Research On Coupling Simulation Of Magnetic Field And Temperature Field Based On Temperature Characteristics Test Of Ferromagnetic Materials

With the development of extra-high voltage and long-distance transmission technology in China, large and super-large power transformers, motor and other electrical equipments are put into operation continuously. The design and performance analysis of these large electrical products usually involve the coupling of electrical, magnetic, thermal, mechanical and other physical fields. With the improvement of computer performance and the development of numerical calculation technology of electromagnetic field, the electromagnetic field numerical simulation software has been widely used to analyze the coupling problem of electromagnetic field and thermal field in large electrical products. However, the magnetic-thermal coupling computation is usually solved by employing a single-way coupling method(hereinafter called the traditional coupling method), in which the magnetic field simulation is firstly carried out to obtain the power loss, and then the temperature rise distribution is solved by applying the calculated loss value as the heat source of the temperature field analysis. The traditional coupling method ignores the temperature effect on electromagnetic properties of ferromagnetic materials. However, the accurate analysis of electromagnetic performance of electrical products is greatly dependent on the accurate description of electromagnetic characteristics of electrical materials. The electrical steel sheets are widely used as motor and transformer core material or magnetic shielding material, and their magnetic properties and loss change with the temperature, which in turn affects the temperature rise distribution of the core. Based on the above analysis, the magnetic thermal coupling problem of the motor and transformer considering the temperature effect of magnetic properties of electrical steel sheet, in this paper,was studied and the temperature effect of material on the electromagnetic and thermal field coupling simulation was investigated, which would provide reference for the safe operation and local overheating prevention of the electrical equipment. The main contents are listed as follows:Firstly, the average magnetization curves, hysteresis loop and the loss curve in a50AW600 non-oriented electrical steel sheet and a 30ZH120 grain-oriented electrical steel sheet with the temperature range of 20℃-120℃ at the interval of 10℃ were measured and analyzed. During experiments, the single-chip electrical steel sheet magnetic properties testerwas put into a constant temperature drying box, in which the temperature range can be controlled at 20 ℃-400 ℃. By controlling the temperature in the drying box the magnetic properties of the electrical steel sheets under different temperatures were measured.Secondly, an iterative magnetic-thermal coupling analysis method taking the temperature effect of magnetic properties of electrical steel sheet into account was developed and implemented by using a magnetic field simulation software, MagNet, and a temperature field simulation software, ThermNet. During the iterative coupling process, the average magnetization curve and loss curve of the material used in magnetic field computation at each iteration step were updated according to the simulation results of the current temperature field,and then the temperature rise distribution was determined by the loss calculated by the current magnetic field calculation. The above process was operated repeatedly until the end.Thirdly, based on the measured data and the iterative coupling method above, the temperature distributions in a permanent magnet brushless direct current motor and the core and the magnetic shielding of a 500 kV extra large power transformer were simulated and were compared with the results calculated by the traditional coupling method without considering the temperature effect of the silicon steel sheet. The results show that it is necessary to consider the temperature effect on the magnetic properties of silicon steel sheet in the magnetic-thermal coupling simulation.Finally, a simple single-phase transformer core model was built and its no-load running was established. The core surface temperature distribution was measured by an infrared thermal imager, and the experimental results were compared with the simulation ones.