# Distinction Between Interturn Short-Circuit Faults and Unbalanced Load in Transformers
## 4 Results
### Infrared Analysis  
As a definitive complement in distinguishing between incipient short-circuit faults and load imbalances, infrared imaging is used to analyze the winding temperature under different operating conditions of the modified transformer. Figure 11 shows the reference frame of the infrared image for the transformer under analysis. In this image, the modified transformer is located at the center, with its secondary winding being the focus of the infrared analysis. Figure 10: FFT of 4-turn short-circuited ISP compared with healthy ISP. Figure 9: FFT of 2-turn short-circuited ISP compared with healthy ISP. Figure 12 shows the infrared image of the modified transformer in a healthy state, operating at full load. The initial temperature for the experiments was 26 \(\pm\) 1.2 \({}^{\circ}\)C. The image was taken after 30 min of operation, at which point the temperature began to stabilize at 65 \(\pm\) 3 \({}^{\circ}\)C. The average temperature increase rate was approximately 1.3 \({}^{\circ}\)C per minute. Figure 13 shows the infrared image of the modified transformer supplying the load with four fewer turns in the secondary winding, operating at full load. The image was taken after 30 min of operation, at which point the temperature began to stabilize at 65 \(\pm\) 2 \({}^{\circ}\)C. By the end of the 30 min period, this temperature did not show any significant difference compared to the transformer operating without a fault, and the average temperature increase rate remained at 1.3 \({}^{\circ}\)C per minute. Figure 14 shows the infrared image of the modified transformer with a two-turn short circuit in the secondary winding, operating at full load. The image was taken after 9 min of operation, at which point the protection was triggered with 48 A circulating in the short-circuited loop. The temperature reached 75 \(\pm\) 4 \({}^{\circ}\)C, exceeding the normal operating range. The infrared analysis of the two-turn short circuit clearly highlights the difference between a load imbalance and an incipient short circuit. The average temperature increase rate was 5.4 \({}^{\circ}\)C per minute. Figure 11: Picture of modified transformer base for the infrared images. Figure 12: Infrared image of the modified transformer in a healthy state at full load after 30 min of operation. Figure 15 shows the infrared image of the modified transformer with a four-turn short circuit in the secondary winding, operating at full load. The image was taken after 2 min of operation, at which point the protection installed in the short-circuited loop was triggered with 95 A circulating, and the temperature reached 79 \(\pm\) 4 \({}^{\circ}\)C, exceeding the normal operating temperature range. Notably, the transformer's thermal-magnetic protection device did not activate. The average temperature increase rate was 26.7 \({}^{\circ}\)C per minute. The infrared analysis of the two-turn short circuit clearly highlights the difference between a load imbalance and an incipient short circuit. When the number of short-circuited turns increased to four, the temperature rise became hazardous for the transformer's operation. Finally, Figure 16 shows the temperature increase trends for each operating condition of the modified transformer. It can be observed that the temperature rise trends for the healthy condition and the four-turn load imbalance follow the same pattern. Although the three-phase sinusoidal signal, the mean ISP value, and the FFT analysis reveal differences between these conditions, the temperature remains as if the transformer were in a healthy state. The temperature trends for the transformer under incipient interturn short-circuit conditions show a rapid increase. As the number of short-circuited turns increases, the  
Figure 14: Infrared image of the modified transformer at full load, operating as a transformer with an incipient 2-turn short-circuit fault after 9 min of operation. Figure 13: Infrared image of the modified transformer at full load with a 4-turn load imbalance after 30 min of operation.