Comparative Analysis of Thermography Studies and Electrical Measurement of Partial Discharges in Underground Power Cables
The principal cause of damage in underground power cable installations is partial discharge (PD) activity. PD is a localized non-linear phenomenon of electrical breakdown that occurs in the insulating medium sitting between two conducting materials, which are at different potentials. The damage to the insulating material is induced by the AC voltage to which the insulator is subjected during the discharge process, and it can be directly or indirectly measured by the charge displacement across the insulation and the cavity defect. Non-invasive detection techniques that help in identifying the onset of the discharge process are required as PD is a major issue in terms of maintenance and performance of underground power installations. The main locations of failure are the accessories at points of connection such as terminals or splices. In this article, a study of electrical detection of PD and image processing of thermal pictures is presented. The study was carried out by controllably inducing specific failures in the accessories of the installation. The temporal evolution of the PD signals was supported with thermal images taken during the test in order to compare the PD activity and thermal increase due to failure. The analysis of thermographic images allows location of the failure by means of intensity-based texture segmentation algorithms. This novel technique was found to be suitable for non-invasive detection of the PD activity in underground power cable accessories.