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How Si-COAT RTV Silicone HVIC Functions
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The purpose of an RTV coating for high voltage insulators
is to suppress the evolution of leakage current. Leakage current
develops along contaminated or ‘dirty’ insulators.
As the contaminant (typically carbon deposits, desert sand,
industrial pollution or, most notoriously, salt deposits from
coastal exposure) settles on the insulator surface and combines
with environmental moisture (rain, fog or dew), an electrically
conductive solution is formed.
Obviously, the primary function of an insulator is to prevent
the flow of electricity from the conductor to the tower and
down to ground. One can imagine, then, if there exists an
electrically conductive fluid on the surface of an insulator,
that insulator’s function is compromised.
It is very common for insulators to become contaminated
in the manner described above. When this happens, small amounts
of electricity leak out of the conductor and along the body
of the insulator. This is what is called leakage current.
If leakage current becomes too great, there is a short circuit
as electricity flows directly out of the conductor and straight
to ground. What ensues is a power outage and extensive equipment
damage.
The development of leakage current is reduced by coating
the insulator. In the case of Si-COAT, leakage current is
nearly eliminated entirely. When the insulator has been coated
and the RTV silicone has fully cured, there remains within
the body of the coating small chain, low molecular weight
silicone (LMWS) polymer that is free to move around within
the body of the coating. Different manufacturers will have
varying amounts of this LMWS in the coating. Studies under
electron microscopes have revealed Si-COAT to have the greatest
concentrations of LMWS.
Figure 1:
Electron microscopic scan A depicting the very rich
and even concentration
of LMWS in Si-COAT versus scan B for the leading competitor
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