Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION 11~4~3'~
The present invention relates to a lightning arrester
or a system for protecting against a lightning discharge an
aerial electric power line supported above the ground by a
tower.
It is well known that aerial electric power lines,
supported above the ground by a tower, are subject to damage
when struck by lightning. One known system for protecting
such aerial electric power lines from lightning is to stretch
a protection conductor wire along the towers supp~rting the
aerial electric power lines, at a position above the aerial
electric power lines, with such protection conducting wire
being grounded by means of a ground wire or by one or more of
the towers, if the towers are metal towers. The purpose of
such protection conducting wire is to receive the lightning
discharge and to conduct the discharge to the earth.
However, such known system for protecting the aerial
electric power lines suffers from an inherent disadvantage.
Specifically, it is not possible to avoid the risk of a
secondary arc discharge between the tower and one or more of
the aerial electric power lines. That is, as the lightning
discharge is passed downwardly along the tower from the
protection conducting wire to ground, there often occurs a
secondary arc ~etween the tower or ground wire and one or more
~f the electric power lines. Such secondary arc discharge
damages the power networ~ of the electric power lines, and
t~us the protection offered by the upper protection conducting
wire is incomplete.
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Furthermore, it is known from applicant's previous
U.S. Patent No. 3,919,956 to protect ships or buildings by
means of a coaxial shielded cable which is connected to a
lightning rod and which is grounded.
SUMMARY ` OF THE INVENTION ~ 4t;37
With the above discussion in mind, it is the principal
object of the present invention to provide an improved lightning
arrester system or system from protecting against a lightning
'discharge aerial electric power lines supported abo~e the ground
by towers.
It is a further object of the present invention to
provide such a system which for practical purposes avoids the
risk, not only of lightning striking the electric power lines,
but which also avoids the risk of a secondary arc discharge
between the system and the electric power lines.
These objects are achieved in accordance with the
present invention by the provision of a shielded conductor
including a central conductor core, an outer conducting sheath,
and an insulating layer between the core and the sheath. The
upper end of the core is electrically connected to a conducting
member adjacent the top of the tower which supports the electric
power lines above the ground. Both the lower end of the core
and the lower end of the sheath are grounded. The sheath
extends from substantially the area of connection of the core to
the conducting member to a position bel~w the power line, with
the lower end of the sheath being spaced below the power line at
least by a distance sufficient to exclude the formation of a
secondary arc discharge between the core and the power line.
The coaxial shielded cable may ~e employed on all of
the towers which support the aerial electric power lines.
1104637
However, such arrangement is not necessary, as long as those
towers which are most susceptible and exposed to lightning
are each provided with a coaxial shielded cable. Those
skilled in the art would be readily able to determine which
towers are most exposed to lightning merely by studying
historical statistics of a given power line system or
similar power line systems. Normally, lightning discharges
occur most frequently on hills or where the tower is located
in wet or marshy ground.
The coaxial shielded cable which is employed as a
lightning arrester or as a system for protecting the electric
power lines from lightning di~charge may be the coaxial
shielded cable ~isclosed in the above mentioned U.S. Patent
No. 3,919,956, or may be any other similar coaxial shielded
cable which includes a central conductor core, an outer
conducting sheath coaxially surrounding the central conductor
core, and an insulating layer between the central core and
the outer sheath.
The upper end of the core is electrically connected
to a conducting member positioned adjacent the top of the
tower. Such conducting member may be a conventional protectiGn
conductor wire supported by and extending along the towers at a
position above the aerial electric power lines. Alternatively,
the conducting member may be one or more conventional lightning
rods located at the top of the tower. Further, the conducting
member may be a metal portion on the top of the tower. The
upper end of the outer coaxial sheath is not electrically
connected to the conducting member or to the central core.
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Both the lower end of the core and the lower end
of the sheath are grounded, The upper end of the sheath is
located adjacent the area of connection of the core to the
conducting member. The sheath must extend downwardly to a
position below the lowermost electriC power line such ~hat
the lower end of the sheath is spaced below the lowermost
electric power line at least by a distance sufficient to
exclude or prevent the formation of a secondary arc
discharge between the core and any of the electric power
lines. Thusl the outer conducting sheath, which is
insulated from the central conductor core, acts as a shield
to prevent a secondary arc discharge from the core which
operates to ground a lightning discharge striking the
conducting member and any of the electric power lines. The
1~ distance by which the lower end of the sheath must be spaced
from the lowermost electric power line to prevent such
secondary arc discharge would be readily determinable by one
skilled in the art, and would be somewhat dependent upon the
susceptibility of a given tower to being struck by lightning,
and by the voltage being conveyed through the electric power
lines.
Both the core and the sheath of the shielded
conductor may coaxially extend downwardly to a position
adjacent the ground at the bottom of the tower, and the core
and the sheath may be grounded separately or jointly to the
surface of the earth.
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The tower itself might be grounded, and the ground
connection of the tower may form the ground connection for one
or both of the core and the sheath.
Further, the sheath may end at a position spaced
above the ~round, it being understood that the bottom end of
the sheath extends below the lowermost electric power line by
a distance at least sufficient to exclude the occurrence of a
secondary arc discharge between the core and the lowermost
electric power line. In this instance, the core may extend to
the surface of the ground and thereat be grounded, or
alternatively the core may be connected to the ground by a
conductor which extends between the lower end of the core and
the surface of the ground. In such case the sheath would be
electrically connected to the core, or if the tower is a metal
tower and is grounded, the lower end of the sheath may be
electrically connected to the tower.
Further alternatively, both the lower end of the
sheath and the lower end of the core may end at a position
spaced above the surface of the ground, again as long as the
lower end of the sheath is spaced below the lowermost electric
power line by a distance sufficient to exclude a secondary arc
discharge between the core and the lowermost electric power
line. In this case, the tower must be conducting, such as a
metal tower, and the tower most be grounded. Further, the
lower end of the core and the lower end of the sheath must be
electrically connected to the metal tower. Alternatively, the
lower end of the sheath could be electrically connected to the
lower end of the core, and the lower end of the core would be
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electrically connected to the tower.
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Although the fundamental object of the present
invention is to protect the electric power lines from a
secondary arc discharge, it will further be apparent that
. in certain instances the arrangement of the present
invention will also protect the tower itself from being
struck by lightning. For example, when the tower is not
: conducting, for example when it is formed of a material
such as reinforced concrete, then the coaxial shielded
cable may extend from the upper conducting member entirely .
to ~round. Such an arrangement wiil operate to reduce the
risk of the tower itself being struck by lightning.
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BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the present
invention will become apparent from the following detailed
description of preferred embodiments thereof, taken with the
accompanying drawings, wherein:
Figure 1 is a schematic view of a high voltage tower
equipped with a lightning arrester in accordance with a first
embodiment of the present invention, wherein the entire coaxial
shielded cable extends to the ground;
Figure 2 is an enlarged partial view of the ground
connection of the coaxial shielded cable of Figure-l;
~ Figure 3 is an enlarged view illustrating one manner
- of connection of an upper protection conducting wire and the
conducting core of the coaxial shielded cable of Figure 1.
Figure 4 is a cross-sectional view through one arrange-
ment of a coaxial shielded cable which may be employed in the
present invention;
Figure 5 (see the sheet containing Figure 1) is a
,i schematic view of a second embodiment of the present invention,
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~` wherein the sheath does not extend entirely to ground and wherein
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,~ 20 the core is extended to ground by a conductor;
Figure 6 is a schematic view of a third embodiment of
the present invention, wherein both the lower end of the core
and the lower end of the sheath terminate above the surface
of the ground and are grounded by electrical connection to a
metal grounded tower; and
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11~34~3'^~
- - Figu~e 7 is a partial schematic view-of an
arran~eMent of the present invention wherein the tower
does not include an upper protection conducting wi:re,
but wherein the coaxial shielded cable is connected to
a metal member such as a lightning rod located at the
top of the tower.
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DETAILED DESCR:rPTION OF THE I~VENTION
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With reference now to Figure 1 of the drawings,
there is shown a first embodiment of the present invention.
Specifically, there is shown a metal tower 1, of conventional
construction, supporting a plurality of electric power lines
4 by means of insulators in a conventional manner. Tower 1
also supports at the top thereof a conventional protection
conducting wire 2 by means of an insulator 3. In the
drawings there are shown three electric power lines 4 being
s 10 supported, However, it is to be understood that the towers
could support a lesser or greater number of electric power
lines as would be understood by those skilled in the art.
The novel lightning arrester or lightning
protection system of the present invention involves a
coaxial shielded conductor or cable 20 which extends along
the tower. In Figure 1, the cable 20 extends along an edge
of the tower, but it should be understood that the cable 20
could be otherwise supported along the tower, for example
along the axis of the tower.
The coaxial shielded cable 20 includes a central
conductor core 30 coaxially surrounded by an outer
conducting sheath, with a layer of insulating material
between and electrically separating the core 30 and the
sheath 40. The upper end of core 30 is electrically
2~ connected to protection conducting wire 2. The upper end
of sheath 40 is not electrically connected to line 2 or to
the core 30. In the embodiment of Figure 1, the entire
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coaxial shielded cable 20, i,e. both the core 30 and the
sheath 40, extends along the entire length of the tower
to the surface of the ground whereat both the lower end
of the core and the lower end of the sheath are grounded.
In Figure 2 there is shown in more detail.how
the lower ends of the core 30 and the sheath 40 are
grounded. Specifically, Figure 2 shows that core 30 is
grounded separately from sheath 40 which has its own
ground connection 25. It is however to be understood
that both core 30 and sheath 40 could be jointly grounded
by a single ground connection.
Figure 3 shows that electrical connection
between core 30 and protection conaucting wire 2 is
achieved by means of a clamp 21 which is operated, for
example by bolts, to clamp conducting members 2 and 30
together. It will however be understood that the
electrical sonnection between core 30 and wire 2 could
be achieved by different means as would be apparent to
those skilled in the art. For example, the core 30 could
be connected to the protection conducting wire 2 by means
of two conducting strands or wires, one on each side of
insulator 3. Even further, the upper end of the coaxial
`1 shielded cable could be combined with insulator 3, and
, the upper end of core 30 could pass through the center
-~ 25 of insulator 3 and be electrically connected to wire 2.
Other possible connecting modifications will he apparent
to those sXilled in the art.
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Figure 4 shows a cross-section through a preferred
arrangement of the coaxial shielded conductor or cable 20 in
accoraance with the above mentioned U,S. Patent No. 3,919,956.
Specifically, cable 20 includes a central conductor core 30
which is coaxially surrounded by an outer conducting sheath 40.
Central conductor core 30 includes a central element 32 formed
of an insulating material coaxially surrounded by a plurality
of metal conducting wires 31, thus forming a hollow coaxial
. central conductor. Outer sheath 40, which forms an electrical
shield around core 30, is formed of a plurality of metal wires
41 which are coaxially surrounded by a layer of insulating
material 42. Sheath 40 is coaxially separated from core 30 by
means of a layer of insulating material 43. The purpose of
the conductor core 30 is to pass the current from a lightning
1~ charge to ground, while the purpose of the sheath 40, and
insulating layer 43, is to form a coaxial shield which is
capable of protecting electric power lines 4 from a secondar~
aXc discharge from core 30. That is, sheath 40 and
insulating layer 43 operate to protect the surrounding
environment, particularly electric power lines 4, from the
lightning charge which from time to time will pass through
core 30. Inversely, sheath 40 and insulating layer 43
operate to form a shield which protects core 30 against
potential influences of the surrounding environment.
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The arrangement of coaxial shielded cable 20 shown
in Figure 4 is a preferred configuration. The specific
materials and sizes of the various ele~ents and portions of
cable 20 may be as disclosed in U,S. Patent No. 3,919,956,
or may be altered as will be apparent to those skilled in
the art to achieve the desired protection capabilities
discussed herein. Further, the specific configuration of
the cable 20 may be other than is disclosed in Figure 4, as
long as the cable includes a central conductor core, an
outer conducting sheath coaxially surrounding the core, and
an insulating layer separating the core from the sheath, and
as long as the cable operates in the desired manner
disclosed herein.
It has been found that the type of coaxial shielded
conductor or cable described above possesses the capability
of absorbing the discharge from lightning and channeling such
lightning to ground without any interference, i.e.
specifically without any secondary arc discharge, to the
electric power lines.
Although the tower shown in Figure 1 is a metal
tower which itself is grounded, it is to be understood that
in accordance with the present invention the tower itself
eould be formed of a non-conducting material, for example
eoncrete or reinforced concrete. Such an arrangement would
thereby make the tower itself less susceptible to being
struck by lightning.
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As noted above, however, the fundamental purpose
of the present invention is to protect the electric power
lines 4 from a secondary arc discharge. Accordingly, in
accordance with further features of the present inventicn,
when the tower 1 is itself formed of a conducting material,
such as metal, and when the tower is itself grounded, it is
possible to terminate the coaxial shielded cable 20 at a
position above the surface of the ground and to then conduct
, the current from a lightning discharge from such point to
¦ 10 the earth, either through the tower itself or through a
¦ special conductor.
Such arrangements will be discussed below with
regard to Figures 5 and 6. It is however to specifically be
, understood that in these embodiments of the present invention
the shielded cable 20, and specifically the outer sheath 40,
must extend below the lowermost electric power line 4 by a
distance which is at least sufficient to exclude the
possibility of a secondary arc discharge between the core 30
and any of the electric power lines 4. As discussed above,
the determination of such distance would be readily possible
to one ordinarily skilled in the art, depending upon the
particular parameters involved in a given installation.
¦ In t~e embodiment of Figure 5, at least the sheath
40 terminates at a position spaced above the surface of the
! ` ground In the embodiment specifically illustrated in
Figure 5, the entire cable 20 terminates at such position
spaced above the surface of the ground, a clamp 22 electrically
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connects the lower end of sheath 40 to the metal frame of
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tower 1, and a conductor 23 extends from the lower end of
core to a ground connection 24, Thus, the lower end of
core 30 is grounded by conductor 23 and ground connection
24, while the lower end of sheath 40 is grounded by the
metal tower 1 and the ground connection 5 of tower 1. It
would be possible however, for conductGr 23 to be replaced
by an extension of the core 30 itself. Further, the lower
end of sheath 40 could be electrically connected to the lower
end of core 30 or to conductor 23. Such an arrangement would
be employable in a situation wherein tower 1 is not formed of
a conducting material such as metal. Further in such an
alternative arrangement, the lower end of sheath 40 could be
grounded by a separate conductor similar to conductor 23.
In the arrangement shown in Figure 6, tower 1 is
formed of a conducting material such as metal and is grounded
by a ground connection 5. Both the lower end of sheath 40
and the lower end of core 30 terminate at a position spaced
above the surface of the ground. The lower end of sheath 40
is electrically connected to the metal frame of tower 1 by a
clamp 22, and the lower end of core 30 is electrically
connected to the metal frame of tower 1 by a clamp 26. Thus,
the lower ends of both the core and the sheath are grounded
by tower 1 and ground connection 5. In this embodiment of
the present invention, it would also be possible to
electrically connect the lower end of sheath 40 to core 30.
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11( )4637
i In all of tne aDove discussed embodiments of the
.¦ present invention, the upper conducting member to which the
¦' upper end of the core is attached is shown in the form of a
protection conducting wire 2, However, it is to be under-
stood that the novel concept of the present invention is
I applicable to electric power line tower arrangements wherein
¦ no such protection conducting wire 2 is provided.
Specifically, as shown schematically in Figure 7
wherein there is not provided a protection conducting wire 2,
the upper end of core 30 of cable 20 is electrically
connected to an upper conducting portion 7, for example
formed of a metal conducting material, of tower 1. In the
specifically illustrated arrangement of Figure 7, the upper
end of core 30 is shown as being electrically connected to a
conventional lightning rod. It is however to be understood
that the upper end of core 30 could be connected to a
plurality of such conventional lightning rods. Further, the
upper end of core 30 could be connected to any other top
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portion of tower 1 which is formed of a conducting material,
such as metal. It is specifically to be understood that the
remaining features of the alternative embodiment of Figure 7
would be as discussed above with regard to the structural
arrangements shown in Figures 1 through 6 of the drawings.
' It will be apparent from the above discussion that
by the arrangement of the present invention, it is possible
to prevent interference with or damage to the aerial electric
power lines 4 upon the occurrence of the tower being struck
by lightning. Specifically, the cable 20 extends below the
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lowermost eiectric power line 4 at least by a distance
-sufficient to exclude the occurrence of a secondary arc
discharge between core 30 and any of the electric power
lines. The outer coaxial conducting sheath 40 provides
. S a shield which coaxially surrounds the lightning discharge
. which is being grounded by the core 30.
. It will further be apparent that although the
. above description is directed to specific and preferred
. structural embodiments of the present invention, such
specific structural arrangements are intended to be
. exemplary only, and not limiting to the scope of the
~ present invention, since various modifications may be
: made to the above specifically described and illustrated
. arrangements without departing from the scope of the
present invention.
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