The decommissioning of fluid-filled cables for the transmission system is often an intense, complex and lengthy process. The conventional nitrogen purging method could only remove about 40% of the oil in cables during the initial purge and would commonly need another 5 years of subsequent purging to remove the remaining oil. The large amount of excavation required could cause significant disruption to local communities while the remaining oil could pose risk to the surrounding environment. This project would look to trial a novel, bacteria based decommissioning method that could remove more than 95% of the all the cable oil in 14 to 16 weeks and thus could substantially reduce the disruption to local communities while mitigating the risk to the surrounding environment.
Benefits
Should the project be successful and prove that the proposed technology can be applied for transmission, then the decommissioning time, excavation and other required civil work for fluid-filled cables could be reduced dramatically. This would in turn lead to significant reduction in disruption to the local communities and local traffics. The environmental risk for potential oil contamination is also much decreased.
Learnings
Outcomes
Year 2023/24
1. Oil sample analysis and hydrocarbon profile determination
Aim: To assess the condition of the oil and determine the profile for the bacteria.
Success criteria:
- Accurate identification of contaminants, including PCBs.
- Understanding the hydrocarbon profile to guide decontamination efforts effectively.
Outcomes:
- Hydrocarbon profile determined through analysis provided insights into the types and present concentrations.
- PCBs not found.
2. Upgrade of ODB System modules for increased voltage
Aim: To upgrade existing ODB System modules to accommodate requirements up to 400kV.
Success Criteria:
- Successful modification of existing modules to enhance voltage capabilities.
- Ensuring compatibility and functionality of upgraded modules with the ODB System.
Outcomes:
- Rigorous testing and modification of existing ODB System modules were conducted to increase voltage capabilities.
- Compatibility and functionality of upgraded modules were verified through performance testing and simulations.
- Modification process documented successful upgrades.
The outcomes demonstrate significant progress towards achieving project aims and success criteria. The analysis of oil samples provided critical insights into the hydrocarbon profiles, guiding the bacterial degradation efforts. Additionally, successful upgrades of ODB System modules further align the project with its objectives and contribute to its overall success.
Year 2024/25
Successful implementation of remote oil cable decommissioning technology:
- The ODB system was successfully deployed in a live operational environment, demonstrating its capability to remotely extract and manage oil from decommissioned underground cables with high efficiency and minimal disruption to surrounding infrastructure.
Enhanced Operational Efficiency
- The project showcased significant time savings using pre-installed modules, resulted in a fast mobilisation phase and reduced on-site intervention.
Improved system resilience and automation
- Electricity outages interrupting the system were resolved through the development and integration of new software capable of automatically managing fault scenarios. This has greatly improved the reliability and autonomy of the ODB platform.
Accurate monitoring and increased oil recovery
- High volumes of recovered oil were extracted per each phase, which underlines its effectiveness and the importance of predictive planning. The need for earlier and more frequent oil collection was met with responsive logistical adjustments.
Knowledge generation for future projects
- Cable samples from treated and untreated phases were collected for detailed laboratory analysis. These results will inform the final project report and support further optimisation of biological oil decommissioning processes.
Scalability and replicability demonstrated
- The learnings and technical adaptations from the ODB project have laid the foundation for scalable deployment across other sites, with key insights feeding into future project planning and applications.
Lessons Learnt
Co-ordination to ensure electricity supply and chlorine free tap water access requirements need to be understood and prepared in advance based on project specifications and requirements.
Clearly defining responsibilities for tasks such as initial oil-purging, tank emptying, cable head preparation, and bypasses is essential to ensure timely completion. It's also vital to prioritise coordination and approvals for ODB module placement to prevent delays and ensure ompliance with regulatory requirements.
Cable head preparations will be streamlined by providing valves pre-configured for the ODB System. These cable head valves will be installed by the operations team prior to mobilisation, significantly reducing installation time.
Where feasible, a fixed power supply should be prioritised over generators to ensure stable and continuous operation.
A permanent water connection will support fully remote operation, allowing dosing and refilling to be managed from a single location.
Containers may be positioned outside the compound area to facilitate easier access for oil collection and other logistical operations.
Heated connection tubing enables extended distances between container units and cable head interfaces, supporting greater flexibility in site layout.
Stop-joint bypasses and cable head terminations must be configured to allow for bi-directional flow, ensuring full system functionality.
