We measured the frequency dependence of hysteresis loss in non-striated and striated
YBCO coated conductors in the frequency range from 1 mHz up to 350 mHz at 77 K. At
these frequencies the coupling losses in YBCO coated conductors do not exist and in
filamentary YBCO tapes they can be practically neglected. The dominant loss component
is the hysteresis loss. We have found that for magnetic fields above the full penetration field
the hysteresis loss increases with increasing frequency and this dependence can be
described by a power law function. For magnetic fields below the penetration
field the hysteresis loss decreases with frequency. This behaviour supports the
previous theoretical results indicating that the field dividing the behaviour of
hysteresis losses versus frequency is the penetration field. The experiments with
YBCO samples on non-metallic substrate at frequencies up to 600 Hz show that
the dependence of hysteresis losses measured at millihertz frequencies can be
extrapolated to higher frequencies of the order of 100 Hz. We propose a simple
procedure to separate the hysteresis losses from the total measured losses based on the
measurement of the frequency dependence of losses at low frequencies. Taking
into account the frequency dependence of hysteresis losses we can considerably
reduce the errors in the separation of hysteresis losses from the total measured
losses.
The properties of a small pancake coil made with a 10mm wide copper-stabilized YBa2Cu3O7−x (YBCO) coated conductor were investigated. The radial component of the magnetic field was mapped at the coil edge in both the dc and ac regimes and differs significantly from that calculated assuming a uniform current distribution. The observed hysteresis indicates the strong influence of the ferromagnetic properties of the substrate. The ac losses of the coil were measured for ac frequencies between 60 and 1000Hz. The differences in properties of the YBCO coil and a similarly prepared copper coil are discussed.
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