US3036239A - Lightning arrester - Google Patents

Description

United States Patent Office 3,036,239 Patented May 22, 1962 poration of Pennsylvania Filed Nov. 28, 1958, Ser. No. 776,979 3 Claims. (Cl. 315-66) The present invention relates to lightning arresters and, more particularly, to an improved means for providing good voltage distribution in a high voltage lightning arrester.

High voltage lightning arresters are made up of a suitable number of lightning arrester elements of standard voltage ratings, each of the elements consisting of a number of spark gap devices and valve resistance elements assembled in series relation in a single stack and enclosed in a porcelain housing with end fittings. The individual arrester units are placed end to end in a vertical column and the end fittings of adjacent units are bolted together for electrical and mechanical connection so that all the units are connected in series. This type of construction results in a vertical column of great height as compared to its diameter.

A problem in the design of high voltage lightning arresters of this construction is that of obtaining sufiiciently uniform voltage distribution across the tall column of arrester units. The arrester is connected between a transmission line conductor or other protected device and ground so that it is subjected to the line-to-ground voltage but, because of the height of conventional arresters, the voltage does not divide uniformly between the individual arrester units. Around a series of gaps, such as is utilized in valve type lightning arresters, subjected to a potential below that producing sparkover, there is an electrostatic field. The electrostatic field is not of uniform intensity and as a result of this, the voltage distribution across the series of gaps is not uniform. Some of the gap elements will be subjected to a greater portion of the total voltage than others. The highest voltage stress usually appears on the gaps nearest the line end and the lowest on those near the ground end. Because of the greater stress on the gap nearest the line end, its sparking voltage will be reached before the voltages on the remaining gaps have reached their sparking voltage. The sparkover of the complete series of gaps thus may be a kind of cascading process. Consequently, the overall sparkover of such an arrester is lower than expected and is also inconsistent.

Satisfactory operation requires a reasonably uniform distribution of the voltage. Various means are available to correct the voltage distribution across an arrester. One way would be to adjust the spacings of the individual gaps proportionately to the voltage stress to increase their individual spark potential. This is a cumbersome process and hardly suited to economic production and interchangeability in the field. Grading rings which control the electrostatic field surrounding the arrester may be used to make the voltage distribution sufficiently uniform for satisfactory operation. In high voltage lightning arresters of considerable height, however, it is quite difficult to obtain satisfactory voltage distribution in this way and it is frequently necessary to employ relatively elaborate grading ring structures which are of large diameter and undesirably increases both the cost and the space required for the arrester to provide the necessary clearance distances to other nearby apparatus.

Another solution to the voltage distribution problem across an arrester is to shunt the gaps by high resistance to permit a small leakage current to flow through the arrester continuously while it is connected to an energized system. The IR drop in the resistors controls the sixty-cycle voltage distribution, because the gap electrodes are then connected to points of what amounts to a resistance potentiometer which fixes their potentials. Thus, a desired voltage distribution can be achieved. It has also been proposed for this purpose to shunt the gaps by capacitors forming a capacitor potentiometer. When resistance is used to control the leakage current, considerable leakage wattage must be wasted. Use of capacitors has been found to be effective with very much less wasted energy.

The problem in the use of capacitance lies in the present lack of an adequate scheme for installing the capacitors inside the arrester units. Presently known means are bulky, cumbersome, expensive and require severe modification and design of conventional lightning arresters.

The principal object of the present invention is to provide a high voltage lightning arrester assembly in which an improved construction is employed for obtaining substantially uniform voltage distribution across the arrester.

Another object of the invention is to provide a high voltage lightning arrester assembly in which the gap devices are shunted by substantial impedances in order to improve the voltage distribution.

A more specific object of this invention is to provide a high voltage lightning arrester assembly in which the gap devices are shunted by substantial capacitance for improved voltage distribution with the capacitors mounted in hollow tie rods which hold the assembly together.

The invention will be more fully understood from the following detailed description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a vertical sectional view of a lightning arrester unit embodying the invention, the arrester elements themselves being shown in side elevation; and

FIG. 2 is a schematic diagram showing the equivalent electrical circuit of the arrester.

In the preferred embodiment of the invention shown in the drawing, for the purpose of illustration, the arrester unit is contained in a generally cylindrical housing 10, which is prefer-ably made of porcelain, although any suitable weather-resistant insulating material might be used. The housing 10 is provided at each end with metal end fittings 12 of any suitable design which are secured to the housing 10 by cement as indicated at 14 or in any other desired manner. The ends of the housing 10 are closed by diaphragms 16 which are secured to the end fittings 12 in any suitable manner as by bolts (not shown). A gasket 18 is interposed between each of the diaphragms and the housing to seal the interior of the housing. It will be understood that any suitable construction may be used for the end fittings and closure means of the housing, the end fittings providing for electrical and mechanical connection of the unit in a column of similar units in the usual manner.

Within the housing 10 between end fittings 12 there are disposed in a column a plurality of lightning arrester elements. The arrester unit shown in FIG. 1 has two arrester units 20 and 22, but it will be understood that any suitable number may be used. The arrester elements 20 and 22 shown in FIG. 2 are. identical. Therefore, only element 24) will be described in detail. Arrester element 20 consists of a spark gap unit 24 stacked in series with a plurality of valve blocks or non-linear resistance elements 26 within an insulating tube 28 between insulating end members 30. Although the specific embodiment shown and described consists of a single spark gap unit 24 and valve blocks 26, it will be understood that any desirable number of spark gap units and valve blocks may be stacked in arrester elements 20 and 22. Arrester element 20 or 22 may contain all spark gap units, all valve blocks, or any combination of the two.

The spark gap unit 24 is shown comprising a plurality of gap devices 32 arranged in a column in a porcelain tube 34. The gap devices 32 may be of any suitable type and are shown as being of the type disclosed and claimed in a copending application of A. M. Opsahl and T. L. Dyer, Serial No. 560,146, filed January 19, 1956, now U.S. Patent No. 2,985,788 and assigned to the assignee of the present invention. As more fully disclosed in that application, each of the gap devices 32 consists of a flat electrode plate 36 and a formed electrode 38 having an annular ridge which cooperates with the electrode 36 to form an annular gap space, the electrodes 36 and 38 being spaced apart by an annular spacer 40 of high resistance material.

An annular permanent magnet 42 is disposed in the space formed by the ridges of adjacent electrodes 38 to provivde a magnetic field in the gap space to effect movement of the arc to facilitate its extinction. A-ny necessary number of spark devices 32 may be provided depending on the desired voltage rating and they are disposed in the tube 34 in a vertical column. The ends of the porcelain tube 34 are closed by metal end caps 44 which are sealed to the porcelain tube 34 in any suitable manner as by soldering to a metallic glaze (not shown) on the porcelain tube 34.

The valve blocks 26 may be any suitable type of valve element or non-linear resistor, and are preferably made of granular silicon carbide molded to the desired size and shape with a binder of water soluble silicate and baked to provide valve elements of a usual type.

The arrester elements 20 are mounted in a column within insulating tubes 28. The insulating tubes 28 are closed at their ends by insulating end members 30 and held together by hollow insulating tie rods 46 extending through flanges 48 on end members 30. The end members 30 may be made of any suitable insulating material and each of the end members is generally circular with a flange portion 48 as shown in FIGURE 1. Openings 50 are provided in a flange portion 48 of each of the end members 30 for receiving tie rods 46 which may be of any suitable shape in cross section. The openings 50 are made of corresponding shapes to receive the tie rods 46.

Contact means 52 are provided in the end members for making electrical connection to the column of arrester elements at line and ground and for connecting the elements 20 in series. The contact members 52 extend out of the end members 30 through slots 54. The conducting plates 56 and 60 are received on tie rods 46 at the top or line end and bottom or ground end of the arrester assembly. Intermediate the arrester elements 20 and 22, a conducting plate 58 is received in slots or openings 62 in the tie rods 46. The contacts 52 of the arrester elements 20 which extend through slots 54 in the end members 30 are connected to their respective adjacent conducting plates 56, 58 and 60.

Disposed in a stack within the hollow tie rods 46 are a stack of capacitor units 64. The capacitors 64 have terminals 66 extending longitudinally of the tie rods. The capacitors 64 are stackedwith their terminals in engagement so as to connect them in series. The adjacent capacitors which have their terminals extending to a point intermediate to the upper and lower arrester elements 20 and 22 are separated by a U-shaped conducting spring clip 62 which connects the capacitor at this point to the conducting plate 58. A U-shaped conducting spring support 68 is inserted at each end of the stack of capacitors 64 in the hollow tie rod 46 with the open side extending outward. A conducting bushing 70 having internal and external threads is threaded into each end of the tie rods 46. A bolt 72 is received in the bushing 70. A fiat plate 74 engages the spring support 68 at its free ends. The bolt 72 engages the plate 74 which biases the capacitors 64 into good electrical connection.

The diaphragms 16 have extending inwardly toward the arrester elements 20 and 22 a plurality of internally threaded bosses 76. A spring ring 78 having spaced holes about its periphery engages the bosses 76 and is held in place thereon by means of screws 80 extending through the openings on the periphery of the spring ring 78 into the threaded openings in the bosses 76. Intermediate the bosses, the bolts 72 pass through the spring ring 78 and the conducting plates 56 and 60 at the top and bottom of the column of the arrester elements, thereby connecting the capacitors to the conducting plates 56 and 60. The conducting plates 56 and 60 are spaced from and electrically connected to the spring rings 78 by conducting bushings 82. The spring rings are electrically connected to the diaphragms 16 through the bushings 82 and screws 80. The diaphragrns are electrically in contact with the end members 12. The end members 12 serve as means to stack the arrester units with other arrester units or may be used to connect the arrester between line and ground.

Thus, it can be seen that the arrester elements comprising gap devices and valve resistance elements are connected in series from the line end to the ground end. The upper end fitting 12 is connected to the upper diaphragm 16 which is connected to the spring ring 78. The spring ring 78 is in turn connected to the conducting plate 56 through conducting bushing 82. The conducting plate 56 is connected to the upper end of the column of arrester units through contact 52. The intermediate contact 52 connects the lower end of arrester element 20 and the upper end of arrester element 22 together through intermediate contacts 52. The ground end of the element 22 is connected to the ground terminal through lower end fitting 12 in a manner identical to the line end of the arrester. A portion of the column of capacitors 64 is connected in parallel with each arrester element through spring support 68, bolt 72, bushing 82 and spring ring 78, and the intermediate arrester elements by spring clip 62 and conductor plate 58.

When the arrester is connected between line and ground to an energized system, there is a continuous small leakage current through capacitors 64 to ground. It will be apparent that each spark gap is shunted by capacitance. This results in a sufiiciently uniform distribution of voltage across the elements of the arrester unit so that correct and consistent values of breakdown voltage are obtained. FIG. 2 shows the equivalent circuit of the arrester with all of the elements of the arrester unit connected in series and the capacitors connected in parallel with each arrester element.

It should now be apparent that a lightning arrester has been provided which results in good voltage distribution across the arrester due to the substantial capacitance connected in parallel with the arrester elements. The arrangement of the capacitor elements within the hollow tie rods results in a compact arrangement with little change in design of the usual valve type arrester structure.

A particular embodiment of the invention has been shown and described for the purpose of illustration, but it will be apparent that variations, modifications and other embodiments are possible within the scope of the invention. For example, an arrester assembly with the arrester elements arranged in series-connected columns disposed side by side in the housing may be used with the bolts having capacitors connected in parallel with a separate column. Similarly, numerous other modifications and embodiments will be apparent to those skilled in the art, and all such modifications and embodiments are within the scope of the invention.

I claim as my invention:

1. A lightning arrester comprising a plurality of spark gap devices and a plurality of valve type resistance blocks, said gap devices and said resistance blocks disposed in columns between end members to form an arrester element, a plurality of arrester elements stacked in seriesconnected columns, contact means at the ends of each of said elements, conducting means intermediate said elements to engage the contact means of adjacent elements, insulating tie rods hollow for their entire length extending through said end members, securing means at the ends of said tie rods to clamp the end members and arrester elements in a unitary assembly, a plurality of capacitors disposed in a .column extending substantially the entire length of a rod within at least one of said tie rods, means for connecting the ends of said columns of elements to the adjacent ends, respectively, of said column of capacitors, and means for connecting said intermediate conducting means to adjacent points on said column of capacitors.

2. A lightning arrester comprising a plurality of spark gap devices and a plurality of valve type resistance blocks disposed in columns between end members to form an arrester element, a plurality of arrester elements connected in series-connected columns, contact means at the ends of each of said elements, conducting means intermediate said elements to engage the contact means of adjacent elements, insulating tie rods hollow for their entire length extending through said end members, securing means at the ends of said tie rods to clamp the end members and arrester elements in a unitary assembly, a plurality of capacitors disposed in a column extending substantially the entire length of a rod within at least one of said tie rods, spring means within said tie rod at the ends thereof for engaging the capacitors to hold them in good electrical contact with each other, means engaging said spring means for connecting said spring means with said columns at each end thereof, and means for connecting said intermediate conducting means to adjacent points in said column of capacitors.

3. A lightning arrester comprising a plurality of spark gap devices and plurality of valve type resistance elements, said gap devices and said resistance elements disposed in columns between end members to form an arrester element, a plurality of arrester elements stacked in series-connected columns, insulating tie rods hollow for their entire length extending through said end members, securing means at the ends of said tie rods to clamp the end members and arrester elements in a unitary assembly, contact means at the ends of each of said arrester elements, conducting means intermediate said arrester elements to engage the contact means of adjacent elements, a plurality of capacitors disposed in a column extending substantially the entire length of a rod within at least one of said tie rods, said tie rods having openings at points adjacent said conducting means for receiving conducting clips, said conducting clips electrically connected to a pair of adjacent ones of said capacitors and an adjacent conducting means, whereby a section of said capacitor column is connected in parallel with each arrester element.

References Cited in the file of this patent UNITED STATES PATENTS 2,611,107 Rydbeck Sept. 16, 1952 2,611,108 Rydbeck Sept. 16, 1952 2,618,765 Vogelsanger Nov. 18, 1952 2,623,197 Kalb Dec. 23, 1952

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