Air Moisture the Cause of Losses in High-Tension Power Transmission

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With Science

Air Moisture Causes

Costly Losses in

Power Transmission

Important Discovery Is Made at Harvard

Cambridge, Mass. — Losses in high-tension power transmission are expected to be considerably reduced through the discovery at the Harvard graduate school of engineering that moisture in the air is the hitherto unsuspected cause of the costly inefficiency 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 perfection of a high-voltage bridge with which it is possible to detect the tiniest flaws in high-voltage insulation, 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 efficiently by revealing the causes of insulator "flashovers" which so frequently paralyze power lines. Tentative findings also indicate that one of the causes of radio interference is due to high-voltage "static" discharges over the surface of these insulators.

Unknown for Thirty Years.

That moisture in the air could cause such flashovers and short circuits was unknown during the 30 years that insulators of this type have been in use until the two Harvard scientists began a series of delicate measurements with the Dawes bridge. These showed that atmospheric humidity, or moisture in the air, produces not only a pronounced power loss over the insulator but that the loss is greater over a period of time than if the scientists began with a clean insulator.   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 a permanent deposit forms on the surface of the insulator and decreases its efficiency, an assumption later confirmed by observations through a special "dark-field" microscope which readily reveals minute surface irregularities. The deposits, it was found, takes the form of millions 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 probably amounts to only a watt or so per hour for each insulator. With the accumulation of deposit, however, this loss increases with time, and for some systems may amount to a tremendous number of kilowatt-hours per year.

More important, however, according to Prof. Dawes, is the fact that the deposit is semi-conductive, and reduces the length of the insulating path over the insulator surface.