Study On Local Over-heat Of Porcelain Type Cable Terminal Based On Electric-thermal Field Simulation And Infrared Detection

The cable accessories need to be installed in the operating site. The complexity of defects and high failure rate are caused by on-site installation. Therefore, the effect of typical defect to accessory running state needs to be studied, so that protecting the safety and reliability of urban grid. The article uses finite element to simulate temperature field of cable terminal in view of the water defects. The simulation experiment of terminal water defects and infrared image defection are also studied. The research content is as follows:At first, in this paper, the infrared detecting temperature datas of porcelain type cable terminal were counted in Guangzhou from 2008 to 2013. The data analysis shows that single-phase and different-phase temperature differences of cable terminal are approximate normal distribution. In turn, according to the principle of noamal distribution and the statistical distribution of large amounts of data, the surface of the three threshold estimation parameters which is note value, abnormal value and risk value for single-phase and different-phase temperature difference of cable terminal are concluded.Secondly, the electric-temperature sequential coupling field finite element simulation model of porcelain type cable terminal is established based on the theory of electromagnetic field and heat transfer. The simulation calculation shows that electric field near the stress cone will produce different degrees of electric field distortion because of water into cable terminal, especially the distortion is serious when a large amount of water at the bottom. Heat production of dielectric loss will increase with the change of water. Therefore, the temperature field results display that the stress cone area of terminal appears different degree of abnormal temperature rise.Thirdly, the state detecting experiment of water defect has been carried out for porcelain type cable terminal. The experimental results show that the abnormal temperature rise of the lower terminal part is mainly caused by voltage-caused heating when the water is small. At this time, the current have little effect on over-heat. The abnormal heat of the lower terminal part is caused by the combination of voltage and current when the water is large. At this time, the increase of water has no significantly impact on terminal heat, while current load will affect the thermal process in a large extent.Finally, an adaptive optimal threshold edge extraction algorithm based on improved Sobel operator is proposed in this paper. The algorithm can be used for infrared image edge extraction of porcelain type cable terminal. The simulation experiment shows that infrared image detecting results have a good continuity, accuracy and noise resistance by using the algorithm. It can extract abnormal heat location and scope of infrared image in a larger noise environment. And the result lays the foundation for identification and classification of porcelain type cable terminal in the condition of different over-heat.