Rotordynamic Aspects Of A New Hermetically Sealed Pipeline Compressor.

Abstract

Mopico is an oilfree motor pipeline compressor of fully integrated design with no sealing requirements against atmospheric pressure and supported on magnetic bearings. The application of magnetic bearings for this machine represents todays extreme combination of weight and speed, The rotor weighs one ton and runs at a maximum speed of I 0000 rpm. Hence, it is not surprising that a variety of rotordynamic problems had to be solved before the machine could be operated safely. The magnetic bearings are described and the experience gained during the development of the machine is reported, based on the experimental and theoretical investigations. The important properties of magnetic bearings are the capacity limits, the damping and stiffness of the bearing and destabilizing effects, which are of a different nature to those known for compressors supported on conventional oil bearings. In the failure case, the rotor is dropped into auxiliary bearings, which are ball bearings with clearance between rotor and the inner race. The most severe condition in this emergency case is a whirling motion of the rotor, with the clearance as the radius of the orbit. The load generated on the bearings due to the centrifugal forces of this motion are very high and can destroy the bearing, if it lasts for an extended period. A corrugated ribbon between the outer race of the bearing and the housing has a damping effect in the circumferential direction and stops the whirling after a short time.