US3621107A

US3621107A - Line pole grounding system

Info

Publication number: US3621107A
Application number: US51221A
Authority: US
Inventors: William H Duvendack
Original assignee: Joslyn Manufacturing and Supply Co
Current assignee: Joslyn Manufacturing and Supply Co
Priority date: 1970-06-30
Filing date: 1970-06-30
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16
Also published as: CA928812A

Abstract

An improved grounding system for line pole crossarms is provided to reduce line pole fires due to leakage currents. A pair of crossarm bands having an adhesive conductive material on their inner surface are wrapped around the crossarms spaced on opposite sides of the pole, and grounding means shunts the leakage currents to ground around the gains where the arm meets the pole.

Description

United States Patent 2,331,098 10/1943 Whiteetal.

Inventor William H. Duvendack Butte, Mont. App1.No. 51,221

Filed June 30, 1970 Patented Nov. 16, 197l Assignee Joslyn Mfg. and Supply Co.

Chicago, Ill.

LINE POLE GROUNDING SYSTEM 5 Claims, 8 Drawing Figs.

US. Cl 174/6, 174/40 CC, 174/45 R, 339/251, 339/278 C Int. Cl HOZg 7/00, H0 1 r 3/06 Field of Search l74/2, 6,40 R, 40 CC, 45 R, 117 A; 339/251, 278 R, 278 C References Cited UNITED STATES PATENTS 2,399,899 5/1946 Tinnerman 174/40 CC 2,427,883 9/1947 Score et a1. 1 174/40 CC 2,808,352 10/1957 Coleman et a1... 174/117AUX 2,844,643 7/1958 Cofer et a1 174/6 3,344,225 9/1967 Jureit et a1. 174/45 R OTHER REFERENCES Electrical World, Straps and Washer Stop Pole-Top Fires," Vol. 141, No. 22, pages 92 and 98. TKIE6. Copy in 174' 45R,

Primary Examiner-Laramie E. Askin Attorney-Mason, Kolehmainen, Rathburn & Wyss ABSTRACT: An improved grounding system for line pole cross-arms is provided to reduce line pole fires due to leakage currents. A pair of crossarm bands having an adhesive conductive material on their inner surface are wrapped around the crossarms spaced on opposite sides of the pole, and grounding means shunts the leakage currents to ground around the gains where the arm meets the pole.

LINE POLE GROUNDING SYSTEM The present invention relates to an improved line pole apparatus, and more particularly, to means designed to direct leakage current from the arms of a line pole to ground.

Heretofore, difficulty has been experienced with pole fires due to leakage currents. Pole fires have been an increasing problem and are particularly intolerable since the line may travel through remote, almost inaccessible areas where repair is extremely difiicult, costly and time consuming. In a typical bumdown, the juncture of the arm and a pole catches fire until the arm breaks away from the pole, after which the fire generally goes out. Examination shows that the arm and pole are both badly charred in the gain area around the through bolt. The side of the arm facing the pole generally has a cratershaped burn centering around the bolt hole, while the pole generally has a large pocket-burn in the same area and the bolt hole is charred and enlarged. The arm breaks away from the pole either because it weakens and cannot support the load, or because the bolt becomes so hot that it softens and fails.

Most fires seem to occur after long, dry spells when dust contamination has an opportunity to build up on the surfaces of insulators and crossarms. Then, when moisture from alight rain or condensation wets this dust, surface resistivity is reduced by hundreds or thousands of times and high leakage occurs. The fact that high leakage occurs is not necessarily harmful as long as the entire leakage path is wetted. However, if portions of the pole and crossarm, especially near the juncture of the two, are shaded from moisture and remain relatively dry, line voltage or very near line voltage may be impressed across a high resistance area only inches wide. High IR losses at this point initiate arcing and subsequent burning. Currents of only 8 milliamps are sufficient under the right conditions to cause ignition.

But even arcing and tracking in a dry area will seldom result in a fire if they occur on the outside surfaces of the arm or pole where the heat either may be radiated out or convected away by the wind. On the other hand, if the arcing takes place in the gain area where heat can be confined and radiated from one surface to another, serious burning is likely to occur.

Heretofore, several methods have been proposed for eliminating pole fires. An effective method would be to ground the suspension insulators. This is particularly impractical on existing lines because additional insulator bells would be required, reducing ground clearance and increasing the radius of line swing. Moreover, such additional insulators on new lines are costly and require redesign of the lines structure.

It has also been suggested to install a high-impedance plastic gain between the pole and arm to force arcing to occur over the outside of the arm to the grounded through-bolt where it can be easily removed. However, this method is also impractical in existing installations because the installation of the gain would have to be done with the line deenergized, and the cost of assembling and reassembling all of the structures on an existing line would be prohibitive. Moreover, the installation of a high-impedance plastic gain on new line construction is both costly and would require redesign of the pole line apparatus.

Accordingly, it is an object of the present invention to provide a new and improved line pole apparatus for directing crossarm leakage to ground.

Yet another object of the present invention is to provide a line pole apparatus which shunts leakage currents from the crossarms to ground around the gains.

Yet another object of the present invention is the provision of a new and improved line pole apparatus minimizing pole fires due to leakage currents from the crossarms.

Still another object of the present invention is the provision of a new and improved line system for directing leakage currents from the crossarms around the gains of the pole.

Further objects and advantages of the present invention would become apparent as the following description proceeds and the features of novelty which characterizes the invention will be pointed out with particularity in the claims which form a part of this specification.

In accordance with these and other objects, there is provided an improved line pole apparatus directing leakage currents from a crossarm of a line pole to ground around the gains of the pole. More specifically, there is provided a pair of armbands, spaced on opposite sides of the pole, with resilient conductive material on the inner surface of the bands providing a substantially continuous electrical path between the band and the arm. The arms in turn are grounded around the gains of the pole. In a preferred embodiment of the invention, the conductive material is bonded to the band in a scalloped-shaped molding so that the molding on the band with the band in place on the cross arm is thickest at the center of the flats of the crossarm and thinnest at the corners thereof.

Advantageously, the armband according to the present invention insures contact with the wood throughout the length of the band as the dimension of the arm changes due to moisture content and the temperature and age.

For a better understanding of the present invention, reference may be had to the accompanying drawing wherein:

FIG. 1 illustrates a line pole apparatus including a utility pole and crossarm joined by a through bolt, and incorporating the present invention;

FIG. 2. is a cross-sectional view of the line pole apparatus taken along line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken FIG. 2;

FIG. 4 illustrates a preassembly of bands and grounding straps according to the present invention;

FIG .5 is a side elevation view of the armbands shown in FIG. 4;

FIG. 6 is a cross-sectional view of the armband line 6-6 in FIG. 5; and

FIG. 7 is a cross-sectional view of the armband taken along line 7-7 in FIG. 5; and

FIG. 8 is a cross-sectional view of the armband shown in FIG. 5 having an uncured conductive sealant.

Referring now to the drawings, and particularly to FIG. 1 thereof, there is illustrated a line pole apparatus 10 incorporating the present invention. The line pole apparatus 10 includes a utility or line pole l1 and a crossarm 12 connected thereto by a through bolt 13. A known type of wire clamp 14 is secured to the arm end of the through bolt 13. A grounding wire I5 runs from the top of the pole to a suitable ground.

In accordance with the present invention there is provided an improved arm band assembly 20 for directing leakage currents from the crossarm 12 to the ground over the gain area of the line pole apparatus 10. Referring more specifically to FIG. 4, the armband assembly 20 includes a pair of spaced

armbands

21 and 22 having a suitable banding buckle 23 at one end and interconnected by a cross conductor 24. The cross conductor 24 may be spot welded to the armbands. A grounding strap 25 is joined to the cross conductor 24 in any suitable manner such as by welding, as illustrated in FIG. 4. The

armbands

21 and 22, buckle 23, cross conductor 24, and grounding strap 25 may, of course, be of any suitable conducting material, and stainless steel has been found to work advantageously. To insure contact between the

armbands

21 and 22 and the wood arms through the length of the bands, the armbands contain suitable conducting resilient material 28 on its inner surface formed in a scalloped shape so that when the band is in place, the conducting material 28 is thickest at the center of the

flat faces

12a, 12b, 12c, and 12d of the crossarm, and thinnest at the comers.

In a particular embodiment of a strap configuration, as best illustrated in FIG. 5, for a crossarm having approximately 9.4 by 5.4 inch cross section, it has been found that formation of a conducting resilient material 28 to a minimum thickness t of 0.175 inch and a maximum thickness t at the high point of 0.625 inch performs satisfactorily. Under such a geometric configuration, the radius of curvature along the long arms r, is about 25 inches, and the radius of curvature of the conducting resilient material along the short walls is about 7 /2inches. It has been found that a silicone rubber adhesive-sealant, such as along line 3-3 of taken along Dow Corning Corporation No. 735, forms satisfactorily for the conductive resilient material 28.

The band may be fabricated with the conducting resilient material by first laying a length of stainless steel flat in a bottom of a wooden mold, the top of which is cut in a scalloped configuration. Next, a suitable quality of conductive resilient material 28 such as silicone rubber adhesive-sealant is squirted into the mold with a suitable caulking gun, and a tool is run over the top of the mold to conform the conducting resilient material 28 into a scalloped-shaped form having a groove 29. The adhesive-sealant is then cured. and because the rubber is nonslumping, the assembly may be immediately removed from the mold and either hung up or laid down to cure at room temperature.

The conductive silicone rubber sealant is easy to work with, has adequate conductivity, has good weather and sunlight resistance, and withstands the high temperatures to which it may be exposed during arcing. The material also bonds well to stainless steel, even without a primer.

Installing the banding system on a crossarm is a relatively fast and simple operation which can be done with the line energized. Referring to FIG. 2, the lineman preferably first wraps around the arm, and staples down, a strip of common copper screening 30 at a point of about inches from the center of the pole. Several inches overlap is allowed so that a ground conductor can be sandwiched in between. Next, the lineman places an uncured adhesive sealant 280, which can be of the same type as the material 28, into the groove 29. Finally, the band is placed in place over the screening around the arm and tightened and locked with a banding tool.

The use of screening is advantageous for a number of reasons. It tends to pick up the leakage current first and therefore keeps arcs away from the conducting resilient rubber. lt conducts away heat that may be generated in the rubber. It makes a lower resistance contact with the ground than is possible with a conductive rubber alone. The uncured conductive sealant 28a is preferably placed into the groove 29 to insure intimate contact between the band, the screening and the wood.

After the

bands

21 and 22 have been secured to the crossarm, the grounding strap 25 may be grounded to the through bolt 13 by means of the were clamp 14, as best illustrated in FIG. 1, and may be grounded to the pole ground 15 by a suitable connector clamp 32.

It has been found that pole fires due to leakage currents are substantially eliminated by the application of the arm band assembly according to the present invention.

Although the present invention has been described by reference to only a single embodiment thereof, it will be apparent that numerous other modifications and embodiments may be devised by those skilled in the art, and it is intended by the appended claims to cover all modifications and embodiments which fall within the true spirit and scope of the present invention.

What is claimed as new and desired to ters Patent of the United States is:

1. An arm-grounding system for a line pole crossarm wherein a crossarm is joined (thereto) to a line pole by a through bolt, said system comprising:

a pair of armbands for a pole arm adapted to be spaced on opposite sides of a pole,

a resilient conductive material on the inner surface of said bands for providing a substantially continuous electrical path between the band and an arm throughout the length of each band, and

means for grounding said bands.

2. The system defined in claim 1 wherein said conductive material is conductive silicone rubber sealant.

3. The system defined in claim 1 wherein said conductive material is an adhesive.

4. The system defined in claim 1 in combination with utility pole, a crossarm, and a through bolt securing said crossarm to said pole, said bands being wrapped around said arm on opposite sides of said pole.

5. The system defined in claim 1 wherein said conductive material is bonded in a scalloped-shaped molding to said bands so that when the band is in lace on a crossarm, the material is thickest at the center of the flats of a crossarm and thinnest at the corners to provide compressive force distributed all around the arm.

be secured 20 by Let-

Claims

1. An arm-grounding system for a line pole crossarm wherein a crossarm is joined (thereto) to a line pole by a through bolt, said system comprising: a pair of armbands for a pole arm adapted to be spaced on opposite sides of a pole, a resilient conductive material on the inner surface of said bands for providing a substantially continuous electrical path between the band and an arm throughout the length of each band, and means for grounding said bands.

5. The system defined in claim 1 wherein said conductive material is bonded in a scalloped-shaped molding to said bands so that when the band is in place on a crossarm, the material is thickest at the center of the flats of a crossarm and thinnest at the corners to provide compressive force distributed all around the arm.