The quality of the power systems is related to their capability to predict failures, avoid stoppages, and increase the lifetime of their components. Therefore, science has been developing monitoring systems to identify failures in induction motors, transformers, and transmission lines. In this context, one of the most crucial components of the electrical systems is the insulation devices like bushings, which are constantly subjected to dust, thermal stresses, moisture, etc. These conditions promote insulation deterioration, leading to the occurrence of partial discharges (PD). PDs are localized dielectric breakdown that emits ultra-violet radiation, heat, electromagnet, and acoustics waves. The most traditional techniques to identify PDs on bushings are based on the current, UHF, and acoustic emission analysis. However, thermal analysis stands out as a noise-resistant technique to monitor several components in the power systems.

Although the thermal method is applied to detect different types of faults, such as bad contacts, overloads, etc, this technique has not been previously applied to perform PD detection and evaluate its evolution on bushings. Based on this issue, this article proposes two new indexes to characterize the PD evolution based on the infra-red thermal analysis: the ARC (Area Ratio Coefficient) and the RGBRC (RGB Ratio Coefficient). Seven PD levels were induced in a contaminated bushing, and an infra-red thermal camera captured 20 images per condition, totalizing 140 images. ARC and RGBRC were used to perform the identification of PD evolution. Results indicated that values of the new indexes increase with the PD activity. Thus, the new imaging processing approach can be a promising contribution to literature, improving the reliability and maintenance planning for power transmission systems.