Finding causes for low-frequency vibration in centrifugal machines with magnetic bearings
Kistoychev A.V., Ur’yev E.V. (The Ural Federal University named after the first Russian President Boris Yeltsin, RF, Yekaterinburg), Lun-Fu A.V. (OOO Gazprom Transgaz Tomsk,RF, Tomsk)
Presently, magnetic bearings are in widespread use with natural gas compressors. In addition to other known advantages, no stiffness cross-coefficients apply to such bearing designs. As a result, there is little probability for non-conservative circulation forces to emerge causing low-frequency rotor self-oscillations. However, this would by no means avoid such forces to occur in compressor flow channel. Under normal operation of Iskra’s NTs-15 DKS/100 centrifugal compressors, dynamic stability loss was reported in its rotor-supports section – when both rotating frequency and compression ratio rose by 0.6–0.7 of respective ratings. This paper presents estimates and tests which confirm that labyrinth packing circulation forces appear to be the main cause of such self-oscillations. The proposed dummy packing upgrade helped us reduce flow twisting and ensure normal operation without any constraints.
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