A New Approach for Investigation of the Turbine Generator Oscillatory Behavior Affecting Power System Quality and Reliability

Transients following switching in the network and/or the tripping of generating unit auxiliaries can excite oscillatory torques on the turbine-generator-rotor-shaft system. The oscillations can be damped or amplified with time. Damped oscillations affect the power quality and if the oscillations grow with time they may even lead to generating unit outages (and damages) resulting in possible system instabilities. Deregulation of electricity markets has resulted in separation of Utility Companies (responsible for power generation) and Transmission Companies (responsible for power transmission). The decision making is no more under the same umbrella. Companies on both the sides have severe cost reduction focus and each side is tempted to make independent decision favourable to it. The Transmission Companies want to enhance transmission capacity of existing systems by introducing measures like series capacitor compensation. However incorporation of series capacitor compensation may under certain conditions lead to oscillations and also snbsynchronous resonance. Currently, there is an urgent need to establish a systematic methodology to investigate the root cause of such oscillations so that preventive measures can be taken by both the Utility Companies and the Transmission Companies. This paper is a contribution in this direction. In this work, comprehensive dynamic model of synchronous generator system has been developed in software Matlab/Simulink. Generating unit start up and ramp loading to rated load has been simulated to get deeper insight into the oscillatory behaviour of the synchronous generator. Block loading of the turbine generator and sudden load shedding due to auxiliary trip have been investigated in detail. Further, power system network with bus connected parallel generating units and parallel transmission lines, having different series capacitor compensation ratio have been simulated in power system software NETOMAC. Transient conditions have been modelled to investigate the oscillations and the consequent torsional torques and angles between adjacent masses of the rotor shaft system causing fatigue life reduction. This work has very clearly revealed the complex dynamic interrelationship among variables responsible for power system oscillations.