Centrifugal compressor and magnetic bearing backup system for centrifugal compressor

A centrifugal compressor used to compress refrigerant and adapted to be used in a chiller system including an evaporator, a condenser, and an expansion mechanism, the centrifugal compressor comprising:

• a casing having an inlet portion and an outlet portion;
• an impeller attached to a shaft rotatable about a rotation axis;
• a motor configured and arranged to rotate the shaft in order to rotate the impeller;
• a diffuser disposed in the outlet portion downstream of the impeller;
• a magnetic bearing rotatably supporting the shaft, the magnetic bearing being arranged on a magnetic bearing portion of the shaft;
• and
• a magnetic bearing backup system configured and arranged to support the shaft when the magnetic bearing stops operating, the magnetic bearing backup system including
• at least one dynamic gas bearing and at least one hydrostatic gas bearing arranged on a backup bearing portion of the shaft so as to be adjacent to each other in an axial direction of the shaft, and
• a refrigerant supply line arranged to supply a refrigerant gas to a first gap between the at least one hydrostatic gas bearing and the backup bearing portion,
• the first gap being smaller than a second gap between the magnetic bearing portion and the magnetic bearing,
• the at least one dynamic gas bearing and the at least one hydrostatic gas bearing being disposed radially inwardly relative to the magnetic bearing.