Pyrex Suspension and Strain Insulators.
These insulators are not
an overnight achievement, but are the result of a
deliberate, long-time development program extending
over many years.
A mere duplication of
conventional insulator designs would have resulted
in useful insulators because of the high insulating
value of Pyrex electrical resistant glass. But it
was recognized that much superior insulators could be
developed through improved design and scientific
integration of the parts.
A suspension insulator is not
a composite of an insulating body and hardware, but
a unit in which the component parts reinforce each
other mechanically and together result in the highest
possible electrical insulation value. Therefore,
designs were studied, insulators were made and methods
of assembly tested. More than a hundred pin designs
were utilized in the development period, and thousands
of complete insulators tested under long-time
continuous loads and to destruction. Power company
engineers were consulted at each forward step, and the
present design was evolved as the solution.
Glass is one of the oldest
and most widely used of materials, and its properties
can be altered over a wide range. In general, glasses
are insulators of electricity, but their conductivity
can be varied over a wide range.
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Pyrex suspension insulators installed in 1930. The
installation shown on page five was
also made at
that time.
In respect to corrosion, some glasses are relatively
soluble in water, whereas some of the better ones can
be attacked by only a few combinations of the stronger
acids or by hot alkali solutions. Some glasses are
readily broken by temperature changes, being unable to
stand sudden dipping in hot water. Others withstand
shocks of several hundred degrees without distress.
The glass employed in the
manufacture of Pyrex insulators is one of the best
electrical insulators known, requiring a gradient (60
cycles) of over 2,000,000 volts per inch for thin
sections to puncture. It is transparent to solar
radiations, hence Pyrex insulators are raised only one
or two degrees above air temperature in brilliant
sunshine. Its hardness (75 on Moh's Scale diamond = 10)
and its resistance to acid and alkalies, already
mentioned, mean long continued preservation of the
perfectly smooth surface. These qualities are not
common properties of glass, but, like the alloy steels,
are the result of the careful compounding, fusing and
working of quite definite proportions of specially
treated raw materials.
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