The Dependence of Transport AC Loss on Temperature and DC Parallel Magnetic Field in an Eight-Strand YBCO Roebel Cable

Both AC loss and wire cost in coil windings are critical factors for HTS AC machinery applications. We present AC loss measurement results in three HTS coil assemblies at 77 K and 65 K which have hybrid coil structure comprising one central winding (CW) and two end windings (EWs) wound with ReBCO and BSCCO wires with different self-field Ic values at 77 K. All AC loss results in the coil assemblies are hysteretic and the normalized AC losses in the coil assemblies at different temperatures can be scaled with the Ic value of the coil assemblies. The normalised results show that AC loss in a coil assembly with BSCCO CW can be reduced by using EWs wound with high Ic ReBCO wires, whilst further AC loss reduction can be achieved by replacing the BSCCO CW with ReBCO CW. The results imply a flexible hybrid coil structure is possible which considers both AC loss and wire cost in coil assemblies.

Section: Resultsmentioning

confidence: 73%

“…Voltage taps were attached in the end of the coils for both I c, coil and AC loss measurements. The coil assemblies were put into a double-wall structured LN 2 dewar as shown in figure 4(b) [24]. The temperature of the LN 2 was varied between 77 K and 65 K by reducing the pressure in the dewar.…”

Section: Measurement Methodsmentioning

confidence: 99%

AC loss measurements in HTS coil assemblies with hybrid coil structures

Jiang

Long

Staines

et al. 2016

“…There are two reasons for the result: one reason is the increase of I t /I c due to decrease of cable I c with applying the external magnetic field; the other reason is due to interaction between the self-field and the external magnetic fields seen in single HTS wires and stacks [24][25][26][27][28][29][30]. In figure 9, the cable I c values at self-field and B perp = 100 mT (B perp is the magnetic field perpendicular to the cable wide face) were determined by the load line method using the I c (B perp ) dependence of a Roebel strand [31,32]. As shown in the figure, the determined self-field cable I c value and cable I c value at B perp = 100 mT are 201 and 97.5 A, respectively.…”

Section: Total Ac Loss Q Totalmentioning

confidence: 99%

Total AC loss measurements in a six strand Roebel cable carrying an AC current in an AC magnetic field

Jiang¹,

Komeda²,

Amemiya³

et al. 2013

We measured the total AC loss in a 6/2 (i.e. 6 strands of 2 mm width) Roebel cable by incorporating a transport measurement method for Roebel cable into a total AC loss measurement system. The amplitude and frequency of the external magnetic field and applied transport current, and the field angle θ (the angle between the field and the normal vector to the cable surface) were varied. The results for θ ≤ 60 • scale with the perpendicular magnetic field component, and increase with increasing transport current. In the high magnetic field region, the total AC loss values for a current amplitude I I c agree with the Brandt model for a 2 mm-wide Roebel strand, not for a thin strip with the Roebel cable width. This shows the advantage of a Roebel cable over equivalent stacks composed of wider conductors. The total AC losses in a parallel magnetic field become more independent of the field amplitude with increasing current amplitude due to the increased dominance of the transport AC losses in the total AC losses. No frequency dependence was observed in the total AC loss data. A maximum entropy model was successfully constructed for the total AC loss results in a perpendicular magnetic field.

The scaling of transport AC losses in Roebel cables with varying strand parameters

Jiang

Staines

Long

et al. 2014

A Roebel cable is a good candidate for low-voltage windings in a high-temperature superconductor (HTS) transformer because of its high current-carrying capability and low AC loss. Transport AC loss measurements were carried out in 1.8 m long 15/5 (fifteen 5 mm wide strands) and 15/4 Roebel cables. The results were compared with those in many Roebel cables composed of 2 mm wide Roebel strands. Comparison of the AC losses hinted that the intrinsic difference in normalized transport AC losses is due to differences in the g/w (ratio of the horizontal gap between the Roebel strands over the Roebel strand width) values. The intrinsic difference was confirmed by measuring transport AC loss in a series of horizontally arranged parallel conductor pairs with various g values. A method to scale transport AC losses in Roebel cables with varying strand parameters was developed. The scaling method will be useful for a rough assessment of AC loss in one-layer solenoid winding coils, such as in a HTS transformer.