Research On Multiphysical Field Coupling Method Of Oil Immersed Transformer For Digital Twin Application

Applying digital twin technology to the power industry is of great significance for improving the functions of intelligent monitoring,control and real-time interaction of new power systems.With the introduction of the concept of digital twin of power transmission and transformation equipment,the construction of digital twin models that are equivalent to physical equipment and operate synchronously has become the current research focus.By analyzing the defects of the current calculation methods of vibration and heat transfer of oil-immersed transformer applied to the digital twin model,this thesis proposes a method of building the digital twin model based on the multi-physical field model,studies the theory and finite element method of structural vibration and fluid-solid coupling heat transfer of transformer winding,and deduces the multi-physical field coupling finite element calculation model.Further considering the defect that the high degree of freedom model has too long calculation time in the transient calculation of physical field,a model reduction method combining the finite element method and the proper orthogonal decomposition(POD)is proposed.Finally,a digital twin model of temperature field is established for a 220 k V large oil-immersed transformer to verify the feasibility and superiority of the proposed method.Detailed work contents are as follows:(1)The realization architecture of digital twinning of oil-immersed transformer based on IoT is established,and the realization process of transformer digital twinning modeling and simulation calculation based on multi-physical field model drive is given.The axial vibration and thermal characteristics of oil-immersed transformer windings are further studied,and the physical field mathematical model of winding magnetic leakage,axial vibration and transient fluid-structure coupling heat transfer problem is built,which provides theoretical support for the subsequent multi-field coupling.(2)Combined with the physical field mathematical model and the finite element method,the Galerkin finite element discretization schemes of electromagnetic-vibration coupling field and electromagnetic-fluid-temperature coupling field are derived respectively,and the full-order finite element calculation model is established.Taking a 100 k VA/10 k V small oil-immersed transformer as a basic calculation example,and combining with the actual short-circuit test,the basic characteristics of the finite element method to calculate the structural vibration equation and the transient fluid-structure coupling equation are analyzed.The error meets the actual requirements,and the validity of the calculation method is verified.At the same time,the vibration signal and temperature distribution under different working conditions are analyzed by modifying the load coefficient and load loss.(3)In view of the problems of high degree of freedom of the model and calculation time up to hours in the calculation process of structural vibration and transient fluid-structure coupling heat transfer,a model reduction method combining eigen-orthogonal decomposition and finite element method is proposed,and the principle of POD reduction calculation model for structural vibration and transient fluid-structure coupling equation is deduced.The reduced model is constructed from the point of reducing the order of finite element equation,so as to reduce the calculation amount and realize the second order fast calculation.The proposed method is applied to establish different order reduction models for small oil-immersed transformers with different capacity levels and calculate the corresponding temperature field distribution.The calculation error and calculation time of each order model are compared and analyzed,and the accuracy and efficiency of the proposed reduction calculation method are verified.(4)Apply the proposed method to carry out digital twinning modeling and analysis of temperature field for a 240000 k VA/220 k V oil-immersed main transformer,drive the twinning model calculation with real operation data,reflect the operation status of physical equipment through the twinning model and provide operation and maintenance decisions.The results show that the temperature rise error conforms to the standard specifications,and the calculation results can be used as a criterion for the safety and stability of the thermal characteristics of oil-immersed transformers.