US3524107A

US3524107A - Low voltage lightning arrester spark gap

Info

Publication number: US3524107A
Application number: US723370A
Authority: US
Inventors: Roderick Reitz
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1968-04-23
Filing date: 1968-04-23
Publication date: 1970-08-11
Anticipated expiration: 1987-08-11
Also published as: AU5231669A

Description

Aug. 11, 1970 R. RElTz 3,524,107

LOW VOLTAGE LIGHTNING ARRESTER SPARK GA? Filed April 2s, 196e y Zia/77a United States Patent Office 3,524,107v Patented Aug. 1l, 1970 3,524,107 LOW VOLTAGE LIGHTNING ARRESTER SPARK GAP Roderick Reitz, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Filed Apr. 23, 1968, Ser. No. 723,370 Int. Cl. H02h 3/22, 9/06 U.S. Cl. 317-61 14 Claims ABSTRACT OF THE DISCLOSURE My invention relates to lightning arresters, and more particularly, to a low voltage lightning arrester of simplified and rugged construction that can be manufactured to precisely predetermined dimensions by mass production techniques.

Lightning arresters designed for protecting low voltage circuits must be capable of discharging overvoltage surges at an accurately predetermined sparkover voltage level, and such arresters must embody structural components that can be manufactured with mass production methods so that the cost of the individual arresters remains competitive in the commercial markets where most of these arresters are sold. While these desirable characteristics have long been recognized, prior art low voltage lightning arresters generally include spark gap assemblies of relatively complex design that incorporate structural features which are either quite expensive to reproduce in mass production or difficult to keep within close manufacturing tolerances so that accurately predetermined spark gap voltage ratings can be maintained for all arrester units produced in a given production run.

The primary object of my invention is to provide a low voltage lightning arrester having simplified components that can be economically manufactured with mass production methods to afford an accurate predetermined sparkover voltage for the arresters.

Another object of the invention is to provide a low voltage lightning arrester having a spark gap assembly with a unique electrode structure that affords inexpensive and reliable preionizing means to assure sparkover of the arrester at a predetermined voltage.

A further object of the invention is to provide a low voltage lightning arrester of simplified rugged construction having a minimum number of component parts each of which are preformed by inexpensive manufacturing processes which adapt the parts to be assembled to form an accurate spark gap.

In one preferred embodiment of the invention, a low voltage lightning arrester is formed by positioning a block of nonlinear resistance material within a ceramic lightning arrester housing and mounting a spark gap assembly on the valve resistance material in electrical contact there; with. The spark gap assembly includes a cup-shaped electrode and a star-shaped electrode which are assembled to define an accurately predetermined spark gap between the pointed ends of the star-shaped electrode and the inner walls of the cup-shaped electrode. The star-shaped electrode is secured in position on an insulating disc by a rigid metallic terminal inserted through both the electrode and the disc in rivet fashion, and the insulating disc is adapted to be press-fitted into the cup-shaped electrode in a manner such that the relative dimensions of the two electrodes and the insulating disc determine the length of the spark gap defined between the electrodes in their assembled relative positions. In addition to the foregoing components, a 'block of insulating material is disposed adjacent to the star-shaped electrode and the spark gap defined between the two electrodes so that an electric field formed between the respective teeth of the star-shaped electrode will serve to ionize the surface of the block of insulating material and, thus, preionize the spark gap to thereby stabilize its sparkover voltage.

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

FIG. 1 is a cross sectional side elevation of a spark gap assembly embodying a preferred form of my invention.

FIG. 2 is a top plan view, partly in cross section, taken along the plane 2-2 of FIG. l.

FIG. 3 is a side elevation view, partly in cross section, of a low voltage lightning arrester assembly embodying a second form of my invention.

Referring now to FIG. 1 of the drawing, there is shown a spark gap assembly 1 consisting of a cup-shaped electrode 2 that is formed of brass or other suitable conducting material which may be stamped or drawn into a predetermined shape within close manufacturing tolerances. A star-shaped electrode 3 (also see FIG. 2) is mounted on a block of insulating material 4 by a rigid terminal member 5 that is inserted through apertures 3a and 4a in the electrode 3 and the insulating disc 4, respectively, in rivet fashion. The terminal member 5 is provided with an integral flange or flared head portion 5a which serves to bias the star-shaped electrode 3 against the insulating disc 4 when the terminal S is press-fitted through the aperture 4a in the insulating disc 4.

It will be appreciated that pursuant to my invention the insulating disc 4 is formed of any suitable organic or inorganic material that can be readily molded or otherwise preformed to adapt it to be press-fitted into the cupshaped electrode 2 and, at the same time, to have the rigid terminal 5 press-fitted through its central aperture 4a. Due

vto their simplified cylindrical configurations, both the cupshaped electrode 2 and the rigid terminal 5 can be economically manufactured to close predetermined dimensions that afford accurate spacing between these component parts in their assembled positions. It is also a unique feature of the star-shaped electrode 3 that its central disc-shaped portion 3b is disposed in the same plane as each of its generally pointed teeth 3c. This substantially flat arrangement of the entire body of the star-shaped electrode 3 allows it to be formed by inexpensive manufacturing processes, such as by mechanically stamping, or cutting, a plurality of such electrodes from a flat sheet of metallic stock, e.g., brass, copper or other suitable conductive material. Therefore, it will be seen that when the rigid terminal 5 is press-fitted through the aperture 3a in electrode 3, and these components are assembled as described above within the cup-shaped electrode 2, a plurality of spark gaps 6 of predetermined accurate length are defined between the generally pointed ends 3c of starshaped electrode 3 and the inner wall of cup-shaped electrode 2. Those skilled in the spark gap field will appreciate that it is common practice to refer to the gaps 6 collectively as a single spark gap, since they are all of equal length and they are each defined by the same two electrodes, 2 and 3. However, to maintain consistency, the gaps 6 will be referred to in plural form herein.

In order to assure the sparkover of the plurality of spark gaps 6 at a predictable voltage, a cup-shaped block of insulating material 7 is disposed within the cup-shaped electrode 2 between it and the star-shaped electrode 3. Referring to FIG. 2, it will be seen that the respective side surfaces of the generally pointed teeth 3c of the star-shaped electrode 3 intersect each other to define a plurality of notches 3d around the periphery of the central disc-shaped portion 3b of the star-shaped electrode 3. In the preferred embodiment of the invention depicted in FIGS. 1 and 2, the respective acute angles formed bythe intersecting side surfaces of adjacent teeth 3c is slightly modified by rounding these notches 3d into semi-circular form. It will be appreciated that other notched configurations may be employed without departing from the scope of my inventiin. The significant feature of this particular aspect of the invention resides in the fact that an electric field having a relatively steep voltage gradient is formed by the acute angle between adjacent teeth 3c when a voltage drop exists across the

electrodes

2 and 3. Due to the unique arrangement of the component parts of my invention, this steep voltage gradient causes the surface of insulating block 7, which may be formed of ceramic, mica, or other suitable material, to be ionized at a voltage appreciably below the normal sparkover voltage of the spark gaps 6. When the upper surface of the insulating block 7 is thus ionized, due to its proximity with the plurality of spark gaps 6, these gaps are heavily pre-ionized so that the sparkover at a predetermined relative low voltage is assured. It will be noted that the block of insulating material 7 is maintained in its desired relation with the star-shaped electrode 3 by the combined positioning action of the flanged head 5a 0f terminal 5 disposed in the cupshaped depression 7a in the upper surface of the block 7 and by the press fit of the insulating disc 4 into electrode 2, which serves to bias the star-shaped electrode 3 against the insulating block 7.

In order to facilitate an understanding of the relation between the spark gap assembly 1 and a block of nonlinear resistance valve material of the type that is normally used in a low voltage lightning arrester, such a valve resistor is shown in outline form as the member 8 in FIG. l. It will be understood that the spark gap assembly 1 and the valve resistor 8 will normally be mounted in electrically conducting relation within a suitable insulating housing (not shown) formed of ceramic or other conventional insulating material. It will also be appreciated by those skilled in the lightning arrester art that the rigid terminal 5 will normally be electrically connected by a suitable flexible conductor, such as the strip of aluminum 9 that is suitably secured to it, to a terminal (not shown) mounted on such a lightning arrester housing, while the lower surface of valve resistor 8 will be electrically connected to a terminal on the opposite end of the housing.

In order to further demonstrate some of the advantages of my invention, a second embodiment of it is illustrated in FIG. 3 of the drawing. In FIG. 3, component parts similar to those described above with reference to FIGS. 1 and 2 are identified with like reference numerals. Accordingly, in FIG. 3 there is shown a spark gap assembly 1 consisting of a drawn cup-shaped brass electrode 2, a star-shaped electrode 3, a first block of insulating material 4, a second block of insulating material 7 and a rigid terminal member 5. In this form of my invention, the cupshaped electrode 2 is provided with an integral flange 2a extending laterally from its vertical side Wall. The outermost diameter of the tiange 2a and the diameter of insulating block 4 are preformed to identical dimensions so that these respective component parts can -be quickly and easily aligned during the assembly of a lightning arrester constructed according to the teaching of my invention, in the manner described in more detail below. Another unique feature of this form of my invention is its incorporation of a resilient annular member 10 formed of silicone rubber or other suitably flexible material. The resilient member 10 is compressed between the flange 5a of rigid terminal 5 and the bottom surface of insulating disc 4 when the respective component parts are assembled as shown in FIG. 3. In this compressed position, the resilient member 10 maintains a firm electrical contact between the bottom surface of the rigid terminal member S-Sa, as well as serving to bias the star-shaped electrode 3 against insulating member 7. To complete the assembly of this form of my invention, a block of nonlinear resistance material 8 is secured in electrical contact with the flange 5a of rigid terminal 5 by its engagement with the insulating housing 11. This housing 11 may be formed of any suitable insulating material, but in this embodiment of my invention the housing 11 is formed of an epoxy that is molded around the spark gap assembly 1 and the nonlinear resistance material 8 when they are assembled in the relative positions shown in FIG. 3. As noted above, it will be understood that in this assembled position the resilient member 10 is under compression so that it reacts against the confining forces of the housing 11 to bias the respective functional component parts together, in the manner described above.

In this embodiment of the invention, the respective apertures through the centers of star-shaped electrode 3, and insulating blocks 4 and 7 interact with the press fitted rigid terminal -5 to retain these component parts in a precisely predetermined spaced relation such that a spark gap 6 of accurate predetermined length is defined between the generally pointed ends 3c of star-shaped electrode 3 and the inner walls of cup-shaped electrode 2 when the outer peripheral edge of the insulating disc 4 is aligned with the outer peripheral edge of the flange 2a on cup-shaped electrode 2. In order to retain this simply achieved accurate spacing of the spark gap 6 during that portion of the manufacturing process wherein the housing 11 is cast around the spark gap assembly 1 and the valve resistor 8, the liange 2a may be cemented or otherwise temporarily secured to the upper surface of the insulating block 4. `Of course, after the housing 11 has been molded around these component parts, it serves to secure them in position and forms an hermetic seal around the spark gap assembly '1.

While specific embodiments of my invention have been illustrated and described for the purpose of teaching the invention, it will be apparent that various modifications and other embodiments are possible, and the invention is not restricted to the particular arrangement shown but rather includes all equivalent embodiments and modications which come within the true scope and spirit of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a lightning arrester, a spark gap assembly comprising a first electrode having a generally disc-shaped central portion with a plurality of pointed teeth radiating outward therefrom, said teeth being disposed in the same plane as the major axis of said disc-shaped central portion, a second electrode, a block of insulating material, and mounting means for holding said first and second electrodes in fixed predetermined positions with respect to said block of insulating material such that a plurality of gaps of predetermined length are formed between the respective pointed ends of each of said teeth and said second electrode.

2. The invention as defined in claim 1 wherein said second electrode has a generally cup-shaped surface, and said first electrode is adapted to nest within the space defined by said cup-shaped surface.

3. The invention as defined in claim Z wherein said mounting means includes portions of said cup-shaped surface adapted to cooperate with said block of insulating material to retain it in a predetermined relation v therewith, and said mounting means further includes a 4. The invention as defined in claim 2 including a second block of insulating material disposed between said cup-shaped surface and said first electrode, said second block of insulating material being adapted to ionize said plurality of gaps 'when a predetermined voltage exists between said first and second electrodes.

5. The invention as defined in claim 2 wherein the central portion and the pointed teeth of said first electrode are disposed in a single plane and the pointed ends of said teeth are disposed at substantially equally spaced points that define points of a circle.

6. The invention as defined in claim 2 in combination with a nonlinear resistance valve material disposed in said lightning arrester and electrically connected to one of said electrodes.

7. A spark gap assembly comprising a first electrode having a center portion with a plurality of pointed teeth radiating outward therefrom, a second electrode having a surface adapted to cooperate with said teeth to define a plurality of spark gaps between said teeth and said second electrode, a first block of insulating material, mounting means for retaining said block of insulating material in a predetermined relation between said first and second electrodes, a second block of insulating material disposed between said first and second electrodes and adapted to ionize said plurality of gaps when a predetermined voltage exists across said second block between said first and second electrodes, means defining a plurality of notches in said first electrode adjacent the periphery of its center portion, each of said notches defining an acute angle that is disposed adjacent a surface of said second block of insulating material to cause a steep voltage gradient on said surface and thereby enhance the ionization of the surface of said second block of insulating material.

8. A spark gap assembly as defined in claim 7 wherein said acute angles in said notches are defined respectively by intersecting side surfaces of adjacent pairs of said pointed teeth.

9. A spark gap assembly as defined in claim 7 wherein said second electrode has a generally cup-shaped surface, and said first electrode is adapted to nest within the space defined by said cup-shaped surface, said first block of insulating material being adapted to be force-fit -between the inner walls defined by said cup-shaped surface thereby to press said first electrode against the second block of insulating material.

10. A spark gap assembly as defined in claim 9 including resilient means adapted to urge said first electrode into engagement with said second block of insulating material.

11. A spark gap electrode comprising an electrically conductive, generally disc-shaped central portion with a plurality of teeth radiatingoutward therefrom, each of said teeth being in substantially the same plane as said central portion, and said teeth being rigidly positioned in fixed relation with respect to said central portion.

12. A spark gap electrode as defined in claim 11 wherein each of said teeth has side surfaces that are adapted to cooperate with a surface of an adjacent tooth on either side thereof to define acuate angles in the periphery of said central portion on both sides of the base of each of said teeth.

13. A spark gap electrode as defined in claim 11 wherein each of said teeth has a sharp point at its outermost extremity, each of said sharp points being disposed at substantially equally spaced distances with respect to one another and arranged to define points on a circle, and means defining an aperture through a precisely predetermined area of said disc-shaped central portion.

14. A spark gap assembly comprising a rigid cup-shaped electrode, a rigid star-shaped electrode having an aperture through its center, a cup-shaped insulator, a rigid terminal member, and a disc-shaped insulator having an aperture through its center, said cup-shaped insulator being disposed substantially concentrically within said cup-shaped electrode, said rigid terminal member being disposed through the respective apertures in said starshaped electrode and said disc-shaped insulator and having its ends extending beyond the outermost surfaces thereof, said rigid terminal member being adapted to restrain relative movement between said star-shaped electrode and said disc-shaped insulator, one end of said rigid electrode being positioned within the cup-shaped space defined by said cup-shaped insulator, said disc-shaped insulator `being disposed at least partially within the cup-shaped space defined by said cup-shaped electrode in a manner such that a spark gap of predetermined length is formed between the pointed teeth of the star-shaped electrode and the inner wall surface of said cup-shaped electrode, said cup-shaped insulator being adapted to be ionized by an electric field concentrated at the respective 4bases of the pointed portions of said star-shaped electrode when a predetermined voltage is applied across said electrodes.

References Cited UNITED STATES PATENTS 2,473,850 6/ 1949 Beck et al. 317--68 2,650,330 8/ 1953 Stoelting 317-67 3,017,539 1/ 1962 Robinson 317-66 JAMES D. TRAMMELL, Primary Examiner U.S. Cl. X.R.