Publication: The Journal of Electricity, Power and Gas
San Francisco, CA, United States
A series of interesting tests of insulators has been completed recently in connection with the plans for the Ocean Shore Railway, which will parallel the shores of the Pacific Ocean for nearly eighty miles between San Francisco and Santa Cruz, California. The transmission line is to be operated at 33,000 volts in connection with various sub-stations distributing the power along the line. It will be close to a dusty county road for much of its length and is exposed to salt spray from the ocean in several places. Consequently there is great danger of burnouts caused by the insulators becoming coated with dust from the road and salt from spray and fog.
In order to save time the test was conducted under artificial conditions approaching the natural as closely as possible, except in regard to time duration. "Fog boxes" were tried. The insulators included a 16-inch, 60,000-volt porcelain with corrugated top, a 14-inch, 60,000-volt, smooth top, a 9-inch top 35,000 volt porcelain, a Kern type insulator and one of special design.
The results showed that such insulators must be cleaned every third or fourth year if used for 33,000 volts or over. The "fog boxes" increased the time between cleanings for the smaller insulators but were impractical for the larger on account of size and expense. The fog caused but little trouble, the main difficulty being experienced with salt and dust. An insulator that would probably prevent arcing is one made up of several pieces of porcelain or glass shaped like the ordinary insulator tops and placed one below the other, exposing a large part of the surface to wind action. A flat top is advisable.