| The stator bar is one of the core components in a high-voltage generator,and is a component with multiple stress concentrations such as electrical,thermal,mechanical and environmental.According to statistics,insulation faults account for 56%of hydrogenerator faults,while stator insulation faults account for two-thirds of the insulation faults.The stable performance of the stator bar has a great influence on the stable operation of the generator.Once the stator bar has a problem,it will cause the generator to stop,and even cause damage to the stator winding,causing significant economic losses.Therefore,increasing the electrical life of the stator bar of the high-voltage generator is an important means to ensure the stable operation of the generator and increase the operating life.This paper conducts a systematic research on the optimization of the insulation structure of the stator bar of a high-voltage generator,and establishes a rapid electrical life evaluation method for evaluating the optimization effect of the stator bar structure,which effectively improves the electrical performance and operational stability of the stator bar and winding.The optimization of the ground wall insulation structure of the stator bar slot of the high-voltage generator is systematically studied.A new empirical model of the internal fillet radius and the electric field nonuniform coefficient under the fillet electrode structure is established.On this basis,the calculation method of the ground wall insulation thickness of the stator bar is determined,and the relationship between the ground wall insulation structure parameters and the electrical life of the bar is obtained.With the life of stator bar as the objective function and the bar size and slot full rate as the constraint conditions,an optimization method for bar insulation structure is proposed based on genetic algorithm,and the the ground wall insulation thickness and inner fillet radius are obtained.Compared with the traditional method,the maximum electric field in the ground wall insulation is effectively reduced,and the electric life of the stator bar is improved.Based on the FEM combined with the Nelder-Mead optimization algorithm,a new double-layer ground wall insulation optimization structure is established,and the maximum internal electric field is further reduced.Two ground wall insulation materials were used to prepare model bars for experiments,which verified the correctness of the proposed double-layer ground wall insulation optimization method.The electric field at the end of the stator winding of the high-voltage generator is analyzed,and the analytic form of the hypotenuse electric field of the same phase and different phase windings is obtained.A new ground wall insulation structure at the end of the stator bar is proposed,Including the ground wall insulation thinning structure at the end and the ground wall insulation outer fillet increasing structure.The calculated effects of these two new structures on the internal and external electric fields of the stator bar can greatly reduce the electric field at the end of the winding and increase the level of winding corona voltage without affecting the performance of the bar.By setting up a 1000MW,24kV grade hydro-generator simulation winding test platform to carry out ultraviolet corona test,it is obtained that the corona inception voltage of the ground wall insulation thinning bar at the end is increased by 20%,and the outer fillet radius increases the corona inception electric field is increased by 45%,which effectively improves the corona voltage of the real generator winding,and improves the electrical performance and stability of the stator winding.The anti corona structure optimization of stator bar end of high voltage generator is systematically studied.The nonlinear anti corona calculation model at the end of the winding bar is established,and the optimization effect of different anti corona materials and structures is analyzed,and the optimization range of nonlinear coefficient of two anti corona structure is obtained.Based on the limitation of traditional anti corona structure,a new anti corona optimization method based on continuous variation of resistance is proposed.The anti corona optimization method can further reduce the electric field at the end of the bar on the basis of the existing multi section nonlinear anti corona optimization.The non-linear coefficient of anti corona material is extracted,and the anti corona structure is designed and optimized.Through the corona tests of stator winding,the corona inception voltage of winding is increased by 15%,which verifies the effect of anti corona optimization.Through the method of discretization,the general mathematical model of electrical stress test life prediction of generator bar is established,and the life evaluation methods of electrical aging test,rapid-rise test and step-by-step test are further derived,and the versatility is very good.The breakdown voltage and breakdown time of step-by-step test are predicted and verified.Based on the analysis of IEC standard and Weibull distribution method,the Weibull distribution parameter relations of two groups of similar tests,electrical aging and electrical breakdown tests are obtained.The relationship between the Weibull probability lines of the two tests is further obtained.A new rapid evaluation method and evaluation process for the electrical life of stator bars is established.The test time is only about 2.6%of the traditional evaluation time,realizing the rapid evaluation of different types of test electrical life and distribution state.By comparing the predicted data with the test data of model bars,the correctness of the fast evaluation method of electrical life is verified. |
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