Study On Water Hose Pressing Method Of Transformer Winding

The vigorous socio-economic development has led to the rapid construction of the power system.Among them,large transformers,as important voltage conversion and current delivery equipment,their manufacturing and production processes are considered to be an important part of ensuring equipment performance.According to statistics of transformer damage accidents,most of the failures occur in the winding part of the transformer,and the winding needs to be pre-compressed before leaving the factory to resist external forces such as electric power caused by short-circuit current,and enhance the mechanical and electrical properties of the winding.At present,China’s transformer manufacturers have little research on the theory of winding compression structure,and have not analyzed in depth the influence of various specifications on the structural compression law.There is a certain gap between the analysis and research of internal structural changes and developed countries abroad.Therefore,analyzing the changes in the winding structure and simulating the force and deformation of the winding during compression are essential to the performance and safe operation of the transformer.In this thesis,the compression method of the water hose of the transformer winding is studied in depth.The compression process of the main components of the winding is analyzed through the compression mechanical properties test,and the mathematical model of the stiffness of the transformer winding is established based on its change law.The finite element method is used to simulate the dynamic characteristics of the water hose compression process.The stress and displacement distribution laws of the windings are obtained,and the transformer water hose compression test bench is designed and built.The stress distribution and axial displacement changes of the windings after the water hose is filled with pressure are studied,and the compression effect of the water hose is analyzed.The specific research content is as follows:(1)Using an electronic universal testing machine,the compression properties of the main components(insulated pressboard,copper flat coil)of the winding under three pretreatment conditions(undried,dried,oil-immersed after dried)were tested,the changes in its stiffness value were analyzed,and the structural changes of some specimens were observed through a light mirror,and the mechanism of the change in its stiffness value was studied in detail.The curve of the compression process is further fitted through the model,and a mathematical model of the stiffness of the multilayer winding of the transformer under the influence of multiple factors is established.The research found that the stiffness of the transformer winding is related to factors such as the number of winding roots,the number of insulated pressboard layers,and the pretreatment conditions of the winding.Drying and oil immersion treatment can reduce the compression strain value of the insulated pressboard,and significantly increase the degree of compression strain of the copper flat coil,the stiffness value of the two components suddenly decreases in the early stage of loading.This is because the pressboard is filled with oil after pretreatment,which is easier to deform,and the density of the pressboard structure and the outer insulating paper of the coil is improved after compaction.(2)Firstly,using finite element software,the process of compressing the winding of the water hose is simulated,the displacement and stress distribution of the winding compression process are analyzed and compared,and the cavity volume changes of the water hose during the pressure filling process are studied.The study found that the volume growth rate of the outer water hose is higher than that of the inner side,and the axial displacement of the winding is mainly concentrated on the coil between the spacers.Compared with the lower half of the winding,the displacement and force value of the upper half are greater.Secondly,the displacement situation is mainly distributed according to the corrugated shape.The peak of the wave is located in the lower half of the spacer,and the displacement of the coil at the top of the winding is the largest,showing a concave trend.At the same time,the stress is mainly concentrated near the spacer,and the stress on both sides of the spacer gradually decreases.(3)In order to clarify the size of the compression force generated by the water hose,analyze its changing trend and law,according to the actual installation structure of the transformer,through the equivalent transformer winding of the damper equipment,the transformer water hose compression test bench is designed and manufactured,and the equilibrium equation of the water hose compression process is established.The loading force generated on the winding structure during the expansion of the water hose is calculated,and the corresponding internal pressure and the axial displacement of the downward pressure are analyzed.The relationship between the change of internal pressure and the axial displacement of the downward pressure is analyzed.The study found that as the internal pressure of the water hose gradually increases,the axial displacement caused by its compression force and downward pressure increases.At the same time,the size of the compression force is related to the transverse and longitudinal contact length of the water hose.The compression force increase of the inner water hose is higher than that of the outer water hose,and part of the volume increase of the outer water hose appears in the water hose cavity outside the winding.Through experimental and simulation analysis methods,this thesis studies the water hose compression process of transformer windings.Based on the compression test data of the internal components of different specifications and pretreatment conditions,a mathematical model of transformer winding stiffness is established,and the compression force change trend of the water hose compression process and the stress and displacement distribution of the windings are analyzed.It provides reliable data support and theoretical guidance for the research and engineering application of water hose compression methods for transformer windings,which is of great significance to improve the performance of transformers and optimize the compression process of transformers.