US2999960A

US2999960A - Lightning arrester

Info

Publication number: US2999960A
Application number: US702370A
Authority: US
Inventors: Francis V Cunningham
Original assignee: McGraw Edison Co
Current assignee: McGraw Edison Co
Priority date: 1957-12-12
Filing date: 1957-12-12
Publication date: 1961-09-12
Anticipated expiration: 1978-09-12

Description

Sept. 12, 1961 F. v. CUNNINGHAM LIGHTNING ARRESTER Filed Dec. 12, 1957 INVENTOR.

FRANCIS V. CUNNINGHAM M QM AT TO RN EY United States Patent 2,999,960 LIGHTNING ARRESTER Francis V. Cunningham, Milwaukee, Wis., assignor to McGraw-Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Dec. 12,1957, Ser. No. 702,370 9 Claims. (Cl. 315-36) The present invention relates to improvements in an overvoltage protection device for electrical equipment, and more particularly to an improved type of isolating gap for a lightning arrester.

When applying valve type lightning arresters which include a series of a plurality of totally enclosed spark gaps, it has been common practice to connect the arrester line lead directly to the primary bushing terminal of the transformer or other electrical apparatus to be protected. It has also been the practice of providing an open air gap between the arrester line terminal side and the line terminal of the transformer or the like. In either case, trouble might develop if, in the first instance, the arrester has broken down and if, in the second instance, the gap is shorted out by a bird or other object. To minimize the possibility of trouble developing in either case, I have provided a novel combination of a protected gap and arrester on the line side of the arrester.

It is an object of my invention to provide an isolating gap of minimum spacing designed to meet the requirements of withstanding normal line voltages under all operating conditions and which is effectively shielded from rain, sleet, snow, contaminated atmosphere and contact by birds, insects, animals, etc.

An object of this invention is to provide an isolating gap for valve type lightning arresters and the like which aifords a physical connection of the arrester with a transformer or the like on the line side without sacrificing the protective valve to the arrester but which is itself fully protected and electrically isolates the arrester.

It is an object of this invention to provide an isolating gap of the type aforementioned which is totally enclosed and of the type where the gap is factory adjusted so that it may not become fouled, shorted or misadjusted in transit.

It is another object of this invention to provide a lightning arrester isolating gap as aforestated which is truly isolating at rated voltage since the sparkover is not adversely affected by rain, fog, sleet or snow or by contamination by dirt or the like.

It is a further object of thisinvention to provide an enclosed isolating gap which has venting means associated with the enclosure which prevents development of excessive pressures in area enclosing the gap.

It is also an object of this invention to provide an enclosed isolator gap having arc shielding means associated therewith, said shielding means being adapted to intercept a normally flaring short circuit are to thereby prevent carbonization of the major portion of the enclosure to thereby maintain a major portion of the creepage distance between electrodes at high dielectric strength.

A still further object of this invention is to provide a housing for an isolating gap which is having an internal interrupting surface, which increases the creepage distance between the spaced electrodes, which is formed of high dielectric material such as porcelain or the like, which is easy to manufacture by mass production techniques, which fits compactly over standard valve type lightning arrester enclosures, which is easily bonded to said valve type lightning arresters, which accommodates a high range of tolerances and which is otherwise well adapted to the purposes for which it was designed.

The novel features of the invention are set forth with particularity in the appended claims. The invention it:

Patented Sept. 12, 1961 self, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood by the following description of specific embodiments when read in connection with the accompanying drawings in which:

FIG. 1 is a view in side elevation of a valve type arrester and novel protective gap, parts being broken away showing the interior of the gap enclosure.

FIG. 2 is a fragmentary view partly in section showing a modified form of isolating gap for a valve type lightning arrester.

While the following to be described isolating gap is shown in conjunction with a particular type of valve type lightning arrester, it is to be expressly understood that the isolating gap is well adapted to be mounted on any of several types of valve type lightning arresters and, hence, the drawing and description of the latter is not intended to restrict the application of applicants inventive contribution.

Returning now to the drawings, the reference numeral 10 shows a standard valve type lightning arrester, the housing of which may be made of high grade electrical porcelain or glass 11 closed at its upper end by a conductive cap 12 made of copper or the like and sealing the upper end of the housing against the entrance of moisture. As shown in FIG. 2, internally of the housing 11 is negative resistance valve material 13 and an internal spark gap structure 14, the latter functioning to interrupt power follow current as well understood in the art. The particular gap structure 14 shown is more particularly shown and described in my copending application, Serial No. 571,543, filed March 14, 1956, and assigned to the same assignee, and which matured into U.S. Patent No. 2,891,193, granted June 16, 1959.

The cap 12 is formed with a centrally located protuberance 13 designed to accommodate the mounting means (not shown) for holding the series gap 14 in fixed relationship to the valve material 13 within the housing 11.

External isolating gap means for the lightning arrester is provided by

spaced electrodes

15 and 16, the former being somewhat elongated and the latter being of an inverted dish-like configuration and of slightly larger diameter than the conducting cap 12. As shown, the central portion 17 of the electrode 16 is spaced above the protuberance 13 on the cap 12. The peripheral portion of the electrode 16 is provided with a plurality of radially extending slots 18, preferably six in number, spaced equidistantly from each other around the circumference of the electrode and extending radially inwardly a sufiicient distance so that there is communication between the interior of the gap housing or enclosure 20 and the venting means hereinafter more fully explained. The peripheral portion of the electrode 16 extending outwardly beyond the cap 12 serves as support for the gap housing or enclosure means 20.

The housing means 20 for the spaced electrodes shown in FIG. 1 is composed of an upper housing portion 21 and a lower housing portion 22. The lower portion 22 is somewhat of a funnel shape and is so formed that the inner diameter thereof at its lowermost extremity is larger than the housing 11 and fits thereover and provides a shoulder 25 formed midway on the internal surface of the lower housing 22 engaging the periphery of the electrode 16 and supported thereby. The shoulder 25 serves as means for fixing the dimension of the gap spacing between

electrodes

15 and 16. The upper re-entrant portion 23 of the lower housing means 22 extends transversely from the outside periphery of the housing means and is substantially reduced in diameter to define an aperture 24 at its upper extremity. The upper housing portion 21 extends over the upper portion 23 of the housing portion sulphur cement or the like.

3 22 and is bonded directly to the mating outer surface of the lower housing portion 22 before firing operations.

The entire isolating gap enclosure 20 may be bonded to the arrester housing 11 by suitable cement 26 such as However, before the cement 26 is placed in position, it is preferred that suitable filter material 28,,such as glass wool be inserted around the periphery of the cap 12 and adjacent the periphery of the electrode 16. The cement 26 is then placed in position, as illustrated in FIG. 1, and provided with a series of apertures 27 which may be formed by inserting tapered pins in the cement 26 during the curing operation and withdrawing the same after the cement has set. Thus,

'the interior of the gap housing 20 is placed in communication with the exterior through the filter 28 which prevents entry of bugs and insects to the interior housing '20. It will thus be seen that the interior of the enclosure or housing 20 and the outside thereof are placed in communication through the electrode apertures 18, interstices of the glass wool 28, and the apertures 27 in the cement 26, thereby affording a venting arrangement Which allows gases generated in the housing 20 to escape and prevent contamination of the interior by foreign materials. It is advantageous to vent the spark chamber because arcing between

electrodes

15 and 16 generates heat which causes the surrounding air to so expand that excessive internal pressure may develop to the point which, if unrelieved, would tend to damage or even burst the housing. Venting also prevents excessive contamination of the upper portion 23 of the lower housing 22 due to deposition of metal and carbon from vapors evolved during arcing between the

electrodes

15 and 16. In the event of heavy follow current due to failure of the valve type lightning arrester 10, the evolved vapors would tend to remain in the spark chamber and, if no venting were provided, (1) may alter the breakdown characteristics of the spark gap and (2) carbonize and metallize the interior of the housing walls, which may eventually result in a breakdown voltage along the shortest creepage path which is lower than the power line voltage.

Returning now to the upper electrode 15, it will be noted that it is formed with an enlarged head portion 31 and shank portion 15a, the latter being surrounded by insulating means 30 which is preferably a fibre sleeve. The function of the fibre shield 30 is to prevent elongation of an arc in the event the arrester fails to interrupt follow current. The upper section 23 of the lower housing 22 acts as an arc shield which prevents burning or carbonization of major creepage distance of the housing portion 21 by an arc. The are shielding portion 23 also greatly increases the creepage distance between

electrodes

15 and 16. The terminal 15 extends through the housing 20 and is adapted to be connected to a distribution line at 33 as, for example, directly to the line terminal of a transformer, or the like, and the stud 35 is adapted to be connected to ground. The area in the housing portion 21 disposed about the portion 31 on the electrode 15 is preferably sealed in any suitable manner to prevent water and other material from entering the housing 20;

The embodiment shown in FIG. 2 of the drawings is substantially similar to FIG. 1, identical parts being shown by the same reference numeral.

The essential differences between the embodiment shown in FIG. 1 and that shown in FIG. 2 lie in the depending, re-entrant, undulating skirt portions 32 which are formed on the internal surfaces of the housing 20', thereby increasing the creepage distance between the spaced electrodes 15' and 16. The electrode 15' is of a slightly different configuration than previously noted with reference to electrode 15 and has no fibre shield therearound. In the FIG. 2 modification, the housing 20 is molded as a one piece unit, thus affording some economies in manufacture. The terminal end 33 of line electrode 15' is covered by a suitable insulating cap 34 which shields the terminal against contact. Obviously the terminal 33 of the electrode 15 in FIG. 1 may be provided with a cap 34. V

Although specific embodiments of the invention have been shown and described, it is with full awareness that many modifications thereof are possible. The invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

What is claimed as the invention is:

*1. In combination, a valve type lightning arrested having one side connected to ground and including a housing having a conductive closure cap and enclosing a spark gap structure and a negative resistance element in series with said spark gap structure, and protective gap means in series relation with a power line and said conductive closure cap, said protective gap means comprising a housing, and first and second relatively spaced electrodes disposed within said protective gap housing, said protective gap housing having a re-entrant surface adjacent said first and second electrodes for increasing the creepage path between said first and second electrodes, one of said electrodes being adapted to be connected to said line and the other of said electrodes being supported by said conductive closure cap and supporting said protective gap housing.

2. In combination, a valve type lightning arrester having one end connected to ground and including a housing having an electrically conductive closure cap and enclosing a gap structure and a negative resistance valve element in series with said conductive cap and said gap structure, protective gap means in series relation with said lightning arrester, said protective gap means including a housing open at one end, and first and second relatively spaced electrodes disposed within said housing, one of said electrodes being adapted to be connected to a power line, the other of said electrodes being generally dish-shaped and in engagement with said conductive gap, said dish-shaped electrode closing said open end of said housing and having a plurality of venting apertures adjacent the periphery thereof, and filter means associated with said venting apertures to prevent entry of contaminating solids into said protective gap housing and to afford adequate venting of gases from said housing.

3. A gap structure comprising a housing open at one end, first and second relatively spaced electrodes disposed within said housing, one of said electrodes being adapted to be connected to a power line, the other of said electrodes closing said open end of said housing and being dish-like in shape, said other electrode having a plurality of apertures adjacent the peripheral margin thereof and being adapted to be connected in series with a lightning arrester, said apertures affording ventilation of said housing, said housing further characterized by having an inner re-entrant surface portion for increasing the creepage disstance between said electrodes along the internal peripheral surface of said housing.

4. In combination, a valve type lightning arrester having one side connected to ground and including a housing enclosing a gap structure and a non-linear resistance element in series therewith, protective gap means in series relation to said gap structure and valve element, said protective gap means including a housing, and first and second relatively spaced electrodes disposed within said housing, one of said electrodes being adapted to be connected to an electrical power line, the other of said electrodes being adapted to be connected to said lightning arrester, the internal surface of said gap housing between said first and second electrodes having a re-entrant portion traverse to said internal surface, whereby the creepage distance between said electrodes and the breakdown strength of said protective gap is increased.

5. In combination, a valve type lightning arrester having one side connected to ground and including a housing enclosing a gap structure and a non-linear resistance element in series with said gap structure, protective gap means in series relation with said gap structure and valve element, said protective gap means including a housing, first and second relatively spaced electrodes disposed within said housing, one of said electrodes being adapted to be connected to an electrical power line, the other of said electrodes being adapted to be connected to said lightning arrester, the portion of the inner surface of the gap housing defining the shortest surface path between said first and second electrodes having undulations extending in a direction transverse to said shortest surface path, whereby the breakdown strength of said protective gap is increased.

6. In combination, a valve type lightning arrester having one end connected to ground and including a housing having an electrically conductive closure cap and enclosing a gap structure and a non-linear resistance element in series with said gap structure, protective gap means in series relation-with said gap structure and valve element, said protective gap means including a housing open at one end, first and second relatively spaced electrodes disposed within said housing, insulating means surrounding at least one of said electrodes to prevent elongation of the power arc between said first and second electrodes, in the event said arrester fails one of said electrodes being adapted to be connected to a power line, and the other of said electrodes being oppositely disposed relative thereto and being generally dish-shaped and in engagement with said conductive closure cap, said dish-shaped electrode closing said open end of said housing and having a plurality of venting apertures adjacent the periphery thereof, filter means associated with said venting apertures to prevent entry of contaminating solids into said protective gap housing and to afford adequate venting of gas from said housing, the internal surface of said protective gap housing between said first and second electrodes having a portion transverse thereto for increasing the creepage distance between said electrodes along the internal surface of said protective gap housing.

7. In combination, a valve type lightning arrester having one end connected to ground and including a housing enclosing a gap structure and a non-linear resistance valve element in series with said gap structure, protective gap means in series relation with said gap structure and valve element, said protective gap means including an inverted cup-shaped housing of insulating material having an aperture through the transverse portion thereof, a first electrode adapted to be connected to an electrical power line and extending through said aperture a substantial distance into the interior of said cup-shaped housing, and a second electrode oppositely disposed relative to said first electrode and closing the open end of said cup-shaped housing and adapted to be connected to said lightning arrester, the internal surface of said protective gap housing between said first and second electrodes having a portion transverse thereto, whereby the creepage distance between said electrodes along the internal surface of said protective gap housing is increased.

8. In combination, a valve type lightning arrester having one end connected to ground and including a housing enclosing a gap structure and a non-linear resistance valve element in series with said gap structure, protective gap means in series relation with said gap structure and valve element, said protective gap means including an inverted cup-shaped housing of insulating material having an aperture through the transverse portion thereof, a first electrode adapted to be connected to an electrical power line and extending through said aperture a substantial distance into the interior of said cup-shaped housing, and a second electrode oppositely disposed relative to said first electrode and closing the open end of said cup-shaped housing and adapted to be connected to said lightning arrester, said cup-shaped housing having an annular arc shield of insulating material of smaller diameter than the interior of said housing extending into the interior of said housing in spaced relation to the internal surface thereof and surrounding said first and second electrodes, whereby an are between said electrodes is prevented from flaring out and carbonization of the surface defining the creepage path between said electrodes is prevented.

9. In combination, a valve type lightning arrester having one end connected to ground and including a housing encasing a gap structure and a non-linear resistance element in series with said gap structure and having a con ductive closure cap, protective gap means in series with said arrester including an inverted cup-shaped housing of insulating material, a first electrode adapted to be connected to an electrical power line extending through the bottom wall of said inverted cup-shaped housing a substantial distance into the interior thereof, and a second electrode disposed opposite said first electrode and defining a protective gap therewith, said second electrode closing the open end of said cup-shaped housing and being in electrical engagement with said conductive closure cap, said cup-shaped housing being supported on said second electrode and having an annular arc shield of insulating material extending into the interior of said housing in embracing relation to said electrodes and in spaced relation to the internal walls of said housing, whereby an arc between said electrodes is prevented from flaring out and carbonization of the surface defining the creepage path between said electrodes is prevented.

References Cited in the file of this patent UNITED STATES PATENTS 1,268,049 OGorman May 28, 1918 1,312,646 Sonneborn Aug. 12, 1919 1,689,781 Jacobs Oct. 30, 1928 2,239,940 Stroup Apr. 29, 1941 2,304,334 Boucher et al. Dec. 8, 1942 2,591,370 Nelson Apr. 1, 1952 2,593,955 Ackermann Apr. 22, 1952 2,642,549 Pummer June 16, 1953 2,650,330 Stoelting Aug. 25, 1953 2,663,817 De Val et a1. Dec. 22, 1953 2,677,072 De Val Apr. 27, 1954 UNITED STATES PATENT. OFFICE CERTIFICATE OF CGRRECTION Patent N0. 2,999,960 I September 12, 1961 Francis V. Cunningham It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. I

Column 4, line 66, for "traverse" read transverse I Signed and sealed this 6th day of February 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES PATENT. OFFICE CERTIFICATE OF CORRECTION Patent Nor. 2,999,960 I September 12, 1961 Francis V. Cunningham It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. I

Column 4, line 66, for "traverse" read transverse V Signed and sealed this 6th day of February 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patent