US1825650A - Clamp for cables or the like - Google Patents

Description

Oct. 6, 1931.

A. O. AUSTIN CLAIP Fon cAaLEs'oR 'ma LIxn Filed Feb. 12. 1929 eq INVENTQR Arf/wr 0. Ausf/fz Bydf /MMK ATTORNEY ur* 'df/ Patented Oct. 6, 1931 Search Heem UNITED STATES PATENT OFFICE ARTHUR O. AUSTIN, OF NEAR BARBERTON, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THE OHIO BRASS COMPANY, OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY CLAMP FOR CABLES OR THE LIKE Application led February 12, 1929.

This invention relates to clamps for holding the conductors of electrical transmission lines or other strands or cables subjected to relatively high mechanical tension and has for one object the provision of a clamp of the class named in which the gripping action will be distributed substantially uniformly throughout an extended portion of the cable and in which the various strands composing the cable will be held against the movement relative to one another.

A further object is to provide a clamp in which holding is effected by a snubbing action distributed along a portion of the conductor, the snubbing action at any point along said portion being inversely proportioned to the tension in the cable at such point.

Other objects and advantages will appea` from the following description.

The invention is exemplified in the combination and arrange-ment of parts as shown in the accompanying drawings and described in the following specification, and it is .more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is aside elevation of a conductor clamp showing one embodiment of the present invention.

Fig. 2 is an elevation looking from the right in Fig. 1.

Fig. 3 is a section on line 3-3 of Fig. 1.

Fig. 4 is a fragmentary elevation of a portion of a modified form of construction.

Fig. 5 is a section on line 5 5 of Fig. 1.

Fig. 6 is a fragmentary elevation of another portion of the modified construction.

Fig. 7 is a section on line 7 7 of Fig. 6.

In clamps for holding electrical conductors, particularly those used on high tension transmission lines where it is desired to maintain a high mechanical tension in the conductor without damage to the same, it is exceedingly difficult to provide the necessary gripping means for holding the conductor. This is particularly true in conductors such as steel reinforced aluminum conductors or hollow conductors either with or without a spacer member to prevent collapsing.

In my previous patent, No. 1,002,113, a,

Serial No. 339,304.

form of clamp is shown in which the conductor` enters a. curved seat used for taking up a portion of the stress by snubbing before the final grip members act to apply the necessary friction for withstanding the remaining stress. In clamps of this type, it is seldom possible to develop more than 30% of the grip in the snubbing portion. Where very large sized conductors are used, composed of many layers, it is exceedingly difficult to apply enough pressure by the gripping means to hold the inner layers in order to develop the approximate ultimate of the conductor. It is therefore, desirable with this class of conductors greatly to increase the grip or friction in the snubbing ortion of the clamp. Where the holding is e ected largely by the snubbing portion of the clamp, the tension in the conductor, particularly that in the core of a steel reinforced aluminum conductor, will produce pressure between the inner and outer layers of the conductor so that friction will be developed between these layers and the va.- rious layers will be held against relative movement.

Vhile the incoming conductor, from the transmission line, lies in the axis of the strain insulator used for supporting and insulating the clamp and conductor from the tower, it is necessary to continue the lead or conductor past the insulator either to apparatus or to a clamp place-d in similar manner on the opposite side of the tower. In general, this jumper or portion of the conductor leading past the supporting insulator is brought downward at an angle from the incoming conductor. The angle between the incoming conductor and uniper is usually greater than 900.

It is evident that a clamp may be built up having a helical groove with uniform radius. A clamp made up in this way, however, would be much larger than needed and would have a greater' reactive effect and considerably more weight for a given grip. In the present invention it is desired to design an eflcient clamp taking the greatest possible advantage of the snubbing friction without endangering the conductor.

In general, the snubbing friction exerted by the clamp between two spaced points on the conductor, depen-ds upon the angle between the portions of the conductor at these two points. It is, therefore, desirable to include as large an angle as practical between the portions of the conductor at the point where it enters the clamp. and the portion at its exit. The pressure produced at any point between the conductor and the clamp will be directly proportional to the tension in the conductor at that point and inversely proportional to the radius of curvature of the clamp seat at that point.

In order to prevent the conductor from bearing too hard upon the clamp seat and to prevent one portion of the conductor from bearing too hard upon another portion, such as the steel core upon the soft outer layer of aluminum, all that is necessary is to use a curvature at any given point having a given conductor tension of sufficient radius to reduce the pressure to the desired amount. As the conductor progresses along the snubbing groove or seat in the clamp, the tension in the conductor will be transferred to the seat in the clamp and will thereby be reduced. If advantage is taken of this reduction in tension, it is possible to decrease the radius of curvature of the seat so that the total snubbing angle from the point of entry may be gained with a shorter length of seat than would be possible if a uniform radius of curvature were maintained and, in addition, the grip may be approximately the same for equal lengths of the seat. To take advantage of the reduction in tension and maintain uniform snubbing throughout the clamp seat, the seat may follow the contour of a logarithmic spiral. If T2 represents the tension in the incoming conductor and T1 the tension or friction developed by the grip members at the inner end of the snubbing seat, the hyperbolic log of In the above equation f is the coefficient of friction and n is the angle in degrees included in the seat divided by 360. The above equation holds true for any size of conduct-or and in order to lay out a clamp, all that is necessary is to decide upon the minimum radius possible at the point of entry for a given conductor. The effective coeiiicient of friction f will depend upon the conductor as well as upon any wedging action in the clamp seat which may be regarded as increasing the effective coefficient of friction. lVhile the coefficient of friction is not increased, the wedging action increases the pressure for a given tension which is equivalent to increasing the effective coeficient for design purposes. By utilizing the above principle, it is possible to develop very high snubbing frictions in the clamp seat, thereby permitting very light clamping means in order to develop a high tension in the conductor.

If T2 is the tension in the conductor entering the clamp and 'I1 is the friction developed by the gripping members, it is frequently possible to so design the clamp that the ratio of T2 to T1 may run from 2% to 5, depending upon the effective coefficient and the amount of wedging produced in the seat. In other words, the friction produced by the clamping members may be multiplied from 21/2 to 5 times in most designs. It is, of course, possible to change these limits very materially by including a larger snubbing angle or in special cases.

In the form of the invention shown in the drawings the entering conductor 10 traverses a groove or seat 11 in the clamp body 12 which is equipped with ears 13 for attachment to an insulator string or other support. The conductor 10 traverses the curved seat 11, which has a continuously decreasing radius, until the grip member or clamping piece 14 is reached. The clamping piece 14 is pressed against the conductor 10 by tightening the nuts 15 which are placed on U-bolts 16 or other suitable holding means. In some cases an additional clamping piece 17 is used in order to produce additional friction and guide the conductor upon leaving the clamp. The groove 11 in the clamp produces a complete turn and passes itself at one side at the point 18.h The portion of the seat near the grip members 14 is usually displaced slightly from that which would be developed by a true logarithmic spiral in order to provide the proper clearance for the grip members and to keep the clamp as small as possible. lVhere very heavy currents are encountered, it may be advisable to use a non-magnetic material or a material of high conductivity so that heating will be reduced to a minimum.

As the conductor, in following the clamp seat, makes a complete turn, there will be a tendency for the current flowing in the conductor to induce an opposite current in the short circuit turn formed by the clamp body if the portions of the body are connected where they cross each other. There will also be a tendency for a portion of the current to leave the conductor and flow directly to the crossing portion through the clamp body without following the loop formed by the conductor. This may have a tendency to produce heat where the current leaves the conductor and enters the clamp seat which, in some cases, may be objectionable. It is usual to place a lining in the seat of the clamp made of sheet aluminum or other suitable soft metal and, in some cases, it may be desirable to place "i" .-1. u www."

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at the point 21. As the voltage at these points will be very small, it is possible to use insulation such as fibre or asbestos which will withstand the weather and have the necessary mechanical strength. A slight amount of heat generated in the clamp is usually an advantage as it tends to prevent the formation of sleet and keeps all parts dry, insuring the best possible working conditions in order to insure a long life in the conductor and hardware.

In a clamp such as that shown in Fig. l, danger from crystallization or damage to the strands of the conductor is reduced very materially over one where the conductor is griped by a socket, sleeve or other means in which the axis of the conductor and clamp are a straight line throughout the length of the gripping means. In a clamp such as that shown in Fig. l, it is evident that such a large part of the load is taken up in the snubbing portion that a tension in the conductor which would reduce it in diameter could not possibly aifect the diameter of the conductor and its grip for any great distance along the seat. Since the effectiveness of the grip in the clamp depen-ds upon the tension and the snubbing angle to a very large extent, it is seen that even tensions which will reduce the diameter of the conductor at the point of entry will not alfect the gripping efficiency of the clamp. In clamps where snubbing is not possible, but grip is obtained by direct pressure, it is seen that reduction in cross section due to tension may tend to relieve the grip at the point of entry, thereby transferring` the full tension to a greater distance in the clamp. Since tension in the conductor reduces its diameter radially, it is seen that it is not advisable to place compression normal Yto the axis of the conductor until the stress or tension in the conductor is reduced. Otherwise, the tendency to deform the conductor in addition to the deformation due to tension, will be increased.

In dead-end or strain construction, particularly where very high voltages are used, the limit in flashover voltage for the installation is usually determined by the voltage at which a discharge will take place from the jumper to the supporting structure. This can always be made the limit for any structure as it is possible to increase the length of the strain or dead-end insulator sufliciently to cause ashover between jumper and tower. A strain or dead-end tower differs materially from a suspension tower in this connection. If therefore, the flashover voltage between the jumper and the structure can be increased over that in a normal installation, it is possible to obtain higher insulation by simply lengthening or increasing the strain insulators. In double circuit towers or where the conductors are placed on the outside of the tower, it is possible greatly to increase the effective clearance of the conductor by utilizing the clamp to hold the jumper 22 at a distance from the structure. In other words, the jumper may be held not only downward, but outward from the tower as well, or even upward in the case of the center phase in a fiat single circuit construction or its equivalent.

In many cases the jumpers have caused serious trouble owing to the fact that they did not have sulicient clearance from the structure or swung into the structure during heavy winds. In many installations it has been necessary to stiffen or hold the jumpers by angle construction which greatly increases the mass attached to the conductor, forms sharp angles tending to cause discharge and is generally objectionable.

In the present type of clamp, a support or brace for holding the jumper can be readily attached. Such an extension or holding member 23 is shown attached to the body of the clamp and gripping the jumper by a clamp 24. This extension member may be in any form desired and extend for a considerable distance from the clamp so as to insure clearance for the conductor.

I-Iolding the jumper may also be of material advantage in that any vibration or oscillation in the clamp will tend to set up friction between the strands in the jumper, thereby tending to dampen out oscillations. This is particularly true where the holding member on the jumper extends for some distance from the clamp, tending to magnify any movement.

It will be understood, of course, that where the slack end of the conductor is not continued past the clamp to form a jumper, the exit end of the clamp need not be shaped to give a particular direction to the slack end of the conductor. In a case of this kind, it may not be necessary or desirable to continue the seat at its exit end beyond the contour of the adjacent lap. Of course, the slack end of the cable will be secured to the clamp in some suitable manner but if the end is not continued to form a jumper, the final gripping portion of the clamp may differ from that shown in the drawings where the arrangement is designed to give a particular direction to the slack end of the cable.

In order further to absorb oscillations, an extension member 25 is attached to the body of the clamp at 26 and 27 by suitable clamping means. A frictional device 28 rides over a complementary sleeve or member 29 so that any movement between the members 28 and 29 will cause dissipation of energy which will tend to absorb vibrations. The means used for producing this dissipation of energy may vary considerably without changing the principle involved. The action is similar to that of a shock absorber used in automotive practice and, in fact, devices involving constructions similar to those of shock absorbers might be attached at this point, particularly those equipped with arms arranged so that any relative movement between the conductor and the member 25 would cause relative rotation of frictionally engaging parts with a consequent dissipation of energy. In many cases, however, the frictional means can be quite simple as a slight dissipation of energy will dampen out oscillations which will damage the conductor. The amount of friction required and the length of arm and stiffness of the member 23 will, of necessity, depend upon the conductor and conditions under which it is installed. Where greater relative movement is desired, it is necessary to extend the arm, or place the rubbing surfaces Where the amplitude of oscillation tends to be large.

I claim:

l. A cable clamp comprising a snubbing member having a curved seat for receiving the cable, said seat being disposed in a loop, the axis of which is substantially normal to the load end of the cable, the load end of said cable extending away from said seat in a direction substantially tangent to the curvature of said seat, means for securing a support to said clamp substantially in alignment with the load end of said cable, the radius of curvature of said seat being decreased progressively, said seat being extended to form more than a complete turn and having a substantially straight portion extended from the end thereof, having they lesser radius of curvature, said straight portion being directed away from the load end of said cable at an oblique angle to said cable, and means for securing said cable to said straight portion of said seat.

2. A cable clamp comprising a curved cable seat having any entrance end for receiving the load end of a cable and an exit end from which the slack end of said cable extends, said seat being curved about al progressively decreasing radius from the load end to the. exit end thereof, thus forming a loop, the axis of which is substantially normal to the load of the cable, means for clamping said cable to said seat adjacent said exit end, and an extension secured to the exit end of said seat for directing the slack end of said cable away from said seat.

3. A cable clamp comprising a cable seat having an entrance end for receiving the load end of a cable, a holding member for said clamp arranged substantially in alignment with said cable where it enters said seat, said seat being curved away from the axial line of said cable forming a loop, the axis of which is substantially normal to the load end of the cable and providing a snubbing surface having a progressively decreasing radius of curvature, the curvature of said seat being extended for more than 360, .and means for clamping the slack end of said cable to said seat adjacent the portion of said seat having the lesser radius of curvature.

4. A cable clamp comprising a body member having a curved cable seat provided with an entrance end for receiving the load end of the cable and an exit end from which the slack end of the cable extends, said seat being disposed in a loop, the axis of which is substantially normal to the load end of the cable, means for securing a holding member to said clamp substantially in alignment with the load end of said cable, said seat being curved through more than 360O to direct the slack end of said cable away from the load end of said cable at an oblique angle to said load end.

5. A cable clamp comprising a body member having a cable seat provided with an entra-nce end for receiving the load end of a cable and an exit end from which the slack end of the cable extends, said seat being disposed in a loop, the axis of which is substantially normal to the load end of the cable and following a curve at one side. of the axis of the load end of said cable, the radius of curvature of which progressively decreases from the load end to the exit end of said seat, means for securing said cable to said clamp adjacent the exit end of said seat, said seat being extended through a complete turn, and means for securing a. holding member to said clamp substantially in alignment with the axis of the load end of said cable.

6. A cable clamp having a snubbing seat substantially in the form of a logarithmic spiral, the load end of said cable entering said seat at the end thereof having the greater radius of curvature while the slack end of said cable extends from said seat at the end thereof' having the lesser radius of curvature, the logarithmic curvature of said seat being continued outwardly substantially to the end of said seat at the point of entrance of said cable, means for securing the slack end of said cable to said clamp, and a support for said clamp arranged substantially in alignment with the load end of said cable.

7. A cable clamp having a snubbing seat curved to form more than a complete turn, adjacent portions of the different laps of said seat being mechanically attachedbut electrically insulated from each other at their crossing.

8. A cable clamp comprising a cable scat having its entrance end substantially tangent to the load end of said cable and having a supporting portion substantially in alignment with the load end of said cable, said seat being curved away from the axis of the load end of said cable upon a curve having a progressively decreasing radius of curvature, said seat making more than one complete turn and being provided with an exit portion directed away from the axis of the load end of said cable at an oblique angle thereto, said exit portion being offset lateral- 1y to pass the adjacent lap of said seat, means secured to said exit ortion for directing the slack end of said ca le, means for clamping said cable to said seat adjacent the exit end thereof, a vibration damping device secured to said clamp adjacent the entrance end thereof and engagingr the. load end of said cable to damp out vibrations thereof, and means for insulating adjacent portions of the different laps of said seat from each other.

In testimony whereof I have signed my name to this specification this 9th day of February, A. D. 1929.

ARTHUR O. AUSTIN.

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