Ruben Vogelsang
Time to
breakdown of high voltage winding insulations
with respect to microscopic
properties and manufacturing qualities
Reprint of Diss. ETH No. 15656
1st
edition Konstanz 2004, 160 pages. EURO 75,00. ISBN 3-89649-965-3
The main factors that influence time to breakdown of
high voltage winding insulations are described in this work. Micrographs of
industrially-made winding insulations with different raw materials, production
techniques, types of taping and manufacturing qualities are analysed and
imperfections in the microscopic structure of the insulations are shown. The
effect of electrical tree inception and tree propagation on time to breakdown
is described and it is identified why and where trees are initiated in the material.
Electrical treeing is analysed depending on material properties and it is
quantified which insulations lead to fast and which to slow tree propagation.
The knowledge about the tree propagation has been used to develop a method that
allows testing of winding insulations with far less effort. Similarities and
differences to tests according to the standards are described. Properties of
winding insulations from the production lines of different companies are
identified in micrographs and their influence on time to breakdown is
quantified with the new method. Due to a high practical relevance, the
impregnation and the type of taping were thereby given special consideration
for vacuum pressure impregnation (VPI) and resin rich insulations. Finally, the
influences of electric field, temperature and mechanical vibrations on time to
breakdown are described. The results of all tests show that the manufacturing
quality plays a major role to wards time to breakdown (or lifetime) of winding
insulations. To extend lifetime, more attention has to be paid to the
manufacturing process. Concluding, characteristics for high quality insulations
with a long potential lifetime are given in this work.
Keywords: Electrical, Tree, Epoxy, Mica, Winding,
Insulation, Breakdown.
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