Influence of turbogenerator set parameters on the calculation of shaft transient torsional strains

Abstract

The paper involves an analysis of the impact of some turbogenerator set parameters which considerably influence its mechanical behaviour on the calculations of torsional strains. The analysis is carried out for a caSe of a three-phase short circuit at one of two parallel lines through which a generator is supplird followed by a fault clearing. Maximum torsional tor-qucs and critical fault clearing times at which they occur are presented. The mechanical parameters which have the largest influence on the torsional strains in the shaft are the stiffness coefficients of the shaft sections and the mechanical time constants (or moments of inertia) of the generator and the turbine rotors. The influence of mechanical damping coefficients is less significant. Maximum torsional torques are also indirectly influmiced by electrical parameters of the generator, prirriarilly by the subtransient and the transient synchroinouis rcactance, but their impact is minor. CalcuLated time responses off torsional t o r q u a for the combined failk show that inaccurately defined mechanical paran:ieters can lead to wrong conclusions concerning inaxiinum values of torsional torques which could occur during a fault.