US3328631A

US3328631A - Lightning arrester with semiconductor electrodes

Info

Publication number: US3328631A
Application number: US462375A
Authority: US
Inventors: Greber Henry
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-06-08
Filing date: 1965-06-08
Publication date: 1967-06-27
Anticipated expiration: 1984-06-27

Description

June 27, 1967 H, GREBER 3,328,631

LIGHTNING ARRESTER WITH SEMICONDUCTOR ELECTRODES Filed June 8, 1965 llllllllllllllll, {/maw INVENTOR United States Patent 3,328,631 LIGHTNING ARRESTER WITH SEMICONDUCTOR ELECTRODES Henry Greber, 225 W. 80th St., Apt. 8D, New York, N.Y. 10024 Filed June 8, 1965, Ser. No. 462,375 4 Claims. (Cl. 31536) ABSTRACT OF THE DISCLOSURE This lightning arrester consists of a series of gaps between disc-shaped electrodes made of semiconducting material, such as Carborundum, graphite, carbon, with each disc serving as an electrode of a gap and also as a resistance in series with this gap, in addition, each disc is provided with a groove along its periphery, where the air between the Walls of said groove is broken down electrically when the voltage drop in the disc surpasses the breakdown voltage of gap between the walls of the groove, so that said disc is then bypassed with an arc.

The purpose of this invention is to provide a simple lightning arrester of shorter duration of the discharge voltage-as the voltage drop on the lightning arrester during its discharge is being called-in comparison to that of lightning arresters known in the art. It is common knowledge, that the characteristic, which is the curve showing the duration of an overvoltage in function of its value, of a lightning gap is more convenient than that of lightning arrester. For a lightning gap, the overvoltage due to a lightning stroke rises quickly, until the gap is bridged by an arc. From this moment, at which the discharge through the gap begins, the overvoltage falls rapidly to zero. In contrast, in .a lightning arrester, when the fast rising overvoltage causes the discharge through this device, the large voltage drop on the arrester lasts for a while, and only gradually falls down to zero. Even though the duration of the discharge voltage on the lightning arrester amounts only to a few microseconds, an insulation breakdown of the equipment protected by this lightning arrester may take place during this time. This is so because the longer the duration of a given voltage surge, the smaller its value that can be withstood by the insulation. Another, not less important objective of this invention is to provide a lightning arrester whose electrodes would be free from corrosion, in spite of its housing not being hermetically sealed from the ambient air. A further purpose of this lightning arrester with semiconductor electrodes is the uniform distribution of the voltage on its internal gaps. The last objective is achieved by means of resistance grading, which in this case consis-ts in application of tubular spacers of high resistance, placed between the internal gaps. The first objective is achieved by using electrodes of semiconductor material, such as Carborundum, graphite or carbon with proper binders, for the electrodes of the discharge gaps. These electrodes, in form of discs play a dual role. While serving as electrodes of the gaps, they also function as semiconductor resistors connected in series with the gaps. Since these electrodes are made of semiconductor material, they, naturally, are not subject to corrosion. Hence, there is no need to seal hermetically the housing of the lightning arrester. The lack of such sealing not only simplifies the design of the lightning arrester, but also reduces its cost. To make the characteristic of the lightning arrester resemble that of a simple gap, the semiconductor dis-cs, mentioned above, are provided with grooves running along their circumferences. If only one groove per disc is used, this groove is placed about in the middle of the height of the disc. The horizontal sidings of such 3,3286'3]. Patented June 27, 1967 channel serve as additional gaps, which are broken down when the voltage drop along a disc surpassed the breakdown voltage between the horizontal side walls of the groove.

In FIGURE 1 is shown a longitudinal cross section of the lightning arrester in its usual vertical position. Porcelain tube 1, provided with the three skirts 2, has threads 3 on both of its ends. Also porcelain tube 4, has such threads 5, and skirts 6. The two tubes (1 and 4) are connected by means of porcelain coupling 7, which is threaded on its internal surface. The lower end of tube 4, is closed by means of metal cap, which also has a thread on its internal surface, that fits to thread 5 of tube 4. Metallic cap 8 is linked to ground 10, by means of wire 9. The last two items are shown diagrammatically. Porcelain tubes 1 and 4 contain eight semiconductor discs numbered 11, 12, 13, 14, 15, 16, 17, and 18. These discs are separated with tubular spacers designated with the numerals: 19, 20, 21, 22, 23, 24, all made of ceramic material containing conductive additives such as Carborundum, graphite, or carbon. In detailed consideration of disc 15, for example, as a representative of all

other discs

11, 12, 13, 14, 16, 17, and 18, which are all exactly alike, it can be seen that it has its terminal surfaces beveled, 25 and 26. It can also be seen that said disc has groove 27, cut along its vertical circumference, about in the middle of its height. "In FIGURE 1, only one groove per dis-c is shown, for the sake of simplicity. In actuality, several such channels per disc may be em ployed. The bottom disc 18 is in direct contact with the metallic cap 8, and through it with ground 10. The upper disc 11 is connected to the protected phase conductor, which is not shown, since it is not a part of this lightning arrester. This connection is made through wire 28, which is provided with the Wide lug 29. This lug is pressed towards disc 11 by means of spring 30. The top of the lightning arrester is closed by porcelain cap 31, which is provided with thread 32 fitting to thread 3 of porcelain tube 1. It can be seen that cap 31 is provided with channel 33, through which wire 28 is brought out. Cap 31 is not hermetic, and fits loosely on tube 1, through the intermediary of threads 3 and 32. No attempt is made to prevent insects from entering into cap 31 through channel 33, since these creatures could in no way influence the functioning of the lightning arrester.

In operation of this lightning arrester, the overvoltage appearing between wire 28 and ground 10, in consequence of a lightning stroke to the protected phase conductor, distributes itself evenly on the gaps formed by the consecutive semiconductor discs. The uniform voltage distribution over the gaps is enforced by the tubular spacers, which though made of ceramic material with little conductive additives, so that they can be considered as being insulators, are at the same time resistors inserted in series with the gaps. At a certain value of the overvoltage caused by lightning stroke, or by switching, the gaps between the

discs

11 and 12, 12 and 13, 13 and 14, 15 and 16, 16 and 17, 17 and 18, are overbridged with arcs. If the intensity of the discharge current is not too great, the overcharge will flow to ground through these arcs. They will be extinguished as soon as the overcharge will have passed, and the resistance of the semiconductor discs will prevent the follow current from flowing through the arrester. In case of great intensity of the discharge current, the voltage drop on each disc will be considerable, and delay the discharge through the lightning arrester. It looks as if the overcharge were dammed up in front of the lightning arrester, which because of the resistance of its semiconductor discs, would let this overcharge flow to ground only gradually. The longer the overcharge is piled up ahead of the lightning arrester, and has to wait to be discharged to ground,

the greater is the danger of dielectric breakdown of the insulation of the electric equipment to be protected. Therefore, at great intensity of the discharge current, the discs themselves are shunted with gaps. These consist, for simplicity, in channels cut along the circumferences of the discs. As soon as the magnitude of the discharge current drops, the arcs within the channels of the discs are extinguished, so that the full resistance of the discs is inserted into the circuit through the lightning arrester.

It is obvious that the grooves in the semiconductor discs can be replaced with metallic electrodes forming gaps around the discs. However in this invention, the use of metallic electrodes is consistently avoided, in order to avoid corrosion of such electrodes. Also many other modifications and variations of this invention can be made within its concept as defined by the following claims.

I claim:

1. A lighting arrester with semiconductor electrodes consisting of a series of semiconductor discs with high resistivity spacers between them arranged so that discharge gaps are maintained between said discs, with each disc having at least one groove out along the circumference of its vertical wall, said discs being arranged so that the top disc is connected to the protected phase conductor and the bottom disc is connected to ground.

2. A lightning arrester as in claim 1, with said semiconductors discs having beveled edges of their top and bottom horizontal surfaces.

3. A lightning arrester as in claim 1, with a housing consisting of several porcelain tubes, provided with skirts and threads on both of their ends, said tubes being connected to each other :by means of porcelain couplings having threads on their interal surfaces.

4. A lightning arrester as in claim 1, with said spacers made of ceramic material with conductive additive of Carborundum added in such proportion that the resistance of said spacer would amount to about one thousandths of the resistance of said semiconductor disc.

References Cited UNITED STATES PATENTS 1,778,829 10/1930 Harrington 3l33l1 2,151,559 3/1939 M-cEachron 315-36 2,891,194 6/1959 McStrack 3 1536 DAVID J. GALVIN, Primary Examiner.

Claims

1. A LIGHTING ARRESTER WITH SEMICONDUCTOR ELECTRODES CONSISTING OF A SERIES OF SEMICONDUCTOR DISCS WITH HIGH RESISTIVITY SPACERS BETWEEN THEM ARRANGED SO THAT DISCHARGE GAPS ARE MAINTAINED BETWEEN SAID DISCS, WITH EACH DISC HAVING AT LEAST ONE GROOVE CUT ALONG THE CIRCUMFERENCE OF ITS VERTICAL WALL, SAID DISCS BEING ARRANGED SO THAT THE TOP DISC IS CONNECTED TO THE PROTECTED PHASE CONDUCTOR AND THE BOTTOM DISC IS CONNECTED TO GROUND.