US2906910A

US2906910A - Spark gap device

Info

Publication number: US2906910A
Application number: US770798A
Authority: US
Inventors: Jr Tom L Dyer; Robert T Innis
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1958-10-30
Filing date: 1958-10-30
Publication date: 1959-09-29
Anticipated expiration: 1976-09-29

Description

Sept. 29, 1959 T. 1.. DYER, JR., ETAL SPARK GAP DEVICE Filed Oct. 30, 1958 S W & m 2 mnm Y I & TW E ND 5 E T O mm M 00 TR Y. H B .w 9 3 Q .W 4 PM W F.

United States Patent 9 SPARK GAP DEVICE Tom L. Dyer, Jr., Bloomington, and Robert T. Innis, Eliettsville, Ind., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of The present invention relates to improved spark gap devices, and more particularly, to a unique construction of a spark gap particularly useful for valve type lightning arresters which utilize arc splitters and are capable of interrupting higher power follow currents than is possible with conventional valve type arresters.

Valve type lightning arresters consist essentially of a spark gap, or a series of spark gaps, of fixed lengths, connected in series with a resistance element having valve or non-linear characteristics; that is, a resistor whose resistance decreases with increasing voltage, so that under normal voltage conditions it offers a very high resistance and at overvoltage conditions ofier a low resistance, so as to permit a surge to be discharged to ground with low discharging voltage; and which is capable of thereafter increasing its resistance to reduce the follow current at normal voltages to a small value. The series gap device normally insulates the arrester from the line to which it is connected, but sparks over under a predetermined overvoltage to connect the arrester between line and ground to allow the surge to be discharged to ground. After discharge of the surge, the valve element of the lightning arrester reduces the power follow current, which tends to flow due to the normal line voltage, to a small value which is interrupted by the gap to again insulate the arrester from the line.

Recent improvements in lightning arresters of this type have resulted in lower protective characteristics of the valve element and, in particular, in reduced discharge voltage. The eifect of this lower discharge voltage characteristic is to increase the power follow current which flows through the arrester after a discharge, and which must be interrupted by the series gap. At normal line voltage, the valve elements act as an appreciable resistance against the flow of follow currents, and with previous discharge voltage characteristics, the series gap of fixed length is well able to interrupt the power follow current flow at the first current zero and remains physically unchanged. However, with higher follow currents resulting from the improved protective characteristics mentioned above, the static type of series gaps are inadequate to interrupt the power follow current flow at the first current zero. The flow of power follow current for an appreciable time is highly undesirable because it raises the temperature of the gap electrode, which is usually made of brass, above its melting point and thus causes deformation or serious burning of the electrode. Such deformation is likely to cause a sufficient change in the shape of the electrode to reduce the effective spacing between the electrodes, thus changing the sparkover voltage of the gap, so that interruption of the arc is made more difficult.

A spark gap device capable of interrupting higher follow currents than simple spark gaps is disclosed and claimed in the copending application of Tom L. Dyer, Jr., Serial No. 590,137, filed June 8, 1956, now Patent No. 2,862,132 and assigned to the Westinghouse Electric Corporation. This construction employs electrodes spaced apart to form a spark gap between them, radially extending arc splitters, and permanent magnets within a housing. The magnets provide a field perpendicular to the path of an arc arcross the gap. Since the arc is at right angles to the magnetic held, it will move parallel to the magnetic faces towards the arc splitters. In this and other known types of gaps utilizing arc splitters, it is conventional to employ all metallic arc splitters. The simple spark gap employed in many conventional valve type lightning arresters has a relatively low cut-01f voltage. The cut-oft voltage is defined as that voltage existing across the arrester at which current flow is so small that it may be readily interrupted by a simple spark gap structure on alternating current.

The relative performance of a gap can be judged by the cut-off voltage of an arrester using the gap. A higher cut-off voltage indicates that the gap is more effective in aiding the arrester in its ability to clear or interrupt the follow current which flows through the arrester after a surge has disappeared. In the simplest type of arrester gap this cut-off voltage is nearly zero. The magneticgap, however, causes the arc to go out before the normal current zero occurs and while there is still appreciablevoltage across the arrester. The magnitude of the voltage across the arrester at the time of current interruption is a measure of the ability of the gap to aid the arrester in clearing.

Provision of arc splitters in magnetic gaps in a lightning arrester spark gap creates certain problems in the arrangement of parts and physical structure of the arrester. In the series gap of a valve type lightning arrester, a number of short gaps is preferred to a single gap or a few longer gaps, because in a series of short gaps there is a greater ability to quench follow current than one long gap of equivalent spark-over voltage. It is desirable, therefore, to provide flat disc-shaped gap assemblies which may be stacked one upon another. To provide such gap assemblies with are splitters and magnets in the proper position results in costly and complex assembly methods. Misalignment of parts during assembly has been a major problem. Another serious problem is the protection of the permanent magnet from demagnetizing influences.

The principal object of the present invention is to provide a spark gap device which has improved arc interruption ability and higher cut-off voltage.

Another object of the invention is to provide an improved spark gap device which has improved are interruption and higher cut-off voltage and which is simple and economical to assemble and which utilizes a minimum of parts and connections.

A further object of the invention is to provide a spark gap device which exhibits improved arc interruption ability and higher cut-oft voltage and which utilizes a permanent magnet and ceramic arc splitters having metallic tips to increase the interrupting ability, and which is particularly useful in valve type lightning arresters.

Still another object of the invention is to provide an improved spark gap device utilizing permanent magnets enclosed in formed electrodes and arc splitters having metallic tips in which the components are fitted together in such a manner as to simplify assembly and alignment of the components and which results in improved are interrupting ability.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, in which:

Figure 1 is a longitudinal sectional view of one embodiment of the invention;

Fig. 2 is a perspective view of the gap separator and arc splitters of the invention; and

Fig. 3 is a top elevational view of an electrode employed in the gap device of this invention.

The present invention is particularly useful in lightning arresters although it will be understood that its usefulness is not necessarily limited to this specific application. The gap shown in the drawings for purposes of illustration employs two generally disc-shaped gap separators and 12 aligned in juxtaposition one upon the other. The

gap separators

10 and 12 may be of identical con struction and have integrally formed on one surface thereof a plurality of radially extending mc splitters 1d. The separators lti and 12 shown are of ceramic material but it will be understood that any suitable insulating material may be used. A semi-circular raised portion 16 is formed on one face 17 of the separators 1t) and 12. The arc, splitters are disposed in circumferentially spaced relationship on the raised portion 16. Disposed circumferentially about the other half of the face 17 of the

gap separators

10 and 12 are a plurality of radially extending recesses 13. At the ends of each of the arc splitters 14 and each recess 18 adjacent the center of the separator is a depression 20.

Aligned longitudinally along a diameter extending from the, center of the raised semi-circle to the center of the are formed by the periphery of the lower half of the gap separator are an electrode-receiving opening 22 and an electrode-receiving depressed portion 24. The depressed portion 24 is a substantially triangular shaped portion in a plane parallel to the surface of the separator having its apex at a point adjacent the center of the separator and extends to the periphery of the separator. The opening 22 is substantially triangular in shape and has its apex adjacent the center of the separator and extends to the inner circumference of the raised portion 16. The raised portion 16 slopes outwardly and upwardly toward the periphery of the separator 12. At its outer circumference the raised portion 16 has a flat annular portion 23 along its circumference. Adjacent the opening 22 is a further elevated portion 26. The triangular depressed portion 24 has an inwardly off-set portion along its side wall from which point it flares outwardly to the periphery of the separator 12. The radial recesses 18 and the outwardly flared portions of the recess 24 of one

separator

10 or 12 constitutes female portions for the reception of the arc splitters 14 and elevated portion 26 of the other of the

gap separators

10 and 12. It can be seen that the separators fit together with the splitters 14 of one received in the recesses 18 of the other and the raised portion 26 received in a portion of the recess of the depressed portion 24. Metallic balls 31 are positioned in the depressions 24 adjacent the inner ends of the arc splitters and the recesses. When the separators are disposed in face-to-face relation, the balls are held in place between opposed depressions 24).

On the faces 25 of the

gap separators

10 and 12 opposite the above-described faces 17 is an annular flange 28 forming a pocket 3%). As can be seen in Fig. 3, the electrodes 27 consist of a circular sheet of conducting material, preferably brass, although any suitable material may be used. The electrodes have substantially triangular projections 33 which constitute the sparking tips. The electrodes have an annular upstanding flange 35 at the end of which is an annular flange 32 perendicular to and outward from the upstanding flange 35, forming a disc-shaped electrode having a peripheral border. A pair of electrodes 27 are disposed in face-toface relationship with their upstanding flanges 35 opposed and annular flanges 32 lying adjacent each other to form an enclosure for a permanent magnet 34. The magnets 34 are received between pairs of electrodes and the electrodes are secured together by the flanges 32 by any suitable means such as, for example, welding or brazing forming an electrode assembly. An electrode assembly 36 is received in each of the pockets 29 in

separators

10 and 12 with the projections 33 extending periphery of the lower semi-circular portion of the opposing separator. The slope of the raised portion 16 provides an open space between

gap separators

10 and 12 as do the triangular portions of the recess 24. Thus, a gap space exists between opposed raised portions of the electrodes 27. The magnets are magnetized in the axial irection and disposed in magnetic attraction. Any suitable permanent magnetic material may be used. Either ceramic magnetic material, such as barium ferrite or any other magnetic ferrite, may be used or a conventional permanent metallic magnet.

it will now be apparent that any number of gap assem blies may be stacked together in a simple manner without difiicult alignment problems. A gap separator may be gether to provide correct alignment.

positioned upon the electrode 27' with the projection 33 extending through opening 22. A second separator may be positioned on the first separator with its splitters 14 received in the recesses 13 and its recesses 18 receiving the splitters 14 in the lower gap separator. As many gaps as necessary or required may be stacked one upon another in this manner in order to obtain a correct voltage rating of the arrester. Electrical connections of the stack may be made in any usual or desirable manner such as spring contacts at each end of the stack. Correct assembly with respect to magnetic polarity is readily indicated by attraction of the magnets and incorrect assembly is also readily indicated by repulsion of the parts. Two of the

gap separators

10 and 12 are used together to form a complete arc splitter assembly whereby two pieces key to- At the time of assembly, the splitter tips 31 are placed in the small holes 29 and once assembled are held captive. V

The operation of the gap device can be seen from the above detailed description. When a high crest voltage surge impinges upon the line electrode of the gap device, the gap sparks over in the open space between the projections or sparking tips 33. An arc is im'tiated in the gap space. The path of the arc is in a plane substantially parallel to the arc splitters 14. A strong magnetic field having lines of force perpendicular to the path of the arc is concentrated in the space between adjacent electrode sparking tips 33. Since this magnetic field is perpendicular to the are it drives the arc radially outward toward the arc splitter tips 20. The arc continues to be driven outward to the arc splitters since it always move at right angles to the magnetic field. After the arc enters the splitters it is elongated and broken into small segments. At some point outwardly of the gap the arc will be extinguished because of extension of the arc path, cooling of the gases, and failure to reignite after current zero has passed.

It has been determined by experiment that a small conducting tip at the inner end of the arc splitters gives greatly improved performance. Tests show some differences in performance of all-metal splitters against that of ceramic splitters. Improved results are obtained by using the ceramic arc splitters. However, greatly improved results are obtained far above what would normally be expected by using the metal tips. With a crest follow current of approximately 400 amperes at 60 cycles, the cut-off voltages were as follows expressed as percents of the steady state no-load voltage. All-metal splitters were approximately 33% of the steady state or no-load voltages. The cut-off voltages of all-ceramic splitters were approximately 36 to 39% of the steady state or noload voltage, while the ceramic splitters with metallic tips had cut-off voltages 50% to 52% of the steady-state or no-load voltage. Use of the metal tipped ceramic splitter design will permit the manufacture of arresters with lower protective levels with use of lower resistance valve blocks. This new gap now aids the block by taking a portion of the voltage and thus permits the non-linear blocks to valve-off quicker. With no metal tip on the splitters, the gap tends to lose its higher cut-off voltage as the current, limited by the blocks, approaches zero.

It should now be apparent that a spark gap device as has been provided, which is particularly useful for use in valve type lightning arresters; that a spark gap device, as herein described, is capable of interrupting higher follow current than is possible with known types of arrester blocks due to the utilization of unique types of arc splitters consisting of a longitudinal radially disposed ceramic portion and a metallic tip.

It should also be apparent that a specific construction of gap device has been provided which eliminates the problem of proper alignment of parts, which is simple and economical to manufacture, Which eliminates assembly difiiculties and in which any number of gaps can be stacked one upon another. No additional electrical connections are required. Electrical connections to a stack can be made in the usual manner conventional in the present types of non-splitter valve arresters as for example by spring pressure on the unused electrode surfaces at the top and bottom of the stack.

A specific embodiment of the invention has been shown and described for the purpose of illustration but it will be apparent that various modifications and other embodiments are possible and are within the scope of the invention.

We claim as our invention:

1. A spark gap device comprising a pair of electrodes -spaced apart to form a spark gap between them, a permanent magnet positioned adjacent said gap and having a field perpendicular to the path of an arc across said gap, a plurality of ceramic arc splitters extending radially outward from said gap in a plane parallel to the path of an arc across said gap.

2. A spark gap device comprising a pair of electrodes spaced apart to form a spark gap between them, a permanent magnet positioned adjacent said gap and having a field perpendicular to the path of an arc across said gap, a plurality of arc splitters extending radially outward from said gap in a plane parallel to the path of an arc across said gap, said are splitters being of ceramic material having electrically conducting tips at the ends adjacent said gap.

3. A spark gap device comprising a first pair of electrodes including first and second electrodes enclosing a permanent magnet, one electrode of said pair of electrodes having a portion positioned adjacent a portion of a third electrode, said electrode portions spaced apart to form a spark gap between them, the field of said permanent magnet extending perpendicular to the path of an arc across said gap, a plurality of arc splitters extending radially outward from said gap in a plane parallel to the path of an arc across said gap.

4. A spark gap device comprising a first pair of electrodes enclosing a permanent magnet, including first and second electrodes, one electrode of said pair of electrodes having a portion positioned adjacent a portion of a third electrode, said electrode portions spaced apart to form a spark gap between them, the field of said permanent magnet extending perpendicular to the path of an arc across said gap, a plurality of arc splitters extending radially outward from said gap in a plane parallel to the path of an arc across said gap, said are splitter being of ceramic material and having metallic tips at the ends adjacent said gap.

5. A spark gap device comprising a pair of disc-shaped gap separators, said gap separators each having radially extending ceramic arc splitters on one face thereof, an

annular flange on the other face of each of said separators forming a pocket, a permanent magnet received in at least one of said pockets, said separators disposed with said faces having arc splitters thereon in face-to-face relationship and a pair of electrodes spaced apart to form a spark gap between them intermediate said gap separators.

6. A spark gap device comprising a pair of disc-shaped gap separators, said gap separators each having ceramic arc splitters extending radially outward on one face there of, said are splitters having metallic tips at their inner ends, an annular flange on the other face of each of said separators forming a pocket, a permanent magnet received in at least one of said pockets, said separators disposed with said faces having arc splitters thereon in faceto-face relationship and a pair of electrodes spaced apart to form a spark gap between them intermediate said gap separators,

7. A spark gap device comprising a pair of disc shaped gap separators, each of said separators having a plurality radially extending arc splitters on one face thereof and a plurality of radially extending recesses formed on said one face for receiving said arc splitters on the other separator of said pair, an electrode receiving opening ex tending through each of said separators from face-to-face, said separators disposed with said one face of one separator in opposed relation to said one face of the other separator and said are splitters on one separator lying in said recesses of said other separator, an annular flange about the periphery of the other face of each of said separators, said flanges extending perpendicularly from said other faces and outwardly therefrom to form pockets on each of said other faces of said separators, an electrode received in each of said pockets having a projection thereon extending through said opening of the adjacent separator, and permanent magnets received in each of said pockets and overlying said electrodes.

8. A spark gap device comprising a pair of disc shaped gap separators, each of said separators having a plurality of radially extending ceramic are splitters formed integrally on one face thereof and a plurality of radially extending recesses formed on said one face for receiving said arc splitters on the other separator of said pair, a depression adjacent the ends of each of said splitters and the ends of each of said recesses, an electrode receiving depressed portion on said one face of each of said separators, an electrode receiving opening extending through each of said separators from face-to-face, said separators disposed with said one face of one separator in opposed relation to said one face of the other separator and said are splitters on one separator lying in said recesses of said other separator, said depressions adjacent the ends of corresponding arc splitters and recesses being disposed in opposition to each other, conducting tips forming arc splitter tips received in said depressions, an annular flange about the periphery of the other face of each of said separators, said flange extending perpendicularly from said other faces and outwardly therefrom to form pockets on each of said other faces of said separators, an electrode received in each of said pockets having a projection thereon extending through said opening of the adjacent separator and overlying the recess of the other separator and permanent magnets received in each of said pockets and overlying said electrodes.

References Cited in the file of this patent UNITED STATES PATENTS