Dielectric Materials for HVAC and HVDC Electrical Power Transmission Components (Nanocomposite Insulating Materials)
Submitting InstitutionUniversity of Leicester
Unit of AssessmentGeneral Engineering
Summary Impact TypeTechnological
Research Subject Area(s)
Chemical Sciences: Inorganic Chemistry, Macromolecular and Materials Chemistry
Engineering: Materials Engineering
Summary of the impact
Electrical power companies are tasked with operating a highly reliable
and robust power system. Electrical power outages (blackouts) have serious
consequences for the companies concerned as well as society. The health of
electrical insulating materials is critical for the reliability of these
systems as it often determines equipment lifetime.
Leicester was the first to demonstrate experimentally that polymer based
nanocomposite materials could increase the service life and reliability of
electrical insulation as used in high voltage power transmission systems.
Its research has also led to the development of measurement techniques to
assess the health and the extent of thermal ageing of HV power cables.
National Grid has used Leicester's research findings to manage and
monitor its electricity transmission equipment, with resulting impacts on
its safety, efficiency and financial economy. Borealis, a major
international supplier of insulating materials has used the research to
solve manufacturing problems and to set up test facilities for medium
voltage cables. A Knowledge Transfer Partnership with Alstom Grid
has led to the the establishment of a £1M commercial size HVDC cable test
facility which has attracted £0.5M investment from cable manufacturers
The research in the High Voltage Laboratory at Leicester has focused on
reliability issues and lifetime studies of the materials used as
electrical insulators in components for high voltage alternating current
(HVAC) and high voltage direct current (HVDC) applications. Key Leicester
academic personnel: Prof. J.C.Fothergill (1984-2012, now Honorary Visiting
Professor following a move to be Pro VC at City University) Prof.
L.A.Dissado (1995- 2008, now Emeritus Professor) and a more recent
academic appointment Dr S.J.Dodd (2007-).
Electrical insulation components are usually made from a polymer (such as
epoxy resin or cross-linked polyethylene) in which micrometre sized
mineral based filler particles (silica) are introduced to form a
microcomposite. However, the incorporation of filler particles into a host
polymer matrix results in materials that have decreased electrical
properties such as electrical breakdown strength owing to the introduction
In 2002, under an EPSRC grant [G1], novel work at Leicester
carried out by Fothergill and Dissado with W. Peasgood (RA, 2001-2004) and
in collaboration with a visiting researcher, Prof. Keith Nelson
(Rensselaer Polytechnic Institute, USA), led to the discovery that
significant enhancement of the electrical properties of polymers could be
achieved by the incorporation of nanometric sized solid particles of low
volume fraction into the host polymer matrix to form a nanocomposite and
was first publicised in CEIDP, the main rapid communication route for
discoveries in the field of electrical insulation .
Although nanometric fillers (having dimensions of one-thousandth that of
conventional micro-fillers) had been shown to improve the mechanical
properties of polymers, this work showed for the first time that
incorporation of nanometric fillers at low volume fraction produced
fundamental changes in the way that electrical charge is stored within the
polymer composite and therefore alters the macroscopic electrical
properties and performance of the base polymer for both HVAC and HVDC
applications. This research indicated that huge improvements in the
lifetime of such nanocomposite insulation systems would be possible with
the potential for large increases in the voltage withstand of insulator
components. It was first published as a journal article in Nanotechnology
. This work has also led to a US patent no. US 7,884,149 B2
Nelson et al, on Nanostructured Dielectric Composite Materials,
which claims considerable improvements in electrical insulation materials
for AC or DC high voltage applications and references the Leicester work.
Leicester is at the forefront of research in materials for HVDC as
evidenced by the work on materials for HVDC applications  and
the invitation to Fothergill to give the invited keynote address "Ageing,
Space Charge and Nanodielectrics: Ten Things We Don't Know About
Dielectrics" at ICSD 2007, the leading IEEE sponsored European conference
on materials for high voltage insulation. Leicester has demonstrated
leadership through a EU Framework 5 grant [G2] in collaboration
with a number of European utilities. Fothergill has also contributed a
book chapter on nanodielectrics .
The quality of the work is recognised internationally, for example, by
industry partners. Work with Schneider Electric [G3], France
(electrical insulator manufacturer) has shown that interfacial moisture
accounts for the observed dielectric behaviour in nanocomposites,
(Fothergill, Dissado and PhD student Zou Chen ) and work
sponsored by Borealis [G4], Norway, (a manufacturer of high grade
polymers for HV power cables), demonstrated that the bulk electrical
conductivity of polymeric insulation in HV cables could be used to assess
the extent of thermal ageing of the insulating material, (Fothergill,
Dissado, Dodd and PhD student T.Lau ).
Recently, a Knowledge Transfer Partnership (KTP), 2011-2012, in
association with Alstom Grid [G5], has established a new unique £1M
HVDC test facility at Stafford in the UK along with new strategic
partnerships with a number of major international HVDC cable
manufacturers, in particular Nexans, France, and Viscas, Japan. The KTP
was awarded the highest grade of "Outstanding" by the KTP Grading Panel
for its achievement in meeting KTP's Objectives.
References to the research
1. `Towards an understanding of nanometric dielectrics',
Nelson, J. Keith; Fothergill, John C.; Dissado, L. A.; Peasgood, W., IEEE
International Conference on Electrical Insulation and Dielectric Phenomena
(CEIDP), Annual Report, (2002), p 295-298.
2. `Internal charge behaviour of nanocomposites', Nelson, J.K.
Fothergill, J.C., Nanotechnology, volume 15, issue 5, (2004) p 586 - 595.
This is the key paper relating to the discovery (157 citations —
Thomson Web of Science on 26th September 2013.).
3. `Influence of thermal treatment and residues on space charge
accumulation in XLPE for DC power cable application', Fu, M.; Chen,
G.; Dissado, L. A., Fothergill, J.C., IEEE Transactions on Dielectrics and
Electrical Insulation, Volume: 14 Issue: 1 Pages: 53-64 DOI:
10.1109/TDEI.2007.302872 Published: FEB 2007.
4. `Electrical Properties', John Fothergill. Chapter in Dielectric
Polymer Nanocomposites, (ed. J K Nelson) Springer 2010,
5. `The effect of water absorption on the dielectric properties of
epoxy nanocomposites Zou, Chen; Fothergill, J.C.; Rowe, S.W. IEEE
Transactions on Dielectrics and Electrical Insulation, v 15, 2008, p
106-117. (50 citations).
6. `The Measurement of Very Low Conductivity and Dielectric Loss
in XLPE Cables: A Possible Method to Detect Degradation due to Thermal
Aging', J.C. Fothergill, T. Liu, S.J. Dodd, L.A. Dissado, U.H.
Nilsson, IEEE Trans. Dielec. and Elec. Insul., 18(5):1544-1553, October
G1. Fothergill, J.C. and Dissado, L.A.: Nanocomposite Materials
for Dielectric Structures, EPSRC: GR/R71788/01, £47,963, Jan — Jul 2002.
G2. Fothergill, J.C. et al, co-ordinator of the EU Framework 5
grant on "Benefits of HVDC Links in the European Power Electrical System
and Improved HVDC Technology (HVDC)", €1,694,434 = £1.16 million, 1/1/2003 - 30/6/2006.
G3. Fothergill, J.C. and Dissado L.A.: The Development of
Nanocomposite Dielectric Structures, A joint proposal under the NSF/EPSRC
request for cooperative activities in materials research between US and
European investigators, EPSRC contribution £85,055 + €30,000 (=£20,500)
from Schneider Electric, Jan 2004-Dec 2006, GR/S30672/01. Also:
Fothergill, J. C. "Nanocomposites", Schneider Electric, €30,000, 2005 - 2007.
G4. Fothergill, J.C. and Dissado, L.A.: "Development of
understanding of Insulation Ageing" Borealis AB, S-44486 Stenungsund,
Sweden, 2006-2009, £35,000.
G5. Fothergill, J.C. and Dodd, S.J.: KTP between University of
Leicester and Alstom Grid. Development of a HVDC Cable test facility at
Alstom. KTP008177 £68,304 + £79,304 (company contribution), Jan 2011-Dec
Details of the impact
Reliability of high voltage electrical insulators is of paramount concern
to the electricity generation, transmission and distribution industries as
failure of electrical equipment due to breakdown of the HV insulation
leads to power outages (blackouts). The electricity industry needs to
satisfy the demands of the Regulator (Ofgem) in terms of security of
supply. Failure of HV power equipment, such as high voltage power cables
capable of transporting all the power from a large power station (cost
£0.3M per km), high voltage power transformers (cost £2-5M each), bushings
and switchgear insulation, has significant financial penalties for the
industry in terms of repair costs and fines imposed by the Regulator.
These costs will ultimately have to be borne by UK business and domestic
consumers in the form of increased energy costs [A]. The stakes are
high: the typical cost of a 2GW HVDC link is of the order of £1
Billion and the cost of failure can result in loss of ~£1M revenue per
day due to lost electricity transmission alone. 2GW also represents
a significant fraction of the UK's generation capacity (~70GW) and could
potentially cause power to be redirected through an already congested AC
transmission network reducing network security. Reliability of electrical
insulation is of major concern not only to electricity suppliers but also
to HV equipment manufacturers whose products must be warranted against
defects and failure over a 40-year operating time. The R&D Specialist,
National Grid, states "This research has provided the fundamental
basis for many asset management decisions related to electricity
transmission assets. The typical failure mechanism for high voltage
assets is failure of the insulation and although not a frequent event,
when it does happen is catastrophic leading to potential loss of supply,
replacement of major assets and therefore increased costs (a single
transformer for instance costs £2M-£5M). This research has provided
knowledge on both the mechanisms but also on the potential for
monitoring the health of the assets" [A].
The research at Leicester on nanocomposites has informed industry in
terms of new and improved electrical power products, research and
development as evidenced by Leicester's contribution to "Polymer
Nanocomposites: Fundamentals and Possible Applications to Power Sectors"
published by CIGRÉ.(International Council on Large Electric Systems).
CIGRÉ is one of the leading worldwide organizations on electric power
systems, covering their technical, economic, environmental, organisational
and regulatory aspects with aims to "facilitate the exchange of
information between engineering personnel and specialists in all
countries, to develop knowledge in power systems and to add value to the
knowledge and information exchanged by synthesizing state-of-the-art world
practices". The Senior Scientist at Hydro-Québec Research Institute,
states "The work of Fothergill and Nelson carried out in Leicester
2002-2004, on the electrical properties of nanodielectrics was the first
experimental work designed to relate the presence of nano-sized
additives in a polymer with its impact on dielectric properties. This
work showed improved electrical performance of nanodielectrics over
conventional microcomposite polymeric systems. These results have had a
significant technical contribution to the CIGRE report on `Polymer
Nanocomposites: Fundamentals and Possible Applications to Power Sectors'
which was first published in 2011, particularly the chapters in the
report relating to electrical and space charge properties" [B].
This document has substantial reach by demonstrating how nanocomposites
could and are being usefully used by manufacturers and end users in the
following HV systems: switchgear, DC power cables, enamelled wires,
rotating machines, capacitors, all solid insulated substations, outdoor
insulation and power electronics.
Polymers are the preferred choice for electrical insulation in electrical
power cables and other HV power applications such as transformer bushings,
cable terminations etc., as used on the electrical power transmission
grid. The promise of improved electrical properties of polymeric based
nanocomposites, as first shown experimentally at Leicester, has
been embraced by a number of polymer manufacturers who supply the raw
materials for insulation components. Borealis is probably the largest
materials producer for polymers for the high voltage insulation industry
in the world. They have been supporting many projects in the development
of the incorporation of nanoparticles into their materials "both in
internal projects and in external networks" [C]. Similarly, ABB
have also invested in nanocomposite technology for their electrical
insulation components [D]. Evonik Industries manufacture a range of
epoxy based nanocomposite materials as master batches that are especially
designed for electrical and electronic applications [E]. Similar
products have been introduced for improved performance from manufacturers
such as PMT Prepreg Resin systems and 3M. "The Liu work project
[G.4] had a clear impact as it demonstrated the use of dielectric
spectroscopy as a tool for characterisation of insulating material. We
(Borealis) have then proceeded to use Novocontrol equipment at Chalmers
University in Gothenburg in order to solve various problems. The project
gave also valuable knowledge in measurement techniques, knowledge that
was utilised when setting up our system for tan delta measurement of
medium voltage cables", Technical Manager, Borealis [C].
Leicester's recent involvement in a Knowledge Transfer Partnership (KTP),
2011-12, led to the creation of a new £1M HVDC cable test facility at
Alstom Grid in the UK [F]. Alstom are a well-established
engineering company who manufacture state-of-the-art HVDC converters for
HVDC transmission systems. A DC transmission system offers a flexible and
efficient means of electrical power transmission and represents a new
international market for their products. This world-leading and unique
long-term HVDC cable ageing evaluation centre, opened in 2012, combines
three online measurement probes to characterise the electrical properties
of commercial size 200kV cables whilst undergoing an industry standard
programme of thermo-electrical ageing. This has raised Alstom's
international profile as suppliers of HVDC systems and attracted
considerable international interest from manufacturers and end users, such
as National Grid, leveraged the establishment of industrial partnerships
with international cable manufacturers such as Nexans (France) and Viscas
(Japan) who have provided in-kind investment of £0.5M and each company has
installed cables for long term ageing tests. The innivation has enhanced
Alstom's profile as a world leader in HVDC technology and has enabled it
to compete on the international stage with other HVDC technology
suppliers, such as ABB and Siemens, who offer established turnkey
solutions. "We are very keen for your research group to continue to
support this key project to back-up the on-going work in Stafford to help
us analyse and understand key ground breaking work associated with
space-charge measurements in HVDC cables systems under VSC type converter
stresses in years to come. The expertise that your research group is
able to provide our company with is very unique within the industry and
has proven to produce real impacts". Managing Director, ALSTOM Grid
Research & Technology Centre [F].
Sources to corroborate the impact
[A] Email from R&D Specialist at National Grid, UK
[B] "Polymer Nanocomposites: Fundamentals and Possible
Applications to Power Sectors" published by CIGRÉ (International Council
on Large Electric Systems), Technical Brochure No 451, February 2011 and
supporting email from Senior Scientist, Hydro-Québec Research Institute
[C] Email from Technical Manager, Borealis Group
[D] ABB Group, "Polymer nanocomposites as electrical insulation in
high voltage applications", Presentation by Henrik Hillborg, Senior
principal scientist, ABB Corporate Research, November 2010.
[E] NANOPOX® E Products, Technical Bulletin, Evonik Industries,
[F] Letter from Managing Director, ALSTOM Grid Research &