## 5 Result of Testing
### Temperature Rise Test  
The temperature rise test of the oil-type transformer was important due to the fact that oil is a liquid that could cool the transformer and keep the transformer from running at full efficiency. For the test of temperature rise, the circuit for the test was similar to the power loss test at the main junction of the transformer. The supply power was equal to the total loss of power at the 75 \({}^{\circ}\)C temperature of the transformer. The power supply continued until the temperature of the top oil was stable, which is determined by the temperature differences in the last 3 h (a difference not more than 1 \({}^{\circ}\)C). When the oil temperature is stable, it reduces the current to the rated current of the transformer for 1 h, then cuts off the current to the coil and measures the resistance of the primary and secondary windings against time. The results of resistance to time were plotted with time in order to find the resistance at the point of the cutting current (\(\Omega\)), then calculate the average temperature of the windings according to Equations (15) and (16), the results of which are shown in Figures 11 and 12 [15]. Figure 10: The test circuit of over-induced voltage. \begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Value** \\ \hline HV-LV & 26,400 Mohm \\ \hline HV-G & 25,600 Mohm \\ \hline LV-G & 18,600 Mohm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The insulation resistance test. \[\theta_{w}=\frac{R_{o}}{R_{a}}(235+\theta_{a})-235 \tag{16}\] \[\Delta\theta_{w}=\theta_{w}-\theta_{a} \tag{17}\]  
where:  
\(\theta_{w}\): average temperature of the coil (\({}^{\circ}\)C). \(\Delta\theta_{w}\): temperature rise of the coil (\({}^{\circ}\)C). \(R_{o}\): resistance value obtained from the graph at 0 min. Figure 11 shows the ambient temperature when the transformer operation in order to find the temperature rise. The x-axis shows the operating hours of the transformer for 10 h. The y-axis shows the ambient temperature in degrees Celsius. The data were recorded three times in order to average which line in the graph was averaged from the three data. It was  
Figure 11: The ambient temperature during transformer operation. Figure 12: The oil temperature during transformer operation. found that the maximum ambient temperature was about 35 \({}^{\circ}\)C, caused by the operation of the transformer after the 6 th hour. However, when the transformer continues to operate from the 6 th hour to the 7 th-10 th hour, it was observed that the ambient temperature decreased due to it being during the evening time, thus reducing the temperature. Figure 12 shows the oil temperature during the transformer operation in order to find the temperature rise. The x-axis shows the operating hours of the transformer for 10 h with the same as Figure 11. The y-axis shows the top oil temperature (blue line and mark) and temperature rise (red line and mark). It was observed that both top oil and temperature rise were trending to increase when transformer operation increased. The top oil was measured and recorded each hour. However, the temperature rise was a subtraction between the top oil and the average ambient temperature. It was observed that the temperature of the top oil was stable in the 9 th hour. In addition, the top oil temperature was about 83 \({}^{\circ}\)C. The average ambient temperature was about 31 \({}^{\circ}\)C. It could be calculated that the temperature rises to the top oil by about 52 \({}^{\circ}\)C.  
Figure 13 shows the loss comparison between the IEC 60076 standard and transformer test result, which consists of no-load loss, load loss and total loss where the orange bar is the IEC 60076 standard and the blue bar is the test result. It was found that the standard value was greater than the test value for all loss items. It was confirmed that the transformer design by the Area Elimination Technique made it possible to create a transformer due to the results of the loss test being less than the standard values.