The Coolidge examiner., 1937-07-22
Keeping Up
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Air Moisture Causes
Costly Losses in
Power Transmission
Important Discovery
Is Made at Harvard

Cambridge, Mass.-Losses
in high-tension power trans
mission are expected to be
considerably through
the discovery at the Harvard
graduate school of engineer
ing, that moisture in the air
is the hitherto unsuspected
cause of the costly ineffi-
cheney of the porcelain and
glass insulators used on the
lines.
The discovery, made by Prof.
Chester L. Dawes and DR.. Reuben
Reiter, was enabled by their per-
fection of high-voltage bridge with
which it is possible to detect the
tiniest flaws in high-voltage insula-
tion, a problem that has troubled
electrical engineers for some time.
With the instrument, scientists
can now enter an entirely new field
of research in insulation and thus
possibly bring man closer to his
dreams of managing tremendous
amounts of power safely and eff
GENTLY by revealing the causes OF
insulator ''flashovers" which so fire.
quently paralyze power lines.
Tentative findings also indicate
that one of the causes of radio inter-
ference is due to high voltage
static" discharges over the sur
face of these insulators.
Unknown for Thirty Years.
That moisture in the air could
cause such flashovers and shortcir-
cults was unknown during the 80
years that insulators of this type
have been in use until the two Har-
ward scientists began series Of
delicate measurements with the
Dawes bridge. These showed that
atmospheric humidity, or moisture
in the air. produces not only pro-
nounced power loss over the insu-
lator but that the loss is greater
over a period of time than if the
scientists began with clean insu-
lator The greater the moisture in
the air, it was found, the greater is
the loss. Cleaning the insulator by
vigorous rubbing with a chamois
cloth, however. was found to return
the power to its initial value.
This led to the assumption that
permanent deposit forms on the sur
face of the insulator and decreases
its efficiency, an assumption later
confirmed by observations through
a special "dark-field" microscope
which readily reveals minute sur
face irregularities. The deposit, it
was found. takes the form of mil
lions of tiny islands which, because
of difficulties of observation, are not
visible with an ordinary microscope.
What Causes the Leakage.
The islands are formed, the two
scientists believe. by the activating
effect of high-voltage corona, or
electrical discharge. on the air and
the moisture contained in it. This
action causes the nitrogen in the
air and the moisture to form nitrous
and nitric acid. which, acting with
the metal of the insulator cap and
tin. form the deposit. The exact
composition of the islands is being
further investigated, however, by
chemical, X-ray and microscopic
means.
Under normal conditions of the
corona and atmospheric humidity,
the resulting power leakage prob
ably amounts to only watt or so
per hour for each insulator. With
the accumulation of deposit. how
ever. this loss increases with time,
and for some systems may amount
to a tremendous number of kilo-
watt-hours per year.
More important, however, accord
ing to Prof. Dawes, is the fact that
the deposit is semi-conductive, and
reduces the length of the insulating