US 3106661 A
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2 Sheets-Sheet l BY BARREL D. MCSTRACK ATTORNEY I MRosEcoNbs Oct. 8, 1963 Filed June 24. 1960 Ocf- 8 1963 l.. M. BURRAGE ETAL 3,106,661
LIGHTNING ARRESTER 2 Sheets-Sheet 2 Filed June 24, 1960 INVENTO M.BuR D. Mc STRACK LADwReNce ARREL BY ATToRNEY This invention is vfor a lightning arrester which is plicable to any part of an electric power system which may be designed for any desired voltage.
Primary objects are to provide a lightning arrester which consists of a stack of units connected in series, with each unit so constructed that it provides, as a unitary structure in itself, a spark gap and a section of valve material in series `with the spark gap and a capacitor in parallel to each section of valve material, and also a high ohmic resistor across the spark gap so that the resistors form, in effect, a high resistance voltage divider and thus provide uniform voltage division among the spark gaps.
Further objects are to provide a unit adapted for stacking to form voltage rated lightning arresters of any desired voltage, each unit consisting of a structure having a spark gap, valve material, and a capacitor bridged across a section 'of valve material and in series with the spark gap, and also a voltage divider of high ohmic resistance for the successive spark gaps of a stack.
Further objects are to provide a construction of a lightning arrester having all of the novel features heretofore enumerated which nevertheless is relatively simple and sturdy and of light weight.
Although the lightning arrester is applicable to alternating voltage lines of any desired voltage, nevertheless further specific objects are to provide a lightning arrester for relatively low voltage alternating current lines which has a suiiiciently low impulse ratio to be of value for the relatively low voltage lines but which nevertheless has characteristics which render it sharply responsive to surges of steep wave fronts and which differentiates such surges from the ordinary commercial frequency of the line so that the lightning arrester functions only for surges of a value that might cause trouble and does not function for surges of lesser value which would cause no damage to the low voltage lines.
Further objects are to provide a low voltage lightning arrester ywhich is extremely fast in its action and which does not allow even a steep wave front surge to build up to a dangerous value which might cause complete flashover and failure of the device or damage to other elements connected to the relatively low voltage line.
Further objects are to provide a lightning arrester which is so constructed that it has means for distinguishing between a surge having a very steep wave front and a surge that has a gradually rising wave front. In greater detail the lightning arrester has means so arranged that with a sharp or steep wave front essentially all of the voltage is impressed on the spark gaps, thus causing the spark gap to break down before a very high voltage is allowed to build up and be impressed on the lightning arrester. The lightning arrester is so made that it has the characteristic described immediately hereinabove and it further has means for subsequently impressing the voltage on the valve material in series with the spark gap. lt thus has means for automatically changing over, after distinguishing between a surge having a steep wave front and one having a gradually rising wave front, so that the voltage is impressed directly on the spark gap for a surge with a steep wave front and so that the slowly rising voltapand ggd? rate tet age of a different type of wave front is impressed on both the spark gap and the valve material in series.
Embodiments of the invention are shown in the accompanying drawings in which:
FIGURE 1 is a vertical sectional view through a lightning arrester showing one form of the invention.
FIGURE 2 is an enlarged sectional view of one of the units of FIGURE l.
FIGURE 3 is a view corresponding to FIGURE 2 showing a different type of unit.
FGURE 4 is a sectional View of a unit showing a further form that the invention may take.
FIGURES 5 and 6 show still further forms of the invention.
FIGURE 7 shows the manner in which a different type of capacitor can be employed.
FlGURE 8 represents the voltage time relation in lightning arresters having valve material in series with the spark gap as in ordinary types of arresters, and also shows this relation for the new type of arrester forming the subject matter of this invention.
Referring to FIGURE l it will be seen that the lightning arrester comprises a ceramic body portion of tubular shape indicate by reference character 1. This tubular ceramic insulator may have a plurality of petticoats indicated by the reference character 2 and is preferably provided with upper and lower annular projecting members 3 and l about which the sealing metal disks S and 6 are crimped, suitable sealing gaskets 7 and 8 being interposed between the ceramic body portion 1 and the upper and lower metal plates d and 6.
Referring to FIGURE l it` will be seen that the lightning arrester is composed of upper and lower terminal members 9 and 1t?l of any suitable form. The lightning arrester is provided with a stack of alternate sections of valve material and parallel capacitors, indicated as a unit by the reference character V, and spark `gap sections indicated by the reference character S. The sections V are shown in greater `detail in FIGURE 2 and each of these sections consists of a ring or annular block of valve material 11 which is provided with inner and outer insulating coatings 12 and i3 formed directly on the valve material. A ceramic member of generally cylindrical shape indicated by the reference character 14's is positioned within the central opening of the valve material and is secured to the insulating coating 12 by means of insulating cement 1S. lt 'is to be noted that a transverse web or portion 16 is formed as an integral part of the ceramic member 1d.
The upper and lower surfaces of the valve material are coated with a metalized coating, :the upper metalized coating being indicated by the reference character 17 and the lower metalized coating by the reference character i8. These coatings extend across the valve material and dotwn into the ceramic cylindrical member 14 and across the web 16 and Kthus provide transverse portions 19 and Ztl which are electrically connected to the portions 17 and i8.
The spark gap portions indicated generally by the reference character S consist of upper and lower metal members 21 and 22 which are pressed inwardly as indicated at 23 and 24, to provide electrodes for the spark gap. The metal members 2l and 22 contact the metalized coatings in and 17 of the adjacent Valve material unit or block, see FIGURES l and 2.
Resistor rings 25 are positioned between the members 2l and 22 and are of high ohmic resistance to thus provide a high resistance electrical leak across each spark gap. These resistance members or rings 25 thus constitute a high resistance voltage divider and insure the ystriking or sparking of all of the spark gaps in a simultaneous manner.
The stack of alternate spark gaps and valve material arcs,
sections are supported by a lower cylindrical metal meniber 26 which bears `against the lower sealing disk o at the bottom end and bears against an upper metal plate Z7 at its upper end. lt is to be noted that the spark and sections of valve material are `arranged in series in a stack and alternate spatially and connectively. The high resistance rings and sections of valve material may be Carborundurn which is silicon carbide. in making the high resistance rings and valve material, granular silicon carbide is used and is bonded together by a soluble silicate. The metal plate Z7 is provided with suitable lugs to hold it centrally over the cylindrical support rthe spark gaps in the stack alternate with the sections of valve material spatially and connectively.
The bottom sealing plate 6 is dished or pres ed upwardly as indicated at 29 so as to center the support 2e.
The upper por-tion of the stack of valve material and spark gaps is provided with an upper metal plate 36 w i has lugs 3l to center a heavy coiled steel spring Si?. positioned between the upper sealing plate S and the metal top plate 38; The upper sealing plate 5 is provided with a downwardly dished portion 33 in order to center the upper end of the spring 32. if desired, `flexible conducting ribbons 34 may be provided and positioned kas shown to insure a direct electrical connection between 'the metal plate 35i and the upper sealing plate 5'. A plug 33' extends through the sealing plate and has an internally threaded aperture therethrough normally closed by a small threaded plug, as shown. his construction is for the purpose of allowing any desired gas to be injected into the lightning arrester yand also allows the internal pressure to be adjusted to the desired value. A ilat spring 34 rests loosely on the top of the plug 33 and bears against the under side of the terminal 9 and this forms the electrical connection to the terminal 9.
The upper and lower ends of the lightning arrester are sealed in the upper and lower terminals 9 and l5", respec tively, by the insulating sealing cement 35.
The valve material for the several diderent forms of the invention is either in blocks or rings, in other words preformed as in FIGURE 2 or they may be formed outside of a ceramic portion as in FIGURE 3. The valve material is silicon carbide and this silicon carbide has any suitable binder, such, for example, as sodium silicate, or any other binder that is customarily used.
Referring to FIGURE 3, it will be seen that this form of the invention shows a ceramic central cylindrical portion 36 which is provided with a transverse web 37. The valve material 33 is formed about this cylindrical ceramic member 36.
An insulating coating 39 is formed on the outside of the ring of valve material and a metalized coating lll is formed on the upper and lower surfaces of the valve material 38 and extends downwardly transversely across the web 37 as indicated at lll. This forms the capacitor. The ceramic material has a high dielectric constant.
in the form of the invention shown in FiGURE 4 the valve material is indicated by the reference character fl. It is a block or ring of preformed valve material as described hereinabove and is provided with outside insulating coating 43. A transversely extending ceramic disk 44 having high dielectric constant is used as the dielectric material for the capacitor. llt is provided with upper and lower metalized coatings The valve material block or ring e2 is provided with upper and lower metalized coatings te which extend to the inner edges of the valve material. Metal disks i7 are placed on the upper and lower sides of this valve material block Iand are connected with the metalized coatings i5 by any suitable means, `as for example, by means of the flat springs d8 bent in the form of a U. The disk with its coatings 45 is formed prior to the forming of the insulla-ting cylindrical member 49 and this insulating cylinl drical member #t9 holds the disk in place and is termed on the inner surface of the ring of valve 4material l2.
ln the forni'of the invention shown in FIGURE 5 the device is provided with an annular ceramic member This ceramic member has the outer and inner walls 5l and Si?. which are joined by a transverse annular web 53.
The valve material 54 is formed as a block inside ot the ceramic member Si). lt is provided with upper and lower metalized coatings 55. These coatings extend downwardly on the outer side ol the inner annular wail 52 or the ceramic member .f5-ll and also extend transversely across the web 53 as indicated at d6.
ln the form of ythe invention shown in FIGURE 6 the valve material is indicated by the reference character 57 and is relatively thinner than the valve block heretofore described. tis provided with end walls or annular members 53 and is preformed. Metalized coatings are provided for the upper and lower surfaces and are indicated by the reference character S9. An insulating coating 6G formed on the outside of the disk of valve material 57 and the metal coatings 59 extend upwardly and over the upper edge ot the valve material as shown in FlGUlE 6 and is indicated by the reference character 6l. The dimensions of the disk 57 and the dielectric constant ot the valve material used are such as to produce a capacitor of the desired value to function as previously described.
In the form of the invention shown in FIGURE 7 the valve material is a preformed disk or round block and is indicated by the reference character 62. lt is provided with an outer insulating coating 63 and has upper and lower metalized coatings ed which are in contact with the next adjacent disks 65 and eti of the spark gap 67. rlhis spark gap as previously' described is constructed as in FlGURE l and is provided with the inwardly pressed portions which are spaced apart to provide the actual spark gaps as indicated generally by the reference character 67. The resistor rings n are annular and lit between the successive members of the spark gaps. These resistor rings are high resistance members and serve to electrically connect the successive elements of the spark gap so as to have a uniform distribution of potential as previously described.
ln this form of the invention, the parallel capacitors may be readily available types 69 which have leads or pigtails 7@ that are connected to the opposite sides of the valve material. Either a single capacitor as shown may be used, or a plurality of smaller capacitors may be used depending upon the available space inside the main ceramic housing.
The valve material has the well known characteristic of acting as a high resistance member until the voltage impressed thereon reaches a predetermined high value. At this instant the valve material changes suddenly to a low resistance member and allows the rush of surge current to pass. However, when the alternating current voltage again drops to Zero value, the valve material suddenly changes back to a high resistance member and stops further iiow of power current or follow current.
FIGURE 8 shows the time voltage relation for a steep wave front. The line G illustrates the rise in voltage for a steep wave front across the terminals of an arrester which has the spark gaps and valve material in series. The line H represents the voltage rise across the spark gap alone under the above conditions. The ordinate AC represents voltage and the abscissa AB represents the time in microseconds.
Assume the spark gap breaks down at the point F when the voltage across the terminals of the arrester has risen to the point E along the line G.
lt will be seen that under the conditions of a spark gap and valve material in series, that the voltage rise for the steep wave front is rather high, and the arrester and the associated apparatus is subjected to a rather high voltage before breakdown of the spark gap occurs for the usual type of arrester. Under these conditions there is a considerable amount of air ionized adjacent the lightning arrester which may cause complete flashover with destruction of the arrester and possibly of the devices normally protected by the arrester.
By having capacitors in parallel to the valve material, a steep wave front surge will cause the spark gap to break down earlier because of the fact that the valve material is bypassed by the capacitors in parallel as has previously been described.
lt will be seen that in this lightning arrester, the bypassing of the valve material by the capacitors causes essentially all of the applied voltage to be impressed on the spark gaps thus reducing the time to breakdown from AD to AM. The breakdown voltage is simultaneously reduced from the value AL to AK.
On the other hand, for a slowly rising voltage, relatively speaking, with the valve material and spark gaps in series, it will be seen that the voltage rise has to include the voltage across the spark gaps DF, and the voltage across the valve material FE, and therefore the total voltage across the terminals of the lightning arrester is DE and the time is AD. lt will be seen, therefore, that this lightning arrester distinguishes between a sharp wave front surge and a more gradually rising wave front surge.
The term round is intended to include both a solid, circular disk, or an annular member, or any other configuration of this general type, and is not to be specifically interpreted.
Although the invention has been described in considerable detail it is to be understood that the description is intended to be illustrative and not limiting as the invention is to be interpreted only as claimed.
l. A lightning arrester comprising a stack of units connected in series; each unit consisting of a spark gap connected in series with a section of valve material, and a capacitor connected in parallel with the valve material, the capacitor for each unit having a very large capacitance in comparison to the capacitance of the spark gap of the said unit; the spark gap having a relatively low impedance for a steep wave front surge in comparison to the impedance of the spark gap for a gradually rising wave front surge, the sections of Valve material and spark gaps alternating both spatially and connectively in the stack, the valve material being Carborundu-m which is silicon carbide.
2. A lightning arrester comprising a stack of units connected in series; each unit consisting of a spark gap connected in series with a section of valve material, a capacitor connected in parallel with the valve material, and a resistor bridging the spark gap, said resistor having a high ohmic value; the resistors forming a voltage divider for the successive spark gaps in a stack of units; the capacitor for each unit having a very large capacitance in comparison to the capacitance of the spark gap of the said unit; the spark gap having a relatively low impedance for a steep wave front surge in comparison to the impedance of the spark gap for a gradually rising wave front surge, the sections of valve material and spark gaps alternating both spatially and connectively in the stack, the valve material being Carborundum which is silicon carbide.
3. A lightning arrester comprising a series of alternate sections, the iirst of which is a spark gap section and the second of which is a valve material section, the spark gap section consisting of spaced metal plates having inwardly depressed portions which form the electrodes of the spark gaps and having annular peripheral portions surrounding the depressed portions, the valve material sections having annular blocks of valve material having metalized upper and lower coatings electrically connected, respectively, to the lower annular part of an upper spark gap and the upper annular part of a lower spark gap, and a capacitor for each block of valve material, said capacitor having a centrally locate-d dielectric transverse web with upper and lower conducting coatings electrically connected, respectively, to the upper and lower conducting coatings of the surrounding annular valve material, whereby the capacitors are in electrical parallel to their corresponding blocks or" valve material, the sections of valve material and spark gaps alternating both spatially and connectively in the stack, the valve material being Carborundum which is silicon carbide.
4. A lightning arrester comprising a stack of alternate sections of circular valve material disks and spark gaps formed of spaced metal plates having depressed central portions constituting the electrodes of the spark gaps and having surrounding annular peripheral portions electrically connected to the upper and lower faces of the circular valve material disks, and annular capacitors surrounding the valve material disks and each having a web of dielectric material with upper and lower conducting portions electrically connected to the upper and lower faces ofthe circular valve material disks to provide a shunt Capacitor for each circular disk of valve material, the sections of valve material and spark gaps alternating both spatially and connectively in the stack, the valve material being Carborundum which is silicone carbide.
5. A lightning arrester comprising a stack of alternate sections of round valve material blocks and spark gaps formed of spaced metal plates having depressed central portions constituting the electrodes of the spark gaps and having surrounding annular peripheral portions electrically connected to the upper and lower faces of the round valve material blocks, and round capacitors for the valve material blocks and each having a web of dielectric ma terial with upper and lower conducting portions electrically connected to the upper and lower faces of the round valve material blocks to provide a shunt capacitor for each round block of valve material, the sections of valve material and spark gaps alternating both spatially and connectively in the stack, the valve material being Carborundum which is silicon carbide.
References Cited in the le of this patent UNITED STATES PATENTS