Nobel passive signal acquisition system for PD monitoring of very long cables based on optical fibre

Signal digitization systems connected to electromagnetic sensors require high-performance processing electronics to capture and process signals at tens of megahertz with sampling rates of 100 MSa/s. These detection systems need to have power and communication along the cable at the various points where the sensors are installed. Sensors are usually installed at splice positions near grounding boxes. Temperature, humidity, and possible flooding conditions to which these devices are exposed pose a challenge that can lead to monitoring system failures, generating additional maintenance costs. Additionally, these active devices are exposed to the risk of failure due to voltage surges induced by the electromagnetic field of the high-voltage cable system during switching events, lightning, or short circuits. These monitoring system failure risks sometimes cast doubt on the benefits of implementing monitoring at intermediate points of long cable systems, limiting their use to terminations.

This paper describes a new solution under development within the framework of a European project in collaboration with several manufacturers and utilities. The solution allows the signal capture from sensors at tens of megahertz using a completely passive system implemented with optical fibre. The new capture and transmission system enables the transfer of the signal captured by electromagnetic sensors at tens of megahertz, through PD information encoding onto an optical carrier in the developed optical sensor, to a conventional electronic device capable of processing and analysing PD. This device is installed in the substation environment, kilometres away from the sensor, where the environmental conditions are controlled, and there is no risk of voltage surge coupling.

Architecture of the system under development, including sensor, light translator, interrogator and processing device located at the substation is described. Moreover, the paper includes ongoing development work to integrate the solution into a system with artificial intelligence

(AI), capable of receiving signals and automatically interpreting patterns.

The procedure for high-voltage laboratory tests and the results after validating the prototype capable of detecting PD signals from 10 pC is also described, performing automatic localization along the cable and interpretation using AI.

Future work shows two pilots where real installation will be carried out in HVAC and HVDC cable systems within the framework of the European project [1].