51 research outputs found
AC losses in type-II superconductors induced by nonuniform fluctuations of external magnetic field
Magnetic field fluctuations are inevitable in practical applications of
superconductors and it is often necessary to estimate the AC losses these
fluctuations induce. If the fluctuation wavelength is greater than the size of
a superconductor, known estimates for an alternating uniform external magnetic
field can be employed. Here we consider the opposite case and analyze, using a
model critical-state problem, penetration of spatially nonuniform fluctuations
into type-II superconductors. Numerical simulation is based on a variational
formulation of the Bean model. The analytical solutions, found in a weak
penetration limit, are used to evaluate AC losses for two types of
fluctuations: the running and standing waves. It is shown that for spatially
nonuniform fluctuations the losses are better characterized by the fluctuation
penetration depth than by the fluctuation amplitude. The results can be used to
estimate the AC losses in flywheels, electric motors, magnetic shields, etc.Comment: 18 pages, 5 fugure
Thin shell model of a coated conductor with a ferromagnetic substrate
Coated conductors with magnetic substrates are thin multilayer structures;
their high aspect ratio and nonlinear material properties present significant
difficulties for numerical simulation. Using the high width-to-thickness ratio
of coated conductors we derive an integral formulation for a model based on an
infinitely thin approximation for the superconducting layer and a quasistatic
thin shell approximation for the magnetic substrate. The proposed model
describes electromagnetic response of a coated conductor with a magnetic
substrate and is much simpler than the existing models. A single dimensionless
parameter characterizes the substrate having a finite magnetic permeability and
a finite thickness. An accurate and efficient Chebyshev spectral method is
derived for numerical solution. The influence of a magnetic substrate on the
superconducting current and AC losses is investigated. In the limiting cases
our model solution tends to the known analytical solutions.Comment: Submitted to IEEE Transaction on Superconductivit
Comparison of a Self-Limiting Transformer and a Transformer Type FCL with HTS Elements
A superconducting fault current limiter of the transformer type (inductive
FCL) based on magnetic coupling between a superconducting element and a
protected circuit has been investigated by many authors for various parameters
and performances of a superconducting element. Another design of the device
preventing high short-circuit currents is a self-limiting transformer combining
the functions of a usual power transformer with the functions of a current
limiter. In the presented work we compare the parameters, operation and
application of these two devices. The operation of the devices is investigated
experimentally on small models fabricated using the same superconducting
element. The parameters of the full-scale devices are evaluated. It is shown
that the requirements to superconducting elements are practically the same for
both devices.Comment: submitted to Applied Superconductivity Conference 200
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