Online estimation of turbine–generator shaft fatigue loss-of-life caused by subsynchronous resonance

In this paper, a novel approach is presented to estimate the fatigue loss-of-life (FLoL) of larger turbine–generators that suffer from subsynchronous resonance (SSR) in series-compensated power systems. The most important contribution of our proposed approach is to estimate the mechanical torques of the turbine–generator shaft in real time with the terminal speed of the shaft and the voltage/current of the generator. With the estimated torques and the manufacturer-provided stress/torque-versus-life or S/T–N curves, FLoL can be obtained online by the well-known rainflow cycle counting technique. This approach is embedded in SSR protective or monitoring system to supervise possible FLoL due to system disturbances. As a case study, it was implemented in the torsional stress relay or TSR for the generator of the Shangdu Power Plant, which was threatened by SSR problem caused by fixed capacitor compensation. The response of the TSR during an actual fault of the studied system was recorded. Electromagnetic simulation was conducted for this specific fault. The torques and FLoL were estimated as well as compared with theoretical values and recorded data. The results showed a very good consistency and thus verified the effectiveness of the proposed approach.

► Fatigue loss-of-life of a turbine generator caused by subsynchronous resonance is estimated online.
► Mechanical torque of the shaft system is obtained in real time by using the voltage/current and the shaft speed.
► The approach is implemented in torsional stress relay and then put into engineering applications.
► Field test as well as electromagnetic simulation validates the effectiveness of the proposed approach.