Study On The Deterioration Law And Diagnosis Method Of The Rotor Turn To Turn Short Circuit Fault Of Turbo Generator

The turn to turn short circuit fault of rotor occurs frequently during the operation of the turbo generator,due to the slight short circuit has little effect on the normal operation,and most of the units do not install the on-line detection system for rotor faults,resulting in China's existing large turbine generator units with slight rotor inter turn short circuit operation.Therefore,a timely diagnosis of minor rotor inter-turn short circuit fault is very important.If the generator encounters a bad working condition during the inter-turn short circuit of the rotor,may cause rapid deterioration of short circuit,accurate analysis of the change characteristics of critical electrical quantities,would provide reliable theoretical support and decision support for the maintenance of short circuit fault of the generator running with the disease.The main work of this paper are as follows:(1)A two-dimensional finite element simulation model of a 300 MW turbo generator was established,considering the connection mode of stator and rotor windings,also with the eddy current effect,skin loss and the nonlinearity of the iron core material.And verified the accuracy of the model in two cases of rated load and no-load operation.(2)Considering the damping system of the motor,the effect of asymmetric operation of generator on the deterioration of rotor inter-turn short circuit fault was analyzed.The influence of changing the number of short circuit turns,the short circuit position and the transition resistance of short circuit point on the change of transient electrical quantity was also studied.The heating at the short circuit point was calculated.(3)The change of the key electrical quantity of the generator before and after the demagnetization was analyzed,under the state of open-circuit loss of excitation winding,the influence of the transition resistance of the rotor short circuit,the short circuit position and the short circuit point on the change of the electrical quantity was studied,providing certain decision support for the maintenance of the generator under bad working conditions.(4)A new method for off-line detection of inter-turn short-circuit fault based on excitation step method was presented.By establishing a field coupled time stepping finite element model for a 300 MW motor,the effectiveness and accuracy of the method are verified.