measurements, the old coils
were removed and the stator
thoroughly cleaned before the
core was flux tested.
The flux test is used to
measure the condition of the
stator core insulation and thus
detect any local insulation
damage, which can cause
the formation of larger eddy
currents and local hot spots.
Once complete and with a
clean bill of health, the stator
could be repainted and the
rebuild process got under way.
This generator design consists
of 54 bottom bars and 54
top bars, all of which have
to be manufactured to tight
tolerances in order to ensure
they fit exactly into the stator
slot. Each bar has to be
formed and shaped by hand,
using the CAD-designed,
wooden formers that allow
every bar to be produced with
exactly the right shape and
dimensions. The final shape
is then checked again in the
wooden dummy stator that
was constructed earlier.
Every bar is tested in the
dedicated test cell with the
results recorded and kept
in the engineering archives.
Testing includes tan δ, which
relates to the power factor of
the bars as well as strand-tostrand short circuit testing and
the outer corona protection
(OCP) surface resistance
measurement.
RIGHT
Once all 108 bars have
been installed, the
insulating wedges are
fitted before being
secured to the end
winding brackets
RIGHT
With the stator nearly
complete, the high
voltage terminals were
cleaned and tested
at 25kV to prove their
insulation resistance
“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 deliver
reliable and efficient service
for many years to come.”
Mike Stanley, General
Manager of Sulzer’s
Birmingham Service Centre,
explains: “Improved
production techniques and
insulation technologies allow
modern coils to improve
the efficiency and reliability
of existing equipment.
Throughout the manufacturing
process quality control
is essential to maintain
production of high quality,
uniform coils.
At this point the logistics team
at Birmingham take over,
having already constructed
the shipping crates for the
bars. Carefully packaging
the bars to ensure they
arrive undamaged is crucial
to ensuring a trouble-free
installation in Darwin. The
shipment is timed to coincide
with the disassembly of the
stator on site, so as to avoid
any unnecessary delays.
LEFT
Larger machines more
commonly have bar
wound stators, mainly
because of the sheer
size of a finished coil
makes handling difficult
Once all 108 bars have been
installed and secured to the
end winding brackets, with
wedges in place, each bar
is subjected to a final high
voltage test to be certain that
none of the insulation has
been damaged during the
installation process. With the
test results recorded in the
project file, the next step is
to braze the bar end windings
together in order to create
the final coils, before taping,
sealing and applying the class
“H” top glass tape.
each bar is subjected
to a final high
voltage test to be
certain that none
of the insulation
has been damaged
during the installation
process.
With the stator nearly
complete, the high voltage
terminals were cleaned and
tested at 25kV to prove their
insulation resistance before
they, too, were installed.
Having completed the
checks and minor work to
the rotor, the generator was
reassembled and returned to
service, ready for another 25
years.
Issue 14 PECM
55