Locke electrically testing insulators

Electrical Discharges Showing the Dark Flash.

TO THE EDITOR of THE ELECTRICAL REVIEW:

Your issue of September 2 contains a very interesting article on "dark flashes" of lightning, for the cause of which no satisfactory explanation has been offered. As an addition to this subject, we are sending several photographs of insulators under test, some of which show the same dark lines as are plainly seen on the photographs of lightning discharges.

Photograph No. 1 shows two large insulators under 180,000 volts, and the lines are caused by static and brush discharge of the ordinary blue or purplish color, unaccompanied by any yellow or power arc.

Photograph No. 2 shows an insulator about which a heavy power arc is playing, producing the white fanlike effect, but at the right will be seen the "dark flash," evidently not produced by ordinary discharge, since from photograph No. 1 it is evident such a discharge ought to reproduce the same color as the arc.

Photograph No. 3 shows a curious mixture of light and dark lines, which it hardly seems could be static in any form since the insulator was thoroughly wet all over and approximately 200 kilowatts of energy was being expended in the arc.

Photograph No. 4 shows a Toronto-Niagara insulator under dry high voltage test, and plainly shows light and dark lines.

Photograph No. 5 shows an ordinary insulator under wet test. No black lines are in evidence.

All the above photographs were taken practically instantaneously; i. e., the camera was opened in the dark test cabin and potential quickly applied to the insulator, causing the arc to form and by its draught of current opening the primary circuit-breaker.

THE LOCKE INSULATOR MFG. Co. Victor, N. Y., October 17.