3. Real Pollution Process
■ Dust, micro organism, bird secretions,
flies
■ Desert pollution
sand and dry wind
■ Ice & Fog deposits at high altitudes
■ Coastal pollution
layers are deposited on
• corrosive and hygroscopic salt
the
insulator surfaces
■ Industrial pollution
• smoke, petroleum vapours, dust
5. In the method, the insulator is
energized at the service voltage
which is held constant through the
test, and subjected to a salt fog
whose salinity, ranged from 2.5 to
160 g/m3.
The Salt fog test
6. The basic principle
of long-term Salt fog test
The generation of continuous
discharges by exposing the energized
insulator to a salt water spray.
7. Salt fog reference to real
contamination 1
■
Salt fog test is just particular and rare case
of pollution which is really important and has
more or less correlation with real pollution
process only for Marine coast disposition.
■
The conditions described in ……allow vitiate
severity of conditions in rather wide range.
As result the repeatability of test results is
unsolved problem.
■
The aim of this presentation to get analytic
and to obtain the answer to the questions
“How increase the probability to pass the
test?”
9. Four stages of degradation of
silicone rubber compounds to
flashover at Salt fog test
Leakage current surging with associated dry band formation
and partial arc development along the insulator surface
eventually spanning the whole insulator
Silicone rubber may fail as an insulator
due to the formation of a thick silica
layer which could lead to trapped
moisture and high leakage currents. A
silicone rubber insulator may also fail
due to material erosion exposing the
fiberglass rod.
■
1. loss of hydrophobicity
■
2. dry band arcing
■
3. formation of silica layer
■
4. erosion
11. Hydrophobicity is the
property that
prevents water from
forming a sheet on
the surface of a
polymer.
Hydrophobicity – the main
advantage of SR
Contact angle measurements showing
hydrophilic surface (A), minimum hydrophobic
surface (B), typical hydrophobicity for silicone
rubber (C) and ideal superhydrophobic surface
(D).
12. Main problem of SR degradation
during Salt fog test
■
The tracking and erosion test is an accelerated
test because the hydrophobicity is removed in the
first few cycles, and the test sample is not given
an opportunity to recover the hydrophobicity.
Recovery takes days to weeks, depending first on
the absence of electrical activity, and then on the
silicone compound, environmental conditions,
thickness of the silica layer, and the presence of
cracks in the silica layer.
■
The lack of recovery time is the reason
silicone rubber compounds were not
originally expected to perform as well as
porcelain glaze on the tracking and erosion
test.
13. Typical test results for silicon
rubber
■
A fast reduction of the hydrophobicity is
observed within 200-400 h of the test.
■
Later on, currents of typically more than
100 mA arise, corresponding to unstable,
rather long discharges.
14. Salt fog test results on hydrophobic and
The gap between hydrophobic and hydrophilic performance of silicone is
in the range of 20 % to 30%
15. Three possible ways of Salt fog
Test performance improvement
■ Reducing stress at the test by the
right choice of laboratory
■ Shape optimization
■ Material improvement
Technology
16. Main condition to pass Salt fog
Test!
Materials without an inherent
resistance to tracking and erosion do
not perform well in this test because
the formation of the silica layer
occurs very early in the test.
