Prediction of core temperature and early warning of fault of three-core mining cable

Mining cables are affected by humid environment and are prone to insulation degradation. The coal dust accumulated on the sheath will affect the heat dissipation of the cable, and the abnormal increase in the temperature of the core conductor may eventually cause the cable burst, or even cause an electrical fire, which can lead to some serious coal mine hazards. Aiming at the technical problems that the temperature of the core conductor of the cable cannot be directly measured during the live operation of the cable, and the extremely early characteristic of abnormal temperature rise of the cable core cannot be used to realize the early warning of cable faults, using a combination of theoretical analysis and simulation experiment, starting from the heat conduction law of the radial section of the cable, this paper has developed a three-core mining power cable core temperature calculation method based on the equivalent tri-equal transient thermal circuit model, which can calculate the core temperature in real time from the surface temperature of the cable outer sheath. To overcome the problem that the low thermal diffusivity of cable insulation layer, inner sheath and outer sheath leads to large internal temperature gradient of the material, which will seriously affect the calculation accuracy of the model, by analyzing the distribution characteristics of the internal temperature gradient of cable material, an optimization method of layered calculation of equal heat capacity of the cable insulation layer, inner sheath and outer sheath is used to propose a tri-equal and equal heat capacity layered transient thermal circuit model algorithm. Taking the MYJV22-6/6kV-3×50 mining XLPE cable as the experimental object, through the cable temperature and current experiment, the temperature data of the outer sheath surface and the core conductor of the cable under different current carrying capacity are measured. Through the analysis of experimental data, it is proved that the calculation error of the tri-equal and equal heat capacity layered transient thermal circuit model algorithm decreases with the increase of the number of layers, and it is determined that the optimal number of layers for the cable insulation layer, inner sheath and outer sheath are all 50. The results show that the tri-equal transient thermal circuit model optimized by the equal heat capacity layered method has a high calculation accuracy. When the layering number of cable insulation layer, inner sheath and outer sheath is 50,the maximum relative error is less than 1%,and the average relative error is 0.73%,which can provide a certain theoretical basis for the core temperature prediction and fault warning of mining cable.