| The above chart
is typical of the increasing moisture loading of transformer oil as the
relative humidity increases.
The colour change level of indicating
silica gel is therefore a vital means of assisting in the maintenance and
quality control of transformer oil.
For the last forty years it has been
traditional to use blue to pink indicating silica gel as the primary
desiccant capacity signal to maintain transformer oil quality and
therefore indirectly residual moisture levels.
The blue to pink indicating silica gel
saturation indication had developed over the past 40 years to a consistent
12-14% by weight signal change indication. This is equivalent to a nominal
30% relative humidity.
The introduction of the European directive
classifying cobalt impregnated silica gel as a carcinogen has resulted in
a variety of alternative colour change indication desiccants entering the
market.
The most important criteria to be observed
when assessing or considering an alternative to blue to pink
cobalt-impregnated silica gel is the signal saturation level.
At the present time there are a number of
non-cobalt impregnated alternative silica gels available on the market
with saturation indication signals from 6 to 25% by weight.
To maintain your current level of
performance and quality it is advisable to select an alternative to cobalt
impregnated silica gel with a signal level identical or within an
acceptable tolerance range to the existing standard.
Most manufactures publish the saturation
signal as a percentage adsorption by weight compared to the relative
humidity level.
For example;
14% by weight at a relative humidity of
35%rh at 20° C.
If you have a question or require further
information please e-mail beasleyr@brownell.co.uk |
