Calculation And Analysis Of Stray Loss And Relevant Hot Question Of Power Transformer

With the development of capacity of transformer, the magnetic leakage is increasing which may enlarge the stray losses in the conductive parts of power transformer. The complex structure of large transformer result in the uneven distribution of stray losses in conductive parts, which may cause local overheating and affect normal operation of the transformer. Controlling the quantity of the stray losses and temperature rise of hot spot may be the most important ways to assure the normal operation of transformer. However, the unsuitable measure may be causing other overheating spot. Therefore, it is quite necessary to study leakage magnetic field, stray losses and overheating problem in power transformer deeply and accurately, and adopt effective measures to minimize the losses and prevent the local overheating efficiently.In this thesis, the 3-D geometric model of TEAM Problem 21 and real power transformer was made and linked with FEM by using the software of electromagnetic field and the nonlinear 3-D time harmonic analyze was used to investigate the leakage magnetic field, eddy current losses and hysteresis losses in conductive parts firstly. The calculated results are compared with experimental value. In this way we verify and validate the effectiveness of the calculation method and final results. The previous method was used to analyze the leakage magnetic field and stray losses in signal-phase auto-transformer type 700MVA/750kV.Secondly, the appropriate measures which include slotting tensile plate, adding magnetic shunt and shields to yoke clamps, adding electromagnetic shields and magnetic shields to tank wall are adopted to reduce the stray losses in construction parts according to analysis the distributions of stray losses in transformer. The influences of structure size of tensile plate slot, shields of yoke clamps and tank wall on the losses in construction conductive parts are analyzed and discussed, which can provide the some reference bases for the optimization design of power transformer.Finally, the magnetic-thermal coupling method was used to calculate temperature field distributions and hot spot temperature value in the tank walls and clamps of power transformer. On this basis, the local overheating in power transformer was analyzed, the hottest spot were found, the influences of size of the shields on hottest spot temperature were discussed. Hot spot temperature in tank and yoke clamps are significantly reduced after using magnetic shield, and local overheating are prevented efficiently.