HERE ARE TWO
suspension insulators of the same shape, assembled with
practically the same hardware. Each passes the standard
A.I.E.E. No. 41 tests which are supposed to differentiate
good insulators from bad. Sixty feet up in the air, on a
dark, overcast day they look as much alike as two brother
peas in the pod . . .
But are they alike? Insulator No. 1 is glass--a special,
low-expansion transparent glass of high dielectric
strength. Insulator No. 2 is made from a well-known
competitive material, very different from glass.
Let's take a look a the qualifications, good and bad,
of these two insulators . . .
Questions and answers begin on Page 7
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THE RAW MATERIALS
Each insulator consists of a "shell" coupled,
in one way or another, to a steel cap and a
steel pin. In both cases the caps and pins
are made of the same material, are practically
identical in size and shape.
But the "shells" are not the same.
Shell No. 1 is made from glass -- an amorphous
material, non-crystalline and non-porous, uniform
all the way through, smooth, hard, and highly
resistant to physical or chemical attack.
The particular kind of glass used here has a
coefficient of expansion (32 × 10-7
cm/°C) only one-third that of an ordinary bottle
or window glass, thus minimizing the effect of rapid
temperature changes and power arcs.
The inherent dielectric strength is unbelievably
high -- a 1/16" insulator section will
easily withstand 180 KV in air! The volume and surface
resistivity too is very high, while dielectric
constant and power factor are relatively low.
Because of these favorable characteristics
PYREX brand glasses are used under the most
drastic conditions -- in the atom-smashing
"Cyclotron," in "lightning" generators, in
radio equipment which goes to the North and
South poles.
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