Research On Heat Transfer Characteristics Of Dry-type Air-core Reactor Encapsulation Materials

The modern power industry is developing rapidly,and the power equipment supporting the national grid is the safety guarantee for the stable operation of the power system.Aiming at the problem of abnormally large voltage fluctuations in transmission lines and excess reactive power in the power system,dry-type air-core reactors are used to maintain voltage stability and compensate reactive power.The dry-type air-core reactor winding encapsulation insulation material uses glass fiber impregnated with epoxy resin,which also has a great influence on the heat dissipation of the winding of the reactor.The precursor of reactor failure is often abnormal temperature rise.Therefore,studying the heat transfer characteristics of the encapsulated insulating material can provide important parameters for the simulation and analysis of the temperature rise of dry-type air-core reactors.The structure of the encapsulated insulating material of the dry-type air-core reactor is analyzed,and the heat transfer model is established according to the actual encapsulation structure according to the heat dissipation process of the heat generated by the winding and transferred to the air.The corresponding heat transfer coefficient calculation method is obtained based on the theory of heat transfer.The heat transfer parameters include the thermal conductivity of the insulating material and the convective heat transfer coefficient between the surface of the material and the air.The steady-state dual heat flow meter experiment was used to test the thermal conductivity of the encapsulated insulating material,and the experimental platform was built according to the steady-state method,and the thin specimens with the influence of air thermal resistance and the specimens without the influence of air thermal resistance were respectively made.The results show that the thermal conductivity of the upper surface of the thin sample with air thermal resistance at60.5?,70.7?,79.3?,92.4? and 102.4? are 0.661 W/m·K,0.674 W/m·K,0.659W/m·K,0.639 W/m·K and 0.657 W/m·K.The results show that the thermal conductivity of the upper surface of the sample without air thermal resistance at62.3?,70.5?,81.4?,90.3? and 100.5? are 0.767 W/m·K,0.752 W/m·K,0.747W/m·K,0.731 W/m·K and 0.725 W/m·K.The experimental results show that the thermal conductivity of the thin sheet sample with air thermal resistance on the contact surface with the heat flow meter is lower than that of the sample without the influence of air thermal resistance.The reason is that the thermal resistance of the air is large,which affects the heat transfer.The thermal conductivity of the insulating material measured without the influence of air is closer to the actual value.According to the surface structure characteristics of the encapsulating material,the steady-state method is used to set up the experiment,and the convective heat transfer characteristics between the encapsulated insulating material of the reactor and the air are studied.Temperature of the surface in contact with the air is obtained according to the internal temperature field distribution of the glass fiber epoxy resin composite material.The air temperature of the contact surface is obtained from the data of the internal temperature sensor of the heat flow meter,and the convective heat transfer coefficient between the surface of the insulating material and the air is obtained according to Newton's law of cooling.The thermal conductivity of the encapsulated insulating material without air thermal resistance is measured by the dual heat flow meter method,and the convective heat transfer coefficient is measured by the steady-state experiment method.The heat transfer parameters under different heat transfer modes are obtained and substituted into the heat transfer model established according to the encapsulation structure at the same time.The corresponding heat transfer parameters of the winding-encapsulation insulating material-air convection process can be obtained,which provides a reference for the temperature rise prediction model of dry-type air-core reactors.