Publication: Electrical World
New York, NY, United States
Insulators for High-Voltage Lines.
By F. M. Locke
The frame-type insulator shown in Fig. 1 has been designed for lines of 150,000 volts. It will stand a spray test of 280,000 volts, thus giving a large factor of safety. It will carry a mechanical load of 20,000 lb., and can be constructed to carry as much more as desired by increasing the eye-beams and side rods and the bearing surface of the porcelain; the frames are interlocked like a chain and the line cannot come down. All the porcelain parts are under compression and are designed to have a surface large enough to carry the required mechanical load with a large factor of safety. Under an electrical test this insulator does not show the usual static stresses, and is extremely quiet up to the point of arcing, which takes place between the frames. An arc from lightning would take place between the frames and thus not injure the insulator. These insulators are furnished in any size for line voltages from 70,000 volts up to 300,000, with a factor of safety of two under a spray test, and for any mechanical load desired. It will be observed that this is the only insulator giving unlimited test voltage, unlimited mechanical strength and an unlimited factor of safety on all points. It is designed for the hanging type, but can be supported at either end; it can be used horizontally or perpendicularly. It is manufactured exclusively by the Lima Insulator Company, Lima, N. Y.
Fig. 2 illustrates a 450,000-volt, 150-kw transformer used to test the above-described insulator; this is installed at the Lima Insulator Company's plant and was made by the Central Laboratory Supply Company, Lafayette, Ind. Fig. 3 shows porcelain bushings manufactured by the Lima Insulator Company for the Locke 450,000-volt, 150-kw transformer, and is insulating successfully the lead wires. These bushings are oil-filled and the holes through the top caps are to support the choke coils at each terminal. They weigh about 200 lb. each.