| Pipes are mostly used when cables enter the substation’s sandwich wall.Induced current is generated in the pipes,which has resulted in the temperature rise of pipes.Quantity of heat production is conducted to the outer sheath and insulation of the cables,which accelerates the aging of the protective coverings and of cables,and even causes cable failure.Firstly,the paper analyzes the principle of eddy current loss in the casing and derives its expression based on Maxwell’s equations.The theory deduce the basic principle that the eddy current loss can be reduced by using the slit method.The effect of different factors on the eddy current loss of pipes is theoretically analyzed,and the main factors affecting the eddy current loss are the cable current carrying capacity and magnetic permeability.Then,we use COMSOL Multiphysics simulation to analyze the temperature distribution and influencing factors of the pipes in different working conditions.The results show that the eddy current loss that causes the temperature rise of the pipes is mainly affected by the magnetic flux density in the casing and the permeability of the pipes.Slotting in the casing can reduce the equivalent permeability of the casing,thereby reducing eddy current loss and temperature rise.The relationship between the slit size and the temperature rise was studied by simulation,and the optimal slit width was obtained.Based on the theoretical analysis and 3D multi-physics simulation results,the main factors affecting the temperature of the pipes and its influencing laws are summarized,and a formula for calculating the temperature of the metal casing is proposed.The formula fully considers the material characteristics of the pipes,the current carrying capacity of the cable,the ambient temperature,and the size of the slot of the sleeve on the sleeve temperature,thereby solving the pipes temperature field with many influencing factors,complicated calculations.There is no basis for the design of the slot size,which provides a technical means for accurately assessing the temperature rise of the metal casing and optimizing the slot size.Finally,the temperature characteristics of the pipes at different voltage levels were obtained through field experiments.The experimental data is compared with the simulation results and temperature formula results to verify the correctness of the simulation and formula. |
