US3091721A - Lightning arrester and gap unit with capacitive grading - Google Patents

Description

May 28, 1963 A. G. YOST 3, 7

LIGHTNING ARRESTER AND GAP UNIT WITH CAPACITIVE GRADING Filed Dec. 7, 1954 HIGH HIGH DIELECTRIC RESISTANCE INVENTOR. Arnold G. Yosf.

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AGENT United States Patent LIGHTNING ARRESTER AND GAP UNIT WITH CAPACITEVE GRADliNG Arnold G. Yost, Barberton, Ohio, assignor to The Ohio Brass Company, Mansfield, Ohio, a corporation of New Jersey Filed Dec. 7, 1954, Ser. No. 473,653 tIlaims. (Cl. 317--70) This invention relates to protective devices such as lightning arresters and more particularly to improved grading means for lightning arresters.

A general object of the invention is to improve the impulse ratio of lightning arresters for electric power transmission and distribution systems.

Another object of the invention is to provide non-uniform grading in lightning arresters which will function to produce a high degree of grading between the gaps for stresses due to power line voltages and which will concentrate impulse voltages across a few of the gaps to facilitate the discharge thereof.

Still another object of the invention is to provide an improved lightning arrester in which the aforementioned object is accomplished by a relatively simple gap structure which may be manufactured economically and with a relatively small number of component parts.

One type of lightning arrester, which is particularly adapted to be utilized in electric power transmission and distribution systems and the like, is disclosed in US. Patent 2,640,096, issued May 26, 1953, to I. W. Kalb, and incorporates a gap unit which comprises a column of disc shaped electrode members. These electrode members are separated by a plurality of cylindrical members which are spaced about the electrode members and are retained between each member and the adjacent member by opposed recesses in the electrode members. The separating members are formed of high resistance material to provide a resistance grading arrangement for the spark gap unit.

It is highly desirable that the grading function of the lightning arrester be accomplished in a manner such that .a uniform grading is accomplished for the stresses which are produced in the gaps by line voltages. Particularly, the stresses produced by the line voltage under ordinary stable conditions and the stresses due to transients, such as the recovery voltage transient produced by the power follow current upon the termination of that current, must be uniformly graded to increase the operating voltage of the arrester. However, in order that the intended function of the arrester be accomplished, an opposite result is necessary for stresses which are produced by voltages due to lightning and the like, in order to facilitate the breakdown of the gaps and prevent undue impulse voltage buildup in the power system.

I have found that this result can be accomplished by the use of an arrangement which amounts toa combination of linear resistive grading and capacitive grading. That is, by replacing one of the gap separating members of the arrester of the patent referred to above by a member of the same physical dimensions but formed of a material having a very high dielectric constant, e.g. in the order of 1200, I can effectively obtain a capacitance between the electrode members having a magnitude such that the stray capacitance, e.g. due to the inherent capacity of the electrode members, and that due to the inherent dielectric effect of the resistance separating members, is overcome. By arranging the spark gap unit with a capacitor separating member between each of alternate pairs of electrode members, I am able to obtain a capacitive grading efiect which greatly reduces the impulse break-down voltage while having very little eifect upon the resistance grading, whose effect is predominant insofar as the stresses placed on the gap by the line voltages is concerned.

The invention, together with further objects, features and advantages thereof will be more clearly apparent on consideration of the following detailed specification and claims taken in connection with the drawings:

FIG. 1 is an elevation view of a particular section of the arrester of the invention;

FIG. 2 is a plan view of the spark gap unit taken in the direction 22 in FIG. 1;

FIG. 3 is an elevation view showing the relation of the spark gap electrodes in the arrester and the arrangement of the separating members of the invention; and

FIG. 4 is a schematic diagram illustrating the grading arrangement of the arrester of the invention.

Referring now to FIG. 1, the arrester 10 of the invention comprises a cylindrical porcelain member 11 which has a hollow bore 12 for enclosing the operative elements of the arrester. The arrester includes a plurality of valve elements 13 and 14, at the upper and lower ends of the arrester respectively, a spark gap assembly 15 and a spring 16 for holding the valve elements and the spark gap assembly in contact with each other and with the ends of the housing. The housing incorporates two metallic end plates 17 and 18 which serve as supports for the arrester and as terminals for connecting the arrester to the power line or other external circuit for which the arrester is employed as a protective device and to ground.

Each of the valve elements 13 and 14 comprises a substantially homogeneous block of silicon carbide or the like and has two fiat metallic plates at the ends of the block. Thus, the several valve elements and the gap assembly are connected in series with each other and to the end plates by the engagement of the metallic plates. The metallic plate at the bottom end of the lowermost valve block is engaged with a member which is connected to the end plate 18, the lower most electrode member of the spark gap unit 15 with an annular member 19 and the plate 20 of the upper one of the lower valve blocks 14,

the plate 21 with the member 22 which is engaged with the spring 16, and the plate 23 with the elastic member 24 which in turn bears upon the spring plate 25 associated with the end plate 17. The spring 16 bears upon the plate 26 which holds the annular member 26a against the uppermost electrode member of the spark gap unit 15, and maintains an adequate electrical connection between the several valve blocks, the components of the spark gap assembly and the end plates. The spring 16 is shunted by a conductor 27.

The sealing arrangement between the plates 17 and 18 and the housing 11, as well as the frangible diaphragm incorporated in the plate 18, is described in detail in US. Patent 2,670,398, issued February 23, 1954 to John M. Sheadel.

The spark gap assembly 15 comprises a column of spark gap electrodes 30 which are positioned by a ceramic rod 31 which extends longitudinally through the electrode members. The electrode members are maintained in vertically spaced relationship by appropriate separating members 32 which are positioned about the rod 31 as hereinafter described.

Referring now to FIGS. 2 and 3 each of the gap electrodes Bil comprises a disc-like member of hard brass having a plurality of dished projections formed therein. The projections extend alternately in opposite directions from the body of the disc, e.g. the projections 34, 35 and 36 extend upwardly from the body of the member 33 while the projections 37, 38 and 39 extend downwardly from the body of that member.

The projecting surfaces of the projections constitute the arc surfaces, as e.g. the surfaces of projections 34, 35 and 36, which appear in FIG. 2, form are gaps with the associated projections of an adjacent electrode, while the depressed portions of the projections form recesses for holding the separating members 32, e.g. in FIG. 2 the projections 37, 38 and 39 form recesses for holding the separating members 49, 41 and 42.

Referring now to FIG. 3 the partial view of the gap assembly 15 includes the electrodes 43-, 44, 45, 46, 47, 48 and 49, to illustrate particularly the arrangement of the electrodes and the separating members according to the present invention. As there shown, each two adjacent electrodes form a gap unit and every electrode is a part of two adjoining gap units. Thus, in FIG. 3 the electrode 44 forms a gap unit with the electrode 43 and another gap unit with the electrode 45.

The various separating members are positioned on alternate sides of each electrode, proceeding about the rod 31, because of the arrangement of the projections referred to above. The arrangement is such that each projection acts as a recess for a separating member on one side of the electrode and as one part of an arc gap on the opposite side of the member so that the column of electrode members 30 with the interdispersed separating members forms six columns in which the separating members alternate with the arc gaps. Thus, in FIG. 3 the projections of the electrodes 43-49 corresponding to the projection 34 of the electrode 30 in FIG. 2, form the arc gaps t 51 and 52 and hold the separating members 53, 54 and 55. Similarly, the projections of electrodes 43-49, corresponding to the projection 38 of electrode 30 in FIG. 2, form the arc gaps 56, 57 and 58 and hold the separating members 59, 6t) and 61. It will be apparent that each gap unit incorporate three are gaps and three separating members.

At least one of the separating members 32 of each gap unit is formed of a high resistance material such as carbon and functions as a grading resistor for the gap unit. The grading resistors of the gap units thus produce a linear resistive grading arrangement for the several gap units of the gap assembly 15, and cooperate with the resistors of the valve blocks, referred to above to produce a resistance grading for the several elements of the arrester. In a preferred embodiment of the invention two of the separating resistors at each gap unit would be so formed of resistive material. The considerations atfecting the design of such resistive separating members is known in the art.

In accordance with the invention, at least one of the separating members of each of alternate gap units, is formed of a material having a very high dielectric constant, while the corresponding separating members of the intervening gap units are termed of a material having a relatively low dielectric constant. Thus, in FIG. 3 the eparating members 59, 60* and 61 are formed of high dielectric material while separating members 53, 54 and 55 are formed of porcelain. 'I'he disposition of the various kinds of separating members is, of course, not critical and the dielectric members 59, 6t and 61 and porcelain members 53, 5- and 55 are shown at diametrically opposite sides of the rod 31 only for convenience of illustration.

The separating members 59, 6d and 61 are each formed of material having a very high dielectric constant such, e.g. as a barium titanate and magnesium zirconate ceramic having a dielectric constant in the order of 1200. Such high dielectric constant materials are known in the art as ferro-electric materials and may take several forms, the principal forms being the barium titanate ceramics, either alone or with magnesium zirconate or lead or calcium titanate.

The invention is not, however, limited to the use of such materials but may be practiced by using any dielectric material having adequate mechanical strength and a dielectric constant such that the capacitance between the electrodes of the gap unit produced by the dielectric separating member is in the order of several times the capacitance of the inherent capacity of the plates and the capacitance of the dielectric constant of the resistive separating members. For example, the separating members may be formed of titanium dioxide which has a dielectric constant in the order of 80.

The principal criterion is that of design, e.g. the frequency at :which the capacitive grading is to become substantially effective to produce unbalanced stresses in the gap unit. With the ceramic separating member referred to abovehaving a dielectric constant in the order of 1000 to l200the capacitive grading becomes effective at frequencies in excess of 5000 cycles, e.g. at trequencies in excess of those of the principal components of the power recovery transients.

The separating members 53, 54 and 55 may comprise a ceramic body of porcelain or the like having the usual relatively low dielectric constant, e.g. in the order of 6-8. These members serve primarily as spacers for maintaining the mechanical configuration of the gap assembly.

The mode of operation of the arrester of the invention may be understood by reference to FIG. 4, wherein there is shown a schematic diagram of two successive gap units such as the units formed by the electrodes 43, 44 and 45 of FIG. 3. The upper portion of the schematic diagram, designated generally at 65, represents a gap unit having a porcelain spacer, such as the gap ruiit formed by the electrodes 43 and 44. The gap unit, therefore, includes only the grading resistors 66 and 67 and the arc gap 68, the effect of the capacitance due to the inherent capacity of the electrodes and the capacity due to the separating members being neglected.

The lower part of the schematic diagram, designated generally at 69, represents the gap unit formed by two electrodes having a high dielectric separating member, such as the electrodes 44 and 45, and includes the grading resistors 70 and 71, the capacitor 72 and the arc gap 73. At power line frequencies the impedance of the capacitor 72 is sufiiciently great, as compared with the resistance of the grading resistors, so that the grading resistors determine the voltage division as between the arc gaps 68 and 73 and the voltage across those gaps is substantially equal. As a result of the equal voltage division, no one of the gaps will tend to break down before the remaining gaps break down and the arrester will operate at a relatively high line voltage. Inasmuch as the impedance of the capacitor 72 is still relatively high, as compared with resistance of the grading resistors, at frequencies up to 5000 cycles or thereabouts, the resistive grading effect is predominant and the arrester is stable for line transients which are due to the terminations of power follow up current after discharge.

However, any impulses having very steep wave front, such as those due to lightning voltages, are impressed upon the arrester, the capacitor exhibits a relatively low imped ance, so that it appears as an effective shunt across the gap 73 and the major part of the voltage appears across the gap 68. Gap 68 breaks down, thus producing a partial discharge of the capacitor 72, and causes the voltage across the gap 73 to rise sharply, whereupon the gap 73 breaks down and the impulse is discharged to ground. As a result of the non-uniform impedance frequency characteristics of the gap units embodying the capacitor 72, the arrester breaks down very readily for impulses having a steep wave front so that a high degree of protection is obtained for the power line or system to which the arrester is connected.

The valve elements 13 and 14 are non-linear resistors and connected in series with the gap assembly 15 so as to provide a low resistance path to ground for the relatively high lightning voltages and a relatively high resistance path for the power line voltages.

It is to be understood that the resistors 66 and 70 and 67 and 71 need not necessarily be linear resistors but nonlinear resistors, thus either or both of the series circuit for which these associated resistors form parts may be constructed with non-linear resistors in certain embodiments of the invention.

The gap assembly 15 embodies suitable ionizing means including the tips 75 which bear upon the rod 31 after the teachings of US. Patent 2,615,145, issued October 21, 1952, to G. Rydbeck. Such an ionizing arrangement is, however, not essential to the practice of the present invention.

It is to be understood that the foregoing description is not intended to restrict the scope of the invention and that various rearrangements of parts and modifications of the design may be utilized to give eifect to a liberal interpretation to the claims as herein set forth.

I claim:

1. A spark gap for lightning arresters and the like comprising a plurality of metal discs stacked one above the other, each disc having a plurality of peripherally arranged projections extending alternately in one direction and then in the other from the body of the disc and forming on the one side a recess arranged to cooperate with a similar recess in a next adjacent disc in one direction and on the other side an arc face for cooperating with a similar arc face on a next adjacent disc in the other direction, and columnar spacers of resistive material received in opposed recesses between pairs of adjacent discs of equal resistance as between each pair of all of the pairs of discs to form a uniform grading arrangement between the discs for voltages of line frequency and columnar spacers each comprising a solid cylindrical body of high dielectric material received in opposed recesses of at least one but not all of the pairs of discs, the said discs of the last named pairs of discs having a capacitance at least several times the capacitance of the remaining pairs of discs, all for decreasing the proportion of voltages across the pairs of discs having spacers of high dielectric material and increasing the voltage across the remaining pairs of discs for voltages having steep wave fronts.

2. The invention in accordance with claim 1 and having columnar spacers of low dielectric material received in opposed recesses of pairs of discs which are not provided with spacers of high dielectric material and the said spacers of high dielectric material having a dielectric constant in the order of ten times the dielectric constan of the :said spacers of loW dielectric material.

3. An arcing device for lightning arresters and the like comprising a plurality of metal electrodes stacked one above the other, each electrode having a generally fiat body with a plurality of peripherally arranged projections extending alternately in one direction and then in the other from the said body and forming on the one side thereof an arc face for cooperating with a similar arc face on a next adjacent electrode in the other direction to constitute an arc gap and forming on the other side a recess opposed to a similar recess in a next adjacent electrode in the other direction, and columnar spacers of resistive material received in the said opposed recesses between pairs of adjacent electrodes, the said spacers having equal resistances as between the pairs of electrodes for dividing voltages equally between the electrodes and columnar spacers of dielectric material received in opposed recesses of the pairs of electrodes, each of the same length as the said spacers of resistive materials associated therewith for maintaining the stacked configuration of the said electrodes, and the last named spacer of at least one pair but not all of the pairs of electrodes being formed of a material having a high dielectric constant to form with the pair of electrodes thereof a capacitor in shunt with the resistances and gaps of that pair of electrodes and a capacitance between the said electrodes at least several times greater than the capacity between the remaining pairs of electrodes, such that the arc-over voltage of the remaining pains of electrodes for voltages having steep wave fronts is reduced thereby.

4. The invention in accordance with claim 3 in which the dielectric constant of the material of the spacer having a high dielectric constant is greater than about ten times the dielectric constant of the material of the remaining spacers.

5. A lightning arrester comprising an elongated tubular housing with a terminal at each end thereof, and a stack of arrester elements therein, in series contacting relationship with each other and with the said terminals with spring means for compressively holding the said elements in said contacting relationship, the said stack of arrester elements comprising valve blocks and a plurality of metal electrodes stacked one above the other, each electrode having a generally flat body with a plurality of peripherally arranged projections extending alternately in one direction and then in the other from the said body and forming on the one side thereof an arc face for cooperating with a similar arc face on a next adjacent electrode in the other direction to constitute an arc gap and forming on the other side a recess opposed to a similar recess in a next adjacent electrode in the other direction, and columnar spacers of resistive material received in the said opposed recesses between pairs of adjacent electrodes, the said spacers having equal resistances as between the pairs of electrodes for dividing voltages equally between the electrodes, that improvement which comprises a columnar spacer of dielectric material received in opposed recesses of each of the pairs of electrodes, each of the same length as the said spacers of resistive material associated therewith for maintaining the stacked configuration of the said electrodes, and the last named spacer of at least one pair but not all of the pairs of electrodes being formed of a material having a high dielectric constant to form with the pair of electrodes thereof a capacitor in shunt with the resistances and gaps of that pair of electrodes and a capacitance between the said electrodes at least several times greater than the capacity between the remaining pairs of electrodes, such that the arc-over voltage of the remaining pairs of electrodes for voltages having steep wave fronts is reduced thereby.

6. The invention in accordance with claim 1, the said spacers of high dielectric ceramic material comprising a material having a dielectric constant in the order of 1000.

7. The invention in accordance with claim 1, the said spacers of high dielectric material comprising a ferroelectric ceramic material having the same dimensions as the said spacers of resistive material.

8. The invention in accordance with claim. 6, the said ferro-electric material comprising a ceramic including barium titanate and a small percentage of magnesium zirconate.

9. The invention in accordance with claim -1, all of the separating members having the same cross sectional area and length and the resistive separating members having a dielectric constant in the order of 50 and the dielectric separating member having a dielectric constant greater than that of the resistive separating members by and non-uniform capacitive grading.

References Cited in the file of this patent UNITED STATES PATENTS McEachron Mar. 21, 1933 Pyk July 13, 1943 Teszner May 22, 1951 Rydbeck Sept. 16, 1952 8: Rydbeck Oct. 21, 1952 Vogelsanger Nov. 18, 1952 Kalb May 26-, 1953 Teszner Nov. 17, 1953 Sheadel Feb. 23, 1954 FOREIGN PATENTS Switzerland Aug. 16, 1941 Great Britain Sept. 14, 1953 France June 26, 1939

Claims (1)

1. A SPARK GAP FOR LIGHTNING ARRESTERS AND THE LIKE COMPRISING A PLURALITY OF METAL DISCS STACKED ONE ABOVE THE OTHER, EACH DISC HAVING A PLURALITY OF PERIPHERALLY ARRANGED PROJECTIONS EXTENDING ALTERNATELY IN ONE DIRECTION AND THEN IN THE OTHER FROM THE BODY OF THE DISC AND FORMING ON THE ONE SIDE A RECESS ARRANGED TO COOPERATE WITH A SIMILAR RECESS IN A NEXT ADJACENT DISC IN ONE DIRECTION AND ON THE OTHER SIDE AN ARC FACE FOR COOPERATING WITH A SIMILAR ARC FACE ON A NEXT ADJACENT DISC IN THE OTHER DIRECTION, AND COLUMNAR SPACERS OF RESISTIVE MATERIAL RECEIVED IN OPPOSED RECESSES BETWEEN PAIRS OF ADJACENT DISC OF EQUAL RESISTANCE AS BETWEEN EACH PAIR OF ALL OF THE PAIRS OF DISCS TO FORM A UNIFORM GRADING ARRANGEMENT BETWEEN THE DISCS FOR VOLTAGES OF LINE FREQUENCY AND COLUMNAR SPACERS EACH COMPRISING A SOLID CYLINDRICAL BODY OF HIGH DIELECTRIC MATERIAL RECEIVED IN OPPOSED RECESSES OF AT LEAST ONE BUT NOT ALL OF THE PAIRS OF DISCS, THE SAID DISCS OF THE

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