The loss of oil from Fluid-Filled Cables (FFCs) is a significant technical and environmental challenge for operators. Across the GB approximately 375,000L of oil is lost annually from fluid-filled cables. This project aims to reduce non-catastrophic cable leaks through the introduction of self-healing fluids with the name Anagen. Under normal operation, Anagen will function as insulation oil, but upon the formation of a breach, it will crosslink within the defect to form a solid mass that will stop the leak and prevent further leaks, preserving both the cable and the local environment. This project seeks to advance the Anagen self-healing dielectric fluid to allow the fluid to be implemented in GB’s FFC networks and become Business as Usual (BAU).
Benefits
When a fluid-filled cable starts leaking, operational staff are mobilised to initially locate the leak and then (depending on its severity) repair it or replace the fluid-filled cable. The costs associated with these activities is usually very substantial. An average oil repair cost of a typical single leak is around £45K. Furthermore, the cost of replacing EHV FFC circuits is approximately £500k per km. Introducing the SHF into the leaking fluid-filled cable (a cheaper method than repairing or replacing FFCs) could reduce or even eliminate the need for repairing or replacing the cable.
Learnings
Outcomes
The technical performance of Anagen has been demonstrated in the laboratory, with strong indications that Anagen can be used as a top-up fluid to FFCs. The key project outcomes are:
Phase 3a:
Anagen can be deployed into a leaking cable using a ‘top up method’ wherein the fluid in the tank is exchanged for Anagen (or a new tank containing Anagen connected to the circuit). Over time, the Anagen will progress down the circuit to the leak point until it reaches it and seals the leak. This avoids the need to carry out a full fluid flush on a leaking circuit, and allows treatment to be carried out with minimal changes to existing SOPs.
Anagen is capable of sealing leaks in bituminous compounds, including those used as filling compounds in joint boxes. It has also been observed that Anagen dissolves bituminous compounds more slowly than pristine T3788, indicating a reduced level of chemical aggression.
Phase 3b:
An assessment of moisture content vs. breakdown strength has found that Anagen is significantly more tolerant of moisture than T3788. This meets observations made on other dielectric fluids containing natural esters. Under ambient (unforced) conditions, Anagen fully saturated with moisture (~300ppm) still passes the IEC 60156 specification of 10kV/mm.
Initial assessments of PFT compatibility show that Anagen is compatible with PFT tracers (observed previously in Fluid Cable Care: Phase 2), with samples 30 days post introduction currently being analysed to demonstrate the continued retention of PFT. Self-healing trials have found that the presence of a skin blocks PFT: this was anticipated due to the gas-tight nature of the skin itself.
Trials of open-air self-healing under load cycling conditions have found that Anagen is capable of significantly reducing the leak rate (by approximately 70%). This is in line with previously observed open-air tests where leak rates typically fall between 70% and 100%.
After three months, the cable component aging study has found no evidence of chemical attack of key cable components, either spectroscopically or through trace metals analysis. Conversely, the Anagen itself has continued to self-heal, showing no indication of being inactivated either by the cable components or aging conditions.
At the start of the project, the technology readiness level (TRL) of Anagen was TRL 7. At the end of Phae 3b it is anticipated a TRL 8 will be achieved. After the planned Live Circuit Trials on UK Power Networks’ assets, if they are successful a TRL 9 will be achieved.
Lessons Learnt
General lesson learned in this project includes:
Early stakeholder engagement has allowed Kinectrics to understand the requirements of the DNOs more fully.
This has had a significant impact on the shape of the project and test methodology, including the investigations of new routes for deployment (e.g. the top-up approach). These have helped to ensure that the product can meet the needs of the DNOs and progress more rapidly towards deployment.
Key technical lessons learned from the testing process includes:
The demonstrations undertaken so far have shown that Anagen can be deployed via top-up method and will effectively self-heal leaks within bituminous compounds.
It has been found that since Anagen is manufactured using a natural product (tung-oil), it contains high levels of impurities meaning that filtration should be done over several stages with progressive filtration stages reducing in size.
The dehydration process of Anagen has also been evaluated and improved. It has been identified that a vacuum dehydration unit should not be used until after the filtration process is fully complete, otherwise the dehydration unit could become damaged due to a build up of tung oil mist on the filter.
The impact of pressure on the electrical performance of FFCs is significant, resulting in a strong improvement in the electrical performance of Anagen especially with regard to dielectric losses. It is believed this is because when the solution is under higher pressure, Anagen molecules are less able to rotate when interacting with an electric field resulting in lower frictional losses.
