# Study on Seismic Performance of a Mold Transformer through Shaking Table Tests
## 3 Test Results and Discussion
### Acceleration Response and Dynamic Amplification of Test Specim  
The tri-axial acceleration response histories measured at different locations (top beam, bottom beam, left coil, and center coil) of the mold transformer were used to analyze the test results. Table 4 summarizes the peak acceleration responses of the test specimen in the X, Y, and Z-directions. Figures 12 and 13 present the acceleration response time histories of the test specimen subjected to 75% tri-axial AC156 input ground motion (AC156_75 test) and 300% tri-axial AC156 input ground motion (AC156_300 test), respectively. Figure 12 shows that the acceleration responses at the center coil and the left coil of the test specimen were almost the same. In the Y-direction, where the specimen showed low stiffness, the acceleration response showed a big difference, compared to those in the X and Z-directions, the top beam vibrated severely with 0.7\(\times\)\(g\) being the largest value of response acceleration; in general, the bottom beam showed less vibration than the other locations; however, transient peak accelerations were recorded with a maximum value of 0.51\(\times\)\(g\). Figure 13 shows that the specimen also revealed almost the same acceleration responses at the center coil and the left coil. In the Y-direction, the trend was similar to the test of AC156_75, the top beam vibrated more severely than the other locations with a peak response acceleration of 3.30\(\times\)\(g\); overall, at the bottom beam the level of vibration was not different from those of the left coil and center coil; however, transient peak accelerations were recorded with a maximum value of 2.31\(\times\)\(g\). This can be attributed to the high amplitude of input ground motion, which caused the damage accumulation in the bottom beam and the shift of natural frequency, as well as damping ratio, as presented in the aforementioned section. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Test no. **} & \multirow{2}{*}{**Test Label**} & \multicolumn{8}{c}{**Peak Response Acceleration (\(\times\)\(g\))**} \\ \cline{3-13}  & & \multicolumn{3}{c}{**Top Beam**} & \multicolumn{3}{c}{**Center Coil**} & \multicolumn{3}{c}{**Bottom Beam**} & \multicolumn{3}{c}{**Left Coil**} \\ \cline{3-13}  & & **X** & **Y** & **Z** & **X** & **Y** & **Z** & **X** & **Y** & **Z** & **X** & **Y** & **Z** \\ \hline
4 & AC156\_25 & 0.17 & 0.19 & 0.10 & 0.20 & 0.15 & 0.13 & 0.08 & 0  
Figure 12: Acceleration response-time histories of test specimen of AC156_75. Figure 13: Acceleration response-time histories of test specimen of AC156_300. Figure 14 presents the results of the peak response acceleration of the test specimen with respect to peak input accelerations at different locations. Overall, it can be observed that the specimen showed almost similar peak response acceleration, regardless of location in the X-direction. However, in the Y and Z-directions, it showed big differences in response acceleration at different locations. In the Y-direction, after a PGA of around 0.2\(\times\)\(g\), the peak response acceleration at the top beam and bottom beam were higher than those of the center coil and left coil and reached values of 3.30 and 2.31\(\times\)\(g\) at AC156_300, respectively. Meanwhile, the peak acceleration responses at the center and left coils were 1.10 and 1.47\(\times\)\(g\), respectively. This is because the center and left coils are partly isolated due to the epoxy and vibrated separately from the steel frame core of the transformer. Moreover, Figure 14a also presents the damage stages of the test specimen: the local damage of spacers was observed at a PGA of around 0.15\(\times\)\(g\), the bolts connecting the bottom beam and bed beam were partly loose at a PGA of around 0.20\(\times\)\(g\), the slippages of HV and LV coils were observed at PGA of around 0.30\(\times\)\(g\), and the bolts connecting the bottom beam and bed beam were completely loose at a PGA of around 0.60\(\times\)\(g\).