## 7 Conclusions  
In this paper, the vibration source and vibration path of a converter transformer under a magnetizing irnush current are analyzed, and the mathematical relationship between the vibration mechanism of converter-transformer winding under a magnetizing irnush current is deduced. The finite element simulation model of electromagnetic-force-flow multi-physical field coupling is established by COMSOL, which can efficiently simulate the complex vibration characteristics of a converter transformer under an irnush current. By building a finite-element simulation platform for a electromagnetic-force-flow coupling simulation model, the vibration characteristics of the converter transformer core, winding, converter-transformer box surface, tubing, pressure-relief valve and bushing under the action of a magnetizing irnush current were analyzed, respectively. The time-frequency analysis of the converter-transformer winding, box, tubing, pressure-relief valve, bushing and other components was carried out, and the following conclusions were obtained:  
(1) With the increase of current, the vibration acceleration of the winding also increases, and the acceleration of the winding reaches the maximum when the current reaches the peak. When the irnush current reaches the peak, the vibration acceleration in the middle area of the winding is small. For the same horizontal plane, the vibration acceleration of the middle part of the upper and lower ends of the winding is greater than the acceleration on both sides of the winding, and the vibration acceleration of the winding on both sides of the winding in the middle area is greater than the acceleration of the middle part of the winding. At the point where the winding acceleration is greatly affected by the irnush current, the acceleration content at each frequency is consistent with the distribution of the input irnush current, but the DC-component content in the middle region of the winding is larger and the second harmonic content is smaller. Compared with the effect of the irnush current on the winding, the vibration acceleration of the core is much smaller than that of the winding;  
(2) In the process of vibration signal transmission, the vibration signal of the winding acts on the surface of the box through the insulating oil, and the acceleration of the box increases with time in the first cycle. The surface vibration signal of the box contains a large number of DC and 50 Hz and their frequency-doubling components. Among them, the difference between the DC component and the fundamental wave is about 20%, and the difference of the high-order harmonic content rate at different points is large. The content rate of 100 Hz and 150 Hz is more than 50%, and the high-order harmonic content rate is relatively small;  
(3) In the first cycle, the vibration amplitude of the tubing increases gradually, and its fundamental component (50 Hz) reaches 7.01 m/s\({}^{2}\). At the same time, it contains a large number of DC components and frequency doubling components of 50 Hz, among which the DC component content reaches 66.0%, and the second harmonic reaches 49.2%. When the vibration signal is transmitted to the gas relay along the tubing, if the natural frequency of the internal baffle of the gas relay is the same as the frequency of the vibration, the gas relay baffle will deflect and there is a risk of misoperation;  
(4) The vibration trend of the pressure-relief valve is consistent with the vibration trend of the box, and the vibration amplitude gradually increases in the first cycle. The fundamental component (50 Hz) reaches 35.4 m/s\({}^{2}\). At the same time, the vibration of the pressure-relief valve contains a large number of DC components and a frequency doubling component of 50 Hz. Among them, the DC component content reaches 83.6%, and the third harmonic content is about 26.0%.