US3399269A - High tension wood structure free of radio interfering radiation and burning from leakage current - Google Patents

Description

Aug. 27, 1968 J H. WILLO URE FREE OF R FROM Aug

X 3,399,269 7 HIGH TENSION WOOD STRUCT ADIO INTERFERING RADIATION AND BURNING LEAKAGE CURRENT Filed 51, 1967 I INVENTOR. x LBAQ J! BY "Q T United States Patent 3,399,269 HIGH TENSION WOOD STRUCTURE FREE OF RADIO INTERFERING RADIATION AND BURNING FROM LEAKAGE CURRENT I Hebden Willox, 917 Newcastle Ave.,

Westchester, II]. 60153 Filed Aug. 31, 1967, Ser. No. 664,682 6 Claims. (Cl. 174-45) ABSTRACT OF THE DISCLOSURE The adverse effects of (a) the burning of coniferous wood members of a high tension structure and (b) the generation of radio interfering sparking between closely spaced loose hardware is precluded by the interposition of a compressed helical spring coil between the nut and head of the assembly bolts passing through and joining the wood members, the spring coil having more than one full turn of quadrilateral cross section and flattened arcuate end surfaces coated with a malleable metal softer than the metal forming the coil.

This invention relates generally to wood structures for supporting overhead high voltage energized electric conductors, and specifically to the combination therewith of means effective to provide a structure which is free of both leakage current burning damage and generation of radio interference in the standard broadcast band and the VHF or UHF frequency ranges.

The advantages of wood members over metal members for high voltage kv. and above) electric lines has long been recognized; lower cost and inherent insulating qualities being among the more important. Coniferous soft woods, such as pine and fir, are relatively inexpensive and are readily treated with preservative liquids carrying creosote or penta-chlorophenol. For these reasons, conife'rous wood members are found almost exclusively in wood pole line construction.

As the dielectric strength of the'insulation, including a pine pole and a fir crossarm, varies from time to time with the moisture content of the wood and with surface contamination, such as salt spray along coastal areas, the magnitude of the leakage current from an associated energized conductor similarly increases and decreases. Wood tracking and burning at points of concentration of leakage current, and radio influence and interfering radiation from induced voltage sparking between loose, closely spaced hardware elements are important adverse effects which can be --satisfacto'rily precluded if the contact between the wood members and between the components of the associated metal fasteners is maintained under continuous pressure applied over a sufficiently large area of engagement of the abutting surfaces.

Contra to the achievement of this desired condition are the natural changes in the dimensions of the wood members under weathering conditions, as well as their inherent low side-grain surface hardness, the latter permitting a limited but significant indentation of the wood as the abutting fastener element is continuously pressed against the wood surface.

The correlated problems of leakage current wood burning and radio interference due to loose and corroded connecting hardware has long been recognized by the electric utility industry. Numerous constructions have been utilized in attempts to solve the problems, including the use of numerous shapes of single turn lock washers, lacking, as they do, the substantial axial resilient movement necessary to compensatefor dimensional change of the wood-members. Currently several shapes of hairpin spring washers are in use. In addition to being bulky and costly,

3,399,269 Patented Aug. 27, 1968 hairpin washers, when compressed, effect substantially point contacts with the facing members, instead of the desired distributed pressure, with resultant hot spots at the wood surface from leakage current concentration. Simple helical coil springs of round or rectangular section with square cut ends lack the critically required bearing area, as well as its critical location, and absent the important end tapering, tend to fracture distally from the ends under continuous compressive stress. In addition, square cut ends act as cutting tools upon the mating surfaces, and thus destroy the value of any rust-preventing coating which they may engage.

It is an object of the present invention to provide a leakage-current damage and radio interference free high tension structure embodying coniferous wood structural members, achieved by the association therewith of a spe cifically adapted fastener construction.

Another object is to provide, in a bolted crossarm assembly, a compressed spring coil interposed between an end of the bolt and the surface of the crossarm through which the bolt passes, the coil being characterized by (a) an open helical winding of about 30 degrees less than two full turns; (b) a winding from a wire having a trapezoidal or keystone cross section; (c) the ends being tapered to provide flat mating surfaces and to facilitate bending thereof to conform to the mated surfaces; and (d) the mating surfaces being coated with a soft and malleable metal; e.g., tin, lead or cadmium.

A further object is to provide an assembly embodying a helical spring lock washer of the foregoing characteristics which will function to maintain a continuous pressure upon both the hardware elements of the fastener and the associated wood members under all service conditions, including particularly any and all changes in texture and form to which coniferous woods are susceptible under outdoor weathering.

Another object is the provision of an assembly embodying a helical spring lock washer having no square cut ends or sharp points, this feature enabling reuse of galvanized hardware since the corrosion protection is not scraped away upon either installation or removal.

An embodiment of the invention is illustrated in the accompanying drawing, in which:

FIG. 1 is a perspective view of an upper portion of an electric overhead line structure, showing an exemplary application of the invention;

FIG. 2 is an enlarged section, taken along the line 22 of FIG. 1, in which the fastener elements are drawn twice actual size;

FIG. 3, is a plan view of the helical spring lock washer;

FIG. 4 is a section taken along the line 4--4 of FIG. 3, and

FIG. 5 is a fragmentary section of an end surface of the helical spring lock washer of the invention.

FIG. 1 shows the upper portion of an upstanding wood pole line structure in which the transversely extending wood crossarm 11 has mounted thereon the insulator 12, to which is attached the energized electric conductor 13. The metal through bolt 14 passes through both the pole 10 and the crossarm 11, for the purpose of jointing these members in abutting relationship. One quite common arrangement of the members is a pine pole and a fir crossarm. The fastener elements associated with the bolt 14 are shown more completely in FIG. 2, from which it may be seen that the metal washer 20 is interposed between the pole 10 and the bolt head 21, and the metal washer 17 along with the compressed helical spring lock washer 16 are interposed between the crossarm 11 and the nut 15, the latter threadedly engaging the outwardly extending end of the bolt 14.

As the fastener elements are combined in FIG. 2, the bolt 14 is in tension as the result of tightening the nut 15 to compress the helical spring washer 16, and the washers 17 and 20 are continuously urged against the crossarm 11 and the pole 10 respectively, and, as here illustrated, have indented the soft wood members, as indicated by the numerals 18 and 19.

One function of the helical spring washer is to compensate for any changes in form of the wood members, whether due to change in moisture content or to deformation of the soft wood under pressure. I have found a compressed-condition axial lengthening of the helical spring washer of the order of A to be a critical requirement in connection with coniferous wood members, as here illustrated, for continuously maintaining the necessary stress upon all the associated parts to obviate leakage-current wood burning and aperiodic radio interfering radiation. This resilient expansion requirement is substantially more than that provided by any practicable single turn design, but slightly less than that provided by the most economical open turn helix of two turns. The smooth and wide area soft metal bearing surface, correctly disposed at each end of the helical spring washer, is essential for the continuous proper functioning of the assembly.

As shown in FIG. 2, the particular structure of the helical spring washer, which is the critical element of the assembly, is an open turn helix of more than one turn and less than two turns. The metal wire of the coil is trapezoidal or keystone in cross section, with an open turn spacing as indicated at 27. The cross section is shown in FIG. 4. In this embodiment one parallel side of the trapezoid, indicated at 23, forms the inner periphery of the coil, and the other parallel side 24 forms the .outer periphery of the turns. A suitable material for the coil is SAE 1060 wire, formed on a machine having rolls of 4 /2 degrees taper. After winding, the material is hardened and drawn to a Rockwell C scale hardness not less than 40, -44 to C-46 being a desirable range.

Each end of the helix is severed along a plane coextensive with the axis of the helix and which diverges at an angle .of at least fifteen degrees from a plane coextensive with the axis of the helix which would pass through both ends of a two full turn helix, and indicated in FIG. 3; in other words, the helix of the embodiment shown lacks thirty degrees of having two full turns.

Each end portion of the coil is ground to provide the terminal flats indicated at 25 and 26 of FIGS. 3 and 4. In so doing, at least one-half of the keystone section at each end is removed, thus presenting identical wide bearing end surfaces along the circumferentially spaced end portions extending through an angle of about 120 degrees from each end of the coil. The shape of one of the end surfaces is indicated at 25 of FIG. 3, from which it may be seen that the specified disposition of the keystone cross section results in a bearing surface along the inner periphery of the arcuate end portion extending convolutely beyond the bearing surface along the outer periphery, thereby increasing the total available bearing surface.

The flattened end surfaces 25 and 26 are plated with tin or other soft metal, as indicated by the fragmentary section of FIG. 5, for the purpose of reducing the friction at each end of the washer when it is compressed by turning a nut thereagainst. The relatively soft and malleable metal acts as a spread under sliding frictional stress, lubricating the abutting surfaces. Further, the soft metal readily spreads to fill pin holes or other holidays of an engaged protective coating, which, if remaining unsealed, expose rust-prone metal to corrosive deterioration. The invention herein effectively precludes the degradation of corrosion resistant protective coatings, such as zinc galvanizing, which are commonly destroyed by the use of locking devices having sharp square cut ends, the latter functioning only by biting into and shearing away the protective coating .of the contacted components. The corrosion products of pole line hardware are non-conductors, and

corroded loose hardware is the ideal combination for the generation of adverse radio-influencing radiation from high voltage lines.

The thirty degree circumferential spacing between the ends of the helical coil, in cooperation with the half-stock grind removal and the keystone shape and disposition, effectively eliminate two serious problems presented by all helical washers having unchamfered ends. Oneof these is the deflection of the washer from its desired coaxial position with respect to the associated bolt, which may so bend the latter as to cause ultimate failure. Another is the innate tendency to overstress the metal at the center of the coil when fully compressed. In applicants structure, the chamfered ends, together with theirmutually related circumferential positions, permit the ends to resiliently deform under less stress than that required to deform the full-thickness turn portion of the coil. The necessary resilient axial movement is obtained through the resilient urging of the weakened ends toward the midpoint of the coil, a gradually increasing pressure being equally applied on opposite sides of the associated bolt as the nut is turned, thus limiting the midpoint stress to a safe value even when the coil is fully compressed to turn-to-turn abutting engagement.

The permanently hardware-tight transmission line structure disclosed herein is equally effective for the prevention of (a) leakage-current burning and (b) radio interfering radiation, despite the fact that the conditions favorable for the former differ widely from those favorable for the latter. Leakage-current burning is caused by a concentration of the current due to poor or point contacts in the current path, such as may result from loose hardware, and is most apt to occur in wet or contaminated atmospheres. On the other hand, radio interference is caused by induced sparking between closely spaced loose hardware, and is most apt to occur under dry and uncontaminated atmospheric conditions. In either situation, the basic cause is unstressed or relaxed structural components of unsuitable shape, and this basic cause is effectively eradicated by applicants construction as recited herein..

While I have in the foregoing described and illustrated an embodiment of the invention, it will be apparent that changes and modifications may readily be made by those skilled in the art. It is therefore intended that the drawing and description shall be regarded as illustrative rather then limiting, reference being made to the appended claims to ascertain the scope of the invention.

-What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In an electric transmission line structure including a coniferous wood member, an energized conductor insulatingly mounted thereon, and metal fastener elements associated therewith including a metal bolt having a head at one end and a threadedly engaged nut at the other end, said bolt extending through said wood member for effecting an attachment thereto, said structure being susceptible both to wood burning from leakage current and to generation of radio interfering sparking due to distortion or loosening of said metal fastener elements, the improvement comprising the interposition of a compressed helical spring metal coil between said nut and the head of said bolt, said helical coil having more than one full turn of a wire of trapezoidal cross section, the parallel sides of the trapezoidal wire extending respectively along the inner and outer periphery of the helical turns and the end surfaces of an arcuate end portion at each end of the coil lying in transversely extending parallel planes, said end surfaces having disposed thereon a layer of a metal softer and more malleable than the metal forming the coil.

' 2. The transmission line structure according to claim 1, in which the helical spring coil extends convolutely through an angle of not more than 340 degrees and not less than 320 degrees beyond one full turn.

3. The transmission line structure defined in claim 2, wherein the end surfaces of the helical spring coil lie in axially spaced parallel planes extending normal to the axis of the coil and around the respective arcuate end portions through an angle of at least 120 degrees from each end thereof.

4. The transmission line structure according to claim 3, in which the respective ends of the coil lie in planes intersecting at the coil axis which diverge from one another at an angle of not more than thirty degrees.

5. The transmission line structure defined in claim 4, in which the metal forming the coil is a steel drawn to a Rockwell hardness of not less than C-40, and the metal layer disposed over the end surfaces is tin.

6. In an electric transmission line structure which includes a coniferous wood member, an energized conductor insulatingly mounted thereon, and metal fastener elements associated therewith including a metal bolt having a head at one end and a threadedly engaged nut at the other end, said bolt extending through said wood member for effecting an attachment thereto, the improvement comprising means for precluding induced radio interfering sparking between loosened metal fastener elements, said means including the interposition of a compressed helical spring metal coil between said nut and the head References Cited UNITED STATES PATENTS 152,864 7/ 1874 'Pickels 26 7-61 303,302 8/1884 Ludlum 26761 501,052 7/1893 Brown 151-38 X 2,943,870 7/ 1960 Davis 267-1 X FOREIGN PATENTS 732,313 6/ 1955 Great Britain.

OTHER REFERENCES Carlson, Stainless Steels for Springs, Product Engineering, May 1947, pp. 103-406.

25 LARAMIE 'E. ASKIN, Primary Examiner.

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