TRANSMISSION
Vegetable oil-filled transformers
for a sustainable future
Information from Areva
Two recent projects, one in the UK and one in Brazil, used vegetable oil instead of mineral oil for the insulating fluid. The objective was to be
able to offer customers innovative solutions for a sustainable future.
In the face of increasing demand for
environmentally friendly and safer
transformers and reactors, researchers have
been working to extend the use of vegetable
oils from distribution transformers to HV power
transformers and reactors.
enable comparison of the two transformers
during services. The vegetable oil chosen
for the project was Envirotemp FR3,
manufactured by Cooper Power Systems. This
insulation fluid is a soybean-based vegetable
oil that has been in use since 1998, mainly to
characteristics of the natural ester oil with
mineral oil were carried out by a research
team at the University of Manchester. These
tests compar ed the characteristics of the
materials, their behavior during processing
and manufacturing, and their applicability
to diagnosis techniques. The results enabled
the two transformers (of identical design) to
be satisfactorily manufactured and tested
during 2006. They were erected on site during
2007 and will be fully monitored in service to
obtain valuable comparative data.
A shunt reactor for the Amazon
A power transformer for the UK
EDF Energy Networks has many high voltage
substations located close to densely
populated areas, both underground and
within buildings. It needed to be able
to install environmentally friendly power
transformers with higher safety levels as
part of its network reinforcement program.
It ordered two 132 kV 90 MVA transformers,
one filled with a vegetable-based natural
ester oil and the other with conventional
mineral oil. Both transformers were provided
with comprehensive monitoring equipment to
fill distribution transformers. It is biodegradable
and offers increased fire safely and insulation
life, as well as coming from a renewable
source. This was the first transformer in the
UK at 132 kV to be filled with vegetable
oil. A comprehensive review was therefore
carried out to assess the possible problems
associated with designing and manufacturing
such a transformer. Issues to be understood
included dielectric performance, voltage
stress distribution, thermal and hydraulic
performance, oxidation issues, processing
and in particular impregnation requirements.
As a result, a series of experiments comparing
energize - Jan/Feb 2008 - Page 42
Eletronorte, one of the main Brazilian utilities,
had a similar problem to EDF, but against a
different background. In the environmentally
sensitive Amazon region, environment-friendly
equipment is essential. It ordered four 242
kV shunt reactors (used to control capacitive
voltage in long, lightly loaded transmission
lines), one of which was to be filled with
Envirotemp FR3. This vegetable-based oil
has been used in Brazil since 2002, but not
for high voltage equipment. This 242 kV shunt
reactor was probably the first of its voltage
class in the world to be filled with a vegetable
oil. Using the knowledge gained from the
work on vegetable oil carried out in the UK,
these reactors were manufactured and fully
tested, ready to help Eletronorte to control its
electric power transmission and enable the
use of environmentally friendly vegetable oil
to be confirmed for the future. The solution
developed responds to the customer's
concerns over the use of petroleum-based
fluids in high voltage applications. In addition
to environmental benefits, the use of the
natural ester fluid has allowed the supplier
to design and manufacture a reactor with
enhanced fire safety and life expectancy.
These projects represent a major step forward
for the electricity industry. They will enable
power transmission companies to benefit
from properties that have been available for
distribution networks for some time – more
environmentally friendly, safer equipment with
the possibility of extended useful life.
TRANSMISSION
Four questions were answered by Milan Saravolac of Areva below:
What are the biggest advantages of
vegetable oil?
What particular customer benefit do
these projects bring?
The main benefit for the customers are
the same for both projects. The first is
enhanced fire safely, as the soybeanbased vegetable oil has a fire point of
360°C, which is considerably higher than
the standard mineral oil (approx. 160°C)
used in most transformers and reactors. This
means that our customers will be able to
bring HV equipment closer to consumption
centres (which was not possible in the past
without increased environmental risk) such
as densely populated urban and industrial
agglomerations and ecologically sensitive
areas. In addition, customers may also
benefit from reduced insurance premiums.
The second benefit is better environmental
and health characteristics resulting from the
use of food-grade seed oils and additives.
Vegetable oil has a better environmental and
health profile than conventional mineral oil.
Vegetable oil has the advantage of being
biodegradable, so oil spill management
solutions are made easier. Its unique ability to
absorb moisture contained in ageing paper
can extend insulation life by a factor of as
much as five. It also helps, chemically, to
prevent long cellulose paper molecules from
scission (i.e. ageing) when exposed to heat.
These properties can result in an increase of
overloading capability and longer transformer
insulation life. The results are lower lifecycle
costs and better utilisation of assets.
What do these projects mean for your
company?
With these projects, we stay at the forefront
of technology development. We work
together with our customers and suppliers
on providing innovative and environmentally
friendly solutions, thus paving the way for
long-term sustainable development. These
projects enabled us to develop a capability
to fully utilise the characteristics of this
environmentally friendly fluid and deploy it
across all our plants worldwide while providing
equipment with better performance and
minimum impact on the environment.
energize - Jan/Feb 2008 - Page 43
Does Envirotemp FR3 have other
advantages compared to mineral oil?
As it comes from renewable resources, it
is recyclable and reusable. It offers lower
gassing tendency under electrical stress and
better resistance to sludge formation. Due to
its viscosity and ability to polymerise when thin
layers are exposed to warmth and air flow,
it does not spread along the surface and
into subsurface soil in the case of spillage.
Moreover, the soybean-based vegetable oil
used is fully miscible with traditionally used
mineral oils, so it can be used to refill existing
transformers.
Contact Nadia Bouloudene, Areva,
nadia.bouloudene@areva-td.com v