Research On Wave Process Of Series Transformer Group

The calculation of the wave process of the transformer winding under the lightning impulse is of great significance to the design of the insulation structure.In some special occasions,in order to achieve a more economical voltage regulation effect,the transformer is usually designed as a transformer bank with series voltage regulation.Rectifier transformers for electrolytic aluminum and electric arc furnace transformers are typical applications of this type of transformer.For this kind of multi-body series transformer group for wave process analysis,in order to simplify the calculation process,a single-body equivalent circuit is usually used for analysis while ignoring the effect of other transformer bodies,which will cause certain errors and limitations in the wave process calculation,The insulation requirements will be too harsh and demanding.Based on the research of equivalent circuit of series transformer bank,this paper gives a method to solve equivalent circuit,and develops wave process calculation software on this basis.Firstly,the calculation formulas for the equivalent circuit parameters when solving the wave process are given.Secondly,the numerical solution of the differential equations,the generalized eigenvalue method and the state equation method are used to calculate the equivalent circuit of the single-body on-load tapping transformer.The correctness and application range of the three methods are verified by comparison.On the basis,the model and solution method of multi-body series transformer group are given.Finally,using C# programming language and Matlab mixed programming,a set of transformer wave process calculation software that is simple to use,flexible to operate,and capable of calculating various types of transformer waves is developed.In order to illustrate the guiding significance of the developed software for the design of longitudinal insulation,the potential distribution and potential gradient of the rectifier transformer under the impact of lightning are calculated based on the singlebody equivalent model and the multi-body series transformer group equivalent model.The comparative analysis of the results proves the necessity of establishing the equivalent circuit of series transformer bank when studying the wave process.The field strengths of the winding oil passages when each phase of the three-phase windings of the series transformer group are individually waved are respectively calculated,and the three-phase symmetry of the software is verified when the equivalent circuit is established.The potential gradients of the double pie cell model and the pie-turn mixed model are calculated separately,which reflects the flexibility of the compiled software and provides a reference for the actual engineering longitudinal insulation design.