Effect Of Rotor Eccentricity On The Performance And Protection Of The Large Salient-Pole Synchronous Generator

In a large hydro-generator, air gap eccentricity exists because of procedures of on-site installation and variety of operating conditions, which causes circulating currents among the parallel-connected windings and unbalanced currents in the main protection equipments. In China there are several incidents on the main protections which occurred in the Ertan and Fengtan Hydroelectric Power Plants. However, off-line check on the hydro-generators in these hydroelectric power plants showed that there was no stator's internal fault found and that rotor eccentricity was possible. Based on the above cases, the effects of rotor eccentricity on the performance and protection of the large salient-pole synchronous generator are analyzed systematically and the theoretical and mathematical models are proposed.A model combined FEM with multi-loop method, which is proposed to analyze the effect of the rotor eccentricity in the large salient-pole synchronous generator, can be divided into two parts: One is the solution of the voltage equations which express the generator external characteristics, and the other is the calculation of the electromagnetic parameters which present the internal characteristics. The multi-loop model regarding the stator branch as basic branch with eccentricity is set up.A mathematical method calculating inductance parameters in the salient-pole synchronous generator with rotor eccentricity is proposed in this paper. The quasi-static electromagnetic field in the generator with rotor eccentricity is analyzed using 2D time-stepping Finite Element Method (FEM). The self inductances of stator winding branches, mutual inductances between the stator and the rotor branches and the self inductance of the rotor excitation winding are calculated. The end-winding leakage inductances of the generator with rotor eccentricity, which can not be considered by 2D FEM, are calculated using numerical method which deals with the load end-windings and inter-linkage end-windings by employing the subsection, subarea and mesh division. A branch winding incidence matrix and a unified algorithm are developed to compute the end-winding leakage inductance of each stator branch in the generator. The characteristics of the inductances and the no-load inductive EMFs of stator winding branches in the salient-pole synchronous generator are analyzed. In addition, the effect of the core magnetic reluctance on winding inductance calculation is quantified.Eccentricity ratio is varied on a 3 kW, 12-pole salient-pole synchronous generator under no-load operation and under the three-phase symmetrical resistance load. Simulation and experimental results coincide well, which validates that the analysis method in this thesis is able to simulate the rotor eccentricity in the salient-pole synchronous generator correctly.The effects of the rotor eccentricity on the main protection designs are quantified. The influence on the main protection caused by the unbalanced currents due to eccentricity, such as zero-sequence current transverse differential protection, split-phase transverse differential protection, incomplete and complete longitudinal differential protection, is analyzed in details. Lastly, the model is applied in the main protection design of a 550 MW hydro-generator in Ertan Hydroelectric Power Plant considering the effect of rotor eccentricity. The right values of the main protection configuration scheme can be determined accordingly.