Probability assessment of turbine-generator shaft torque following severe disturbances on the system supply

This paper presents a probabilistic approach to the evaluation of the maximum torsional torques induced in turbine generator shafts following severe supply network disturbances with clearance, during high-speed auto-reclosure, and resulting from mal-synchronisation. In this context the investigations have been conducted on a range of machines taking into consideration the uncertainty of several factors associated with the practical operation of the power system. The results of these investigations are presented in the form of discrete probability distributions of the maximum torsional torques induced in the turbine-generator shaft sections. Also examined is the effect on maximum torsional torques of employing detailed (2d, 3q) and reduced (1d, 1q) damper models of the synchronous generator. First, simulation of turbine-generators with up to 9 masses, using detailed and reduced rotor circuit models where L-L-L, L-L-G, L-L and L-G faults are cleared at fault current zeros and governor and AVR effects are represented, are summarised. Then, probability of disturbances and peak shaft torque at turbine-generator shaft sections following bolted stator terminal short circuits and as a function of fault clearing time and following mal-synchronisation for a range of typical machines are presented. An approach to evaluate maximum turbine-generator shaft torques considering the uncertainties associated with the occurrence of disturbances and their attendant protective switching sequences is outlined.