, the magnetisation loss that depends on the transport current running through the conductor. In this paper the total AC loss is considered and the role of the electric and magnetic components is compared. This comparison is made with an available analytical model for the AC loss in an infinite slab and verified experimentally for a BSCCO/Ag tape conductor. For small transport currents the magnetisation loss dominates the total loss. When the current increases, a field dependent crossover occurs, after which the transport current loss also plays a role. Qualitatively the measurements can be described well in terms of the critical state model. For magnetic field parallel to the wide side of the conductor the CSM for an infinite slab describes the measurements also quantitatively.

BSCCO/Ag tapes are being developed for electrical power applications at liquid nitrogen temperatures. In these applications, conductors are exposed to an alternating magnetic field and fed simultaneously with an alternating transport current. In this contribution the influence of an external alternating magnetic field on the transport current loss of a single tape is studied experimentally. Special attention is paid to the loss as a function of the orientation of the external magnetic field. The transport current loss in a DC external magnetic field can be described well by the decrease of the critical current due to the magnetic field. In the case of an AC external magnetic field this is only a minor effect. Effects responsible for the increase of the transport current loss in external AC magnetic field are investigated with respect to their angle dependency. A model based on a 1 dimensional modelling of the conductor and an average critical current density during the magnetic field cycle is presented. This model describes the measured results reasonably well below the critical current.

The AC loss of various silver-sheathed high Tc superconducting Bi-2223 tapes is measured by means of the transport method, as a function of frequency and current amplitude. The frequency dependence of the power loss (in W/m) is used to separate different loss components: the frequency independent part is attributed to the resistive loss, the linear part to the hysteresis loss (self-field loss in J/m per cycle), and the quadratic part, if it appears, may be assigned to other losses such as the eddy current loss. The separated loss components are evaluated with the existing models and the DC voltage-current characteristics of the sample. In general, the self-field loss is dominant when the transport current amplitude is smaller than the critical current of the tape. For larger currents the resistive loss is the most important component. At small transport current, the AC transport loss signal is very small and is sensitive to the phase correction and other disturbances from the surrounding metallic parts in the vicinity of the sample. The signal picked-up from these disturbances shows the quadratic frequency dependence.

In a typical superconducting coil made of BSCCO/Ag tape, both amplitude and direction of the magnetic field determine the critical current, resistive voltage and AC loss. The distribution of the magnetic field along and across the superconducting tape in a coil is rather complex. This gives rise to the question: how accurate can one predict the critical current, V–I characteristic and AC loss of the AC coil from results of short sample measurements? To answer this question, we have measured and compared the characteristics of a short sample and a small coil employing 14 m of the same tape at 77 K. The comparison is performed as follows. First, a short sample is characterised with regard to the field dependence of the critical current, V–I characteristic and the AC loss. Second, the distribution of the magnetic field along the tape in a coil is accurately calculated. From the data, the voltage along the tape and the loss of the tape in the coil are found. Finally, the resistive voltage and the AC loss of the complete coil are calculated and compared to measured AC losses in the frequency range of 0 to 160 Hz, typical for power applications.