US2264700A - Lightning arrester - Google Patents

Description

Patented Dec. 2, 1941 UNITED STATES PATENT OFFICE LIGHTNING ARRESTER vania Application June 23, 1939, Serial No. 280,676

(Cl. l75-30) 4 Claims.

The present invention relates to lightning arresters, and more particularly to means for improving the contact conditions between the elements of a lightning arrester.

Lightning arresters usually consist of one or more spark gaps, which isolate the arrester from the line under normal conditions, but which break down and permit the passage of surge currents when a high surge voltage occurs, and one or more blocks of resistance material having valve characteristics, that is, which are substantially non-conducting under normal voltage, but which become capable of carrying very large surge currents When a sufficiently high voltage is applied across them. These elements are assembled in series relation in a porcelain casing, a sufficient number of gaps and blocks being used to obtain the desired voltage rating.

It has been found that the contact conditions between adjacent blocks and between the blocks and other elements of arresters of this type have a very important influence on the life of the blocks. These blocks are made of resistance material, and the usual practice has been to apply a thin coating of metal on the end surfaces of the blocks by some process such as spraying to provide electrical contact between adjacent blocks when they are assembled in the arrester. When a spraying process is used, the diameter of the coating is necessarily less than that of the block, so that an uncoated portion is left around the periphery of the block. When a heavy surge current passes through the arrester, the coatings of adjacent blocks are at the same potential because they are in intimate contact and have high conductivity. The uncoated peripheral portions of the blocks, however, may be at different potentials, since the high current flowing through the resistance material of the block causes a potential gradient in a radial direction between the edge of the coating and the edge of the block. If the uncoated portions of adjacent blocks are accidentally in contact with each other, or if they are too close together, sparking may occur between them as a result of this difference in potential, or if there is slight misalignment of adjacent blocks, the contact coating of one block may overlap the uncoated portion of the adjacent block, and this may also cause sparking because of the difference in potential. This sparking is very undesirable and readily induces flashover of the block, leading to failure of the arrester, especially on a surge of relatively long duration.

The object of the present invention is to improve the contact conditions between adjacent lightning arrester blocks or between the blocks and other adjacent elements, in order to prevent the possibility of sparking between them. One means for accomplishing this result is disclosed in our copending application Serial No. 240,680, filed November 16, 1938, and assigned to the Westinghouse Electric & Manufacturing Company. In this application, spacing means are provided between adjacent blocks by applying a second coating of somewhat greater thickness on top of the first coating, or by otherwise securing a thin, conducting spacer concentrically with the blocks to space them far enough apart to prevent sparking. The present invention provides spacing members between adjacent blocks or other elements which are not secured to the blocks, and which can be produced at materially less cost than the second coating disclosed in the prior application.

More specifically, the object of the present invention is to provide spacing members to be used between adjacent blocks or other elements of a lightning arrester which will be inexpensive to produce and which are designed to prevent sparking between adjacent blocks, even if misalignment of the blocks or spacers exists so that it is not necessary to secure the spacers to the blocks.

Further objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, in which:

Figure 1 is a vertical sectional view of a typical lightning arrester assembly;

Fig. 2 is a diagrammatic view on an enlarged scale illustrating the contact conditions between adjacent arrester elements;

Fig. 3 is a perspective view of one of the spacing members of the present invention; and

Fig, 4 is an enlarged elevational view illustrating the improved contact obtained by the present invention.

The lightning arrester shown in Fig. 1 has a generally cylindrical porcelain outer casing l and a porcelain cap 2 which is secured to the casing by suitable cement 3. The arrester consists of one or more cylindrical blocks 4 of resistance or valve material and a plurality of spark gap devices 5. The blocks may be of any suitable type, but preferably consist of granular silicon carbide molded with a suitable binder and either baked or fired to form porous blocks having the desired valve characteristics. Any suitable number of blocks and gaps are used to obtain the desired voltage rating, and they are assembled in series coating only over a limited area.

relation in the casing I, resting on a ground plate 6 at the bottom of the casing. A helical spring I is provided at the top of the casing to insure intimate contact between the elements of the arrester, and the spring bears against a metal cap 8 which is spun over the top of the casing I. A conductor 9 is soldered to the metal cap 8 for connecting the arrester to a transmission line conductor, or other apparatus to be protected, and a ground lead I is secured to the plate 6,

Fig. 2 illustrates the contact conditions between adjacent blocks and other elements when the usual contact coatings only are used. It will be seen in this figure that each block has acoating I I of copper or other suitable metal on each of its end surfaces, and that this coating is of smaller diameter than the block, so that the peripheral portion of the block is left uncoated. The thickness of the coating is, of course, greatly exa erated in the drawing for the sake of clearness, the

actual thickness being of the order of 2 or 3 mils. It will be clear from Fig. 2 that if a difierence of potential exists between the uncoated portions of the adjacent blocks or between these portions and the coatings II, as explained above, there will be danger of sparking between the blocks because of their closeness together, and that if there is even a slight misalignment, the contact coating of one block will overlap the uncoated portion of the other which will also tend to cause sparking because of the very small spacing and the difference in potential.

In order to eliminate this danger of sparking, which readily induces flashover of the blocks and failure of the arrester, the present invention provides spacing members between the adjacent blocks or other elements in order to separate the parts which may be at different potentials a great enough distance to prevent'sparking between them. vAs shown in Fig. 3, the spacing member I2 is a metal disc having a diameter approximately equal to the diameter of the blocks 4, and havinga raised central portion I3 embossed in it. The central portion I3 is made high enough to-provide the desired spacing between the blocks,.and is of smaller diameter than the contactcoatings I I. In assemblin the arrester, two of these spacers are placed between each block and the adjacent block, .as shownin Fig. 4, with the raised portions I3 in contact with the coatings H so .thatthe blocks are spaced apart a great enough distance to prevent any sparking. A single spacer may be placed between the top and bottom blocks and the adjacent elements of the arrester.

It will be seen from Fig. 4 that since thecen tral portion l3 of the spacer has a smaller diameter than the coating I I,-it is in contact with the If any misalignment should exist between adjacent blocks or between the spacers and the blocks, the diameter of the raised portion -l3 is sufliciently small so that it will not extend beyond the coating II even under the worst condition of misalignment that can occur in the assembly of an arrester. Thus, there is no danger of the central portion of the spacer, which directly contacts the coating, overlapping the uncoated peripheral portion of theblock, which may be at a different potential, and thus any possibility of sparking from this cause is eliminated. Because of this relationship of the diameters of provided for improving the contact conditions between adjacent blocks or other elements of a lightning arrester, in order to prevent the pos- .sibility of sparking between the blocks and thus remove the danger of arrester failure from this cause. It will be understood that although a particular embodiment of the invention has been illustrated and described, it is capable of various modifications and is not limited to the exact arrangement shown. The invention is not limited therefor to the exact construction shown in the drawing for the purpose of illustration, but in its broadest aspects it includes all equivalent modifications and embodiments which come within the scope of theappended claims.

We claim as our invention:

1. A lightning, arrester assembly including a plurality of blocks of resistance material and other arrester elements arranged in series relation, each ofsaid blocks having a'coating of conducting material on its end surfaces, .and separate spacing members of conducting material placed between each block and the adjacent blocks or other arrester elements, said spacers having approximately the same diameter as the blocks and having raised contact portions which make contact with said conducting coatings over an area of smaller diameter than that of the coatings.

2. A lightning arrester assembly including a plurality of blocks of resistance material and other arrester elements arranged in series relation, each of said blocks having acoating of conducting material onits end surfaces, and separate spacing members of conducting material placed between each block and the adjacent blocks or other arrester elements, each of said spacers having approximately the same diameter as the blocks and having a raised central portion of smaller diameter than said conducting coatmgs.

3. A lightning arrester assembly including a plurality of blocks of resistance material arranged in series relation, each of said blocks having a conducting coating on each of its end surfaces, and separate spacers of conducting material between the blocks, said spacers being of approximately the same diameter as the blocks and having portions which make contact with the conducting coatings over a limited area thereof.

4. A lightning arrester assembly including a plurality of blocks of resistance material arranged in series relation, each of said blocks having a conducting coating on each of its end surfaces, and separate spacers of conducting material between theblocks, said spacers being of approximately the same diameter as the blocks and having portions which make contact with the conducting coatings and which are of smaller diameter than the coatings.

FREDERICK B. JOHNSON. EDWARDpF. W. BECK.

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