# Study on Seismic Performance of a Mold Transformer through Shaking Table Tests
## 5 Conclusions  
In this study, the seismic performance of the electrical mold transformer was experimentally investigated through tri-axial shaking table tests. The input acceleration time histories were artificially generated according to the ICC-ES AC156 code with a range of different amplitude. A total of 22 shakings were performed during the entire test campaign. Based on the test results, the primary conclusions may be drawn as follows. 1. The dynamic properties of the test specimen were estimated through dynamic identification tests using random input signal. The initial natural frequencies of the mold transformer in the X, Y and Z-directions were 7.78, 2.52, and 23.12 Hz, respectively. Since the damage grew as the input motion amplitude increased, the fundamental frequency showed a decreasing trend; however, the level of frequency deterioration was not significant. 2. The damping ratios of the test specimen were evaluated using the half-power bandwidth method. The initial damping ratio of the test specimen was in the range of 2-4% and showed an increasing trend up to 4-10% with the increase of input ground motion amplitude. 3. In terms of damage stages, overall, at the final test, the specimen neither overturned nor collapsed; however, the spacers located on the bottom region of the transformer showed severe slippage. Simultaneously, the bolts connecting the bottom beam and bed beam were completely loose. Nonetheless, it should be noted that the prototype specimen was tested with conventional \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Name of Test**} & \multirow{2}{*}{
\begin{tabular}{c} **Acceptance Criterion** \\ **(EC 60076-11)** \\ \end{tabular} } & \multicolumn{2}{c}{**Test Results**} \\ \cline{3-4}  & & **Before Shaking Table Tests** & **After Shaking Table Tests** \\ \hline External appearance evaluation & & Good & Good \\ \hline Winding resistance measurement (at 100 & HV winding resistance & 0.174 & 0.179 \\ “C) (\(\Omega\); \(\Omega\)) & LV winding resistance & 0.00846 & 0.000797 \\ \hline No-load current (\%) & \textless{}2.5 & 0.24 & 0.24 \\ \hline No-load loss (W) & & 1476 & 1487.00 \\ \hline Impedance voltage test (\(\forall\); \%) & & 328.6 & 360.00 \\ \(<\)10 & & 4.99 & 5.46 \\ \hline Load loss (W) & & 4859.66 & 5327.99 \\ \hline Full-load loss (W) & & 6335.66 & 6814.99 \\ \hline Efficiency (\%) & \textgreater{}98.6 & 99.37 & 99.32 \\ \hline Voltage fluctuation rate (\%) & \textless{}1.3 & 0.61 & 0.68 \\ \hline Insulation resistance measurement & & Good & Good \\ \hline Separate-source withstand voltage test & & Good & Good \\ \hline Impulse withstand voltage test & & Good & Good \\ \hline Temperature-rise test & & Good & Good \\ \hline Noise level test (dB) & \textless{}70 & 53.69 & 50.9 \\ \hline Partial discharge test & \textless{}10 & 5 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Operational test results. anchoring details; thus, further investigations on the seismic performance of the mold transformers with different anchoring details should be taken into account to assess the damage characteristics of the mold transformer. 4. The dynamic amplification of the mold transformer by means of the acceleration amplification factor was evaluated. The amplification factors during the tests were in the range of 1.0-2.5 in the X, Y-directions, which complied with the ASCE 7-16 and FEMA E-74 Standard. Meanwhile, the acceleration amplification factors in the Z-direction were smaller than the lower limit specified in FEMA E-74. 5. During the shaking table test series, the maximum relative displacements in the X-direction did not exceed the boundary limit of 75 mm, which was recommended by the Korean National Radio Research Agency [25]. Meanwhile, the maximum relative displacements in the Y and Z-directions exceeded the boundary limit of 75 mm around the PGA of 0.50 and 0.47\(\times\)_g_, respectively. Moreover, at the end of the shaking table tests, the maximum strain of the bottom beam and bed beam did not exceed the yield strain. 6.