Fog Boxes for high voltage insulators

[Trade Journal]

Publication: American Electrician

New York, NY, United States
vol. 14, no. 12, p. 577, col. 3

Fog Boxes for High-Voltage Insulators. Mr. J. J. Davis, superintendent of the United Electric Gas and Power Company, which owns a number of plants on the Pacific coast, offers some interesting information regarding experiences with the effect of dust and sea-fog on high-tension insulators. The power house at Santa Monica is located directly on the sea beach, and from there a 22,000-volt line supplies a number of small towns with light and power. The pole line for several miles of its distance is either directly on the coast or but a short distance back from it. Ever since the installation of this high-tension line, the company has experienced the greatest difficulty from current leaking over the surface of the insulators and burning off the pins. This was caused by fogs, which are very thick along this coast. It was found that the line worked perfectly in wet weather, but in dry weather dust would accumulate under the bell of the insulator, and in time of fog, the moist atmosphere would pass under the insulators depositing moisture on the dust, which would form a sort of paste, and so establish a sufficiently low resistance path, so that the high-voltage current would flash across. In a short time the pins would burn off, with the natural result that the wire dropping on the cross-arm would burn the cross-arm off, and ultimately swing against the pole, burning it off. The company tried many schemes to overcome this serious difficulty before they hit upon the novel device of fencing in the pins and glass. This new arrangement has been shown by practical tests to have completely overcome the leakage, and so prevent the burning off of the pins. The fog box is made of one inch redwood, 12 inches square, and 4 1/4 inches deep. It has in its top a round hole 10 inches in diameter which leaves about l 1/2 inches all around the outer edge of the insulators. The boxes come up within two inches of the wire, and are mounted on the cross-arm. Apparently they keep the dust and fog from drifting in under the bells of the insulators.


Researcher notes: 
Supplemental information: 
Researcher:Bob Stahr
Date completed:April 8, 2009 by: Bob Stahr;