TWO-STAGE CENTRIFUGAL COMPRESSOR DRIVEN DIRECTLY BY MOTOR

摘要

A two-stage centrifugal compressor driven directly by a motor which has impellers directly mounted on both end portions of a shaft thereof, and which comprises an inverter-driven high-frequency motor rotatable at a high speed, the rotary shaft being supported rotatably on magnetic bearings, whereby the two-stage centrifugal compressor does not require an oil and maintenance work. A rotor of the motor comprises a permanent magnet, a ring-shaped carbon fiber-reinforced plastic member for retaining the permanent magnet, and a metal sleeve for holding the permanent magnet between the metal sleeve and the carbon fiber-reinforced plastic member, the occurrence of a clearance between the permanent magnet and the rotary shaft which is liable to be encountered during a high-speed rotation of the motor being prevented by utilizing the strength of the carbon fiber. The rotary shaft which is rotated at a high speed causes the motor to generate heat due to an iron loss, a copper loss and a windage loss, and also the magnetic bearings to generate heat in the same manner, a part of an operating gas which has been cooled in an intermediate cooler or a discharge cooler being therefore introduced into a central portion and a labyrinth of a stator of the motor to cool the motor and magnetic bearings.