Self-healing and
self-reporting assets
Improving the resilience of the energy distribution networks
Self-healing and self-reporting concepts
Gnosys is developing the next generation of materials for energy distribution networks. These possess the ability to alert
the network operator to the condition of the asset, the development of faults or imminent failure (self-reporting). They
may also have the ability to autonomously repair themselves to restore full functionality (self-repair). Self-reporting
materials provide important information about asset health to the network operator, allowing them to make informed
decisions about where to focus their attention. Self-healing materials are capable of efficient self-maintenance, effecting
self-repair of assets to substantially extend asset lifetimes by preventing the development of defects leading to failure.
Self-healing and self-reporting materials are of interest to companies operating high value assets, where unexpected
failures can lead to costly and lengthy repair processes that disrupt supply.
Self-reporting materials
A simple, effective evaluation of asset health
Gnosys has already developed asset measurements which report on the
condition of materials. Further developments are investigating the
incorporation of reporting molecules that can undergo a change in
properties in response to changing conditions, such as an increase in
mechanical strain, temperature, or pressure. When selecting a suitable
“reporter”, consideration should be given to determining what asset
changes represent a critical state, as this will inevitably influence the
reporting component used. The same consideration must also be given
to the manner in which the material relays information to inspection
teams; while a change in colour may be an obvious solution, many assets
are not readily accessible and so changes in electrical resistivity or
frequency of transmitted light may prove to be more suitable. Gnosys has
investigated a wide range of materials that can be incorporated into assets
either during processing or later, as self-reporting paints and coatings.
Routes to stimulate self-reporting materials
Self-healing polymeric materials
50 μm
Improved resilience, enhanced lifetimes
Self-healing materials have great potential for many utility assets, particularly those of high value or where the asset is
hard to access or maintain. If the asset is damaged, the self-healing material is capable of undergoing a response that
can lead to repair and restore asset health and functionality. This capability confers a number of benefits to an asset and
its operators, as the ability to autonomously repair minor defects improves resilience, reduces maintenance requirements,
and extends asset lifetime by preventing the development of major faults from minor defects.
Example: Within the UK, underground cables represent between 60 and 70%
of the distribution network, and there is a rapidly growing network of subsea
cables servicing offshore wind-farms and islands. In these instances, the
location of the asset renders it inaccessible, and so routine maintenance is
rare. If the protective sheath is damaged water can enter and degrade the
cable over the course of several years, resulting in premature failure. A cablethreatening defect can develop from holes in the sub-millimetre range to
much larger externally inflicted damage, and also damage that occurs during
manufacturing or installation – this damage may well go undetected.
Cable
makers
currently
protect cables from water incursion with the addition of ‘water blocking
tape’, which consists of a fabric scaffold containing an additive that swells
strongly in water. However, investigations carried out by Gnosys have
found that this material can be ineffective and be dissolved or stripped
from the cable by a sufficient quantity of water, limiting the intended
protection. Moreover, common water blocking tapes must be wound
onto the cable using specialist machinery, which is a time consuming and
expensive process.
In the search for alternatives, Gnosys has investigated a range of selfhealing and water blocking materials that can be incorporated into cable
designs. The requirements on potential candidates are highly
demanding, as they must be capable of undertaking cable repair over a
range of temperatures and pressures in highly aggressive environments.
It is also very important that these materials be compatible with current
cable processing techniques and can be incorporated into a wide range
of designs without negatively affecting the cable performance. Finally, a
successful system must have a price point commensurate with currently
used water blocking systems and also replace these systems.
Potential candidate materials have been selected that possess different
repair mechanisms. One type are supramolecular materials that derive
structural support from labile hydrogen bonds. When broken, the
hydrogen bonds can quickly reform and generate a new matrix
mechanically identical to the pre-damage system.
Another is an advanced water-blocking material that combines an
excellent water blocking response with strong material integrity, thereby
avoiding the problems related to dissociation and additive stripping in
water blocking tapes. Although this material does not truly self-repair, the
swelling response serves to restore the integrity of the cable sheath and
prevent further ingress of water, and so provides a ‘cable repair’.
Further, these materials possess excellent water blocking capabilities that
far surpass those of contemporary water blocking tapes in every aspect.
Importantly, these materials can be incorporated into cables using
conventional extrusion and melt spray deposition techniques. Both
methods avoid the use of expensive tape-winding machines, resulting in
substantial capital savings and increased production efficiency without
sacrificing speed or final quality.
Self-healing fluid systems
Another aspect of self-repair that has been explored by Gnosys is that of
self-healing reactive oils for fluid filled cables (or FFCs). FFCs have been
in use throughout the UK power network since the 1950s, and until the
1980s paper and oil insulation systems substantially outperformed solid
polymeric cables. While these cables are currently being replaced by
XLPE-insulated circuits, there are still approximately 8,500 km of FFC
remaining in the UK. In some cases, these have exceeded their
anticipated operational lifetime by 30 to 40 years.
In the event of a breach on a fluid filled cable, the
insulation oil will leak into the surrounding
environment. While this can be replaced, the leaked
oil represents an environmental hazard and can
potentially contaminate water supplies. Information
from Ofgem (left) shows that approximately 400,000
litres of oil is replaced annually across the entire UK
FFC network, which represents substantial costs in
replacing oil and environmental remediation. In
cables with multiple severe leaks, it is often more cost
effective to replace the system in its entirety.
Unlike solid polymeric cables, fluid filled
cables are no longer being produced on a
large scale, but stock is being held by
network operators to replace damaged
sections. Instead, Gnosys has developed
additives and reactive replacements to the
insulation oil to limit the risks of leaking
cables.
The aim of this is to generate oils that possess similar fluid and electrical
properties currently used insulation oils that would solidify within damaged
regions, thereby preventing the further loss of oil. Gnosys have investigated a
wide range of potential approaches which have yielded a number of different
compositions that can be considered as potential candidates. We have also
developed a range of ‘containment oil’ blends, which act to minimise
environmental contamination by curing within the soil. These form large
pockets that can entrap insulation oils in the region immediately surrounding
the cable, thereby minimising the volume of oil that can enter groundwater and
simplifying environmental remediation.
All potential oil blends are currently undergoing optimisation and cable trialling
in the near future before being trialled in network tests with participating DNOs, prior to full deployment.
Summary
With the help of Electricity Network Innovation Allowance support, Gnosys is developing several technology platforms
that are aimed to substantially enhance the resilience of power distribution networks. Our interest in gas pipeline materials
are also driving novel, self-reporting materials for new assets and coatings development for existing assets. It is hoped
that these will be used to improve asset health monitoring in the future.
Self-healing materials which confer asset self-repair is a second technology
platform. We have found that it is possible to incorporate materials with excellent
water blocking materials into current cable designs with no change to existing
cable manufacturing processes. Improved cable repair technologies should
substantially extend the operational life of cables and reduce the number of
premature failures. This represents substantial operational savings for cable
operators, who would otherwise have to invest significant time and money in
locating, diagnosing, and resolving faults that could be rectified autonomously.
Similarly, our work with legacy fluid-filled circuits promises to substantially reduce
the volume of oil lost to the surrounding environment. This is of substantial benefit
to the operators of the circuits, who are required to report leakages and take
immediate action in severe cases. Testing suggests that some of the proposed
additive systems will enhance the breakdown strength of the insulation oil, which
in turn would improve the quality of the insulation alongside providing the selfhealing function.
Gnosys Global Ltd
17 Frederick Sanger Road
The Surrey Research Park
Guildford, Surrey
GU2 7YD UK
Tel: +44(0) 1483 689 599
enquiries@gnosysgroup.com
For more information visit
http://www.gnosysglobal.com/