US1778829A - Lightning arrester - Google Patents

Description

Oct. 21, 1930. e. F. HARRINGTON LIGHTNING ARRESTER Filed Dec. 13, 1925 INVENTQR George F fiar/"mqfon WITNESSES:

ATTORN EY Patented Oct. 21, 1930 UNITED STATES PATENT OFFICE GEORGE E. HARRINGTON, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA V LIGHTNING ARRESTER Application filed December 13, 1923. Serial No. 680,394.

This invention relates to resistor materials, more particularly to an improved resistor material which is adapted for use in lightning arresters of the disk-pile type.

In the copending ap lication of Joseph Slepia'n, Serial No. 591, 98, filed October 2,

1922 (Patent No. 1,509,497, issued September 24, 1924), for Spark gap structure, and assigned to the Westinghouse Electric & Manu acturing Company is described a lightning arrester which comprises essentially a series of bodies of material having a relatively high specific resistance separated by thin spacers of suitable insulating material, such as mica.

The resistor material set forth in the abovementioned application consists of a mixture of lampblack, kaolin and carborundum, mixed in suitable proportions to give the desired resistivity, molded to the desired form, such as a disk, and then fired or baked at a relatively high temperature.

The above specified material is satisfactory for the desired purpose but considerable difficulty has been encountered in making disks having uniform resistivity and uniform dimensions. The variations in resistivity I have concluded were due to conducting impurities present in the carborundum, such as coarse particles of carbon, and were also due to the conductivity of the carborundum itself and to the irregular density of the material when compressed. The variation in thickness of the molded disks was probably due to the interlocking of the carborundum particles when the molding pressure was applied, which resulted in a failure of the material to slide and thus equalize the density. Furthermore, the particles of carborundum', being relatively large and hard and of irregular shape, tended to concentrate the lampblack upon themselves in an irregular manner and resulted in the disks having different resistivity at different points.

It has been attempted to eliminate these difficulties by omitting the carborundum and using merely a mixture of clay and lampblack. However, in the firing of the clay mixture, a considerable amount of warping takes place, resulting in disks which are generally so far out of shape as to render them useless in a lightnin arrester. It has also been attempted to su stitute various types or forms of silica, such as ground flint, for the carborundum, but it has been found that a mixture of this kind is also unsuitable because of the fact that, in the firing operation, volume changes inthe flint take place, resulting in distortion of the disks.

My invention is intended to avoid the difficulties encountered in the manufacture of materials of the above designated type, it being among the objects thereof to provide a resistor material which shall be capable of being molded and fired without material dis tortion of the fired body.

It is a further object of the invention to provide a fired resistor material which shall have a substantially uniform resistivity throughout.

In practising my in ention, 1 provide a mixture of lampblack or equivalent conducting substance, kaolin, or other suitable binder, and a non-conducting substance which is capable of moving freely under the molding pressure to equalize the density and thus give a more uniform resistivity to the disk. Specifically, I have found that zirconium silicate commonly known as zircon, is well adapted for my purpose. This substance, in finely divided form, slides freely under pressure and is capable of withstanding the high temperature of firing without deterioration.

In the accompanying drawing, constituting a part hereof, the single figure is a vertical sectional view through a lightning arrester made in accordance with my invention.

An insulating member 1, of porcelain or other suitable material, provided with a petticoat 2, has a central opening 3 therein.

The lower end of the insulator 1 is closed by a metal piece 4 having a threaded portion 5 for securing the lightning arrester to any suitable support. Insulating cement 6 holds the metal piece 4 to the insulator l.

A series of disks 7 of my new resistor material are assembled in the opening 3 with interposed thin washers 8 of mica or other suitable material. A metal plate 9 is placed upon the uppermost disk 7 and an annular insulator 10 thereupon supports depending metal ball 11 which, with plate 9, constitutes a series spark gap. A spring 12 holds the various parts in their proper relative positions. A threaded annular member 13 is secured to the top of insulator 1 by means of insulating cement 14, and a metal cap 15is threaded onto the same. A suitable terminal 16 is secured to the cap 15.

The disks 7 are formed by first providing a mixture of clay, lampblack and zircon in suitable proportions to give the desired resistivity. which is generally about 25 to 100 ohms per centimeter cube. The mixture is made plastic with a relatively small amount of water and is compressed in a mold to the desired form. The bodies or disks thus formed are then dried for a suitable length oftime and are fired at a high temperature, about 1500 C,

The relative proportions of materials vary according to the desired resistivity of the product and may be indicated as follows: Klingenberg clay. 14 to 4 percent; North Carolina kaolin. 15 to 23 percent; zircon. to percent; lampblack 6 to 1 percent. The ingredients, when mixed in the foregoing proportions, compressed in a mold. and baked as above indicated, produce a product having a resistivity of the order of ohms per centimeter cube, by which I mean that the ohm is conveniently used as the unit for measuring the specific resistivity, as distinguished from the resistivities of the ordinary conductors, such as copper, which are conveniently measured in units of micro-ohms, or one millionth of an ohm per centimeter cube. In general, it may be said that the resistivity of my material is greater than one ohm per centimeter cube.

I have found that resistor material made in accordance with my invention is capable of withstanding the high temperatures of firing without deterioration. Because of the freedom from conducting material, such as carbon, the addition of zircon does not change the resistance of the mixture. There are no coarse impurities in the zircon and, because of its finely divided form, it flows readily under pressure, giving uniform molded bodies. On condenser discharge or upon subjection to lightning discharges, the material does not disintegrate nor does the resistivity thereof change, even when there is local heating sufficient to burn out the carbon or lampblack at one point.

Altho I have described my invention, setting forth a specific embodiment thereof, va- Iious changes may be made therein within the scope thereof. For instance, I may utilize metals or other forms of carbon than lampblack for the conducting material and I may substitute other binders for the kaolin. My new material may be made into rods or other bodies and may be molded or extruded or otherwise formed to the desired shape.

The rods may, if desired, be cut to provide disks.

I claim as my invention:

1. A glow-discharge lightning arrester comprising closely spaced resistor discs composed of a binder, a finely divided conductor which is oxidizable in the event of abnormal heating at any spot, zirconium silicate, and an inert binding member which remains substantially non-conducting up to temperatures in excess of that at which said oxidation takes place.

2. A glow-discharge lightning arrester comprising closely spaced resistor discs composed of a binder. a finely divided conductor which is chemically transformed in the event of abnormal heating at any spot, so as to have considerably less conductivity when so transformed, zirconium silicate, and an inert binding member which remains substantially nonconducting up to temperatures in excess of that at which said transformation takes place.

In testimony whereof, I have hereunto subscribed my name this 7th day of December,

GEORGE F. HARRINGTON.

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