Vibration Criteria Considered from Case Studies of Active Magnetic Bearing Equipped Rotating Machines

Abstract

The main part of turbo machinery is conventionally supported by oil film lubricated bearings. The rotor vibrations can be suppressed within low levels as to satisfy vibration criteria, e.g., ISO standards for general rotors and API 617 for process compressors. Recently, the sophisticated advantages of the active magnetic bearing (AMB) have been increasing the number of applications to industrial rotors. The AMB vibration control design requires the weak support which induces inevitably large vibration amplitude, though it is normal for AMB itself. Vibration criteria indicated by present standards are thus too strict for AMB equipped rotors. The difference of the bearing dynamic characteristics between the oil film lubricated bearing and the AMB compels us to prepare a new ISO standard which recommends the acceptance of higher vibration levels for AMB operation.In this paper, a case study was executed concerning AMB equipped LP and HP compressors experiencing long-term operation with no major trouble since December, 1992. The rotating rated speed, 10900 rpm, is beyond the first bending critical speed with 5300 kW of power. The average value of the rotor vibration was about 50 μmpp in the site operation. By reviewing the rotor design concept and field data of these AMB equipped machines, new vibration criteria are considered for a proposal of ISO standardization.