POWER December 2014 - 40
Wind PoWer
each can be a daunting task. Auto-lubrication
systems have helped with under-lubrication
issues, but the lubrication systems
themselves must be maintained and properly
adjusted, and the cyclical nature of wind
generation does not lend itself well to strictly
time-based lubrication. Exit ports for the
expended lubricant must be kept free, and
the grease itself must not separate in the
auto-lube reservoir.
Most generators do have thermal monitoring
on the bearings, but a lot of damage
can be done before enough heat is created
to trip the sensors. Many newer turbines include
vibration monitoring as well, but there
are tens of thousands of turbines that have
not been retrofitted.
Induced current on the shaft has continued
to create problems with shortened
bearing life. Grounding brushes have to be
maintained carefully and are easy to forget
for the technician. Insulated bearings
or bearing housings have also helped, but
those systems must be tested regularly as
well for continued effectiveness. Many end
users now specify ceramic hybrid bearings,
in spite of the much higher cost. These have
proven to be a good solution and require no
special maintenance procedures.
Stator Windings. Stator winding insulation
failures can also be divided into
several categories, but most fall within
normal industrial failure modes, with the
exception of the loss of magnetic wedges.
That mode will be considered separately.
Because most of the stators operate at low
voltages, partial discharge is not seen to
play much of a role in these failures, but
especially where the initial excitation voltages
are supplied from an IGBT drive by
induction from the stator windings, there
is always the possibility of damage from
the peak voltage. Most of these windings
do utilize mica as part of the strand and
ground wall insulation systems, but most
also utilize polyester (PET) film, which is
generally unpopular among North American
generator designers.
Collector Rings. Collector rings (generator
slip rings), the metallic/carbon brushes
and the brush riggings and holders together
make up the collector assembly for DFIG
design generators. Like similar industrial
applications, these wear over time and are
considered replaceable components. However,
in an effort to minimize maintenance,
they are often fitted with long brushes that,
over the period of their life, generate a lot of
conductive dust. It is critical that these areas
be checked regularly and that a good cleaning
regime be followed to avoid flashovers.
These are not normally fatal to the equipment,
but they will immediately bring a tur40
3.
Stator magnetic wedge loss. Courtesy: Shermco Industries
4. Catastrophic failure due to wedge loss. Courtesy: Shermco Industries
5. Slot damage due to magnetic wedge abrasion. Courtesy: Shermco Industries
www.powermag.com
POWER | December 2014
http://www.powermag.com
POWER December 2014
Table of Contents for the Digital Edition of POWER December 2014
Contents
POWER December 2014 - Cover1
POWER December 2014 - Cover2
POWER December 2014 - Contents
POWER December 2014 - 2
POWER December 2014 - 3
POWER December 2014 - 4
POWER December 2014 - 5
POWER December 2014 - 6
POWER December 2014 - 7
POWER December 2014 - 8
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POWER December 2014 - Cover3
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