| In the same capacity, the auto-transformer's dimensions and necessary materials lessthan that of ordinary transformer, thereby the loss of the transformer is reduced, and thetransport and installation of auto-transformer is relatively facile. Therefore, theauto-transformer with large-capacity and high-voltage case has been widely used.Transformer insulation issue has been a core issue. Associated with the increase of voltagelevels, the insulation problem becomes even more important. Auto-transformer's insulatingstructure and the reliability of insulating materials have great influence on the transformerreliability. Auto-transformer's insulation compared with the general problem has manydifferent characteristics. The main reason is that auto-transformer windings have bothmagnetic and electrical contact between the primary and secondary.In this paper, the insulation of a large-capacity power auto-transformer is calculated.The surge process need to be calculated before analyzing the insulation of auto-transformer.Here the distribution of electric potential is calculated under thunder surge. Main solutionmethod is, first of all, the equivalent circuit of the auto-transformer which under thundersurge need to be build on. Secondly, auto-transformer equivalent circuit is transformed tomatrix through the cut-set matrix method. At last, MATLAB software is used for findingthe numerical solution of the equation of state. And then potential distribution of eachwinding in vertical insulation is solved. About main insulation, the whole electric field oftransformer is calculated by the finite element analysis software. And according to thecomputing result, the average electric field intensity is calculated by the self-program withAPDL language of ANSYS.Based on the thunder surge process calculations, voltage gradient and are solved, andthen the insulation margin in vertical insulation is solved. Based on the electric fielddistribution of the main insulation, the maximum field intensity is found. In the area of themiddle of high winding and the end of high winding, the average electric field intensity along the power line is also calculated. The related insulation margin in main insulation issolved. |
