## 3 Results and Discussion
### Experiment of the Insulators with EL Coating
The model demonstrated improved accuracy at higher voltages, with errors decreasing to approximately 7% in the 15-20 kV range, indicating particular suitability for typical transmission line operating conditions. This close agreement between experimental and simulated results confirms the coating's dual capability as both a visual indicator and quantitative measurement tool for insulator voltage monitoring. The observed 10% mean error between measured and simulated voltages (Table 2) stems from compounded uncertainties in instrumentation, environmental variables, and model simplifications. Instrumentation limitations primarily  
Figure 7: Electroluminescence performances of ZnS:Cu coating on insulators (**a**) Demonstration of electroluminescence at voltages of 0–25 kV in indoor conditions. (**b**) Demonstration of electroluminescence at voltages of 0–25 kV in nighttime conditions. (**c**) Electroluminescence CIE of the coating at voltages of 0–25 kV. (**d**) Electroluminescence intensity of the coating on insulators at voltages of 0–30 kV. from the Ocean Insight HDX-VIS-NIR spectrometer's NIST-traceable calibration uncertainty (\(\pm\)3%), dark noise (\(\pm\)0.1 cd/mm\({}^{2}\)), and daytime stray light suppression, which collectively contributed -4.2% to the total error, with dominant effects below 10 kV, where signal-to-noise ratios were suboptimal. Model assumptions introduced a \(\sim\)3.3% discrepancy, notably from simulating a uniform relative permittivity and omitting edge-field enhancements at the steel cap-shed junction. Additionally, coating thickness variations and ZnS:Cu dispersion heterogeneity contributed -2.5% through localized electric field distortions. Voltage-dependent trends further contextualize these errors: higher discrepancies at 5-10 kV align with instrumentation limitations under low-photon-flux conditions, while improved accuracy at 15-20 kV reflects enhanced signal stability where model simplifications became the residual error source. To address these limitations, future implementations will employ electrospray deposition for thickness control, integrate real-time temperature compensation using \(\varepsilon_{\mathrm{r}}\)-T relationships from Figure 4, and adopt high-dynamic-range photodetectors to mitigate saturation effects. The above experimental results confirm that the EL coatings can effectively sense the voltage applied to individual insulators. To further validate their capability for detecting zero-value insulators, we conducted tests on a string of seven insulators (including two zero-value insulators) under an applied voltage of 110 kV. The voltage distribution across each insulator and the corresponding luminescence intensity of the coating were measured simultaneously (Figure 8). The coating exhibited distinct luminescence responses that clearly differentiated between functional and zero-value insulators. While healthy insulators showed measurable luminescence intensities proportional to their voltage loads, the zero-value insulators displayed negligible luminescence, as evidenced by the detailed inset in Figure 8. This direct correlation between luminescence absence and zero-voltage conditions demonstrates the coating's effectiveness in identifying faulty insulators within a string. To quantitatively assess this relationship, we performed simulations based on the measured luminescence intensities to predict the voltage distribution across the insulator string. The simulated results showed excellent agreement with experimental measurements, with discrepancies consistently below 10%. Notably, the simulation accurately predicted the near-zero voltage condition of the defective insulators, further validating the reliability of this approach.