Safety in Underground High-Voltage Cable: Effective Solutions for People and Infrastructure Protection

System Operator (TSO) in the area of high-voltage underground cables. In recent years, several incidents associated with failures in underground cables within the transmission network have occurred, prompting the development of specific solutions adapted to each type of installation.

These solutions have been designed to mitigate safety risks arising from various incidents, particularly those caused by electrical faults such as short circuits. At the same time, additional measures have been implemented to anticipate and prevent these failures whenever possible and minimize the unavailability of the assets.

In response to these challenges, the Spanish TSO has deployed a comprehensive set of measures that include containment and mitigation systems. These systems have been designed and tested based on detailed studies quantifying the energy involved in the incidents under evaluation.

Regarding fire suppression and minimizing its consequences, a technological foresight has been conducted to identify advanced solutions capable of ensuring rapid and effective intervention. Additionally, the management of high-pressure gas release has been optimized through the implementation of controlled venting pathways that direct these gases toward safe zones thereby reducing the risk to both equipment and personnel. This optimisation has been implemented in the mitigation systems and in terminations installed in high-risk areas (anti explosion terminations).

Modern technologies have been proved to improve the safety in inspections processes, like the use of drones inside confined spaces or submarine Remotely Operated Vehicle (ROV) in flooded galleries.

Another crucial component of this safety strategy involves predictive and real-time monitoring systems, aimed at detecting early warning signs of potential issues and preventing major failures. The technologies currently implemented by the Spanish TSO include: continuous

Partial Discharge (PD) monitoring using an autonomous and automated pattern-recognition diagnostic system, Distributed Temperature Sensing (DTS) via fiber optics to identify hot-spots in the cables, vibration monitoring through optical fibers (to detect and locate external mechanical aggressions), and current monitoring in cable screens to detect abnormal operating conditions. These systems provide valuable data that feed into predictive maintenance strategies, enhancing the overall reliability of the transmission network.

The adoption of these solutions is not only intended to protect the physical infrastructure of high-voltage cable systems but, above all, to ensure the integrity and safety of the people working on or near these installations. For this reason, critical assets have been prioritized based on their risk level, considering both their accessibility (impact on personnel safety) and their strategic importance for the transmission network (impact on system availability in the event of failure).

Complementary actions are also fundamental to ensure operational readiness. These include continuous staff training on the use and interpretation of monitoring systems and the implementation of frequent emergency simulations to validate response protocols and maintain a high level of preparedness (for example, simulations against fluid leakage in Oil-Filled cables).

In conclusion, ensuring safety in underground high-voltage cable installations requires an integrated approach that combines advanced technologies, rigorous operational procedures, and a proactive safety culture that evolves over time. The solutions developed in recent years— based on lessons learned from previous incidents—and the subsequent implementation of corrective and preventive action plans have proven highly effective in mitigating risks, protecting personnel, and improving both the resilience and availability of critical infrastructure within the transmission network.