| The impulse voltage withstand value of the high voltage equipment box designed according to OV3（Over Voltage 3,125k V）standard in plain area cannot meet OV4（Over Voltage 4,170k V）standard in high altitude area.Increasing the box size is the most direct way to increase the lightning impulse voltage,but the space reserved for the high voltage equipment box in the equipment cabin is limited,this measure needs to relayout design the electrical equipment in the equipment cabin,which is not easy to achieve in a short time.In engineering,the method of installing silicone rubber insulation sheath is commonly used to improve the insulation level of electrical equipment,but the thermal conductivity of ordinary silicone rubber material is only 0.27W·m-1·K-1,so the heat dissipation of electrical equipment after installing insulation sheath has also become an urgent problem to be solved.What’s more,the local electric field of some metal electrodes in the high voltage equipment box is concentrated,which is easy to induce corona discharge,and the performance and life of the insulation sheath will be adversely affected under the long time operation.In this paper,the temperature distribution and transient process of the cable connector in the high voltage equipment box after the installation of insulation sheath were analyzed.For the strong electric field area on the fittings,a special shielding ring was designed to adjust the electric field.The main research contents and conclusions are as follows:This article uses equivalent series capacitance method to equivalent the model of the cable connector installed with the insulation sheath,and the discharge process between the cable connector and the inner wall of the box is analyzed by the dielectric barrier discharge（DBD）theory.A three-dimensional model of the cable connector with the insulating sheath was established.Based on the finite element software,the influence of the thickness of the insulating sheath,thermal conductivity,working current and ambient temperature on its temperature transient changes were analyzed,and analyzed the three-dimensional axial temperature distribution of insulation sheath under thermal stability state.Finally,infrared thermal imager is used to verify the validity of the simulation results.The results show that influenced by the temperature coefficient of the fittings,the rise of interface temperature of insulation sheath is non-linear with the increase of working current and ambient temperature.Thermal conductivity of insulating sheath material is the main factor affecting its temperature transient change and distribution.The higher the thermal conductivity,the shorter the time for the sheath interface to reach thermal equilibrium,and the farther the heat travels in the same direction.Based on the finite element software,the electric field distribution of the cable connector under the standard lightning impulse voltage was analyzed,and combined with the structure of the high voltage fittings,a special shaped shielding ring was designed to adjust the partial area where the electric field intensity are concentrated.Besides,the optimal parameters of the shielding ring under different working conditions were determined by the orthogonal design.Finally,utilizing ultraviolet imaging technology and image processing method,the discharge intensity of cable connector fittings were characterized.The results demonstrate that the maximum electric field strength on the surface of bolts and metal electrode can be reduced by 57.8%and 72%;Ultraviolet discharge facular area had an exponential relationship with the applied voltage,the initial discharge voltage of cable connector can increase by 243%after installing the shielding ring. |
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