Radial Stability Analysis Of Windings In Larger Power Transformer

Radial unstability of inner windings is one of factors that cause breakdown, sothe study of radial stability of inner windings will help designers to check the abilityto withstand short-circuit impact when external short-circuit faults happens in alarger power transformer.As a case study on a220kV/180MVA three-winding transformer in this paper,the model with field-circuit coupled method established to gain the biggest short-circuit current、the leakage magnetic、the distribution of electric dense and theaverage magnetic dense on medium voltage winding three-phase short-circuit at theexit conditions in the larger power transformer and then gain the short circuitelectromagnetic force on every coil along axial trend and choose the biggest as thebasis for study of radial stability of winding.The analysis of radial dynamic stability mainly depends on model, so at firstthis paper propose three models called single-span and gain critical collapsing load inthree models and then proves that the model with elastic supports is closer totransformer actual running than the model with hinged supports and fixed supports.Secondly, it proposes the model called multi-span with elastic supports that issimplified, assumed and checked according to actually running. According to criticalcollapsing load, this model is more safe and reliable when radial unstabilty ofwinding in a larger power transformer. This paper used computational method of alinear eigenvalue to gain the critical collapsing load. Considering the impact ongeometric nonlinearity, it used computational method of a large deformationnonlinear to comparative analysis and then proves that computational method of thelarge deformation nonlinear is more accurate.Radial unstability of a larger power transformer has various causes, the initialgeometric defects of transformer winding is one of the major reasons. This paperuses a method that simulate different spring constants in different conditions includemicro-oblate of transformer winding、 asymmetry distribution of transformersupports along circle trend of inner winding and failure of transformer supports and so on. According to safety coefficient, it shows the effect on the radial stability oftransformer windings.Because of more number of transformer supports and the smaller span betweenadjacent supports, so the study on snap-through buckling of transformer windingswill be extremely important. This paper is theoretical basis on the flat arch in-planebuckling and combines with actual structure of transformer, it gain the relation thatsnap-through buckling and deflection of winding、span of supports and externalload in the large power transformer.