www.sulzer.com
GENERATOR
REPAIR KEEPS
THE LIGHTS ON
IN DARwIN
he power station in
Darwin started life
as a 200MW gas
fired installation
with three gas turbine
generators that started full
production in 1987. Having
provided the population of
Darwin with electricity for
25 years, it was important
to ensure the generators
continued to provide reliable
service. This led to the
owners calling on the services
of Sulzer to carry out an
overhaul of the generator
including a rewind of the
stator.
T
The 42kVA generator,
operating at 11.5kV, was
originally built in 1986, but
after more than 25 years in
service, the time had come
for an overhaul. Using the
OEM drawings, combined with
the latest CAD, the engineers
at Sulzer were able to start
on the initial design stages
and plan the logistics that
would allow the contract to be
completed on time.
Once the project was
underway, two teams of
Sulzer engineers, on opposite
sides of the world, set about
the wide range of tasks
required to complete the
refurbishment. The service
engineers on site in Darwin
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PECM Issue 14
began with dismantling
the generator, while in
Birmingham, UK, the coil shop
worked on the design of the
new high voltage bars and the
dummy stator that would be
used to check the dimensions
of every one of the 108 bars
as well as the support blocks
for the windings.
Generators can be installed
with a variety of coil designs,
including ‘frog-leg’ coils and
diamond coils but larger
machines more commonly
have bar wound stators,
mainly because of the sheer
size of a finished coil makes
handling difficult. Once the
bars have been installed the
coils are formed by connecting
the relevant bar ends
together, brazing and then
taping.
it was important to
ensure the generators
continued to provide
reliable service.
Throughout the manufacturing
process quality control is
essential; starting with the
controls over raw material
quality to measuring every
coil for dimensional accuracy
to the final electrical tests.
Every process is checked
against the original drawings
and specifications to ensure
that the finished product
can be easily assembled and
produce efficient and reliable
service for many years to
come.
For Sulzer, the production
process for the new bars
starts with the raw copper,
which is processed using its
own in-house facilities to
draw and anneal the base
copper. The copper strip is
manufactured to exacting
tolerances before being
coated with the first layer of
insulation and cut to length.
Each strip is then layered
together with many others
to make up the basic bar
construction, but, its position
within the bar must be
transposed by 360° in order
to reduce eddy current
losses. This is a crucial design
characteristic and is more
commonly known as the
Roebel transposition, which
would be required in the bar
design for this generator.
Once the strips have been
properly arranged, a resin
tape is applied and they are
consolidated in a heated,
hydraulic press which
ensures the alignment of the
conductors within the slots;
this is crucial for delivering
the maximum efficiency of the
refurbished generator.
Meanwhile, in Darwin,
the generator was being
dismantled and showing
signs of its age with some
considerable oil contamination
of the stator windings being
discovered. Having recorded
all of the necessary
ABOVE
The 42kVA generator,
operating at 11.5kV, was
originally built in 1986,
but after more than
25 years in service, the
time had come for an
overhaul