Research On Thermal Problems Of In-situ Measurement Of Thermal Conductivity Of Solid Insulating Materials Under Electric Field

Improving the thermal conductivity of solid insulating materials has always been a research hotspot in the power and electronics industry and related disciplines.The development of polymer matrix with high thermal conductivity,the use of mechanical stress or electric field force to orient polymer molecular chains,and the filling of thermally conductive fillers are other technologies.Common and effective technical means.However,these methods will more or less affect the electrical insulating properties of the insulating material itself.Under the working conditions,the insulating material works under the combined action of the electric field and the temperature field.Therefore,the thermal conductivity of the solid insulating material under the high field has attracted the attention of this research group.If the electric field has the effect of regulating the thermal conductivity of the insulation,it will have no effect.The advantage of destroying the electrical insulation performance and not affecting the atomic structure.However,the current academic community lacks a test system that can measure the thermal conductivity of insulating materials under the action of an electric field,and naturally it is impossible to know the thermal conductivity of insulating materials under an electric field.In order to solve this problem,based on the longitudinal heat flow method in the steady-state thermal conductivity test method of materials,combined with the insulation resistance test technology,this paper proposes an in-situ test technology for the thermal conductivity of solid insulation materials.First,the structure of the test platform needs to be designed in principle.In this paper,the two-electrode system is used as the framework to realize the longitudinal heat flow method.The heat transfer analysis proves that the structure has axial heat loss,so a symmetrical electrode structure is proposed as The solution is to extend this structure to the three-electrode system.In order to solve the influence of the current measurement protection gap in the three-electrode system on the temperature distribution of the cold surface of the sample and the radial heat loss of the system,a system that can be controlled in real time with high voltage is designed.The electrode maintains the thermally driven protection electrode at the same temperature and the same potential.Numerical simulations have proved the suppression effect of this structure on the axial and radial heat loss,thus completing the principle design of the system and giving the experimental method;Based on the principle design,computer modeling was used to complete the physical design and production of the electrode and the support module,and the temperature control module,focusing on solving the problem of the physical structure of the electrode that requires a variety of built-in components,the support problem of the sample to be tested,and the thermal drive protection The problem of temperature follow-up control in the electrode;again,the one-dimensional heat transfer of the high-voltage end of the test system is verified by the method of heat transfer experiment;finally,a flat polyethylene sample is used as an example to analyze the coupling of electricity and heat by means of numerical simulation.Electric field distribution and Joule heat distribution under transient and steady-state conditions in a flat specimen under an electric field.Through experiments and theoretical studies in this article,it is found that compared with the traditional longitudinal heat flow method,the test system adopting an axially symmetrical structure and radially introducing a thermally driven protective electrode can eliminate the heat loss of the electrode system in the axial and radial directions,thereby effectively ensuring heating The one-dimensionality and uniformity of the source heat transmission;the steady-state Joule heat and electric field distribution in the sample are obtained through numerical simulation,which eliminates the influence of Joule heat on the temperature distribution in the sample,and calculates the effects of different heating powers and external electric fields The transition time of the physical field in the sample from the transient state to the steady state process,it is concluded that the experimental system needs to reach the steady state test condition only after the coupling field acts for a minimum of 40 minutes.The research in this paper solves the related thermal problems for the follow-up research of the research group,and provides a basis for accurately obtaining the thermal conductivity of solid materials under the electric field.