Electrical Contracting News (ECN) May 2016 | Page 35

POWER DISTRIBUTION

TRANSFORMING
THE MARKET

A transformer is expected
to last the life of a building.

Transformers are perhaps one of the single most important aspects of a building’s services,
acting as the key connection between the national grid and the premises’ internal power
distribution network. For years, oil transformers have been the go-to choice for consultants and
specifiers, yet advances in rival technologies are now putting credentials of the age-old favourite
under the microscope. Here Steve Marr at Legrand UK delves deeper into the debate.

L

ike so many other aspects
of the electrical industry,
the transformer debate
is one full of nuances
and historical bias. Oil
transformers have long
been the transformer of
choice for many specifiers
and consultants. The technology has been
in use for over 100 years and has formed
a reliable power conduit for industrial and
commercial projects across the world for
decades. However, the rise in alternative
transformer technologies, typified by the
development of cast-resin transformers

(CRTs) in the 1980s, sparked a debate
into whether the days of the oil transformer
are numbered.

Turning point
Over 25 years on and the debate is still
going, however the tide may be turning
in favour of CRTs, with consultants and
specifiers firmly focused on sustainability
going forward with new projects. A
transformer is expected to last the life of a
building, and with most buildings generally
lasting 20 years before they are refitted or
repurposed, it would be very unusual for a

transformer to be replaced during this time,
bar a serious technical issue. However,
it is the sustainability factor – taking into
account a transformer’s emissions and its
overall total life cost – which may give CRTs
the edge of their older counterparts.
Despite their reliability over the years, oil
transformers do present a number of issues
– both during the installation stage and their
subsequent operational life – which CRTs
do not, all of which should certainly be
factored in during the specification process
for new transformers.
In oil transformers, the windings are
inserted inside an enclosure filled with a liquid

– generally mineral oil, which has the double
function of guaranteeing adequate insulation
between the windings and the earth, and
dispersing the heat generated by the normal
operation of the transformer itself. The oil
increases in volume as the temperature of the
surroundings of the transformer itself rises.
To compensate for these variations of volume
within the insulating liquid, some transformers
have an ‘expansion vessel’, situated in the
upper part. This tank communicates with
the outside by means of filters to remove
the humidity which, if it accumulated, could
impair the dielectric properties of the oil, and
consequently the transformer itself.

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11/04/2016 14:23