Axial-field HTS machine with integrated magnetic coupling
Résumé
The construction and the tests of an axial-field high temperature superconducting (HTS) machine with an integrated magnetic coupling are described. The originality of the prototype concerns the torque transmission from the cold inductor to the load at room temperature. This constitutes an interesting alternative to torque tubes currently used in HTS motors and generators. This drive solution has multiple advantages: less thermal losses, less vibrations on the shaft, natural protection against over loads, etc.
The HTS machine consists of a 3-phase stator with copper windings, a HTS rotor and a permanent magnets (PM) rotor. The HTS rotor contains 8 pancake coils, made of BSCCO tape, manufactured in our Laboratory. Four coils (double pancakes) create the magnetic field which interacts with the stator field (machine side). The four remaining coils (single pancakes) are used to transmit the torque to the load connected to the PM rotor (coupling side).
The HTS rotor has been immerged in a fiberglass cryostat and cooled at 77 K (liquid nitrogen). Several tests have been carried out as follows
Voltage vs. current curve of each manufactured coil has been measured to check its integrity,
Static torque measurements on the PM rotor have been performed for several current values and load angles,
No-load and short-circuit tests allowed us to determine the equivalent circuit parameters,
Load tests in generator mode at rated conditions showed a smooth and effective power conversion.
Most of the measured external quantities have been checked by 3D finite element computations. A good agreement is noticed.