Analysis Of Short Circuit Faults For Hydro-generator With Asymmetric Brand Windings

In the hydro-generator design process, the choice of rated speed should not onlyconsider basic parameters, such as rated voltage, rated power factor and stator lineload, but also consider the turbine speed. As affected by hydraulic conditions in thedesign of hydraulic turbine speed, these parameters often do not match each other. Inorder to improve the generator design rationality asymmetric branches windingconnection method is adopted. In this paper， a300MW hydro-generator withasymmetric brand winding is taken as an example, the transient processes of statorwinding and field winding short-circuit faults are analyzed and simulated based on2-D finite element method.Firstly, the symmetry condition of the stator winding was analyzed, and putforward two methods which were suitable for the asymmetric brand windings,according to the traditional winding connection of the lap winding and the wavewinding. Then the method was used to get two wave winding connection schemesand two lap winding connection schemes. Establishment of a2D field-circuitcoupled finite element model to simulate load operating conditions analysis andmany useful physical quantities were obtained, such as branch current waveform,phase voltage waveform and harmonic content, etc.Secondly, in the no-load operation condition, simulation analysis of three-phaseshort circuit, two-phase short circuit and single-phase short circuit three kinds ofcircumstances, Get three phase current, each branch current and the excitationwinding current transient waveform in the fault time. Analysis the rules of the branchcurrent in different winding connection method, reveals the branch currentcharacteristics of asymmetric branches winding of turbine generator fault time. Atthe same time, damping winding influenced on stator current and excitation windingcurrent of these three kinds of faults was studied.Finally, changing rule of excitation winding current and fraction-harmonics ofbranch current were studied, through the analysis of excitation winding inter-turn short circuit fault on the no-load operations, and the position of fault influenced oncharacteristics of brand current was studied too. Using this analysis as a foundation,a detection method of excitation winding inter-turn short circuit fault ofhydro-generator with asymmetric brand windings was put forward. Compared withthe searching coil method and method based on the stator circulation characteristics,this method can effectively diagnose the excitation winding inter-turn short circuitfault of the hydro-generator with asymmetric branches winding, because this methoddid not use current between stator branches as the basis.