Discussion on the Defects in HVDC Cables and Their Relation with the Occurrence of Partial Discharge Phenomena

Extruded cables for high voltage (HV) applications, particularly for HVDC systems, must be manufactured to a high standard to ensure their quality and design life. Any deficiencies or imperfections during the manufacturing processes can lead to defects that negatively impact the performance of the final product during operation. There are methods available to detect weaknesses both through end-of-line tests and continuous monitoring of the assets. One innovative diagnostic technique gaining recognition in the HVDC cable industry is Partial Discharge Analysis (PDA). This technique can identify prospective defects early on, preventing accelerated degradation of the insulation material, and potentially leading the cable system to failure. This paper discusses some of the various types of defects that can arise in cables due to poor manufacturing practices, as well as during their operational lifespan, and the corresponding types of PD phenomena that may occur. Examples of imperfections will be presented, debating their probability of occurrence based on the manufacturing processes and materials, and their associated PD signals when exposed to DC electrical fields. Most of the samples used in the investigation originate and have been collected in the ongoing activities within the NEWGEN project, which is fully funded by the European Union Grant Agreement No.101075592.