Numerous important applications, such - PowerPoint Presentation

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Numerous important applications, such as motors, transformers, of superconducting wires and cables are used under rapidly changing magnetic fields. Turbo-electric distributed power aircraft design calls for a motor/generator set to deliver power to motor-driven fans positioned along the wings. There is some power loss associated with the conversion, this is more than made up for by the increased efficiency by what is in effect an enhancement of the fan by-pass ratio. YBCO coated conductor is of great interest because of its high Tc (90 K), and its high critical current density. However, it has significant AC loss in these environments because of its wide tape geometry. In addition it is difficult to fabricate the filamented types favored for hysteretic loss reduction. Existing test devices have serious limitations: they can either reach the target B or the needed dB/dt, but not both simultaneously. In this work, we discuss the development of a machine (Spin- Around-Magnet, SAM) which can provide both an acceptably high B as well as dB/dt for the needed study and analysis of coated conductors (and small windings) required for the windings of motors and generators. Good agreement was obtained between the results of the SAM AC loss measurement and the solenoidal magnet AC loss measurement . This more detailed work is based on our previous work[1] on the machine.

8-pole permanent magnet rotor. in a Halbach configuration. The N-S-N variation of the poles around the rotor periphery are consistent with the N-S-N arrangement of the magnets aligned along This test instrument has a 1.5 inch annular gap to permit placing HTS samples or test windings for exposure to a high dB/dt environment.Outside of this region, the presence of the back-iron allows the sample or coil to be in a field which is relatively uniform along the radial direction but changing with time (or angular position). The SAM machine is under vacuum during operation to minimize heat leak to the calorimeter, and any accompanying LN2 boil-off baseline.

Figure. 3. Calibration of calorimeter. P(W) = -0.0096+2.7581*GF + 1.0575*GF2 -0.2346*GF3

the smaller one is for one- watt resistors soldered in series (each 33 at room temperature and 126.6 at 77 K) the larger one includes two aluminum plates with a total surface area of 90 x 39 x 5 mm surrounding a Kapton film heater (Omega #KHLV 103/5-P, measuring 51.3 at 77 K).

A new facility for the measurement of AC loss in superconductors at high dB/dt has been developed. In addition, the relatively large sample space will allow the insertion of small windings, which will effectively allow a small scale generator test bed for prospective motor/generator coils. The radial and tangential fields are approximately sinusoidal, 90Ω out of phase, and with peak amplitudes of 0.566 T for the radial direction, and 0.242 T for the tangential direction. The rotor can reach 3600 RPM, the frequency 240 Hz, the radial dB/dt 543 T/s, and the tangential dB/dt 249 T/s.Loss is measured using nitrogen boiloff from a double wall calorimeter feeding a gas flow meter. The data for all samples agreed well, and the range of the data spread for a given ramp rate was ± 5%.

AC loss in YBCO Conductors and Cables at High dB/dt Measured using a Spinning Magnet Calorimeter (Stator Testbed Environment)

1 University of Dayton Research Institute, Dayton, OH 45469-0073 USA 2 Universal Energy Systems, Dayton, OH 45432 USA 3 Aerospace Systems Directorate of the Air Force Research Laboratory, Wright-Patterson AFB, 45433 USA 4 CSMM, Department of Materials Science and Engineering, The Ohio State University, Columbus OH 43210 USA

M.D. Sumption4, J. P Murphy1,2, N N. Gheorghiu2,3, T. Haugan3, M. Majoros4, and E.W. Collings4

3. AC loss and Calibration

2. The SAM machine structure and materials used

First, the calorimeter was filled with LN2 as was the outer can of the double wall calorimeter. With the resistor excited with DC current and the current and voltage recorded the flow rate of the nitrogen gas boil-off, GF, was measured by the flowmeter in standard liters per minute (SLPM).

References & Acknowledgement

1. Introduction

This work was supported by the Air Force Office of Scientific Research (AFOSR), the Air Force Research Laboratory, and the Summer Faculty program at WPAFB.

4. Results

the hysteretic loss

:

𝑃ℎ𝑦𝑠,𝑣≈𝑤𝐽𝑐𝐵𝑚𝑎𝑥𝑓 *

the normal metal eddy current loss :𝑃𝑒𝑑,𝑣=

power loss per unit length

*Originally from the work of Brandt

[2,3]

and then in a modified form in Muller [4]

5. Summary

1. J.P. Murphy, M.J. Mullins, P.N. Barnes, T.J. Haugan, G.A. Levin, M.Majoros, M.D. Sumption, E.W. Collings, M.Polak, and P. Mozola, “Experiment Setup for Calorimetric Measurements of Losses in HTS Coils Due to AC Current and External Magnetic Fields”, IEEE Trans. Appl. Supercond. 23 (2013) 4701505.

2. E.H. Brandt, M. Indenbom, Phys. Rev. B 48 (1993) 12893 3. E.H. Brandt, Phys. Rev. B 49 (1994) 9024 4. K.-H. Muller, “AC power losses in flexible thick-film superconducting tapes”, Physica C 281 (1997) 1-10

Figs. 1 and 2

. Configurations of the SAM machine

Fig. 6.

. CORC

cable loss per unit meter of tape, as compared to tape loss per unit meter of tape. CORC cable was oriented horizontally

.

Fig. 5.

Power

loss (per unit length) normalized by

B*f

vs

B*f for SMC (shown in red) (YBCO-2) and solenoidal susceptibility rig (shown in black, for YBCO-1).

Fig. 4. Power Loss for YBCO tape samples 2 and 3. Black line is Brandt equation fit with Ic = 38 A, and red line includes eddy current contribution for RR (77 K) = 4.0.

Fig

. 7. CORC cable loss per unit meter of tape multiplied by the factor /2

Samples were striated

L = 10 cm, untwisted