Investigation Of Power Transformer Electromagnetic Vibration And Noise Problem Based On Fluid-Structure Coupling Method

The vibration noise of power transformer has always been one of the most important problems of transformer industry. with the improvement of the transformer capacity and voltage class, the noise pollution has also increased. Since 12 th five-year, the requirement for the environmental protection and noise of the electrical equipment has been more strict than before. How to take effective measures to reduce transformer noise has become urgent problem for the power department and transformer manufacturers. In this paper, based on the mechanism of transformer vibration noise generation, and combined with its transfer paths, the electromagnetic field-structure field-acoustic multi field coupling model of transformer is established, The theoretical analysis and experimental study on the vibration noise of the transformer are carried out, the method of magnetic force thermal stress analogy and fluid structure coupling is proposed, and the concrete measures for reducing the vibration noise of the transformer body are given, and engineering application effect is analyzed. At the same time, the practical calculation program of power transformer noise is developed. The main research contents are as follows:(1) In order to analyze the contribution of the transformer core’s magnetostrictive effect to the vibration of the transformer, the magnetostrictive force thermal stress analogy method is proposed. Firstly, the power transformer 3D transient electromagnetic field numerical calculation model has been established, and flux density of the core values at different times for each node has been extracted, the error between the calculation value and the design one is less than 3% through the comparison of the central column magnetic flux density which can verify the correctness of the proposed method; Then the magnetostrictive force under the time domain and vibration displacement under the frequency domain are calculated according to the magnetostrictive force- thermal stress matching method, the size and distribution of magnetostrictive force is closely related to the core flux density, and the vibration displacement decrease from 100 Hz to 500 Hz.(2) The 3D eddy current calculation model is established, and the leakage flux distribution of transformer winding is obtained by finite element method, and the short-circuit impedance of the transformer is calculated by using the magnetic field energy method, the error of the short-circuit impedance values is-1.41% that can verify the correctness of the leakage flux field calculation. Then the electromagnetic forces of various nodes in transformer winding are obtained by calculation, and the distribution characteristics are summarized, the contribution of electromagnetic force to the vibration is obtained, which provided the premise condition for the calculation of vibration noise.(3) In order to simulate the transmission process of the vibration and noise of the transformer effectively, the power transformer acoustic-structure coupling model can be designed by using the finite element software to calculate power transformer body vibration and noise based on fluid-structure coupling theory. Then the core magnetostrictive forces and windings electromagnetic force loaded into the structure field and sound field calculation model, the vibration characteristics and sound field distribution of core and transformer body are obtainedug by the reasonable simplification establishes power transformer vibration noise fluid- structure coupling calculation model for power transformer body vibration noise issues. And the correctness of the method is verified by comparision the calculation values with the experimental ones.(4) The regular emprical formula of transformer vibration noise are summarized, and based on that, the power transformer noise calculation program are designed, and compared with the typical product test data, the error is within 5%, which meets the engineering requirements. Meanwhile the magnitude of transformer tank is calcuted and analyzed by structrure finite element method, and verified tank’s intensity and stiffness by the results of strain and stress.(5) The concrete measures of vibration noise reduction are summarized, and the vibration noise reduction measures are applied on the extra high voltage generator transformer. Firstly, the body vibration noise is optimized by reducing flux density, when the core flux density has been reduced 0.05 T, the maximum sound pressure calculation result of the core body has been reduced about 1.26 dB; then the vibration noise has been optimized by increasing the tank wall thickness and tank strength, the tank wall increases from 10 mm to 12 mm, the transformer maximum sound pressure value is reduced about 3dB.