# Partial Discharge Inception and Breakdown Voltage Analysis in PCB-Based Electrode Structures
## 4 Results of the Breakdown Test Procedure
### FE_0.3 mm Sample  
Figure 16 shows the PRPD patterns recorded during the breakdown test of a representative FE_0.3 mm sample (one of the eight tested samples) with a PDIV of 5 kV, as shown  
Figure 14: Image of the FE_0.5 mm sample before and after testing.  
Figure 15: FE_0.5 mm sample breakdown test results.  
in Figure 16a. The results indicated that the discharge quantity was primarily concentrated in the positive half-cycle, particularly in the range of 10-to-20 pC. In the first quadrant, sporadic discharge events occurred in the range of 25-to-100 pC, suggesting a distribution that exhibited a growth pattern approaching 90\({}^{\circ}\).  
Figure 16b shows the PRPD pattern at an RPDIV of 6 kV. The discharge distribution was similar to that shown in Figure 7b, with a larger-but-sparser discharge in the positive half-cycle and a smaller-yet-denser discharge in the negative half-cycle, which is characteristic of the typical surface discharge behavior.  
Figure 16c shows the final PRPD pattern recorded before breakdown of the sample, which ultimately broke down at 18 kV with a maximum discharge quantity of approximately 22 nC. This pattern, similar to that shown in Figure 4c, was not observed during the actual breakdown process. The discharge activity and voltage timing diagram is shown in Figure 16d for a testing duration of approximately 33 min.  
Figure 17 shows the images of the FE_0.3 mm sample before and after final breakdown, with the red circle marking the breakdown location. Breakdown occurred in the region closest to the intersection of the two electrodes and at the central point, where the carbonized area confirmed the electrical conduction between the positive and negative terminals.  
Figure 18 shows the statistical results of the breakdown tests on the eight FE_0.3 mm samples. The average PDIV was 4.59 kV and the average RPDIV was 5.6 kV. The overall average breakdown voltage of the samples was 15.3 kV.  
Figure 16: Breakdown test results of the FE_0.3 mm sample.  
Figure 17: Images of the FE_0.3 mm sample before and after breakdown.  
Based on the breakdown test data, which included the average results of eight samples for each of five different electrode configurations, the TE sample exhibited a PDIV of 6.13 kV and an RPDIV of 8.04 kV, with a breakdown voltage of 14.9 kV, indicating strong dielectric activity. The RE sample reached a PDIV of 5.76 kV and an RPDIV of 7.19 kV, with a breakdown voltage of 13.3 kV, particularly at the right-angled junction of the electrodes. The FE_0.5 mm sample recorded a PDIV of 5.08 kV and an RPDIV of 6.53 kV but did not experience internal breakdown, highlighting surface discharge characteristics instead. In contrast, the FE_0.3 mm sample showed a PDIV of 4.59 kV and an RPDIV of 5.6 kV, with final breakdown at 15.3 kV.  
The PDIV for all samples started at approximately 5 kV and breakdown occurred at approximately 15 kV. Based on these results, it is recommended to increase the amount of epoxy insulation material around the copper electrodes or enclose the entire sample in an epoxy-sealed case or box when the voltage exceeds 5 kV. This is important because PD events occurred above 5 kV, and breakdown can potentially occur at any point once this threshold is surpassed. These precautions can help prevent premature breakdown and enhance the longevity of the insulation system.  
Overall, these results confirm the accuracy of the design locations and provide insights into the dielectric properties of the samples under electrical stress. The findings can be directly applied to improving the design and reliability of high-voltage PCBs used in power electronic applications.