Design Of High Voltage Side Of Solid Insulation Thermal Conductivity Test System Under Electric Field

With the increase of power equipment capacity and the high integration of electronic devices,the thermal conductivity requirements of insulating packaging materials are improved.Polymer insulation is widely used in the electrical field.Improving the thermal conductivity of polymer insulation has become a research hotspot.The conventional thermal conductivity test method does not involve the electric field factor,while the insulating material works under high field strength,and the conventional thermal conductivity test environment is inconsistent with the actual working conditions of the material.At present,there is a lack of relevant testing technology to solve the problem of the influence of external electric field on the thermal conductivity of materials and whether the self-adaptive control of thermal conductivity of materials can be realized.In this thesis,the principle of measuring the thermal conductivity of solid insulation under electric field is proposed.The conductivity three electrode system is symmetrically set,the independent heating source is built in the high-voltage electrode as the hot plate,and the grounding electrode and measuring electrode as the cold plate.Based on the idea of protective hot plate method,the high-voltage electrode is designed as the main heating electrode and auxiliary heating electrode to eliminate the radial loss of heat flow and realize the measurement of thermal conductivity under electric field.The feasibility of the test principle is verified by simulation,and the thermal conductivity test system of solid insulation under electric field is designed.In the hardware part of the test system,the magnetic core geometric constant method is used to design and manufacture the low potential and high voltage isolation transformer of the secondary winding,forming the Faraday cage electrical isolation measurement and control module.The electrode module is designed according to the size of heat source and sensor,and the influence of electrode structure on thermal conductivity test is analyzed by thermal field simulation.The results show that the poor thermal conductivity at the opening of the contact surface between sample and electrode seriously affects the temperature measurement,and the error percentage decreases with the increase of heat source power.Improving the thermal conductivity at the opening can effectively improve the axial one-dimensional heat transfer of the sample and significantly reduce the influence of the sensor harness.In the measurement and control part,STM32 single chip microcomputer is used to realize the 14 channel temperature data acquisition on the high voltage side based on SPI protocol.The calculation results of entropy method show that the weight of each temperature channel is close to the average value,and the temperature of the electrode is uniform.The fault of temperature sensor is judged by weighted residual detection method.The electrode temperature rise has hysteresis.Two integral separated PID control is used to control the output voltage of the main and auxiliary heating sources,and then control the temperature of the main and auxiliary heating electrodes.The temperature measurement results show that the temperature control of the main and auxiliary heating electrodes is stable,the heat shielding effect is good,and the heat flow is one-dimensional heat transfer along the axial direction.When the temperature control requirements are met,increasing the output voltage can effectively shorten the temperature rise time.The Bluetooth wireless module is used to realize high potential data transmission,and the serial and parallel input methods are used to calculate the multi-channel temperature data fusion value based on Kalman filter.The serial input has high convergence and the parallel input filtering effect is obvious.The functions of serial communication,data monitoring,data fusion,data storage,parameter calculation and so on are realized by writing Lab VIEW program.The thermal conductivity of LDPE without electric field is measured by the test system.The test result of thermal conductivity corrected by radial equivalent thermal path model is close to the empirical value.