US 3263117 A
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July 26, 1966 E. NILSSON 3,263,117
MEDIATE ELECTRODE FORM SPARK GAP DEVICE HAVING AN INTER SERIES SPARK GAPS Flled June 14, 1961 5 sh t sh t 1 ING TWO I N VEN TOR. 5P4 W0 a/n July 26, 1966 E. NlLS 3,263,117
SPARK GAP DEVICE HAVING AN INTER I E ELECTRODE FORMING TWO SERIES SPARK GAPS Filed June 14, 1961 5 Sheets-Sheet 2 IN VEN TOR.
E. NILSSON SPARK GAP DEVICE HAVING AN INTERMEDIATE ELECTRODE FORMING TWO July 26, 1966 SERIES SPARK GAPS 5 Sheets-Sheet 3 Filed June 14, 1961 INVENTOR. M -r0 United States Patent 3,263,117 SPARK GAP DEVICE HAVING AN INTERMEDIATE ELECTRODE FORMING TWO SERIES SPARK GAPS Erland Niisson, Ludvika, Sweden, assignor to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Filed June 14, 1961, Ser. No. 127,771 Claims priority, application Sweden, June 18, 1960, 6,000/60 11 Claims. (Cl. 315-36) The present invention relates to a spark-gap device, preferably for lightning arre-sters, containing at least two substantially parallel discs of arc-resistant insulating material, which discs form one or several closed arc-chambers in which metallic electrodes are arranged, and provided with devices situated outside the arc-chamber for generating a magnetic field directed perpendicular to said arc-chamber.
Lightning arresters provided to be inserted in an electrical power supply network contain spark gaps. The purpose of these is, at incoming overvoltage, to ignite, and thus open a low-resistance current path through the arrester, and afterwards, as soon as possible to extinguish the arc and thus break this current path and return the arrester to rest condition. After at least the main part of the over-voltage impulse has ceased during an arrester operation, but before the spark gap is again extinguished and the low ohmic connection through the arrester interrupted, a condition exist-s in which the operating voltage of the network drives a current through the arrester. The accepted name for this current driven by the of the network is follow current.
It is known to make spark-gaps by arranging metallic electrodes in closed arc-chambers existing between discs of arc-resistant insulating material stacked on top of each other. It is also known to extinguish an are formed in a spark-gap by arranging an outer magnetic field fed by the arc current and perpendicular to the main plane of the arc chamber. The magnetic field thus influences the arc in such a way that it is lengthened and forced into a narrower part of the arc-chamber, called extinguishing chamber. The are foot-points are thus moved out along the electrodes away from the ignition spots of the arcgap so that this can be tie-ionized and again have a high dielectric strength before the extinguishing of the arc is completed. When the arc has been forced out intothe extinguishing chamber there will be a considerable voltage drop in the are, which is added to the voltage drop in valve resistors which may be series-connected to the, spark gap, and thus contributes to limiting the follow current driven by the voltage of the network. In an extinguishing chamber of the type in question the voltage drop of the arc will be substantially proportional to the length of the are, which should therefore be large. It is further known, from a space saving point of view, to arrange arc chambers on top of each other perpendicular to the longitudinal axis of the arrester, so that the available space for the arc chamber is formed by the space between two discs of insulating material stacked above each other, said discs usually being circular and provided with recesses.
By the development of the present invention, however, it has been found that the function of a spark gap is considerably deteriorated if the ratio between the length of an extended arc in an extinguishing chamber on the one hand, and the length of the arc in the corresponding ignition gap, on the other hand, is too great. In this case the arc voltage drop will be so great that re-ignition in the ignition gap takes place before this has procured sufficient dielectric strength. It has also been found that the recovery dielectric strength grows proportionately more 3,263,117 Patented July 26, 1966 slowly in an ignition gap with large distance than in one with small distance between the electrodes.
The mentioned disadvantages are avoided by means of the present invention, the main idea of which is to divide the above mentioned are into several series-connected arcs. Such a dividing of the arc has great advantages. Because of the decreased distance between the electrodes in each part-gap, the ratio between the permissible recovery voltage of operating frequency and the ignition voltage will be more favourable. The total arc length for the complete pair of discs may be chosen as large as the space within the contour allows so that the pair of discs takes up the greatest possible total voltage drop while, at the same time, the length of are Within each part-gap is suitably limited with regard to the risk of re-ignition.
The invention is characterised in that between the said discs, at least three metallic electrodes are arranged, provided with ignition projections forming foot points to at least two series connected arcs which, each from its own ignition zone with small distance between the electrodes is moved out between the electrodes into the said extinguishing chamber. The metallic electrodes in the are chamber may, according to the invention, be arranged in two different ways. For instance, the metallic electrodes may be so arranged that the ignition gaps formed between the electrodes are substantially of the same size and situated on or near the edge of the discs, and that at least the intermediate electrode or electrodes situated between the outermost electrodes traverses the arc chamber to or near opposite edges of the discs. This placing of the electrodes is most advantageous for a spark gap device having only a few intermediate electrodes and has the advantage that the extended arc is removed a long way from the respective ignition zones, which is advantageous for the de-ionizing of the spark-gap. However, in certain cases the metallic electrodes could advantageously be placed near the middle point of the arc chamber forming an ignition gap between them and the said electrodes going radially from the middle part to the edge of the arc chamber. The last mentioned arrangement of the electrodes is most advantageous when a larger number of intermediate electrodes are to be placed in the arc chamber, because with this arrangement of the electrode a larger partof the periphery of the arc chamber is accessible for the extended arc. The inventon is further characterised in that the intermediate electrode or electrodes between the outer electrode-s are arranged to form Walls for gas-circulating channels running longitudinally in each electrode. The intermediate electrodes are for this purpose suitably formed so that they have a U-shaped profile or so that they have a hair-pin shape and so that the substantially parallel sides running longitudinally in each electrode, coincide near the ignition point of the spark gap. By making use of the intermediate electrodes as walls for gas circulating channels is achieved partly a return-circulation channel to the air in the arc chamber, which the arc pushes in front of it during its movement, so that the are without being restrained by a compressed air cushion is able to reach the edge of the arc chamber, and partly a cooling of the ignition gaps by means of the circulating gas, and this cooling is very important for the de-ionization of the ignition gaps. Further, according to the invention, the intermediate electrodes produce a mechanical support between the discs surrounding the electrodes. This mechanical support has been found to be extreme-1y valuable as the discs of insulating material are subjected to very high mechanical stresses when a high impulse current is led through the spark gap device. The arcs which are formed between the spark gap electrodes have often very high energy and could therefore cause severe burns on the electrodes. The invention is characterised in that the outer electrodes as well as the intermediate electrodes, at least at the ignition zone, are formed with substantially flat or cap-shaped surfaces whose planes form an angle with the main plane of the discs. The electrodes according to the invention thus have greater burning surfaces for the are at the ignition zone, and the risk of burns on the electrodes is thus decreased. In order to obtain a well defined ignition voltage for the spark gap device this is, according to the invention, provided in a manner known per so with a preionizing device. This consists of a pointed metal part salient from an electrode and arranged near to and visible with the naked eye from an ignition gap. Further characteristic of the invention is that each insulating disc is provided with two metallic electrodes, one placed on each side of the plate, which are galvanically connected. The invention is further characterised in that at least two discs are identical and stackable and that two discs stacked upon each other are mutually angularly displaced. Because the discs are identical and the electrodes placed on both sides of each disc are metallically connected, it is possible to arrange the discs in a stack so that all the ignition gaps formed in the stack are series-connected.
The invention will be described below with reference to the accompanying schematic drawing in which FIG- URES 1, 2 and 3 show different types of electrode arrangements within the arc chamber. FIGURES 4, 5 and to the accompanying schematical drawing in which FIG- URE 7, which illustrates a suitable embodiment of the invention, is divided up into FIGURES 7a, 7b and 7c. FIGURES 7a and 7b show different sides of the stackable discs. FIGURES 7c shows a stack of coinciding discs containing arc chamber and spark gap. FIGURE 8 shows a complete spark gap device.
In FIGURE 1 the outer electrodes 2 and intermediate electrodes 3 are placed on the disc 1 so that between them they build an ignition gap 4. Each electrode is provided with ignition projections 5 which in the embodiment shown are placed in the middle region of the arc chamber in such a way that the ignition projections 5 of the two adjacent electrodes are facing each other. Between the outer electrodes 2, at the centre part 12 and around the edge 9 of the disc, the discs are laid one upon the other with no space between. However, free space is left at the other places between the discs. This free space forms the so-called arc chamber, which consists of a relatively spacious ignition chamber 10 and a narrower extinguishing chamber 11. When an over-voltage arises across the outer electrodes 2, an arc is ignited between the ignition projections 5 in each ignition gap 4. The are current which feeds a magnetic blowing coil outside the ignition gap generates a magnetic field directed perpendicularly to the plane of the disc 1. When the arcs generated at the ignition gaps 4 are influenced by said magnetic field, the foot points of the arcs are moved along the edges of the electrodes 2 and 3 out to the edge of the arc chamber and thus forced into the extinguishing chamber 11. The arcs which while being moved are partly extended and partly forced into a narrow chamber thus take up a considerable ar-c voltage drop, which helps to reduce the current through the spark gap device so that the arc can no longer be maintained but is extinguished.
In FIGURE 2 the oval outer electrodes 2 are placed on the disc 1 so that, together with the intermediate electrodes 3 between the ignition projections 5, they form ignition gaps 4 which are placed near the edge of the disc. When an over-voltage arises, series connected arcs are ignited in the ignition gaps 4 and said arcs are by means of magnetic blowing, extended and moved from the ignition chamber 10 to the extinguishing chamber 11 in the same way as in the device according to FIGURE 1.
The spark gap according to FIGURE 3, like the previous spark gap, has two outer electrodes designated 2 whose ignition gaps 4 are placed near the edge of the disc 1. In FIGURE 3 only one intermediate electrode 3 is shown which traverses the disc 1. The electrode 3 shown in the figure is hair-pin shaped and has substantially parallel sides. An are produced in the ignition gaps 4 is forced by an outer magnetic field into the extinguishing chamber 11 of the spark gap in the manner described above. The air in the chamber is thus compressed and pressed through the gas-circulating channel 6 formed by the electrode 3 and the relatively cool air thus cools both the electrode 3 and the ignition zone 4.
The outer electrodes 2 and the shown intermediate electrodes 3, from the space point of view are made of metal sheet or strip. In the enlarged ignition chamber 10 between the discs 1, however, the electrodes are bent so that the ignition gap 4 is formed between large, essentially flat, surfaces of the electrodes and not between their narrow edges. In this way the are, immediately after ignition, when the high impulse current from the over-voltage shall pass, has larger electrode surfaces to spread over, which reduces burn damages on the electrodes.
Such a bending of the electrodes is shown in the FIG- URES 4, 5 and 6, showing vertical cross-sections in different forms of ignition gaps. The reference numbers in these figures are the same as in FIGURES 1, 2 and 3 and it is seen from the figures that by bending of the electrodes, broad ignition gaps 4 are obtained in the spa cious ignition chamber 10 formed between two parallel discs 1.
FIGURE 4 shows an oblique intermediate electrode 3 and in parallel with this, the edges of the outer electrodes 2 provided with ignition projections 5. In FIG- URE 5 the outer electrodes 2 are bent in a square angle and the intermediate electrode 3 is made with a Z-formed profile. In this figure the ignition projections are arranged on the intermediate electrode.
In FIGURE 6 are also shown outer electrodes 2 bent in a square angle and between these an intermediate electrode 3 with a U-shaped profile. In this figure preionizing devices 7 are shown in the form of projecting metal tongues, visible with the naked eye from respective ignition gaps. At over-voltages, such preionizing devices cause glow discharge which facilitates the ignition in the spark gap so that a more precise ignition voltage is obtained.
FIGURE 6 forms a detail of the elements more completely shown in FIGURE 7.
In FIGURE 7, as in previous figures, the discs are designated 1 and the oval outer electrodes applied in the discs 2. The intermediate electrodes 3, which in the embodiment shown, have been given a U-shaped profile, are provided with gas-circulation recesses 6, and are otherwise so shaped that they form a mechanical support between the plates 1. The intermediate electrodes 3 reach from the ignition gap 4 of the spark gap to the opposite edge of the arc chamber. In the discs 1, the recess for the ignition chamber is designated 10 and for the extinguishing chamber 11. Further each disc is provided with guiding bosses 13 to hold each disc in the stack rigidly. On the outer electrodes 2 the preionizing device 7 is in the form of projecting metal tongues which are visible with the naked eye from respective ignition gaps. At over-voltage, a glow discharge arises around the said preionizing device 7, which facilitates ignition in the spark gap and reduces dispersion in the ignition voltage of the arrangement. FIGURE 7a shows the underneath of a disc 1 which, taken together with the disc 1 in FIG- URE 7b, between them forms a closed arc chamber comprising two outer electrodes 2 and an intermediate electrode 3. Each disc is provided on each side with an outer electrode 2, which electrodes are connected with metallic connections 8. FIGURE 7c shows three discs 1 stacked upon each other, which between them form two are chambers and four series connected spark gaps.
The elements of a more complete lightning arrester are shown in FIGURE 8, showing two discs 1 of the type shown in FIGURE 7 and two end discs 14. The reference numbers 1-13 are the same as in FIGURE 7. The end discs 14 are formed on the side facing the discs 1 in the same way as the other discs and provided with electrodes corresponding hereto. On the other side the end discs are covered by a metal plate 15 forming a connection to a magnetic blowing coil 16. Generally such a magnetic blowing coil is parallel connected to a valve resistor which suitably could be inserted in the middle of the coil as shown by 17.-
Thus it is seen that the complete lightning arrester comprises the series connection of a magnetic blowing coil 16, an end disc 11, a number of normal discs 1 (only two are shown), another end disc 14 and so on. If desired, magnetic blowing coils could be inserted between pairs of discs similar to those shown in Patent No. 2,909,694.
The embodiments of the invention exemplified here have been found particularly suitable. It is, however, possible within the scope of the invention to use, for
' instance, other electrode configurations without in principle altering the method of operation of the invention.
1. Spark gap device comprising at least two substantially parallel discs of are resistant insulating material, each two adjacent discs forming between them a closed arc chamber, metallic electrodes arranged in said are chamber, said are chamber comprising a spacious ignition chamber part and a narrow extinction chamber part, electromagnetic means for generating a magnetic field directed perpendicular to said parallel discs for lengthening and moving each arc in the spark gap device from the ignition chamber to the extinction chamber, each arc chamber containing two outer electrodes and at least one intermediate electrode arranged between said outer electrodes, said electrodes forming at least two series connected spark gaps between them, said spark gaps being situated in said are chamber and each comprising a narrow ignition gap part situated in said ignition chamber, all of said electrodes extending divergently from the ignition gap parts in said ignition chamber to points adjacent the outer edge of said extinction chamber so that said spark gaps also extend substantially to the outer edges of said extinction chamber.
2. In a spark gap device according to claim 1, said ignition gaps formed between the electrodes being substantially equal in size and being located near the edge of the discs, said one intermediate electrode crossing the arc chamber to a point near the opposite edge of the discs from the ignition gaps.
3. In a spark gap device according to claim 1, having a plurality of intermediate electrodes, said ignition gaps between the electrodes being situated near the middle point of the arc chamber, and said intermediate electrodes extending radially from the middle part of the arc chamber to the edge of the arc chamber.
4. In a spark gap device according to claim 1, said intermediate electrode forming walls of gas-circulating channels running longitudinally therein.
5. A spark gap device according to claim 4, said intermediate electrode'having a U-shaped profile.
6. In a spark gap device according to claim 4, said intermediate electrode being hair-pin. shaped, the substantially parallel sides running longitudinally in the electrode.
7. In a spark gap according to claim 1, the outer electrodes and the intermediate electrode, at least near the ignition gaps,having substantially flat surfaces whose planes form an angle with the main planes of the discs, said surfaces forming ignition projections.
8. In a spark gap device according to claim 1, a preionizing device comprising a pointed metallic part projecting from one of the electrodes arranged near to and in alignment with an ignition gap.
9. In a spark gap device according to claim 1, at least one of the metallic electrodes of the arc chamber forming a mechanical support between the discs surrounding said are chamber.
10. In a spark gap device in accordance with claim 1, each disc being provided with two metallic plates, one placed on each side of the disc, metallic connections between said plates, said disc together with an adjacent disc forming an arc chamber, one plate from each of said discs forming said outer electrodes. 9
11. In a spark gap device according to claim 1, at least two discs being identical and stackable.
References Cited by the Examiner UNITED STATES PATENTS 2,554,278 5/1951 Teszner 313156 2,862,132 11/1958 Dyer 3l774 X 2,890,383 6/1959 Olsen 315--36 2,906,910 9/ 1959 Dyer et a1. 313-156 2,917,662 12/1959 Cunningham 317-74 HERMAN KARL SAALBACH, Primary Examiner. ARTHUR GAUSS, DAVID J. GALVIN, Examiners. S. CHATMON, JR., Assistant Examiner.