Stressing of Large Turbine-Generators at Shaft Couplings and LP Turbine Final-Stage Blade Roots Following Clearance of Grid System Faults and Faulty Synchronisation

The paper examines transient torque phenomena which can arise at LP turbine blade roots and at shaft couplings of large synchronous-generators following a grid network disturbance. Fault clearance and faulty synchronisations for two 3000 rpm 660 MW turbines and a 3600 rpm, 300 MW turbine is examined. Peak torque at various shaft locations and at the LP turbine final-stage blade roots is computed as a function of the fault clearing time or the synchronising angle respectively. Stresses induced at LP turbine blade roots where the shaft system is protected against excessive stress by use of a turbine/generator shearing coupling is examined for one turbine only. Sustained 3-phase and line-to-line faults at the generator stator terminals are also considered.