In recent years we have successfully designed, built and tested several reluctance motors
with YBCO bulk material incorporated into the rotor, working at 77 K. Our last
motor type SRE150 was tested up to 200 kW. The aim of our investigations is
the construction of motors with extremely high power density and dynamics.
In comparison to conventional motor types the advantage of HTS reluctance
motors with respect to size and dynamics could be demonstrated. Some fields of
possible future applications will be described. These motors show a significant
improvement in performance using high quality HTS bulk elements in the rotor. Until
now the motor parameters have been limited by the current density which could
be obtained in the bulk material at 77 K and by the geometric dimensions of
the segments available. Therefore we expect further improvements in the case of
these materials. Since the total motor including stator and rotor is working at
low temperature we have to optimize the windings and the magnetic circuit to
these operation conditions. A new design of a 200 kW motor in order to achieve
increased power density and the theoretical results of our calculations will be shown.
Results on an established batch process preparing melt-textured YBCO of high
quality and in large quantities are reported. We used a standard composition
Y1.5Ba2Cu3O7−x+1 wt % CeO2
without further doping to fabricate single domain YBCO monoliths in different sizes and
shapes (cylindrical, quadratic) as well as rectangular multi-seeded YBCO monoliths. Up
to 2–3 kg of melt-textured YBCO blocks were grown, reproducible in one box
furnace run. Top seeding by a self-made SmBCO was improved and rationalized.
Optimization of an oxygen annealing treatment led to macro-crack free YBCO monoliths.
Each YBCO monolith was characterized by integral levitation force and field
mapping. In a single domain, a quadratic monolith with a edge length of 38 mm, a
maximum induction of 1.44 T at 77 K and a distance of 0.5 mm was frozen. The
reproducibility of the batch process is guaranteed. Mean maximum induction
from 1.1 to 1.2 T at 77 K per batch was reached. A trapped magnetic field of 2.5 T
was achieved between two single domain monoliths in a gap of 1.5 mm at 77 K.
Depending on the application, function elements with different sizes, designs and more or
less complex geometry are constructed in several working steps by cutting, machining,
bonding and passivation. Selected function elements were checked with field mapping
at 77 K. The results of our function elements in HTSC reluctance motors with
an output power of up to 200 kW using single domain material are shown. We
report on a fly wheel system DYNASTORE and a system to levitate people.
Two new types of HTS electric machine are considered. The first type
is hysteresis motors and generators with cylindrical and disc rotors
containing bulk HTS elements. The second type is reluctance motors with
compound HTS-ferromagnetic rotors. The compound HTS-ferromagnetic rotors,
consisting of joined alternating bulk HTS (YBCO) and ferromagnetic (iron)
plates, provide a new active material for electromechanical purposes. Such
rotors have anisotropic properties (ferromagnetic in one direction and
diamagnetic in the perpendicular one). Theoretical and experimental results
for HTS hysteresis and reluctance motors are presented. A series of hysteresis
HTS motors with output power rating from 1 kW (at 50 Hz) up to 4 kW (at
400 Hz) and a series of reluctance HTS motors with output power 2-18.5 kW (at
50 Hz) were constructed and successfully tested. It was shown that HTS
reluctance motors could reach two to five times better overall dimensions and
specific power than conventional asynchronous motors of the same size and will
have higher values of power factor (cos φ⩾0.7 to 0.8).
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