Study Of Effect For Load Models And Fault Clearing Time On Subsynchronous Resonance

As the rapid development of China power industry, especially with theimplementation of the strategic plan of “transmission of electricity from the west to theeast, exchange electricity between the south and the north, and the interconnection ofpower grids”, Nowadays, modern power system has entered the era of highvoltage,large unit and long distance transmission. In order to enchance the transmissioncapability of the corridos, series capacitive compensation measure has been widely used.But in the high series compensation degrees transmission system, the subsynchronousresonance(SSR) caused by the interactions of the high-capacity generator units and thelarge-scale gird can not be ignored. This paper studied on the characteristics ofsubsynchronous resonance, the main contents include the following tow points:①In this paper, tow load models which can be used in the SSR study have beenchoosed, and the linearized load models of constant impedance, constant current anddynamic integrated load are derived in the synchronous machines. Added the loadmodel to the IEEE first benchmark model, The FBM network model including load hasis established. Contrast to the original standard model, the linearized models containingthe load models of constant impedance, constant current and dynamic integrated loadfor analysis on SSR is established,then calculated and drawn out the trace of thesystem’s torsional mode damping containing different load models in differentcompensation degree. Therefore，it is necessary to take the load characteristic intoconsideration when analyzing the SSR stability.②In order to reduce the impact of transient torque amplification to steam turbineshaft, a methodology considering shaft torque as the torsional system response ofapplied force is given in this paper. The maximum shaft torque is finally deduced as ananalytic function of fault clearing time using a simplified four-DOF model. The resultsshow that the natural oscillation frequencies of the shaft inspired by the disturbance arein the form of torsional vibration cosine, and that fault clearing at even numbers of halfcycles of one torsional mode will generally provide appropriate torques.PSCAD/EMTDC simulation results demonstrate the validity of the conclusion.