POWER August 2018 - 19

2. Retrofilling. A key contributor to the reliability of a transformer is the dielectric fluid,
which is used to cool it. Replacing the fluid in the unit is known as retrofilling, which is a smaller
investment than replacing a transformer. A retrofilled transformer is pictured here. Courtesy:
MIDEL Dielectric Fluids Global
to be replaced. But with the right approach,
operators can significantly extend
their lifecycle, defer the cost of decommissioning,
and help keep the lights on as
the world's electricity demand grows ever
stronger.
-Barry Menzies is managing director for
MIDEL Dielectric Fluids Global.
Small Modular Reactors:
'Sealing' the Deal
Small modular reactors (SMRs), defined by
the International Atomic Energy Agency
(IAEA) as a reactor less than 300 MW, are
fast emerging as a promising option for
nuclear energy. They offer flexible power
generation capabilities and enhanced
safety qualities.
Their modular designs and interchangeable
components allow them to be factory
produced. Additional units can be added
incrementally should a capacity increase
be required. Examples of potential applications
include remote sites such as
maritime shipping locations and military
installations, where a single SMR could
power an entire community.
Electrical penetration assemblies
(EPAs) are a small but important component
for
nuclear power generation,
ter fluids-which are able to absorb far
greater amounts of moisture without
compromising their dielectric strength-
could be key in the fight to extending the
lifecycle of existing transformer fleets.
And there are multiple benefits. First,
the greater moisture tolerance of ester
fluids leads to a slower degradation of
the cellulose paper contained within the
transformer. This prevents the present status
of the asset from deteriorating further,
which in turn prolongs its life.
The extent to which the life is extended
will depend on the degradation of the cellulose
paper and the age of the transformer,
but in many cases the added life could
be several years. There is also the fact
that, in terms of financial planning, retrofilling
is a much smaller investment than
replacing a transformer. Retrofilling (Figure
2) allows asset managers to defer the
lengthy and costly outage brought about
by decommissioning and installing a new
August 2018 | POWER
transformer. In this sense, retrofilling is
an invaluable financial planning tool.
Retrofilling also allows for more output
from transformers. Ester fluids can
operate in temperatures of up to 20C
(68F) higher than mineral oils. This allows
for more power to be produced from
the same footprint. In the context of rising
electricity demand, the implications
could be significant-though it should
be noted that there are technical implications
when considering retrofilling and
a more detailed technical assessment
may be needed for transformers above a
rating of 66 kV.
Transformers are among the most critical
and numerous pieces of infrastructure
in the electricity grid. Crucially, retrofilling
transformers with ester fluids is a
proactive approach, which is about prevention
rather than cure.
Ultimately, no matter how well-maintained,
a transformer will eventually need
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especially in the operation of SMRs.
Electrical and instrumentation cables
must be fed into the reactor through its
containment structure to monitor and
control it. These containment structures
are entirely sealed-off constructions
designed to safely contain the reactor.
The EPAs must provide a leak-tight passthrough
for the necessary cabling while
simultaneously maintaining the pressure
boundary integrity of the entire containment
structure. This is of the highest
importance and is the most essential
function of the EPA: maintaining the
pressure boundary in the event of a severe
accident helps to prevent radiation
and gas leakage, and keeps monitoring
systems and reactor control systems intact.
EPAs
are manufactured using one of two
standard sealing material options. The
first option is the use of organic, polymerbased
sealing materials, such as epoxy or
polyetheretherketone (PEEK). The second
option is the use of inorganic materials
such as glass. The seal must remain
leak-tight over the operational lifetime of
the reactor in order to maintain effective
safety levels and avoid costly downtime
for maintenance and replacement.
The seals are exposed to radiation, humidity,
and fluctuating temperatures and
pressures. With organic materials, degra19

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POWER August 2018

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