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Патент USA US3087104

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April 23, 1963
w. H. NASH
‘3,087,094
LIGHTNING ARRESTER
Filed July 13, 1956
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April 23, 1963
w. H. NASH
3,087,094
LIGHTNING ARRESTER
Filed July 15, 1956
2 Sheets-Sheet 2
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3,ii87,094
Patented Apr. 23, 1963
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3,987,094
sistance spacers are constantly subjected to 60 cycle volt
age, requiring them to be of such construction to also
‘LIGHTNING ARRESTER
William H. Nash, South Milwaukee, Wis., assignor t0
provide adequate tracking distance.
In the case of using the high ohmic resistance, either
McGraw-Edison Company, a corporation of Delaware
linear or non-linear resistances are used. However, there
Filed July 13, 1956, Ser. No. 597,627
5 Claims. (Cl. 317—70)
is a modern tendency to use non-linear resistances as
they tend to equalize the voltages across each gap.
In addition to the above, the gap assemblies of the
present invention contemplates a structure that will op
The present invention relates to lightning arresters, and
particularly pertains to an improved spark-gap assembly
therefor.
erate under surge conditions to provide a non-uniform
Among the objects of the present invention is the pro
vision of an improved spark-gap assembly which .is
adapted to maintain relatively uniform voltage distribu
voltage division, in order that the gaps will sparkover at
a lower value and provide a means of piling up the volt
age on certain of the gaps to ‘accomplish this. When they
do this, they will make up for the inherent impulse ratio
tion across all of the insulating gaps of a series of gaps
during sparkover at relatively low line frequencies, and‘ 15 of the gap alone, which is generally greater than one,
which assembly permits a shift to non-uniform voltage
and tend to push it back to one or less.
distribution under relatively high frequency surge voltage
may be accomplished by use of inherent stray capacity
of the arrester to ground, but this is only partially effective,
conditions to ultimately provide an arrester with an im
pulse ratio of one or slightly less than unity.
In part, this
as it is not especially controlled, nor is it high enough in
capacitive value to upset the resistance grading.
It is a primary object to provide insulating members
The present invention provides an arrester which ac
for a series spark gap assembly which are cooperable
with the spark gap electrodes to establish a predetermined
centuates the non~uniform stray capacity by intentionally
introducing non-uniform capacity. This is accomplished
by adding capacitive elements of relatively high dielectric
capacitance division throughout the electrode assembly
and which are of a selected dielectric constant to provide
a- non-uniform sparkover voltage level between gap elec 25 constants and having a 60K cycle capacitive reactance that
is high enough not to effect the 60‘ cycle voltage grading
trodes under surge conditions.
A more speci?c object of this invention is to provide
of the resistors. However, under frequencies associated
with surges, the capacitive reactance of the elements will
a spark gap assembly which includes a cooperating series
become relatively low so that they will predominate over
connected grading resistor which may be of a helical
con?guration and extending substantially the axial length 30 the resistors which are used for grading purposes. There
of said assembly to provide increased tracking distance.
fore, almost all of the voltage will appear across the gaps
In general, arrester gap requirements include the fol
at the lower dielectric constant spacer end.
The present invention will be more clearly explained
lowing factors:
with attention being given to the following speci?c de
The gap assemblies must maintain relatively high line
frequency sparkover in order that they will not operate 35 scription aided by the drawing, in which:
under normal voltages and surges which are below a level
FIG. 1 is a vertical view, in partial section through a
which might be dangerous to protected equipment.
lightning arrester, which includes a spark-gap assembly
of the present invention;
It is to be noted that throughout the present discussion
line frequency will be represented by 60 cycles per second,
although it ‘will be understood that the improved spark
40
PEG. 2 is- a cross section of the arrester taken on lines
2—2 of FIG. 1, and showing only components of the
gap assembly will function satisfactorily under any normal
spark-gap assembly contained therein;
line frequency supply without departing from the scope of
FIG. 3 is a vertical section taken through the spark
gap assembly along lines 3-3 as indicated on P16. 2;
the invention.
Gap assemblies ordinarily do not operate unless the 45
FIG. 4 is an elevational view, in partial section, of a
sparkover voltage is 11/2 to 2 times the normal system
spacer member of this invention.
FIG. 5 is a representative electrical circuit diagram.
operating voltage rating of the arrester. This rating is
indicating the arrangement of resistors and capacitive ele
selected in such a way that the \arrester will never ex
perience linefrequency voltage to ground in excess of the
ments providing the uniform voltage distribution across
rating even under fault conditions and adverse weather 50 the series gaps at line frequency and the shift to non
uniform voltage distribution ‘at surge frequencies pro
conditions, such as rain or fog. ‘In addition, the arrester
vided by the intentional introduction of non-uniform
should sparkover at a surge crest voltage near the 60
cycle crest sparkover, and preferably slightly below it.
The spark gap assemblies should keep the impulse ratio
capacitive elements plus stray capacities to ground.
at unity or- slightly less than unity. This impulse ratio is
de?ned as the quotient of the sparkover voltage at surge
crest value divided by the sparkover voltage at line fre
modated to a lightning arrester of any type, or to other
suitable equipment, it is shown herein as enclosed in a
Although the spark-gap assembly 19 may be accom
porcelain housing 1 including a series of axially spaced
skirts or petticoats 2, and including metal end caps 3
and 4. The porcelain housing 1 is sealed at the end by
In order that the gap will perform the above functions,
it should be designed so that the 60‘ cycle voltage will be 60 means of compressing and retaining a heavy resilient
gasket 5 between the housing and a conducting cap 6,
divided uniformly among the various gaps, or in propor
which is spun in place over the annular ?ange portion 7
tion to gap spacing; this voltage must be so divided, both
of the housing while the assembly is under pressure in
when the arrester exterior is dry or when Wet, such as in
an hydraulic press. The end caps are held in place ad~
rainy weather. This, in general, requires that the gap
dimension be voltage graded. The grading is usually 65 jacent the housing by means of cement 8 poured between
the end cap and the housing.
accomplished either by shunting the gaps with a high
The electric line 9 to be protected by the lightning
ohmic value resistance, or capacitively by using high re
arrester is connected to the conducting end cap 3 by
actance capacitive ?laments. In general, the use of re
sistance elements has the ‘advantage at 60‘ cycle voltage
means of conventional connectors (not shown) received
because the stray capacities introduced by moisture on 70 in an aperture in one of the integral laterally project
ing cars 10. Connection with ground G may be madev
the exterior of the arrester housing do not tend to upset
in like manner with the projecting ear 11 of the con
this grading as much as capacitive type grading. The re
quency, such as 60 cycles per second.
3,087,094
3
4
ducting end cap
Contained within the housing 1 is a
conventional valve material 15 of suitable quantity and
24. As viewed in PEG. 1, it will be noted that the assem
bly 19 is positioned in the housing 1 with the contact
generally comprising valve blocks or solid mass of a
negative resistance material, such as silicon carbide.
It is to be noted, that if it is desired, the arrester may
contain spark-gap assemblies 19 at one end or at both
plate 36 being positioned in electrical engagement with
the valve material 15. ‘From FIG. 1, it will be seen that
the upper end of the spark gap assembly is in electrical
and mechanical contact with the helical spring 40, the
ends thereof, the latter having the valve material 15
opposite end of which spring engages an embossment all
interposed therebetween.
The improved spark-gap assembly is clearly shown in
impressed in the conducting cap 6. The conducting cap
6 is also in mechanical and electrical engagement with
the relatively enlarged views of FIGS. 2 and 3, wherein
the assembly 19 comprises an are or spark-gap pile which
the end cap 3. During the process of spinning on the
cap 6, as the entire unit is held in compression, the assem
comprises a plurality of spaced, plate-like electrodes 20,
bly 1.9 is maintained in relative operating position by
the component cooperating parts.
and each electrode is substantially identical to each of
Attention is now directed to the insulating spacer mem
the others. Each electrode is formed from sheet mate
rial, and each is formed that when the electrodes are 15 bers 30, an example of which is particularly shown in
FIG. 4. The present invention contemplates the use of
properly assembled, there will be found one or more
insulating spacer members of relatively high dielectric
are gaps 21 (see FIG. 3) between each two- adjacent
electrodes.
constants and differing from one another in those con
As illustrated in FIG. 2, the electrodes 20 may be
stants, with insulating members having the relatively
provided with a radially extending mounting portion 22 20 lower dielectric constant preferably being located at the
having an aperture for receiving a machine screw 23.
end adjacent the valve material 1.5. As the spacers are
For further support, each of the various electrodes are
positioned relatively remote from the said end, the di
arranged in alternate relationship on a rod-like mem
ber or core 24 preferably positioned in a centra open
electric constant of each is preferably of relatively higher
value. For instance, the spacers may be made of titanate
ing 25 in each electrode. The member 24 is of insulat 25 ceramic compositions having dielectric constants in the
ing material, such as steatite which, for the present
order of 5,000 for the spacer 30,, (see FIG. 3), which
purpose, has a ‘relatively low dielectric constant of about
4 to 7 above unity.
decreases in value to a constant of approximately 100 at
the spacer 3%.
Each electrode consists of a disk, preferably circular,
However, as a practical matter, from a manufacturing
including a plurality of embossments or impressions,
cost standpoint, it is preferable to provide the spacers with
which are formed, as viewed in FIGS. 2 and 3, with
the ?rst few sets adjacent the valve material being of the
three depressions 26 and three projections 27 on each
high value of, for instance, approximately 100 and the
face of the disk. It will be noted from FIG. 2 that the
remaining remotely relative spacers being at a value of,
depression on one face is preferably diametrically op
for instance, 5,000. Obviously, if it is expeditious, the
posed to the projection on that face. The number of im 35 spacers may be continually decreasing in dielectric con
pressions per disk may vary, but six have been found
stant, or may include various intermediate values as cost
to be a convenient number, especially for the arrange
permits.
ment of the grading resistors, as will hereinafter be de
It will be apparent from the above description that the
scribed. When the electrodes are assembled in superim
present spark gap assembly will operate to provide rela
posed relation, they are so related that the projections on 40 tively uniform sparkover between gaps at frequencies ap
the face of one disk will be adjacent or opposite those
proximating line frequencies, and will provide desirable
of the adjacent disk to form the spaced spark gaps 21
non-uniformity in sparkover of the gaps during surge con
therebetween. The depressions on the said face of the
ditions.
one disk will be opposite those on the adjacent disk to
As an example, assuming two sections of spacers 30;
form recesses for retaining the insulating spacer mem
for instance, spacers 30,, being of a material having a
bers 30 therebetween.
dielectric constant of 5,000 and spacers 30b of a dielectric
It is also to be noted that grading resistance spacers
constant of approximately 500, the capacitive reactance
35 have also been provided in series relationship with
of 60 cycle current might approximate 10 and 100 times,
the spaced apart gaps along the circumference of the
respectively, of the normal ohmic value of the resistors
electrodes. A preferred form of the resistors provide 50 35. However, at surge, which might have as a primary
sectoral members arranged relative to one another to
component a frequency of approximately 60,000 cycles
provide a helical path circumjacent to the electrode disks
per second, the capacitive reactance of the‘ respective
throughout the entire length of the spark-gap assembly
spacers would be divided by 1,000 (60,000/60) or 0.01
19. This is accomplished by arranging the resistors 35
to 0.1 times, respectively, of the ohmic value of the re
in juxtaposed relationship with each of the ends being 55 sistors 35. Thus, the capacitive elements will determine
in overlap arrangement and joined by the machine screw
the grading, in addition to the minor effect provided by
23.
It will be apparent that it is preferred to arrange alter
nately spaced electrodes 20 with their respective mount
stray capacitance-to-ground.
It will also be apparent that the desired end result
may be obtained with uniform capacitive grading cou
ing ears 22 spaced substantially 120° relative to one 60 pled with non-uniform gap spacing with resistor grading
another to provide a convenient assembly for combined
being in relation to the gap spacing. The resistor volt
mounting with the resistor segments 35 and the respec
age division would be selected to be in proportion to the
tive mounting screws 23.
gap spacing provided by varying length capacitive spacers.
Although, the resistors have been shown and de
Accordingly, the present arrester will accentuate the
scribed as being in helical con?guration circumjacent 65 non-uniform stray electrostatic capacities, by intention
to the various spark gaps, it will be apparent that other
ally introducing additional non-uniform capacity. At 60
conventional ring type resistors (not shown) or cylindri
cycles, or line frequency, the capacitive reactance of the
cal resistor members substituted for one or more of the
added spacers 30 will be high enough that they do not
spacer members 30 (not shown) may be substituted there—
affect the 60 cycle voltage grading provided by the resis
‘for without departing from the scope of this invention. 70 tors 35. But, under the frequencies associated with
Such resistors may be voltage dependent or of a simple
surges, the capacitive reactance of the elements Will be
ohmic variety.
'
The entire assembly 19 is positioned to be seated on a
come low enough that they will predominate over the re
sistors 35. Accordingly, almost all of the voltage will
contact plate 36 and is retained in position means of
appear across the gaps at the end of the spark gap assem
the machine screw 37 threadingly engaging the core 75 bly incorporating the lower dielectric spacers, in this
3,087,094
6
5.
supporting said staggered helical con?guration circum
case 30b. After the sparkover has occurred, the volt
age will tend to distribute itself relatively uniformly
throughout the various gaps 21 of the assembly.
jacent to said spark gap surface throughout the axial
length of said assembly.
2. In a lightning arrester, a spark gap assembly com
The above ‘described operation of the various com
ponents will be further clari?ed when studied in connec
tion with the diagram of FIG. 5. The circuit through
prising a plurality of spaced electrode plates de?ning op
posed uniform spark gap surfaces, each of said electrode
plates further de?ning an opening therein, an insulating
rod traversing the said opening in each of said electrodes,
a plurality of uniform in size insulating electrode spacing
the gap assembly, when used in combination with a valve
type'arrester element, is shown in the diagram with the
symbol C representing the capacitive values provided by
the various spacer members 30- and their respective elec 10 members being received and retained between each of
said electrode plates and providing-Ia means of establish
trodes, plus any-stray capacities to ground. It will be
understood that the intentionally added capacitance pro
ing said predetermined gap spacing between said spark
vided‘ by the preselected spacer members, will predominate
gap surfaces, said support members each being of an
insulating material having a predetermined dielectric
in any case. The symbol- R relates to the respective re
sistance values provided by the resistors 35, whereas 15 constant and being positioned relative to one another in
the symbol G represent each of the repective gap di
mensions de?ned by the electrodes 20. RV relates to the
non-linear resistance of the valve material. Although
the resistance of the valve material is indicated for pur
poses of explanation, it has very little bearing on the 20
said stacked relationship to provide a gradual variation
in dielectric values in those members positioned remote
ly relative to one end of said assembly, and a plurality
of voltage dependent grading resistors comprising a se
ries of generally arcuate segments, the ends of each of
voltage division throughout the gap ‘assembly.
said segments being supported by and electrically con
For purposes of explanation, in the particular case, it
is assumed that the capacitance is graded in gradual steps
nected to alternate ones of said electrode plates and said
segments joining one another in end to end relationship
with the ends of ‘adjacent segments in juxtaposed endwise
Assuming that R1=R2=R3=R4:R5, and that each of 25 overlapping relationship to provide a staggered helical
con?guration circumjacent to said spark gap surfaces
these values denoted by RH is very much greater than
throughout the axial length of said assembly.
RV; and that C1>C2>C3>C4>C5; and further assuming
3. In a lightning arrester, a spark gap assembly com
that Cn is never equal to Cn—1:
prising a plurality of spaced electrode plates de?ning op
It will then be apparent that at line frequency, such as
60 cycles per second, any one of the resistance values 30 posed spark gap surfaces, a plurality of uniform in size
insulating electrode spacing members being received and
Rn will be much less than the quotient of
throughout the assembly length.
retained between each of said electrode plates and pro
viding a means of establishing said predetermined gap
1r(60*) (C11)
spacing between said spark gap surfaces, and a plurality
It will also be apparent that at the relatively high 35 of grading resistors comprising a series of generally arcu
ate segments, the ends of each of said segments being
surge frequencies denoted by in, that here Rn will be
supported by and electrically connected to alternate ones
very much greater than the quotient of
of said electrode plates and said segments joining one
another in end to end relationship with the ends of ad
l
40
jacent segments in juxtaposed endwise overlapping rela
tionship to provide a staggered helical con?guration cir
cumjacent to said spark gap surfaces throughout the axial
quotient at line frequency, it will be apparent that the
length of said assembly.
voltage division across the spark gap assembly will be
4. In a lightning arrester, a spark gap assembly, com
accomplished by the various resistors, whereas at the
higher surge frequencies, the capacitive reactance will 45 prising a plurality of stacked electrode plates, each of
said plates being formed with a mounting arm portion and
be smaller and thus the voltage division will be deter
Inasmuch as Rn is very much smaller than the same
a plurality of concavo-convex portions arranged to face
alternately in opposed directions to provide a series of
It will also be noted that the preferred helical arrange
opposed convex faces and a series of opposed concave
ment of the resistors 35 will greatly increase the track
ing distance providing an extremely long resistor creepage 50 faces in staggered relationship along the axial length of
the electrode stack, said mounting arm portions disposed
resistance to prevent ?ashover. Thus, the 60 cycle volt
to extend laterally from said stack with mounting arm
age distribution is primarily controlled by the grading
portion of adjacent ones of said electrode plates being
resistor ‘and will be uniform. The overall effect of the
relatively spaced around the periphery of said stack, a
construction will consequently provide a desirable low
mined by capacitance.
impulse ratio.
I claim as my invention:
1. In a lightning arrester, a spark gap assembly com
55 plurality of uniform in size insulating electrode spacing
members being received and retained between each of said
opposed concave faces and further providing a means of
establishing a predetermined uniform gap distance be
tween said opposed convex faces, and a plurality of grad
posed spark gap surfaces, a plurality of uniform in size
insulating electrode spacing members being received and 60 ing resistors comprising a series of generally arcuate seg
ments, said segments joining one another in end to end
retained between each of said electrode plates and pro
relationship with the ends of adjacent segments in juxta
viding a means of establishing said predetermined gap
prising a plurality of spaced electrode plates de?ning op
spacing between said spark gap surfaces, said support
members each being of an insulating material having a
posed endwise overlapping relationship and supported
on and electrically connected to said mounting arms to
predetermined dielectric constant and being positioned 65 provide a staggered helical con?guration circumjacent
relative to one another in said stacked relationship to
provide a gradual variation in dielectric values in those
members positioned remotely relative to one end of said
assembly, and a plurality of grading resistors comprising
to said concave-convex portions throughout the axial
length of said assembly.
5. In a lightning arrester, a spark gap assembly com
prising a plurality of stacked electrode plates, each of said
plates being formed with a mounting arm portion and a
plurality of concavo-convex portions arranged to face
alternately in opposed directions to provide a series of
a series of generally arcuate segments, means electrically
connecting each of said segments to respective ones of
said electrode plates, said segments joining one another in
opposed convex faces and a series of opposed concave
end to end relationship with the ends of adjacent seg
faces in staggered relationship along the axial length of
ments in juxtaposed endwise overlapping relationship to
provide a staggered helical con?guration, and means for 75 the electrode stack, said mounting arm portions dis
3,087,094
8
posed to extend laterally from said stack with mounting
arm portions of adjacent ones of said electrode plates
necting said segments to said electrode plates and support
ing said segments to provide a staggered helical con?gura
being relatively spaced around the periphery of said
rtio-n circumjacent
stack, each of said electrode plates further de?ning an
opening therein, an insulating rod traversing the said
throughout the axial length of said assembly.
opening in each of said electrodes, a plurality of uniform
in size insulating electrode spacing members being re
ceived and retained between each of said opposed concave
faces and further providing a ‘means of establishing a pre
determined gap distance between said opposed convex 10
faces, said support members each being of an insulating
material having a predetermined dielectric constant and
being positioned relative to one another in said stacked
relationship to provide a gradual variation in dielectric
values in those members positioned remotely relative to 15
one end of said stacked electrode plates, and a plurality
of voltage dependent grading resistors comprising a series
of generally arcuate segments, said segments joining one
another in end to end relationship with the ends of ad
jacent segments in juxtaposed endwise overlapping rela 20
tionship with one of said mounting arm portions disposed
therebetween, said mounting arm portions electrically con
to
said concavo—convex portions
References Qited in the ?le of this patent
UNITED STATES PATENTS
1,902,510
2,151,559
McEachron __________ __ Mar. 21, 1933
McEachron __________ __ Mar. 21, 1939
2,324,108
2,611,108
2,615,145
Pyk _________________ __ July 13, 1943
Rydbeck _____________ __ Sept. 16, 1952
Rydbeck _____________ __ Oct. 21, 1952
2,640,096
Kalb ________________ __ May 26, 1953
2,659,842
2,670,398
Teszner _____________ __ Nov. 17, 1953
Sheadel ______________ __ Feb. 23, 1954
FOREIGN PATENTS
‘698,352
730,709
847,379
215,001
Great Britain _________ __
Great Britain _________ __
France ______________ __
Switzerland __________ __
Oct. 14, 1953
May 25, 1955
June 26, 1939
Aug. 16, 1941
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