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#### Transport AC losses of YBCO pancake coils wound from parallel connected tapes

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##### Citation

Grinenko, V., Fuchs, G., Nenkov, K., Stiehler, C., Vojenčiak, M., Reis, T., et al. (2012).
Transport AC losses of YBCO pancake coils wound from parallel connected tapes.* Superconductor Science
and Technology,* *25*(7): 075006. doi:10.1088/0953-2048/25/7/075006.

Cite as: http://hdl.handle.net/11858/00-001M-0000-0010-23DA-5

##### Abstract

The transport AC losses (Q

_{tr}) of YBCO pancake coils wound from n = 1, 2, 4 non-transposed parallel connected (n-tpc) tapes have been investigated experimentally and theoretically. It was found that the Q_{tr}AC losses of the coils with several n-tpc tapes consist of hysteresis AC losses (Q_{h}) and coupling AC losses (Q_{cc}). AC losses Q_{h}of these coils are nearly the same as the AC losses of single-tape coils (n = 1). In contrast, Q_{cc}are unique for coils with n > 1 n-tpc tapes. We found that the distribution of the coupling currents in the coil turns is defined by the magnetic flux penetrating between n-tpc tapes. This flux is related to the self-field component of the coil parallel to the tape surface, which is antisymmetrically distributed (an odd function) with respect to the winding center. This antisymmetrical distribution leads to a compensation effect of the coupling currents if n-tpc tapes are insulated along the turn length, in spite of low resistance between n-tpc tapes in the soldered coil ends. Therefore, AC losses Q_{cc}of such coils are negligibly small compared to AC losses Q_{h}. On the other hand, AC losses Q_{cc}per current cycle are frequency dependent and have a maximum defined by the time constant τ_{eff}if tapes are non-insulated along the turn length. In this paper we estimated τ_{eff}for several special cases. In particular, we found that Q_{tr}of YBCO pancake coils wound from several n-tpc tapes are comparable to Q_{tr}of single-tape coils if the operating frequency f is far from the characteristic frequency 1/τ_{eff}.