Thermally Induced Synchronous Vibration Instability in a Magnetic Bearing Supported High-speed Rotor

This paper describes a synchronous vibration instability problem that occurred on a two-stage overhung centrifugal compressor. The authors encountered an unbalance vibration that increased spirally in a polar plot at/near the first bending critical speed. An iron loss concentration and a thermal bend by heat have been identified as the cause of the phenomenon, because the vibration stops increasing, when an unbalance force rejection control (UFRC) is applied. In order to exceed the first bending critical speed stably, an rotor unbalance measurement under UFRC and a rapid speed acceleration/deceleration are carried out. The vibration behaviours around the critical speed are simulated and verified experimentally. The stability limit that is depending on rotational speed is calculated and the most important parameter |H/P| in the calculation are determined by measurements.