Calculation Of Strand Current And Optimization Of Transposition Types For The Stator Bar Of The Hydro-generator

With the rapid growth of the electric power industry in China,the unit capacity of the hydro-generator is increasing constantly,and the strand circulating current losses produced by the non-uniform distribution of leakage magnetic field in the stator bar also will increase.Circulating current losses bring the temperature rise of stator bars and causes serious threat to the operation safety of a hydro-generator.Thus,it is necessary to use the transposition in strands to decrease circulating current losses.For the problem that the calculation method of slot leakage reactance is implicit algorithm which is difficult to combine with the optimization algorithm to optimize the stator bar of the hydro-generator,the improved circuit equation method with explicit algorithm of strand slot leakage reactance transposition is presented in this paper.A 140 MVA hydro-generator is taken as an example,and the improved circuit equation method is combined with the optimization algorithm to optimize transposition types for the stator bar of the hydro-generator.Firstly,strand current solving equation is established according to the basic principles of circuit equation method and calculation algorithm of strand end leakage reactance is proposed.Strand end leakage reactance is calculated by using image method and discrete integral method.Then,explicit algorithm of strand slot leakage reactance with incomplete transposition,void transposition and hybrid are deduced.Secondly,strand currents and phase angles are calculated by the improved circuit equation method with explicit algorithm of strand slot leakage reactance,when incomplete transposition,void transposition and hybrid transposition types are adopted for the stator bar of the hydro-generator.Compared with the experimental measurement result and the 3-D finite-element method calculation results,the improved circuit equation method with explicit algorithm of strand slot leakage reactance is proved right.Finally,the minimum circulating current losses are chosen as the optimization objective,the improved circuit equation method with explicit algorithm of strand slot leakage reactance is combined with the basic ant colony algorithm,the genetic algorithm and hybrid ant colony algorithm to optimize transposition types of the stator bar with incomplete transposition,void transposition and hybrid transposition respectively.Then the non-dominated sorting genetic algorithm ?(NSGA-?)is combined with the improved circuit equation method to optimize circulating current losses and strand currents variance of stator bars with hybrid transposition.Besides,in order to facilitate the manufacturer of hydro generators to optimize the transposition types of the stator bar,a software is developed including strand currents variance calculation function,circulating current losses calculation function and optimization function of transposition models for the stator bar.