A Methodology for Estimating the Parameters of Steam Turbine Generator Shaft Systems for Subsynchronous Resonance Studies

Abstract

The increase of coal and nuclear power steam turbines over the past few decades combined with transmission line series capacitors creates a potential drawback known as subsynchronous resonance (SSR) by increasing the risk of interaction between electrical power systems and turbine-generators’ rotor torsional systems. Current work presented here adds to a growing body of solutions and preventive measures developed by power industry professionals to address this problem by proposing a new methodology to estimate the shaft spring constants non-intrusively using measurement signals from the shaft systems. A significant contribution of this work has been in determining, after a thorough investigation of eigen properties of several steam turbine generator shaft systems, which of the non-intrusively available measurement signals, is the best candidate to be used for extracting the shaft torsional modes. The finding that the use of the high-pressure rotor section speed signal is significantly better than the instantaneous power signal in extracting the torsional modes through modal decomposition has been verified using measurement signals obtained from simulations, as well as real measurements. The modal components, which were extracted using Prony’s method, were later used along with rotor section moment-of-inertia values to successfully estimate the shaft spring constants of steam turbine generator shaft systems that were simulated in ATP. In addition, an algorithm has been developed to reorder the output modes of Prony’s method to identify the power system modes.