Analysis Of 3D Leakage Magnetic Field Coupled With Thermal Field In Large Scale Power Transformer

This subject is a part of National Natural and Science Fund Project " Three- dimensional hysteresis characteristics measurement and simulation of ferromagnetic material " (Fund number: 50807039).The large power transformer equipment is composed of metal structural members such as the tank, clamping, pulling plate, and so on. The stray loss produced by leakage magnetic field in these metal structures and corresponding overheating problem are one of complex and classic problems in designing and safe operating of transformers. Based on the comparison of several common electromagnetic, thermal field numerical simulation commercial software, in this thesis, MAGNET and THERMNET software is employed to complete 3-D leakage magnetic field and temperature field coupling calculation of a 240000kVA/500kV power transformer product. The effective subdivision method to solve the "large scale difference" problem in three-dimensional leakage magnetic field analysis is discussed, and the measurement of reducing the local overheating is developed, which provides the reference to designers of the power transformer product. The detailed works are as follows:First of all, the performance of different commercial software in 3-D leakage magnetic field computation is compared by analyzing a power transformer product, on which loss tests are carried. The MAGNET software is decided to carry out the research work of this thesis.Then, MAGNET commercial software is used to complete 3-D leakage magnetic field numerical calculation of a 240000kVA/500kV power transformer tank. For the "large scale difference" problem, the transformer linear dimensions is several meters, while the penetration depth in the oil tank and other solid metal materials is only a few tenths of millimeters, so that it is difficult to achieve reasonable mesh grid. The validity of surface impedance method and layer subdivision method to solve the problem is discussed. Furthermore, the effect of the oil tank shielding type, location and size on the distribution of leakage magnetic field is studied. At the same time the shielding method to other metal members such as clamp and pulling plate generating lot of eddy-current loss.Finally, the coupling analysis between the leakage magnetic field and temperature field calculation is presented with MAGNET and THERMNET software, and the temperature distribution in oil tank, clamping and pulling plate is given.