US2826661A - Flash shield - Google Patents

Description

March 11, 1958 R. G. SANDS FLASH SHIELD Filed Nov. 6, 1952 FIG. 2

FIG?) INVENTOR. ROY c. smns ATTY.

United States Patent Ofiice 2,826,661 Patented Mar. 11, 1953 FLASH SHIELD I Roy G. Sands, Waukegan, IlL, assignor to General Telephone Laboratories, Incorporated, a corporation of Delaware Application November 6, 1952, Serial No. 319,110

2 Claims. (Cl. 200-433) order to keep the vaporized metal away from the line terminals when the fuses blow out and thus permitting the fuses to instantly open the circuit as they are intended to do.

The invention will be described hereinafter with reference to the accompanying drawings, in which,

Fig. 1 is a front and plan view of a commercial protector with a flash shield plate.

Fig. 2 is a side view of the commercial protector with a flash shield.

Fig. 3 is a view of the flash shield plate.

Referring to Figs. 1 and 2 in detail, the Substation Protector consists of a porcelain base 10, equipped with two long tubular type fibre fuses 1 and 2, discharge blocks 15 and carbon blocks 14 and a flash insulating shield plate 42.

The one piece porcelain base is designed substantially rectangular in shape, avoiding straight flat surfaces insofar as possible without weakening the structure, and to minimize surface leakage during damp weather. In order to reduce the area of contact with mounting surfaces, two bosses 43 and 44 are provided on the under side at both ends. tandard terminal studs are used for line, instrument and ground terminals, and the heads of these studs together with the interconnecting links to the discharge blocks are set in recesses in the back of the base 10, which are then filled with insulating cement.

The discharge block or arrester block is substantially the same as that disclosed in my Patent 2,141,490, issued December 27, 1938. The protective equipment comprises a small carbon to carbon block using a very carefully selected grade of carbon and having an extra element in the form of a thin thermo-metal grounding strip (not shown). The relationship of the two carbon blocks 14 is permanently fixed, but on a sustained fault the bi-metal will flex and make contact with the grounding block, thereby extinguishing the are. When the fault has cleared the bi-metal cools and resets itself and restores the air gap as before.

The two carbon blocks such as 14 and the discharge blocks such as 15 required with each protector, are clamped securely back to back between clamp spring members 12 and 13 and a brass ground plate 55 in a circular threaded well in the center of the porcelain base 10 as clearly shown in Fig. 1. Side embossings on the ground plate, together with the action of the clamp springs 12 and 13 serve to hold the blocks 14 and 15 in place and prevent lateral shifting. A cover 11, shown in Fig. 2, is provided in the form of a Bake lite cap which screws down into the opening in the block 10.

The fuses 1 and 2 normally used with these protectors have different power ratings, and consist of lead alloy fuse wire enclosed by treated asbestos tubing with three vent holes 45 on the fiber shell to reduce the chance of shattering itself. The fuses will carry their rated current for minutes without heating, but will blow within 5 minutes at 150% rated current, or a higher overload. When a fuse blows out vaporized metal passes out from vent holes 45 and may at times bridge the gap between the line terminals 50 and 51 and the instrument terminals 52 and 3 thus instantly defeating the purpose for which the fuses are provided.

The mounting base and cover (not shown) required for outdoor use are made of sheet steel and are heavily hot galvanized to resist corrosion. Both cover and base have been made amply large to provide good clearances between the terminals and fuses and the metal housing. The likelihood of high potential currents arcing across the fuses through the housing on sustained faults is therefore much reduced.

In accordance with the invention, the commercial protector, as described above, is provided with the flash shield plate 42 which is made of insulating material and so shaped that it separates the line terminals from the instrument terminals. Tests have shown that when voltages, due to lighting or other abnormal current conditions, above a certain value are impressed on station protectors, the vaporized metal of the fuse wire, resulting from the blowing of the fuse links, conducts an arc across the gaps from the line terminals 59 and 51 to the instrument terminals 52 and 53 and ground post 54. Moreover, the current may be conducted through this medium to a metal cover or housing and thence to the instrument and ground terminals.

Referring to Fig. 3, the flash shield plate 42 is substantially rectangular in shape with irregular cut out portion 47 in the bottom corresponding to the contour of the porcelain base 10, to which the flash shield plate 42 will be held snugly. In addition, the plate has two holes such as 46, through which the fuses will pass.

The flash shield plate is an inexpensive means of overcoming the vaporized metal difliculty and since it is held in proper position by the fuses and its lower contour fitting into the contour of the porcelain base it may be used on protectors with or without covers or housings. The shield plate insures the complete protection of the line terminals from contact with hot metal vapor.

The manner of connecting up the protector and the flash shield plate will now be briefly explained. As shown in Fig. l the two wires from the telephone instrument are brought along side the two binding posts 52 and 53 at which they are respectively terminated in the usual manner. The ground wire is terminated at binding post 54, the two outside line wires are likewise terminated at binding posts 50 and 51. When the connections are completed, the two outside line wires will be connected to the two instrument telephone wires through the fuses, and each side of the line will have a shunt path to ground by way of the discharge gap in the associated arrester blocks. The main feature of the invention, of course, is to provide a flash shield plate between the binding posts 50 and 51 of the outside line terminals, on the one hand and the instrument terminals 52 and 53 on the other to prevent current conduction through the metallic vapor, when and if the fuse blows, thereby instantly protecting the instrument from the faulty high potential current.

Having thus described my invention, it should be understood that the various features thereof could readily be applied to other forms of protectors without departing from the spirit thereof and that the present disclosure should only be considered as illustrative of one embodiment of the invention.

What is claimed is:

1. In a substation protector, a base of insulating material, a pair of binding posts at one end of said base providing the terminals for a telephone instrument, a corresponding pair of binding posts near the opposite end providing the terminals for the outside line, a fuse clip secured by each of said binding posts, two fuses extending between opposite binding posts, each fuse having a metallic fuse Wire adapted to vaporize when false high potential currents are impressed on either one or both of said outside line terminals, a single flash shield formed as a flat plate of insulating material, and means including said fuses for holding said flash shield plate in a vertical position on said insulating base between both said line binding posts and both said instrument binding posts thus keeping the vaporized metal of any one or both fuses away from both line binding posts to thereby prevent the false high potential being conducted to the instrument terminals from either one or both line terminals.

2. In a substation protector, a base of insulating material having a predetermined irregular contour, a pair of binding posts at one end of said base providing the terminals for a telephone instrument, a corresponding pair of binding posts near the opposite end providing the terminals for the outside line, a fuse clip secured by each of said binding posts, fuses extending between corresponding clips of each pair, each fuse comprising a fibre shell and a metallic fuse wire adapted to vaporize when false high potential currents are impressed on either one or both of said outside line terminals, holes in the fiber shell of each fuse permitting escape of said metallic vapor when the fuse blows to prevent shattering of said fibre shell and to open the fuse connection between said clips, detachable flash shield plate of insulating material having a contour corresponding to the contour of said base and having two holes through which the fibre shell of the fuses pass to form the sole means to secure the plate in position in the protector, said fiber shell and said shield plate jointly forming a direct blocking shield for preventing the metallic vapor of a blown fuse from acting as a conductor between either one or both of said line terminals and said other terminals in order to prevent passage of high potential to the instrument terminals.

References Cited in the file of this patent UNITED STATES PATENTS 565,244 Tobey Aug. 4, 1896 982,281 Lincoln Jan. 24, 1911 2,600,407 Kelsay June 17, 1952 2,629,036 Brown Feb. 17, 1953

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