Research On Random Response Of Traction Transformer Cooling Unit Based On Frequency Sweep Test

The cooling unit of the traction transformer is an important heat radiation device,which is installed in the cabinet of the car body underframe with the parent body.When the train is running,the cooling unit is subjected to complex reciprocating loads and prone to fatigue failure.The vibration characteristics and fatigue performance of the cooling unit are studied by means of test and simulation,which is of engineering significance to improve the reliability of the cooling unit and ensure the safety of train operation.In this paper,the vertical sweep vibration test and finite element simulation analysis are carried out to solve the problems of partial structure cracking in the vertical simulation long-life vibration test of a traction transformer cooling unit.The acceleration and strain signals collected in the test were processed by combining the digital filtering technology.STFT was used for time-frequency analysis of the collected signal.The root mean square acceleration of steady state region at each sweep frequency is calculated.The finite element model of the cooling unit was established,and the modal analysis,frequency response analysis and random vibration analysis were carried out.The fatigue damage was calculated respectively by using Dirlik method,Lalanne method,narrow-band method and three-interval method.Different calculation methods were compared through the spectral width coefficient.The improvement scheme was proposed from two aspects of adjusting plate thickness and shock absorber parameters,and the fatigue life of the improvement scheme was evaluated.The test results show that the cooling unit has the first eleven natural frequencies of 6.836 Hz,11.719 Hz,15.625 Hz and 21.484 Hz.The finite element model was established,and the validity of the model was verified by comparing the natural frequency with the experiment with the deviation within 9.53 %.The root mean square of maximum acceleration and the stress distribution under six working conditions were analyzed according to the standard.The positions where the fan box body and the outlet air grid plate are prone to fatigue failure are found.The results of spectral width coefficient show that the stress amplitude distribution is closer to the wideband process.The proportion of influence of increasing plate thickness,increasing damper damping coefficient and reducing damper stiffness on fatigue damage value were analyzed.The improvement scheme is determined that the thickness of the fan box body and the outlet air grid plate is increased by 3 mm and 2 mm respectively,the axial and radial stiffness of the vertical and lateral shock absorbers is adjusted to 75 N/mm and 150N/mm respectively,and the damping coefficient is changed to 0.03.The overall cumulative damage value of the improved structure is less than 1.The results show that the severe resonance at about 16 Hz in the position of the lateral lateral shock absorber near the fan box body of the cooling unit is one of the important reasons for the failure of the structure.The vibration energy of the cooling unit is mainly concentrated in the first four modes,and the lateral response accounts for the main proportion under different loading directions.Dirlik method is more accurate to calculate fatigue damage.Increasing the plate thickness can significantly improve the structural fatigue performance.