Strain insulator with arcing horns

A combined strain insulator and arcing horn assembly. The arcing horns comprise a pair of rods having V-shaped outer ends criss crossing one another along one lateral side of the insulator and arranged to form multiple self-extinguishing wiring gaps emanating from the common gap between the spaced apart apexes thereof. The assembly is eminently suited for installation vertically, horizontally or in an inclined position. The hardware components are identical and integral except for fasteners.

This invention relates to high tension strain insulators, and more 
particularly to a unique strain insulator having a set of arcing horns so 
constructed and arranged as to provide multiple self-extinguishing arcing 
gaps uniquely arranged for high efficiency operation in many positions of 
the insulator including vertical, horizontal and intermediate positions. 
BACKGROUND OF THE INVENTION 
Various proposals have been made heretofore for strain insulators equipped 
with arcing horns to protect a high tension line and the insulator itself 
if a flashover occurs across the insulator. Such flashovers can arise from 
numerous causes including abnormal operating conditions on the line, a 
lightning strike, damage to the insulator caused by impact with foreign 
objects, and the collection of a coating on the insulator due to 
environmental conditions. Serious results can follow unless the insulator 
is provided with a protective device such as an arcing horn. Typically, 
such horns comprise an accessory clampable to the insulator or to its 
terminal hardware and disposed to provide a conductive path for the arc 
suitably spaced from the surface of the insulator. The proper functioning 
of such horns is dependent on the care with which they are secured to the 
insulators and adjusted to provide a desired arcing gap. The gap 
adjustment may be disturbed during installation or may be improperly made 
at the time of installation. The mounting devices add to the cost of the 
insulator assembly and this is further increased by the charge involved in 
adjusting and setting the arcing gap. A further and important shortcoming 
of prior insulators equipped with arcing horns is their lack of 
versatility to meet the needs of differing operating environments and 
their disposition relative to horizontal and vertical planes. It is 
important that the horns diverge upwardly away from a horizontal plane so 
as to be automatically self-extinguishing. This need is easily satisfied 
if the insulator axis is generally horizontal; however this need may not 
be satisfied if the insulator is installed sharply inclined to the 
horizontal. 
SUMMARY OF THE INVENTION 
The strain insulator provided by this invention avoids the foregoing and 
other disadvantages of prior constructions and provides a simplified 
rugged construction formed of three main components rigidly interlocked in 
a predetermined high efficiency relationship. The two horns are integral 
with a respective eyebolt or clevis, the interlooped bight portions of 
which are imbedded in high strength insulation material with their planes 
lying at right angles to one another and with their legs projecting from 
the opposite ends of the insulator. The two horns span one lateral side of 
the insulator and are bent to provide respective V-shaped portions with 
their apexes appropriately spaced to form a desired arcing gap. Preferably 
but not necessarily, the V-shaped legs of each horn diverge at a 120 
degree angle and the legs of the two end portions span another 60 degree 
arcing gap. In consequence, the two horns form three self-extinguishing 
arcing gaps emanating from the single gap between their respective apexes. 
Additionally, and when installed in any of many positions, the three 
arcing gaps lie in upwardly inclined planes generally midway between the 
planes containing the respective insulator hardware. Accordingly, so long 
as the workman installs the insulator with the horns inclined upwardly 
from the horizontal, the insulator and its arcing horns function equally 
efficiently and in a fool proof manner irrespective of whether the 
insulator is installed in a horizontal or vertical line or in one inclined 
to the horizontal. 
Accordingly, it is a primary object of this invention to provide a strain 
insulator with unique multiple self-extinguishing arcing horns. 
Another object of the invention is the provision of a strain insulator 
having self-extinguishing arcing horns integral with the insulator 
installation hardware. 
Another object of the invention is the provision of a strain insulator 
having a set of arcing horns so constructed and arranged as to provide 
multiple arcing gaps each diverging differently relative to the 
longitudinal axis of the insulator. 
Another object of the invention is the provision of a strain insulator 
having a pair of arcing horns integral with the insulator mounting 
hardware and forming more than one self-extinguishing arcing gap disposed 
to one lateral side of the insulator and inclined to both horizontal and 
vertical planes intersecting along the insulator axis. 
These and other more specific objects will appear upon reading the 
following specification and claims and upon considering in connection 
therewith the attached drawing to which they relate.

The strain insulator and self-extinguishing arcing horn assembly, 
designated generally 10, comprises a pair of heavy duty hardware 
components 12, 12 having spaced apart interlooped portions thereof 
embedded in and extending in opposite directions from high strength 
insulation material 13. The interlooped hardware members 12, 12 may 
comprise eye bolts with their interlooped eye portions embedded in the 
strain insulator. As herein shown by way of example, the hardware members 
12, 12 comprise clevises with their bight portions 14 in spaced apart and 
interlooped relation and lying in planes at right angles to one another 
lengthwise of insulator 13. The legs of each clevis terminate in small 
diameter rings 15, 15 seating separate bolts 16 held in assembled position 
by a nut 17 and a cotter pin 18. Bolts 16 serve to connect insulator 
assembly 10 between the adjacent ends of cabling 20, 20. Typically, such 
cabling is connected to or structurally associated with the neutral 
conductor of a high tension power line or to dead end anchoring means for 
such cabling. In certain operating environments the strain insulators lie 
in a generally horizontal plane while in others they are used in a 
suspension assembly wherein the insulator lies in a generally vertical 
postion. These are merely typical. 
The insulation material 13 is formed of suitable high tensile strength 
material, a particularly suitable material being known to persons skilled 
in this art and available on the market under the trademark POLYSIL. A 1/8 
inch thick piece of this material has a dielectric constant of 400 volts 
per mil; an arc resistant factor of at least 240 seconds; a differential 
wet-track index of 11.0 w-min.; a dielectric constant at 60 hertz of 4.3 
to 4.5; a dissipation factor of 0.013 to 0.033; a volume resistivity of 2 
times 10.sup.15 ohms per centimeter; a surface withstand stress level of 
0.9 to 1.3 KV per inch; a splitting tensile strength of 3200 psi; a 
compressive strength of 22,000 psi and a modulus of rupture of 7000 psi. 
A highly important feature of the insulator assembly is the provision of 
self-extinguishing arcing horns 25, 25 having their inner ends integral 
with a respective external portion of the hardware members 12, 12. The 
outer ends of these horns are V-shaped and formed by identical legs 26, 
27. As herein shown by way of example, legs 26 and 27 span an included 
angle of 120 degrees. The legs 27 lie generally parallel to one another 
and are suitably spaced outwardly from one exterior lateral side of 
insulator 13. It follows from the foregoing that the center lines of legs 
26, 26 are approximately 60 degrees apart and each leg 26 of one horn lies 
at an angle of approximately 60 degrees to leg 27 of the other horn. The 
apex portions 30 of the horns are spaced apart to form an arcing gap 31 
which breaks down to form an electrical arc when the cabling 20, 20 in 
which the insulator is mounted is subjected to an abnormally high voltage 
such as might be caused by lightning, the operation of circuit breakers 
serving the power line, or some other abnormal condition. 
The formation of such an arc taking place between the heavy duty metallic 
horn components safeguards the insulator itself from damage and becomes 
gradually self-extinguishing as it rises automatically along the horn legs 
and collapses in accordance with principles well know to persons skilled 
in this art. The arc initiates in gap 31 and typically climbs upwardly 
between that particular set of horns uppermost with respect to gap 31. If 
the insulator is in a generally horizontal position. the arc will climb 
between the legs 26, 26 until it extinguishes. However, if the insulator 
is inclined downwardly to the right as viewed in FIG. 1, the left hand 
legs 26, 27 will be best positioned to support the arc as it expands from 
gap 31 to the point of collapse and extinction. 
From the foregoing it will be apparent that the insulator 10 is unusually 
versatile and mountable in a wide variety of positions without regard to 
which end is uppermost, care merely being exercised to locate the arcing 
horns above the insulator axis when installed in an inclined position. The 
fact that each horn lies generally in a radial plane passing through the 
axis of the insulator and inclined about 45 degrees to the embedded loop 
portion thereof results in these elements being identical. 
While the particular strain insulator with arcing horns herein shown and 
disclosed in detail is fully capable of attaining the objects and 
providing the advantages hereinbefore stated, it is to be understood that 
it is merely illustrative of the presently preferred embodiment of the 
invention and that no limitations are intended to the detail of 
construction or design herein shown other than as defined in the appended 
claims.