Study On Impact Of Electrical System Large Disturbances On Turbine-Generator Shaft Torsional Oscillation

As the development of the power industry, the generator unit has larger capacity and the shaft becomes more flexible, also the interconnected power gird is huger and more complicated, which make the torsional oscillation problem between the unit and grid more and more notable. The torsional oscillation problem will make the shaft endure big torque time and again, which produces the fatigue life loss and even makes the shaft broken. Since the 1970s, many internal and overseas shaft accidents happened, and great loss has been brought. The torsional oscillation is considered as an important problem for the power system safety, and should been studied and resolved.This thesis is focused on the impact of electrical system large disturbances on turbine-generator shaft torsional oscillation. The main work is as follows:(1)A professional program MANDISP2007 is developed to study the shaft torsional oscillation and fatigue loss problem. Use the Visual Studio. Net to develop the new version program MANDISP 2007 version. Then to evaluate the Dongfang Tuibine Generator Company 600MW air cooling turbine generator's shaft torsional oscillation characteristic, simulate the transient torque and figure out the fatigue loss. All these results will be the manufacturer's turbine generator technical specification.(2)During the calculation and evaluation, some faults will lead to great impact on the shaft. So this part of the thesis will analyze the detail of two typical disturbances. Use the synchronous motor equations to calculate electromagnetic torque equations during the faulty synchronizing and three-phase short circuit near the power station. Then use the MANDISP2007 simulation results to compare with the equations results. Also many turbine-generator manufacturers are using the PH0975 program to evaluate the shaft torsional oscillation. In PH0975 program, the electrical and mechanical parts are divided. So before the simulation, the user needs to provide the electromagnetic torque equations for the different electrical disturbances. Then the results of this part can also help them to use PH0975 program.(3)In PSCAD/EMTDC, a self-defined shaft model is developed based on the mode depression method, then a SC system fault is simulated to analyse the shaft fatigue. As the current version MANDISP doesn't have some electrical equipment models (such as SC and HVDC), and now can only consider one detailed shaft model, both of which make this program can't be used in some complicated simulations. So this part will propose a new method based on the EMTDC to analyze the torsional oscillation problem. Since the EMTDC only has the 7 masses shaft model, use the user Module to develop a detailed shaft model. The method is based on the mode transfer and mode depression, and can consider the hundreds of sections. Also a fatigue loss program is developed to evaluate each fault's fatigue loss. Then we use this method to research a real SC power system's shaft torsional oscillation problem.