Further testing can be carried out
on sample hydro-generation coils by
independent laboratories, including
the thermal endurance test, which is
carried out at 30kV for 500 hours, a
simple enough task for a high quality
coil. However, a more arduous test is
done at 35kV for 250 hours, however
all the coils provided by Sulzer have
passed this standard as well.
In the majority of cases, the client
will specify the test parameters for
the coils, which are normally specified
to operate at 11kV. As a baseline
assessment, coils are subjected
to 23.9kV for 400 hours while
being heated to normal operating
temperature, around 120°C. This test
is in accordance with the demanding
IEEE standard 1553, which relates
specifically to hydro generator coils.
Additional coils can be initially
subjected to the withstand test, which
evaluates the ability of the coils to
operate in overvoltage conditions which
may be expected during their life. Coils
are expected to pass this test which is
conducted at 28kV, as well as a further
test at 60kV and an end-winding test
at 22kV, with no detectable issues
with the insulation. While the IEEE
standards set out the framework for
these tests, the exact test voltages
and durations are specified by the
client to ensure that the coils meet
the requirements of the individual
application.
independent repair market.
Globally, Sulzer has invested
in a number of overspeed
balancing pits which can
be used as part of each
repair project for its
clients. Though, due to
their rarity, Sulzer has also
made these available to
OEMs and other customers.
Each pit is equipped with
advanced electronics and
diagnostics to provide stateof-the-art trouble-shooting
capabilities.
Pumped storage systems
Typically used as fill-in generation
at times of peak demand, although
green in terms of generation, they
obviously consume power when
pumping water back up to the high
level storage. Efficiency in the motors,
pump sets and the generators is crucial
to an installation’s viability as they are
normally run on very low percentage
margins.
An improvement in generating, or
pumping efficiency, especially during
routine maintenance work could
Dynamic balancing of
rotating elements is an
important aspect of the
manufacture and the repair
of any turbo machinery. A
rotating element that is out
of balance can cause major
operational difficulties
therefore make the difference between
a site being viable or not.
Some pumped storage installations
use separate turbines and pumps while
others employ reversible turbine/
generators which can act as both
High Speed Rotor Balancing
As the stator is completed, so attention
falls to the rotor, which can also
benefit from the improved insulation
materials technology. Rotor field coils
will usually be reinsulated as part of
a refurbishment project along with
the replacement of any damaged
components. Clearly, the rotor will need
to be re-balanced before it is returned
to service.
Dynamic balancing of rotating
elements is an important aspect of
the manufacture and the repair of any
turbo machinery. A rotating element
that is out of balance can cause
major operational difficulties, which
may prevent the timely start-up of
a facility if it has to be re-balanced.
Furthermore, the unbalanced element
can cause internal damage that will
rob a machine of its design efficiency,
reduce machine reliability, and
increase the costs of operation and
maintenance.
For any applications that require high
speed balancing, this process requires
a specialised balancing bunker, but
very few of these are available to the
RIGHT
Some pumped storage
installations employ
reversible turbine/
generators which can
act as both pump and
turbine
Issue 14 PECM
35