Abstract
This paper focuses on the study of the frequency-dependent transport ac loss of YBa2Cu3O7−δ (YBCO) coils and how it is influenced by flux diverters. A single pancake coil is wound by AMSC 8501 tape and its transport ac losses (in the frequency range of 50–1000 Hz) are investigated through the use of both experimental and finite element methods. The finite element model is based on the H-formulation and E-J power law, and it takes both the magnetic field dependences of critical current density and degradation of critical current density close to the edges into account. Different loss components (namely hysteresis losses in HTS layers, ferromagnetic losses in weakly magnetic substrates, eddy current losses in conventional metal and ferromagnetic losses in flux diverters) of YBCO-NiW coils at different frequencies are calculated by using the numerical model. The calculated ac losses accord well with the measured ones, which validates the numerical model. The influence of the flux diverter on different loss components at low/high frequencies is analyzed numerically. It is found that the flux diverter greatly decreases the hysteresis loss per cycle, but causes an enhancement of both eddy current and ferromagnetic losses per cycle. We propose a new parameter to clarify the region where flux diverters can effectively decrease the transport ac loss per cycle of the YBCO-NiW coil.
Published Version
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