Study On Torsional Interaction Of The Large Combined Cycle Unit With Power Systems

Many large gas-steam combined cycle units are put into service in China nowadays. However, the related torsional interaction problems have not gotten enough concerns. The torsional interaction of large gas-steam combined cycle units with power systems was studied in this thesis, base on the background of the project of 350MW gas-steam combined cycle units in Shenzhen Eastern Plant.Firstly, the data of 350MW gas-steam combined cycle units in Shenzhen Eastern Plant were collected and analyzed in detail. The equivalent inertia and spring constants were estimated based on some useful data. A simulation model of the torsional interaction of 350MW gas-steam combined cycle unit with the power system was proposed with the aid of the SimPowerSystems toolbox in MATLAB.Secondly, the impacts of the different faults at different locations together with the reclosure operation on transient torques between different masses of the shaft system of the combined cycle unit were simulated and discussed. It is illustrated that the maximum transient torque is between the low pressure steam turbine and generator in the case of the 3-phase-to-ground fault nearby the generator. And the impacts of the short faults were counteracted to some extent by the reclosure operation just in the studied cases, but not in all the cases.At last, a simplified steady model of the power output of combined cycle units is developed. And then the torque response of the shaft system is simulated and discussed while the combined cycle unit is used to regulate the peak power. The results show that the change of the torques between different masses is slow and the impact of the peak power regulation on transient torques is very small as well.The thesis work can be used for reference to promote the security and economy of the large combined cycle unit in our nation and the level to introduce and master the foreign technique.