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.

Highlights

  • A few types of active magnetic bearing (AMB) equipped rotating machinery are currently being implemented successfully in the commercial business market since the development phase of the AMB borne rotor was completed

  • It is noted that the decrease of the Nc4 critical speed to the Nc4’ is remarkably recognized by the reduction of the AMB stiffness corresponding upon the selection of the gain Ga

  • Japanese experts have prepared a draft proposal for vibration criterion to be applied to industrial turbo machines equipped with AMBs

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Summary

Introduction

A few types of active magnetic bearing (AMB) equipped rotating machinery are currently being implemented successfully in the commercial business market since the development phase of the AMB borne rotor was completed. AMBs are located at both ends of the shaft including adjacent placements of displacement sensors and emergency (auxiliary) ball bearings. Each displacement sensor detects the shaft position at bearing portions and its signal is fed back to the compensator. The deviation from the bearing center is put into the PID (Proportional, Integral and Differential actions)controller. The controller drives the power amplifiers to sup.ply the coil current and to generate the magnetic force for the levitation and vibration control. Instead of PID, many modern control laws, e.g., LQ and H-infinity, are being investigated for this servo-feedback control design

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