Fault events analysis in underground high-voltage cables

Although the nature of incidents may vary significantly, it is highly beneficial to have a standardized procedure for analyzing root causes. Such a procedure ensures consistency, reliability, and repeatability in investigations. In addition, it is crucial to have a team of professionals with in-depth technical knowledge of underground cable systems and technologies, including accessories and joints, as well as dedicated infrastructure to support training, hands-on exercises, and specific workspaces for post-incident investigations (forensic analysis).

The forensic root cause analysis methodology implemented by the Spanish Transmission and

System Operator (TSO) has been developed through years of operational experience and aligned with the recommendations of recognized international organizations. This method involves a structured and rigorous approach, covering evidence collection, component disassembly, failure mode analysis, and correlation with operational conditions. Documenting this methodology in an official procedure guarantees its proper application across different scenarios, allows the objectivity necessary for this kind of analysis and leaves no room for possible mistakes coming from improvisation actuations.

To facilitate these investigations, the Spanish TSO established its own Underground Cable

Campus, located in Getafe (in the metropolitan area of Madrid). This specialized facility is designed for training, technical exercises, and practical simulations of high-voltage cable systems. It allows technicians to reproduce real-world failure conditions and analyse components extracted from actual incidents under controlled circumstances. The Campus is equipped with advanced diagnostic tools, test benches, and dedicated laboratory areas, making it a key resource for developing specialized competencies and enhancing knowledge within the organization.

Field and laboratory work are carried out by a specific team called “Cable Intervention Group”

(GIC for its initial letters in Spanish), a highly skilled team of technicians specialized in insulated cables, who possess extensive experience in maintenance and diagnostics of cables.

The GIC performs detailed forensic investigations and actively contributes to the continuous improvement of procedures and best practices. Since its inception, the group has successfully completed numerous forensic analyses, accurately identifying the root causes of incidents.

Based on these findings, the Spanish TSO has implemented corrective and preventive measures, which have proven being effective in avoiding similar failures and improving the reliability of underground cable systems.

To summarize the paper, forensic analysis of underground cables represents an innovative and highly effective practice to strengthen the resilience and reliability of power transmission networks. Combining a well-defined technical procedure, a specialized training environment such as the mentioned Campus, and the expertise of the GIC team enables a comprehensive and systematic approach to incident management. This integrated strategy not only improves failure resolution but also fosters preventive maintenance, knowledge development, and technological innovation across the organization.