Characterization & Analysis of the Magnetic Field of a Halbach Array and Its Utilization in Flywheel Energy Storage
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Authors
Khattak, Sadaf J.
Issue Date
1996
Type
Thesis
Language
en_US
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Abstract
The development of High Temperature Superconductors (HTS) has resulted in the
production of highly efficient magnetic bearings with frictional losses several hundred
times lower than losses which occur in bearings where the two surfaces are in contact with
each other. Because of their efficiency, these magnetic bearings are being used in the
development of a flywheel energy storage system. In such a device, electrical energy is
stored as rotational energy in a rotor which spins at speeds of several thousand revolutions
per minute. An array of HTSs are cooled to a critical temperature using liquid nitrogen, at
which point the material becomes superconducting and can levitate a magnet assembly,
creating a nearly frictionless magnetic bearing. The assembly is attached to a rotor which,
when rotated in a vacuum environment, virtually eliminates losses due to frictional forces.
A Flywheel Energy Storage System utilizing the principles described above is
currently being researched at Argonne National Laboratory. During the development of the
device, the decision was made to move away from a conventional spin-up induction motor
to a Halbach magnetic array, a dipole magnet which, in conjunction with a stator coil,
would act as the motor and generator necessary for initially storing energy in the device and
its later retrieval. A Halbach array is a dipole magnet constructed by using several
permanent magnet segments whose permanent axes are aligned to yield a uniform field.
Tests were conducted to measure the magnetic field and determine the magnitude and the
deviation from the expected field for the Halbach array that would be used. A simple two-phase
device was constructed utilizing basic electronic principles to test the Halbach array
arrangement. In the stator assembly, Hall effect sensors are used to sense the magnetic
field and produce a signal proportional to it. After amplification, the signal is fed back into
the coil and generates a magnetic field perpendicular to the field of the Halbach, creating a
torque on the array and the magnet-rotor assembly to which it is attached, thus accelerating
the rotor.
Description
vii, 50 p.
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