Torsional Interaction and Induction Generator Effect

Torsional Interaction and Induction Generator Effect

The shafts of the generators are subjected to a lot of stress and fatigue because of sub-synchronous resonance, torsional interaction, transient torques due to large disturbances and induction generator effects.The life of a shaft is dependent on how many stress/fatigue cycles it has undergone. There is a also a possibility of permanent damage to shaft if the vibrations are strong enough. These stresses can primarily occur due to SSR because of series compensated transmission lines, torsional interaction due to generator excitation controls, prime mover controls and HVDC stations near to the generators.

People often tend to confuse between Torsional Interaction (TI) and Induction Generator effect (IGE). Let us remove this confusion with the below explanation.

The figure represents a simple system where a synchronous generator is connected to an infinite bus (power system) through a step-up transformer and a transmission line which is series compensated.

The electrical system frequency fe in the presence of a series capacitor is given by the below equation where fs is the synchronous frequency (50 Hz or 60 Hz) and X” is the sub-transient reactance of the generator.