Micarta Core Insulator article to be in this issue

Micarta-Core Glass-Disk Insulators

THE problem of the high-tension power-transmission line is closely connected with that of the high-tension insulator. Terminal apparatus capable of withstanding increased working voltage was forthcoming long before line insulators could be found to protect the line conductors. During recent years the porcelain suspension insulator, or string of insulators, has been successfully developed; but it is questionable whether the string of insulators can long retain supremacy in this field. What is wanted is a single insulator of greater capability and less cost than the present string of insulators.

An interesting type of high-tension single insulator is described in this issue by Lincoln Nissley. It consists of a long micarta tube the inside of which is filled with insulating compound, on the outside of which disk glass insulators are strung like large beads. End castings are fastened to the tube and hold the system together. The tube thus takes the entire mechanical stress and also the principal share of the electrical stress, but the superficial electric stress is carried by the glass bead surface, which is appropriately lengthened out. It is claimed that an eleven-disk insulator, only about one meter long, can stand 300 kv. for one minute. The surface distance between the end castings, as measured over the glass, is given as 2.2 meters, or more than twice the total length.

If an insulator of this kind, which substitutes micarta and glass for porcelain, can be made to stand the tests of time and experience, it should be a great boon. Strictly speaking, we should try to use glass for our windows and outdoor insulators, retaining porcelain for teacups and tableware. It is a pity to use our dishes on tower suspensions of high-tension lines.