Calculation Of Transformer Short-circuit Impedance Characteristics And Identification Of Winding States

Among all the electrical equipment,transformers are one of the most important apparatus.Secure and stable electricity supply depends substantially on the reliability of transformers used in a power system.The winding is the main part of the transformer,and the normal stability of the winding structure directly affects the service life of the transformer.In this paper,in order to realize the identification of the winding state after the transformer is short-circuited,a phaseshifting transformer with a model of ZQSC（H）BH15-2500/33 is used as the research model,and the impedance characteristics of the transformer are mainly analyzed.The winding structure is identified after the transformer is short-circuited.The main research contents of the paper are as follows:（1）Research on impedance characteristics of phase-shifting transformers.Analyze the leakage magnetic field and current distribution of the transformer winding,the winding structure of the phase-shifting transformer is different from the typical transformer’s winding structure.High-voltage sides generally adopt extended triangle and polygonal connection methods,and the low-voltage side adopts the axial multi-split connection method.The special structure makes the phase-shifting transformer half-crossing.The short-circuit impedance with split cannot be accurately calculated using analytical formulas,only the full through impedance in symmetrical operation can be calculated accurately.Therefore,a finite element model is established to study the short-circuit impedance calculation of phase-shifting transformers.（2）Short-circuit steady-state current,short-circuit impulse current calculation and structural field analysis,establish a three-dimensional solid model of the phase-shifting transformer through simulation software,conduct coupled simulation analysis of its electromagnetic field and structural field,analyze the stress state of the winding,and find the weak point of the winding after the transformer is short-circuited.（3）Various transformer equivalent circuit models were given,and an appropriate circuit model was selected according to the winding type,and the results of the simulation and computation of circuit parameters in the equivalent circuit model were simulated and calculated using a finite element simulation.The sweep frequency response curve of winding is achieved using simulation software as a tool.For different faults,a variety of winding models are created,and the influence of faults on the equivalent circuit parameters of transformer winding is analyzed.The circuit parameters are determined using the finite element method,and the frequency sweep impedance curve under the fault state is obtained,and then compared with the frequency sweep curve of the normal winding to provide a basis for the identification of the transformer winding state.（4）Research on winding state identification after transformer short circuit.The correlation coefficient method was used to compare the similarity of the swept-frequency impedance curves of the transformer,and the degree of winding deformation was identified.The bat algorithm was used to optimize the support vector machine,and the identification model of the winding state after the transformer was short-circuited was constructed to realize the accurate diagnosis of the faulty winding.