[Trade Journal]
Publication: The Electrical Engineer - London
London, England
vol. 43, p. 508, col. 1-2
A NEW BINDLESS INSULATOR FOR OVERHEAD CABLES.
Engineers who have had experience in overhead pole line equipment will be aware that one of the chief dangers, apart from the breaking of the actual conductors themselves, to which the pole line is subjected, is a failure at the point of support due either to the fracture of the insulator or to the breakage of the binding wire which connects the conductor to the porcelain. Binding wires are apt to break and fall on the supports to which the insulators are secured, thus causing a leakage.
An insulator which is the invention of Mr. W. Copeland, electrical engineer to the Tyne Improvement Commissioners, appears to eliminate to a very large extent the defects which have become apparent in previous types of this class of apparatus. The insulator, which is shown in the attached illustrations (Figs. 1 and 2), consists of four parts, the first being the ordinary bolt, which is coupled with a square collar, serving the double purpose of a supporting surface on the cross-arm and a method of gripping it by means of a key or spanner for the purpose of holding or turning it.. Mounted on this is the insulator, formed of porcelain or other suitable insulating material, formed with the usual sheds to prevent the dampers from gripping to the wrought - iron bolt. The insulator has a horizontal groove around it, which can contain the circular conductor, this circular section projecting slightly beyond the edge of the groove. In the top of the insulator is a screwed socket for a stud bolt, this socket being entirely separated from the socket of the holding bolt by a sufficient thickness of porcelain. This upper stud bolt has an ordinary right-handed screw on each side of the central collar, the top screw engaging with a cap, which can be made of wrought iron, brass, bronze, or copper. This light metal cover is, it will readily be seen, unbreakable by stone throwing, and is, therefore, particularly useful in places adjacent to public roads where stone throwing is possible. Where there is no likelihood of damage by this cause the dome-shaped cover, which is shown, can be made of porcelain. Beneath the collar of the stud and on the top of the inner porcelain is placed a collar of india rubber, to prevent breakage in screwing in the stud too far. The cap, which is shown in the illustration No. 2, has two slots formed in it., so that it can pass over the wire when placed in position, and can come down tight on to the wire When the bolt has been screwed into the shoulder in the usual manner and the stud has also been fixed into position the bolt is put into supports, but not tightened up; the line wire is then placed in the groove and the cap is dropped over into the insulator resting on the stud. The cap is now held by the hand and guided centrally, and the bolt turned round until the upper screw of the stud screws tight into the cap and brings it into close contact against the wire, which is thus firmly fixed. When this is accomplished the bolt is screwed tight into its position.
The advantages of the insulator are that it can be used without a binder, which is expensive to keep in repair and unreliable, inasmuch as binders often break and the wire or cable falls on the arm and slips to the earth; moreover, being bindless, it saves the cast of an insulator guard. It can be used either for a straight or grooved line or for a shackle insulator or any class of cable, or wire for telephone or telegraph work, low or high tension electric transmission even up to voltage pressures of 75,000 volts. A valuable feature, having regard to the increasing use of aluminium for overhead conductors, is that when the covers are made of porcelain they can be used without affecting the wires. It has been found that trouble has been caused by the use of other types of insulators, having binders or grips of metals other than aluminium, due to galvanic action, and this has been entirely done away with. The invention also gets over the difficulty which has hitherto prevented the adoption of insulators made in two parts united by the bolt, because in the present instance the bolt is in two pieces and there is, therefore, no chance of leakage from the upper part to the bolt and through it to the earth, owing to the peculiar shape of the insulator conical with the cap, rounded at the top, and, having no extraneous projections, the insulator has the property of throwing off moisture to a greater degree than other forms. It will, therefore, be seen that it constitutes a distinct improvement on many of the types which are now being adopted for overhead transmission in a climate, such as our own country, of an especially humid nature.
