An Investigation of Excitation Method for Torsional Testing of a Large-Scale Steam Turbine Generator

Presently, the negative sequence current method is widely used in field-testing to determine torsional vibration characteristics of steam turbine generator rotor systems. The natural frequencies of lower modes of vibration can be determined effectively in this way, but higher modes cannot be readily excited. To understand this phenomenon, modal analysis was employed to digitally simulate the dynamic response obtained in torsional vibration testing of a 200MW steam turbine generator rotor system. The calculations were consistent with field experimental results, showing that higher modes are difficult to excite by this method. The research also indicated that higher modes could be excited by certain experimental procedures. The conclusions provide guidelines for future field-testing of large-scale systems.