NAME : Jürgen R. Weidner
COUNTRY : Germany
REGISTRATION NUMBER : 2817
GROUP REF. : SC A1
PREF. SUBJECT : 1
QUESTION N° : 1.2
Nanotechnology in high voltage insulation systems for large electrical machinery
- First results –
Question 1.2: Could nanotechnology be applied beneficially to other machine parts, e.g.
endwinding support structures?
Background information
With the application of specially treated spherical SiO2 nano particles as part of the well
approved epoxy-mica stator winding insulation for large electrical machinery it is possible to
improve the properties of the high voltage insulation system significantly. Resistivity to
partial discharge erosion and electrical treeing is greatly increased and results in longer
lifetime until electrical breakdown. Also, the mechanical and thermal properties, which are
important for stator windings of large turbine and hydro generators, show increased values
due to the influence of nanocomposites.
As a first step, basic investigations on epoxy-mica nanocomposites were carried out on plate
shaped specimens with standardized electrode configuration for screening tests on material
properties. In the second step of development, the new nanocomposite insulation system was
tested at small stator winding bars prepared by the same manufacturing process as the original
stator winding coils. In the third step, the electrical and thermal tests are transferred to fullsize generator stator bars. Compared to the established reference system, the new nano
particle based high voltage insulation system shows a tremendous improvement in the
electrical lifetime.
The final step of development for turbine generators will be the application of epoxy-mica
nanocomposite insulation system for indirect cooled stator windings in global vacuum
pressure impregnation (GVPI) technology with following improvements:
ƒ thinner high voltage main insulation,
ƒ better thermal cooling of winding copper,
ƒ winding leads with higher copper cross-section and increased rated current.
The new nanocomposite stator winding insulation system offers a more effective design of
large rotating machines. It could increase efficiency of about 0.2% for indirect air cooled
turbine generators. For same generator type and size a load up-rate of 10 - 15% should be
possible.
Benefits of nanotechnology to other parts of stator
Using GVPI technology the complete stator including iron core, copper winding and
endwinding structure is impregnated with the new nano-particle epoxy resin system. The
better electrical, thermal and mechanical properties of the resin will improve also the
behaviour of fixing materials in the support structure of the endwindings like fiber glass
lashings, swell mat and spacers.
At the photo in figure 1 the lower part of endwindings of a GVPI stator at connection end is
shown. At this indirect cooled overhang epoxy fiber glass reinforced material is used for the
support rings and braces. All the fixing materials between top and bottom layer bars, support
rings and braces will be impregnated with the new nano epoxy resin and will be part of a
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homogeneous endwinding basket with improved electrical, thermal and mechanical properties
when stressed under the more severe load operation regime with steep load ramps, high
reactive power and peak load conditions given by the new grid code conditions.
Figure 1: Lower part of endwindings of a GVPI stator with circuit rings at connection end
The higher electrical strength of the new nano epoxy resin will of course also result in thinner
high voltage insulation at circuit rings and top-to-bottom bar connections (see fig.1)
improving the cooling of the endwindings.
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