Calculation And Analysis Of Hot Spot Temperature Rise On Converter Transformer Windings

Converter transformer is an important equipment for HVDC transmission.Its safe and stable operation plays an important role in power system.In the operation process of converter transformer,because the load current contains a large number of high-order harmonic components,the winding leakage magnetic field will be enhanced and high-order harmonic loss will be generated,so the total loss will be increased.As the loss increases,the winding heating will increase,which will lead to the winding hot spot temperature rise.The life of transformer is affected by insulation aging,which is related to the hot spot temperature rise,therefore it is very important to study the hot spot temperature rise of converter transformer winding.Under the temperature rise test condition of the converter transformer,since the applied test current is the industrial frequency sinusoidal current which generated load loss is equivalent to the total load loss with high order harmonics.The load current of the converter transformer under the actual operating condition is the non-sinusoidal current with high order harmonics.In order to explore the difference in the temperature rise of the winding hot spot under the two working conditions,this thesis discusses the temperature rise of the winding hot spot from the perspectives of heating and cooling.The eddy current loss generated by the higher harmonic current is larger than that generated by the same amount of sinusoidal current in actual operating conditions,so the eddy current losses of windings are different in the two conditions.The proportion of the eddy current loss and the resistance loss in the winding loss are also changed.The eddy current losses of windings and the distribution of total losses along the axial direction of windings under two working conditions are calculated through the special software MF2 D and the calculation method of high order harmonic eddy current loss in IEC61378-2.The simulation results of load loss under two working conditions are compared with the measured results.The reasons for the change of the ratio of eddy current loss to resistance loss and the distribution of winding loss are obtained,which provides the heat source for temperature rise calculation.In order to explore the differences of winding hot spot temperature rise under the two working conditions,the finite volume method software Fluent was used to simulate the temperature rise of winding hot spots.The loss density of each winding disc is taken as the heat source for temperature rise calculation to reflect the non-uniform distribution of winding loss along the axial direction of the winding.After reasonably simplifying themodel,the temperature rise and position of winding hot spots under two working conditions are obtained through calculation.By comparing the calculation results with the analytical results,It is obtained that the temperature rise of the winding hot spot is 3-4k higher in the actual operating condition than that in the temperature test condition,and the hot spot is closer to the upper end of the winding.In addition,under the actual operating conditions,the influence of core oil channel on the temperature rise of core and winding hot spots.The influence of whether the guide baffle is added to the winding axial oil duct on the winding hot spot temperature rise is studied.The influence of the oil flow rate at the inlet of the winding and the influence of the over-load degree of the converter transformer on the temperature rise of the winding hot spot are also studied,which provides reference for the design and manufacture of the converter transformer.