Multi-Physics Coupling Analysis And Temperature Rise Modelling Of Dry-Type Transformer

With the improvement of power supply reliability requirements and the continuous development of dry-type transformer manufacturing technology in China,dry-type transformers have the characteristics of superior environmental performance,strong safety and reliability and high operating efficiency,and the proportion of dry-type transformers in the distribution network is becoming larger and larger.However,due to the poor heat dissipation efficiency of the dry-type transformers,local overheating is more likely to occur in the overload operation and cooling system failure,which accelerates the deterioration of insulating materials and reduces the operational reliability.Therefore,the accurate calculation of the hot-spot temperature of dry-type transformers is the key to ensure its safe and stable operation.In order to meet the increasing demand for fast calculation and real-time evaluation of hot-spot temperature of dry-type transformers,it is urgent to carry out multi-physical field coupling analysis of dry-type transformers.Based on thermoelectric analogy theory,the transient thermal circuit model of dry-type transformers is constructed to realize fast and accurate calculation of hot-spot temperature of windings.Combined with the advantages of the calculation accuracy of the multi-physical field coupling model and the calculation speed of the thermal circuit model,this thesis studies the multi-physical field coupling analysis and temperature rise modeling of the dry-type transformer.Firstly,based on the electromagnetic field numerical calculation theory,a finite element calculation model for the electromagnetic field of dry-type transformer was constructed to solve the magnetic field distribution and no-load loss of the core during noload operation of the transformer,as well as the leakage magnetic field distribution and load loss of the winding during rated load operation,providing heat source load for multiphysical field coupling analysis.Secondly,the multi-physical field coupling calculation method was studied,and a three-dimensional steady-state electromagnetic-temperatureflow field coupling calculation model was established for the dry-type transformer.Through the multi-physical field coupling analysis,the temperature and internal velocity distribution of each component were obtained.On the basis of verifying the accuracy of the multi-physical field coupling model,the influence of different forced convection heat transfer modes on the cooling effect was studied.The convective heat transfer coefficient of windings is calculated by multi-physical field coupling to establish the basis for optimizing the parameters of the thermal circuit model.Finally,based on the thermoelectric analogy theory,the temperature rise modeling of the dry-type transformer is studied,and the transient thermal circuit models of high and low voltage windings are constructed respectively.The discrete idea of finite element calculation was integrated into the thermoelectric analogy theory.The geometric structure of windings was highly restored while the boundary conditions were strictly matched.The structure of transient thermal circuit model was improved by using single-turn coil as the calculation unit,and the nonlinear convective thermal resistance of the thermal circuit model is optimized by the convective heat transfer coefficient of windings obtained by coupling calculation of multi-physical field.The calculation method of winding thermal time constant is studied,and the influence of cooling ventilator outlet wind speed and outlet air temperature on the winding thermal time constant is analyzed in the case of forced convection heat transfer of dry-type transformer,so as to realize the fast and accurate calculation of the hot-spot temperature of the winding,and meet the increasing demand for fast calculation and real-time evaluation of the hot-spot temperature of dry transformers.