US3363135A - Magnetic drive lightning arrester having a variably spaced arcing gap - Google Patents

Description

Jan. 9, 1968 D. R PARKER 3,363,135 MAGNETIC DRIVE LIGHTNING ARRESTER HAVING A VARIABLY SPACED ARCING GAP Filed Feb. 4, 1965 2 SheetsSheet 1 wlmsssss: INVENTOR g (Q G Delbert R. Parker {WP/U B ATTORNEY Jan. 9, 1968 Filed Feb. 4, 1965 D. R. PARKER MAGNETIC DRIVE LIGHTNING ARRESTER HAVING A VARIABLY SPACED ARCING GAP '2 Sheets-Sheet 2 United States Patent 3,363,135 MAGNETIC DRIVE LIGHTNING ARRESTER HAV- ING A VARIABLY SPACED ARCING GAP Delbert R. Parker, Vienna, Ohio, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 4, 1965, Ser. No. 430,274 6 Claims. (Cl. 313-231) ABSTRACT 0F THE DISCLOSURE A lightning arrester comprising a gap device having spaced annular electrodes enclosed in an arc chamber which includes gas-evolving material, and magnetic means for driving an are around the closed loop formed by the electrodes.

The present invention relates to lightning arresters and more particularly to lightning arresters in which magnetic force drives an are over a closed loop until the arc is extinguished.

One of the primary operating features in a lightning arrester is that of arc extinguishment after an overvoltage surge so as to prevent or interrupt the flow of power follow cuurent. In valve type arresters, valve or block resistance in the arrester circuit becomes sufficiently high after the voltage surge to provide for are extinguishment in the arrester gap. Expulsion arresters provide arc extinguishment by removal of ionized arc gas from the interelectrode space and such removal is greatly accelerated by unionized gas generation induced by are heat applied to insulative material within or about the arc chamber. In each case, the fundamental reason for eventual arc extinguishment is the direct or indirect development of resistance to are current flow in one or more parts of the total arrester circuit.

The present invention encompases arrester structure operating on a similar fundamental basis but incorporating specific structural and operating differences. In accordance with its broad principles, a lighting arrester comprises one or more gap units having an arc chamber casing within which there are supported a pair of generally aligned tubular or ring-like electrodes which have a :predetermined gap space therebetween.

Magnetic flux generating means are also supported within the casing, preferably in the form of ring-like permanent magnets disposed to each side of the interelectrode gap. An interelectrode arc is thus driven along the closed loop path by magnetic force.

The are chamber is vented preferably through one of the electrodes to provide-for expulsion of arc gases and the closed loop path is made sufficiently long and the electrode mass is made sufficiently large to provide for cool operation of the electrodes surfaces as the arc traverses the closed loop path. Arc extinguishment results from the overall resistive and retarding effects on are current flow.

It is therefore an object of the invention to provide a novel lightning arrester having high surge current capacity.

Another object of the invention is to provide a novel lightning arrester in which are extinguishment is efficiently achieved.

An additional object of the invention is to provide a novel lightning arrester in which magnetic force is employed to drive an are over a closed loop path thereby to provide for are extinguishment.

A further object of the invention is to provide a novel lightning arrester in which magnetic drive is employed to provide for the arc extinguishment and in which struc- ICC tural strength is adequate for withstanding relatively high surge current.

It is another object of the invention to provide a novel lightning arrester in which are extinguishment is aided by or primarily produced by cool operation of the arrester gap electrodes.

It is an additional object of the invention to provide a novel lightning arrester in which are extinguishment is achieved by cool electrode operation, lengthening of the are as it is driven by magnetic force, and generation of unionized gas in the arc chamber.

These and other objects of the invention will become more apparent upon consideration of the following detailed description along with the attached drawings, in which:

FIGURE 1 is a top plan view of an arrester gap assembly constructed in accordance with the principles of the invention;

FIG. 2 is a top plan view of a lower half of the gap assembly shown in FIG. 1;

FIG. 3 shows a cross section taken along the reference line IIIIII of FIG. 1;

' FIG. 4 schematically shows a layout view of closed loop electrodes employed in the gap assembly of FIG. 1;

FIG. 5 schematically shows a layout view of modified closed loop electrodes which can be employed in the gap assembly of FIG. 1; and

FIG. 6 shows an elevational view of a plurality of gap units arranged in a stack to form a series arrester circuit of predetermined voltage rating.

More specifically, there is shown in FIG. 1 a gap assembly 16 which operates alone or in combination with additional identical assemblies as a lightning arrester in accordance with the principles of the invention. When used alone or in a stack, the gap assembly 10 can be enclosed in a porcelain or other housing (not shown) if desired.

The gap assembly 10 is generally provided in this case with a circular geometry and it comprises an outer insulative tubular casing 12 within which a pair of axially aligned ring-like electrodes 14 and 16 (FIG. 3) are supported with an annular arc gap 18 therebetween. The electrodes 14 and 16 are directly supported by inner and outer insulat-ive tubular walls 20 and 22 which provide sidewall surfaces 24 and 26 enclosing the gap 18 and thus forming an annular arc chamber between the electrodes l4 and 16.

Preferably, the outer casing 12 is formed by identical upper and lower half portions 28 and 30 having a radially inwardly extending flange portion 32 for captivating the outer arc chamber wall 22 in supported relation. Bolts 34 or other suitable means can be used to secure the outer casing halves 28 and 30 together after the outer arc chamber wall 22 is disposed between the casing flanges 32.

Similarly, the arc chamber walls 20 and 22 are both formed by identical upper and lower half portions 36 and 38 respectively. Each wall portion 36 or 38 is provided with an annular slot 40 or 42 within which magnetic flux generating means, preferably in the form of permanent magnet means 44 and 46 are disposed when the arc chainber walls 20 and 22 are assembled from the wall portions 36 and 38. Although each of the permanent magnet means 44 or 46 can be a solid ring-like structure, a plurality of arcuate permanent magnets 48 and 50 (FIG. 2) are in this instance disposed in side-by-side relation within the annular slots 36 and 38, respectively. The magnets 48 and 5b can be formed from any suitable metallic, ceramic or other permanent magnet material.

The wall portions 36 and 38 preferably are formed from vulcanized fiber to provide for generation of unionized gas (usually water vapor) in the gap 18 when an arc is struck between the electrodes 14 and 16. In the gap 10, arc extinguishment can thus be partly promoted in a manner common in principle to the principal means of arc extinguishment in the expulsion class of arresters previously noted. However, other materials can be employed for the wall portions 36 and 38 depending on the degree of need for are suppression in the gap assembly 10 through the generation of unionized gas. The primary properties required for the selected arc chamber wall'material are mechanical strength for withstanding expected arc chamber pressures, electrical insulation qualities for normally isolating the electrodes 14 and 16, and suitable magnetic permeability for transmitting adequate magnetic flux (FIG. 3) across the gap 18. An example of a suitable material for the walls 20 and 22 is polyester resin, with filler of aluminum tri-hydrate.

The upper and lower ring electrodes 14 and 16 are provided with conductive terminal means 15 and 17 and are formed from a suitable conductive material such as stainless steel. Further, the electrodes 14 and 16 are supported, preferably with a relatively tight fit, in respective grooves 49 and 51 formed by shoulders 52 and 54 on the wall portions 36 and 38. The top electrode 14 is secured and in this instance sealed in place by suitable filler material 56 which can also secure the upper inner wall portion 36 against axial movement relative to the outer wall 22. The lower inner wall portion 36 in turn can be secured in place by bonding (not shown) to the upper inner wall portion 36 or it can be suitably clamped (not shown) thereto. If desired, separate suitable clamping means (not shown) can be employed to secure both inner wall portions 36 in relation to the wall 22 so that assembly strength against arc chamber pressure need not depend solely on the bonding strength of the filler material 56.

To provide pressure relief or to vent arc gases from the gap 18, the bottom electrode 16 is provided with annularly spaced holes 58 (FIG. 2). An annular insulative layer 60 (FIG. 3), bonded or secured to the adjacent wall portions 36 and 38 to provide support therebetween, supports the lower surface of the bottom electrode 16. The vent holes 58 thus also extend through the insulative layer 60.

As schematically illustrated in the layout View of FIG. 4, the electrodes 14 and 16 have confronting annular electrode surfaces 59 and 61 with sparkover surfaces 62 and 64 forming respective limited portions thereof. The length of the gap 18 between the annular electrode surfaces 59 and 61 preferably increases with angular position beginning with the sparkover surfaces 62 and 64 and ending with the 180 point. The length of the gap 18 then decreases until the angular position of the sparkover surfaces 62 and 64 is again reached. Other profiles can be employed for the gap spacing between the confronting electrode surfaces 59 and 61, for example, a uniformly increasing gap length can be provided about the gap periphery with the sparkover surfaces 62 and 64 as a starting and ending point or, as shown in FIG. 5, a uniform gap length as indicated by the reference character 66 can be employed in conjunction with the sparkover surfaces 62 and 64. In the event a gap of increasing length is employed as preferred, are lengthening will promote arc extinguishment through increasing arc resistance associated With increasing arc length.

As an initiated arc is magnetically driven by the fiux from the sparkover region about the closed loop or annular gap 18, a primary causal factor for are extinguishment is the cooling effect produced on the are including that produced by relatively cool operation of the electrode surfaces 59 and 61. Thus, the electrodes 14 and 16 preferably have a relatively large mass (and preferably a relatively large depth along the interelectrode direction) to provide a basis for rapid heat removal from the electrode surfaces 59 and 61 and thereby assure low electrode surface temperatures as the arc feet move rapidly thereover. Maintenance of low arc foot temperatures imposes a restricting effect on arc current flow in the sense that large amounts of are energy are then required for arc maintenance and further in the sense that are restrike is then more readily prevented when the power voltage cycles through zero at the operating level of ionization in the arc chamber atmosphere.

If, as preferred, the walls 20' and 22 are formed from a material such as vulcanized fiber and if the arc chamber is provided with suitable geometry, i.e. if the wall surfaces are relatively close together to be subjected to sufficient temperature rise from the are heat, generation of unionized gas in the arc chamber promotes deionization and arc expulsion and thus can form another primary causal factor in arc extinguishment. In any event, it is preferable that the total are extinguishing effect be adequate to provide arc extinguishment prior to or at the first voltage zero of the power current. This can be realized by are cooling alone or by such cooling in combination with the effect of generated unionized gas and if desired the effect of arc lengthening. The combined effect of these factors is determinative of the power-voltage level to which overvoltage protection can be provided.

Extinguishment of the arc and the preferred timing thereof are preferably achieved principally through appropriate arc cooling, particularly by providing an appropriate size for the closed loop arc path between the relatively large mass electrodes 14 and 16. Thus, the inner diameter of the electrodes 14 and 16 is relatively large to provide a sufficiently long closed loop arc path which, in combination with electrode mass, results in the are cooling necessary to dissipate the energy of the arc discharge current and to quench the power follow current before the temperature of the electrode surfaces rises appreciably above ambient temperature and before the normal current zero. In this same connection, it is noted that the speed at which the arc is driven about the closed loop arc path is a determinant of the rate at which are foot cooling is produced by the electrodes 14 and 16 as well as the rate at which arc cooling is produced by the arm chamber atmosphere as the arc proceeds therethrough. The fact that the inner diameter of the electrodes 14 and 16 is relatively large provides a by-product advantage in utility, ie the gap assembly 16 in a finished arrester unit can have a sufficiently large central opening 68 (FIG. 1) to fit over and thus be mounted about high voltage bushings of electrical equipment such as distribution type transformers.

In FIG. 6, a stack 7t) of gap assemblies 16, suitably connected in series, is provided to form a lightning arrester of higher voltage rating than that obtainable with a single gap 10. For example, if a single gap 10 is rated for 2000 volts overvoltage protection, the arrester stack 70 includes seven gaps 10 to provide a 14 kv. rating.

As shown, intergap space 72 exists between dotted lines 74 which represent outer surfaces of the walls 20 and 22. Vented gases in the intergap spaces 72 can be suitably channeled therefrom as schematically shown by exhaust system 76. The stack 70 can be suitably housed in a porcelain housing (not shown) or the like if desired.

The gap 10 or stack 70 provides reliable overvoltage protection and does so without requiring special resistance blocks in the arrester circuit. Further, such protection can be obtained without the use of unionized gas generating material about the arc chamber, although use of such material increases arc extinguishment effects.

first-mentioned tubular wall so as to form sidewalls of a closed loop arc chamber therewith, a pair of ring-like electrodes supported in relation to said tubular walls to enclose said are chamber with an annular arc gap therebetween, said electrodes having confronting annularly extending surfaces between which said are gap is provided, said electrode surfaces including sparkover portions of limited annular extent and having a relatively small spacing therebetween to form a sparkover region of said gap, the spacing between said electrode surfaces increasing over at least a portion of the total annular extent of said electrode surfaces beginning with said sparkover surface portions, means for venting said are chamber, and magnetic flux generating means for driving an are about said closed loop arc gap for extinguishment.

2. A lightning arrester comprising a gap assembly having an insulative tubular arc chamber wall, another insul'ative tubular arc chamber wall supported within the first-mentioned tubular wall to form sidewalls of a closed loop arc chamber therewith, a pair of ring-like electrodes supported in relation to said tubular walls to enclose said are chamber with an annular arc gap therebetween, said walls having adjacent annularly extending shoulder means to support said electrodes as described, means for venting said arc chamber, permanent magnet means for driving an are about said closed loop arc gap for extinguishment, each of said tubular walls being provided in the form of a pair of annular half portions, said half portions having mating slots therein forming slot means extending angularly about the tubular walls, said permanent magnet means including permanent magnets disposed in the slot means of both tubular walls, and means securing said electrodes on said wall shoulder means.

3. A lightning arrester as set forth in claim 2 wherein said gap assembly includes an outer insulative tubular casing which supports at least the first-mentioned tubular are chamber wall and which is also provided in annular half portions secured together to maintain said gap assembly in assembled relation.

4. A lightning arrester as set forth in claim 2 wherein conductive means extend from said ring electrodes for circuit connection.

5. A lightning arrester comprising a gap assembly having two circular insulating side wall members disposed concentrically and spaced radially to form an annular arc chamber therebetween, a pair of ring electrodes disposed between said side wall members and enclosing the annular arc chamber, the electrodes having opposed annular surfaces to form an annular arc gap within the arc chamber, the electrode surfaces having sparkover portions of limited angular extent and relatively small spacing to form a sparkover region and the electrode surfaces diverging to a greater spacing in other regions of the an nular gap, and magnetic flux generating means encircling at least one of the side walls outside the arc chamber for driving an are about the closed annular arc gap.

6. A lightning arrester as defined in claim 5 in which said side wall members are made of an insulating material capable of evolving gas when exposed to an arc and at least one of said electrodes includes vent means for venting gas from the arc chamber.

References Cited UNITED STATES PATENTS 2,555,971 6/1951 Kalb 313-231 3,230,416 1/1966 Smith 313-231 X 3,278,588 11/1966 Lee et a1. 315-36 JAMES W. LAWRENCE, Primary Examiner.

S. D, SCI-ILOSSER, Assistant Examiner.

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