Vibration Control of a Gas Turbine-Generator Rotor in a Combined Cycle System by Means of Active Magnetic Bearings

It is well known that many lateral vibration problems occur in rotating machinery systems, for which nowadays in most cases passive measures are used to mitigate these vibrations. With the requirements for more powerful, efficient and secure rotating machinery with high availability the demand for more efficient vibration reduction measures increases. Active magnetic bearings (AMB) can be used as a possible solution, since it generates magnetic fields and forces to control the rotor vibrations, without rotor-bearing contact. AMBs are often used in special applications, for example in high-speed/high-performance turbomachinery like turbo-compressors for the oil and gas industry or in machine tool applications. The main problems of implementing active vibration control by means of AMBs are the energy transfer towards the rotating system, best suited concepts to control the lateral vibrations and the design of reliable backup bearings for special applications. One of the most common causes of high vibration amplitudes is the unbalance of a rotor, which leads to 1xN vibrations. In this work it will be shown, how these unbalance vibrations can be best controlled by an AMB. This paper consists of a purely numerical analysis for a combined cycle turbine, in which two separated cases are studied: 1. the complete analysis of the operational setup, where the turbine is supported with radial oil-film bearings (RFBs) only, and 2. The oil-film bearing in the gas turbine side, where the vibration amplitudes are higher due to the unbalance generated by the fluid flow, is replaced by one AMB.