CA1191251A - Synthetic fiber rope guy means - Google Patents
Synthetic fiber rope guy meansInfo
- Publication number
- CA1191251A CA1191251A CA000375354A CA375354A CA1191251A CA 1191251 A CA1191251 A CA 1191251A CA 000375354 A CA000375354 A CA 000375354A CA 375354 A CA375354 A CA 375354A CA 1191251 A CA1191251 A CA 1191251A
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- CA
- Canada
- Prior art keywords
- rope
- potting head
- potting
- bell
- mouth
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
SYNTHETIC FIBER ROPE GUY MEANS
Abstract Of The Disclosure A guy means is provided for an elevated metallic structure. The guy means comprises a dielectric synthetic fiber rope sheathed in a moisture proof jacket. A terminal means is attached to one end of the rope for connecting the rope to the elevated structure. The terminal means in-cludes a potting head in which splayed fibers of the rope are encapsuled in potting material to attach the terminal means to the end of the rope. A corona discharge means is attached to the potting head and disposed annularly around the synthetic rope where the rope enters the potting head to reduce the likelihood of a corona discharge near the rope surface which may cause the rope to burn through and part. Several embodiments of the corona discharge means are disclosed, including a metal torroid connected to the potting head by an electrical conductor, a bell-mouth ex-tension of the neck of the potting head, and a bell-mouth extension of the neck of the potting head in which the inside arc of the bell-mouth is continued through substan-tially three-quarters of a circle to create a collar around the potting head neck.
Two alternative embodiments of such guy means in com-bination with a mast are disclosed. In one embodiment the guy means are directly connected to the mast. The other embodiment is an umbrella antenna in which the guy means are used to support the radiating antenna conductors in the proper array pattern.
Abstract Of The Disclosure A guy means is provided for an elevated metallic structure. The guy means comprises a dielectric synthetic fiber rope sheathed in a moisture proof jacket. A terminal means is attached to one end of the rope for connecting the rope to the elevated structure. The terminal means in-cludes a potting head in which splayed fibers of the rope are encapsuled in potting material to attach the terminal means to the end of the rope. A corona discharge means is attached to the potting head and disposed annularly around the synthetic rope where the rope enters the potting head to reduce the likelihood of a corona discharge near the rope surface which may cause the rope to burn through and part. Several embodiments of the corona discharge means are disclosed, including a metal torroid connected to the potting head by an electrical conductor, a bell-mouth ex-tension of the neck of the potting head, and a bell-mouth extension of the neck of the potting head in which the inside arc of the bell-mouth is continued through substan-tially three-quarters of a circle to create a collar around the potting head neck.
Two alternative embodiments of such guy means in com-bination with a mast are disclosed. In one embodiment the guy means are directly connected to the mast. The other embodiment is an umbrella antenna in which the guy means are used to support the radiating antenna conductors in the proper array pattern.
Description
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SYNTHETIC FI~ER ROPE GU~ MEANS
Backgrou d Of The Invention This invention relates to the use of synthetic fiber ropes as guy means for elevated metal structures, such as masts or antennas. It is known per se to use synthetic fiber ropes as guy means. Philadelphia Resins Corporation of 20 Commerce Drive, Montgomeryville, Pennsylvania, has for the past several years produced synthetic fiber ropes to be used as guys. The synthetic fiber rope produced by Philadelphia Resins is made of an aramid (aromatic poly-amide) fiber known in the trade by the DuPon-t krademark "KEVLAR". These fiber ropes are sold by Philadelphia Resins under the trademark "P~ILLYSTR~N". These synthetic fiber ropes may be braided in either solid or hollow braid, or may be of parallel strands served in cloth or counter-woven thread. These ropes have also normally been produced with a protective sheath, specifically a net-like perfor-ated polyester jacket or an extruded copolymer jacket.
There are si~niEicant advantages in the use of synthetic fiber ropes of the type described above as guys.
The synthetic fibers are siynificantly lighter in weight and more ~lexible than metallic cables of the same strength, resulting in an increased ease of handling and ease of installation. The fibers are also non-corroding, making them relatively maintenance free. In addi-tion to .æ~l resisting rust, the cables are relatively unaffected by air-born effluents or by long-term immersion in salt water. One of the most significant advantages of syn-thetic fiber guys is their dielectric properties.
Metallic cables are electrical conductors, which presents shock hazards to persons in the vicinity. The dielectric properties of the synthetic rope are even more important when used with radiating antennas such as television and radio towers. Metallic cables become part of the radiating structure unless properly insulated, and also may cause distortions in the radiated signals from other antennas if the cable lies in the path of transmission. With the non-conducti.ng synthetic fibers, the guy ropes can be ignored as electromagnetic factors in designing the antenna array.
In spite of the recognized advantages of using syn-thetic fiber guys, there has heretofore been signiEicant problems which have limited the widespread use of such guys on large towers and particularly on high power radiating towers. It is well known that the earth has a significant negative charge. The upper layer of the at-mosphere contains the corresponding positive charge. These two charged layers form a spherical capacitor with a sig-nificant electrostatic field in between. A grounded an-tenna may extend the negative earth charge several hundred feet into the atmosphere. This causes the equipotential lines of elec-trostatic force to concentrate in the vicinity of the tower. When the tower is a radiating antenna, the electrostatic force is compounded by the induced electrical fields of the antenna. The combined electrostatic forces may be even greater when there are electrical storms in the vicinity of the tower.
It is also well known that electrostatic forces tend to intensify and discharge around irregularities, par-ticu-larly sharp surfaces, of a structure. The terminal con-nectors for guy ropes provide such irregular sharp sur-faces, and tend to concentrate and discharge electrostatic "
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energy into the atmosphere. This problem is compounded i when synthetic fi~er ropes are used, as the terminal con-nectors are normally metallic conductors while the guy ropes are nonconductors. Thus, at the point o~ transition from the terminal connector to the guy rope there is a discontinuity in electrical conducting properties, and the electrostatic discharge tends to occur precisely at this irregularity. The discharge which occurs is due to the ionization of the air in the immediate vicinity of the field concentration point, and is commonly known as a corona discharge. In metallic conductors this discharge is merely undesirable in that it represents a loss of power, may cause intereference with communication systems, and may produce ozone which rnay increase the deterioration of the metallic cable. In synthetic ropes, however, the problem is more severe in that the discharge may quickly burn through the synthetic fihers and cause the cable to part.
~1 A significant object of this invention is thereEore .1 ~ to alleviate this corona discharge problem. This and other -~ objects of the invention in producing suitable synthetic fiber guy means will be apparent upon reading the detailed description which follows.
Brief Description Of The Invention A guy means is provided for an elevated metallic structure. The guy means comprises a dielectric synthetic fiber rope sheathed in a moisture proof jacket. A terminal means is attached to one end of the rope for connecting the rope to the elevatecl structure. The terminal means in-cludes a potting head in which splayed fibers of the rope are encapsuled in potting material to attach the terminal means to the end of the rope. A corona discharge means is attached to the potting head and disposed annularly around the synthetic rope where the rope enters the potting head to reduce the likelihood of a corona discharge near the rope surface which may cause the rope to burn through and part. Several embodiments of the corona discharge means L2~
are disclosed, including a metal torroid connected to the . .~
potting head by an electrical conductor, a bell-mouth ex-tension of the neck of the potting head, and a bell-mouth extension of the neck of the potting head in which the inside arc of the bell-mouth is continued through substan-tially three-quarters of a circle to create a collar around the potting head neck.
Two alternative embodiments of such guy means in com-bination with a mast are disclosed. In one embodiment the guy means are directly connected to the mast. The other embodiment is an umbrella antenna in which the guy means are used to support the radiating antenna conductors in the proper array pattern.
Brief Description Of l'he Drawings For the purpose of illustrating the invention, there is shown in the drawings a ~orm which is presently pre-Eerred; it being understood, however, that this invention is not limited to the precise arrangements ancl instrumen-talities shown.
r1~ Figure 1 is a symbolic representation of a mast and guy rope combination showing symbolically the equipotential lines of force concentrated about the mast.
Figure 2 is a longitudinal cross section of a prior art terminal connector and potting head with a synthetic fiber cable potted therein.
Figure 3 is a perspective view of a prior art ter-minal connector showing symbolically the concentration of electrostatic forces on the synthetic Eiber rope.
Figure 4 is a perspective view of a terminal connec-tor according to one embodiment of the presellt invention showing symbolically the dispersion of electrostatic forces around the synthetic fiber rope.
Figure 5 is a perspective view of three alternative embodiments of a terminal connector and potting head according to the present invention.
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Figure ~a, 6b, and 6c are longitudinal sections of -~ potting heads showing the areas of corona discharge.
Figure 7 is a partial longitudinal section of a prior art potting head showing symbolically the concentra-tion of elec-trostatic forces around the neck of the potting head.
Figure ~ is a partial longitudinal section of a potting head according to the present invention showing symbolically the distribution of electrostatic forces away from the synthetic fiber rope.
Figure 9 is a longitudinal section of a terminal connector according to one embodiment of the present in vention.
Figure 10 is a longitudinal section of a terminal connector according to another embodiment of the present invention.
Figure 11 is a perspective view of a synthetic Eiber rope ancl egg-insulator means as a guy for an antenna wire on an umbrella antenna.
~ Detailed Description Of The Disclosure Referring now to the drawings wherein like numerals ;~ indicate like elements, Figure 1 shows a grounded metal mast structure 10 guyed by an array of guy ropes 12~ It is well known that the earth carries a negative electrical charge, and that the upper layers of the atmosphere carry a corresponding positive charge. In between there is created an electrostatic field of varying intensities, as indicated symbolically by the equipotential force lines El through En. As shown in Figure 1, a grounded metal mast may extend the negative earth charge several hundred feet into the air, resulting in a concentration of the lines of equipotential force around the mast 10.
Synthetic fiber ropes have been used as guy ropes.
These synthetic fiber ropes may be of the type discribed in the aforegoing background of the invention, and are gen-`.~, ~9~25~
erally desirable for the proper-ties mentioned therein. In the prior art, these guy ropes have been terminated by terminal connecting means such as terminal connector 14 in Figure 2. Terminal connector 14 is a metallic structure, and has a connector ring portion 16 to be attached to a mast by suitable means. Connector 14 also has a potting head portion 18 which is a frusto-conical structure having a narrow neck 20 opening onto a hollow frusto-conical chamber 22. The chamber 22 is closed at the wide end by a plate 24, which may be integrally formed with connector 14. Potting head 18 is used to connect a synthetic fiber rope to the terminal means 14. As shown in Figure 2, a synthetic fi~er rope 26 comprises a number of fine syn-thetic fiber strands 28 covered by a protective jacket 30.
The fiber strands 28 may be braided in either solid or hollow brald, twisted into a cable as shown in Figure 2, or laid horizontally and wrappecl with either cloth serving or other strands. The jacket 30 has heretofore been pri-marily a net-like polyester sheath although an extruded copolymer has been used.
To attach the terminal connector 14 to the rope 26, a section of the jacket 30 is cut away and one or more wind-ings of tape 32 are applied at the end of the remaining jacket. The exposed fiber strands 2~ are unwoven and splayed apart as shown by strands 34 in Figure 2. The strands 3~ are inserted through neck 20 into chamber 22, and a suitable liquid potting material is poured throuc~h an aperture (not shown) in plate 24 to fill the chamber 22. Such potting materials are well known, and may be for instance an epoxy of polyester resin. The potting material is applied in liyuid form and hardens -through chemical reaction following adittion of a hardener or catalyst.
With some potting materials heat may be applied to speed hardening. When the potting material 36 hardens, the strands 34 are encapsuled (potted) therein and the terminal connector 14 is securely joined to rope 26.
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~ eferring now to Figure 3, a synthetic fiber rope 26 is attached as a guy to mast 10 by terminal connector 1~
and a hook ring 38 which engages connector ring 16. Hook ring 38 is shown only by way of illus-tration, as there are a number of suitable means for connecting the terminal connector 14 to the mast 10.
As shown symbolically in Figure 3, the electrostatic forces represented by the equipotential lines El through En are concentrated at the point where rope 26 emerges from terminal connector 14. Masts 10, hook ring 3~ and terminal connector 14 are metal structures which are electrical con-ductors. Fiber rope 26 is a dielectric. This causes a discontinuity in conduction properties at the point where rope 26 emerges Erom connector 14 and ls accentuated by the small area and sharp corners of nec]c 20. It is in this area that a corona discharge will form if the electrostatic forces become sufficiently powerEul. This corona discharge may burn through the protective jacket and synthetic fiber strands of rope 20, and cause the rope to part under strain. The results could be catastrophic if the par~ing occurred while the mast was subjected to heavy side loads, as from heavy winds associated with thunder storms.
In Figure 4 there is shown a terminal connector 14 according to one embodiment of the present invention. It may be seen from the symbolic representation of the equi-potential lines E1 through En that the field is less concentrated around the synthetic fiber rope 26. This results from the providing of a corona discharge means 40 at the neck of the potting head. Details of the corona discharge means and an explanation of its function are set forth below.
Corona suppression devices have been used with metallic conductors. These may be in the form of corona suppression rings as shown in U.S. Patent 3,179,740, or stress relief cones as shown in UOS. Patent 3,217,091.
In these applications, the corrosion suppression devices -~L~S~
are placed at various points along the conductor to in-crease the effective diameter of the conductor and thus reduce the field intensity surrounding the conductor.
It is not believed, however, that the art has heretofore recognized the importance of preventing corona discharge on a synthetic fiber cable at the point in which the fiber cable enters a metallic terminal connector, and it is therefore believed to be novel to provide a corona dis-charge means at the neck of a potting head of a terminal connector for a synthetic fiber guy.
While any corona discharge means, such as the three embodiments shown in Fiyure 5, are far superior to the prior art terminal connector shown in Figure 2, experiments performed by this inventor indicate certain preferred em-bodiments are substantially superior to others.
Referring now to Figure 5, there are shown three embodiments, (a), (b), and (c), of terminal connectors having corona suppression means. In embodiment (a), the corona suppression means ~2 is a bell-shaped extension Oe the neck of the potting heacl. In embodiment (b), the corona discharge means is a metal torroid 4~ disposed annularly around the synthetic fiber and connected to the neck of the potting head by one or more conductors 46. In embodiment (c), the corona suppression means combines features of embodiment (a) and embodiment (b), and com prises a bell-mouth extension of the neck of the potting head in which the inside arc of the bell-mouth is continued through substantially three quarters of a circular arc to create a collar ~ around the potting head neck. More details regarding the three embodiments and the relative performance of each in preVentincJ corona damage to the fiber rope is discussed below.
Theoretical mathematical computations of field strength effects around a potting head were conducted by this inventor for the prior art potting heads shown in Figure 2 and for potting heads with a corona discharge ., -3~9~
torroid as shown in embodiment (b) of Figure 5. ~ scien-tific paper awaiting publication was written by the inven-tor. While the mathematic solutions go beyond the scope necessary for this application, the following results were indicated:
(a) Maximum electric field strength occurs at the sharp edge of the neck of the prior art potting head, as expected. The intensity of the electrical field at this point varied from 14 to 30 times the intensity of the homogenous electrical field to which the potting head was subjected, the intensity depending on the sharpness of the corner at the potting head neck.
(b) With the torroid potting head, the field inten-sity was greatly reduced, and could be varied by changing either the radial cross-section of the torroid (R in Figure 6a) or the distance of the torroid annular axis rom the longitudinal axes of the fiber rope (D in Fiyure 6a).
SpeciEically, by enlarging the torroid crosssectional raclius R, the electric field strength on the circumference oE the torroid and on the synthetic rope declined in in-verse ratio. By increasing the distance D between the torroid annular axis and the axis of the rope, the electric field strength along the rope declined, while the field strength on the inner circum~erence of the torroid in-creased.
Another variable which was studied and provded to be . . .
of great significance was the distance of the terminal connection from the mast. It was found that the electrical field strength both at the torroid and on the rope in-creased linearly with the distance of the connection from the mast.
From the above mathematical computations, two signi-ficant conclusions were drawn. First, the terminal connec-tion should be made as close to the mast as practical.
Secondly, the torroid might not be the best embodiment for corona suppression with synthetic fibers, as the electrical ,~
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field strength on the inner dimension of the torroid in-creased when the torroid axis was moved away from the rope.
This is signiflcant in that it is desirable to have corona discharge occur, if at all, as far from the synthetic fiber rope as possible, and be directed away from the fiber.
When the axial distance D of the torroid is increased to reduce strength at the rope, the likelihood of a discharge on the inner circumference of the torroid (directed toward the rope) increased.
An experiment was conducted at the Milan Vidmar In-stitute of High Voltage Technics in Ljubljana, ~ugoslavia.
Two large flat copper plates were connected together by a short section of Phillystran, and suspended above the ground so that one plate was the upper plate and the other the lower plate of a large capacitor. The lower plate was connected to the Phillystran by a pottiny head terminal connector. The lower plate was grounded, and the upper plate connected to a high voltage generator. Measurements were made using alternating current at 50Hz, and direct current. Voltages were increased until the onset of a visible corona and then further increased until the sy-nthetic rope burned through.
Referring to Figure 6, it can be seen where the corona discharge occurred. With the prior art potting head shown in Figure 6(c), a visible corona first appeared when the field strength between the plates was approxi-mately 160kV/m. At 190kV/m the corona effect was very intense and caused breakdown. The corona appeared directly adjacent to the fiber rope as shown in the area designated Cl, in Figure 6(c). With the torroid discharge means, a visible corona occurred at 225kV~m in the area marked C2 of Figure 6(a). At 280kV/m the corona effect was very intense and caused breakdown. With the bell-mouth potting head, visible corona occurred at 280kV/m in the area marked C3 of Figure 6(b). Field strength was increased up to 375kV/m without corona occurring at any other point, and the rope was not damaged.
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At the same time as the above test, another test was conducted to determine the effect of rain water saturation on the synthetic fibers. An exposed fiber rope was im-mersed in fresh water for an extensive period of time to allow it to become Fully saturated with water. The rope became immediately conductive when voltages were applied to the upper plate. This lead to the conclusion that the net-like polyester jacket heretofore used would not be sufficient to prevent conduction in a prolonged wet period, and recommendations were made to use only the extruded solid polyurathane jacket.
The above theoretical calculation and testing indi-cated that the bell-mouth extension of the neck of the potting head would be preEerable to a torroid where sub-stantial electrical fields might be present. Elowever, for exceptionally large synthetic cables another embodiment of corona dischar~e means was devised. This is embodiment ~c) of Fi~ure 5, and is shown in more detail in Figures 8 and 10. As shown in Figure 8, the neck 21 oE the potting head 15 is extended by an outward curving surface 50 identical to the bell-mouth embodiment. However, the arc of the outward curve is carried through approximately 270, to the area 52 shown on Figure 8. This creates a large gener-ally circular collar 48 around the potting head neck.
Collar 48 has a large discharge surface, consistent with the previously mentioned mathematical predictions that increasing the cross-sectional radius of the torroid would reduce the field intensity. The collar 48 also adds struc-tural rigidly to the potting head, which may be important where a larye rope is subjected to very high tension.
Comparison of Figures 7 and 8 show the relative in-tensity of the electrical field distribution around the prior art potting head and the potting head with collar respectively. In Figure 7, a sharp peak field distribu-tion (E max) occurs at the potting head neck close to the rope. In Figure 8, field distribution is relatively uni-S~
form around the collar circumference and E max occurs onthe upper-front quadrant away from the ropeA
Referring now to Figures 9 and 10, preferred embodi-ments of terminal connectors are shown. In Figure 9, -terminal connector 14 has a bell-mouth extension 56 of the neck 20 of potting head 18, and in E'igure 10 terminal con-nector 1~ has a collar 54 around the potting head neck 20.
In both embodiments, the potting head 1~ is an hollow frustoconical chamber up to plane 60. At plane 60, top and bottom sides o~ terminal connector 14 are cut away to from parallel clevis posts 62 and 63. An aperture 64 is provided in each clevis post 62, 63 for insertion therein of a clevis pin (not shown). A ring 66 (shown in ~host lines) may be mounted directly on the mast. By placing the clevis posts 62, 63 over ring 66 and securing thereto with a pin or bolt through aperture 64, the terminal con-nection may be made as close to the mast as practical, thereby reducing the electrostatic field intensity at the point where the synthetic Eiber rope emerges from the potting head. This is consistent with the previously discussed mathematical calculations predicting that the electrostatic field intensity would increase linearly with the distance of the potting head/synthetic rope transition from the mast.
However, in at least one application the synthetic fiber guys cannot be attached close to the mast. That is . . .
the situation of an umbrella antenna in which the antenna array includes flexible conductors disposed in a ~laypole type arrangement from the mast. In those situations, the synthetic guy ropes serve to hold the antennas in the proper outstretched position relative to the mast~ In this situation the electrostatic forces may be considerable at the transition point between the conducting antenna wires and the non-conducting synthetic fibers. For this reason i~ may be necessary to introduce insulator means between the antenna wires and the synthetic rope. As :g S~
; shown in Figure 11, two ceramic egg-insulators 68, 70 connected by a metallic rope 72 are disposed between the antenna wires 74 and the terminal connector 14.
The present invention may be embodied in other spe-cific forms without depar-ting from the spirit or essential attributes thereof and, accordingly, reference should be :~ made to the appended claims, rather than to the foregoing ' specification, as indicating the scope of the invention.
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SYNTHETIC FI~ER ROPE GU~ MEANS
Backgrou d Of The Invention This invention relates to the use of synthetic fiber ropes as guy means for elevated metal structures, such as masts or antennas. It is known per se to use synthetic fiber ropes as guy means. Philadelphia Resins Corporation of 20 Commerce Drive, Montgomeryville, Pennsylvania, has for the past several years produced synthetic fiber ropes to be used as guys. The synthetic fiber rope produced by Philadelphia Resins is made of an aramid (aromatic poly-amide) fiber known in the trade by the DuPon-t krademark "KEVLAR". These fiber ropes are sold by Philadelphia Resins under the trademark "P~ILLYSTR~N". These synthetic fiber ropes may be braided in either solid or hollow braid, or may be of parallel strands served in cloth or counter-woven thread. These ropes have also normally been produced with a protective sheath, specifically a net-like perfor-ated polyester jacket or an extruded copolymer jacket.
There are si~niEicant advantages in the use of synthetic fiber ropes of the type described above as guys.
The synthetic fibers are siynificantly lighter in weight and more ~lexible than metallic cables of the same strength, resulting in an increased ease of handling and ease of installation. The fibers are also non-corroding, making them relatively maintenance free. In addi-tion to .æ~l resisting rust, the cables are relatively unaffected by air-born effluents or by long-term immersion in salt water. One of the most significant advantages of syn-thetic fiber guys is their dielectric properties.
Metallic cables are electrical conductors, which presents shock hazards to persons in the vicinity. The dielectric properties of the synthetic rope are even more important when used with radiating antennas such as television and radio towers. Metallic cables become part of the radiating structure unless properly insulated, and also may cause distortions in the radiated signals from other antennas if the cable lies in the path of transmission. With the non-conducti.ng synthetic fibers, the guy ropes can be ignored as electromagnetic factors in designing the antenna array.
In spite of the recognized advantages of using syn-thetic fiber guys, there has heretofore been signiEicant problems which have limited the widespread use of such guys on large towers and particularly on high power radiating towers. It is well known that the earth has a significant negative charge. The upper layer of the at-mosphere contains the corresponding positive charge. These two charged layers form a spherical capacitor with a sig-nificant electrostatic field in between. A grounded an-tenna may extend the negative earth charge several hundred feet into the atmosphere. This causes the equipotential lines of elec-trostatic force to concentrate in the vicinity of the tower. When the tower is a radiating antenna, the electrostatic force is compounded by the induced electrical fields of the antenna. The combined electrostatic forces may be even greater when there are electrical storms in the vicinity of the tower.
It is also well known that electrostatic forces tend to intensify and discharge around irregularities, par-ticu-larly sharp surfaces, of a structure. The terminal con-nectors for guy ropes provide such irregular sharp sur-faces, and tend to concentrate and discharge electrostatic "
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energy into the atmosphere. This problem is compounded i when synthetic fi~er ropes are used, as the terminal con-nectors are normally metallic conductors while the guy ropes are nonconductors. Thus, at the point o~ transition from the terminal connector to the guy rope there is a discontinuity in electrical conducting properties, and the electrostatic discharge tends to occur precisely at this irregularity. The discharge which occurs is due to the ionization of the air in the immediate vicinity of the field concentration point, and is commonly known as a corona discharge. In metallic conductors this discharge is merely undesirable in that it represents a loss of power, may cause intereference with communication systems, and may produce ozone which rnay increase the deterioration of the metallic cable. In synthetic ropes, however, the problem is more severe in that the discharge may quickly burn through the synthetic fihers and cause the cable to part.
~1 A significant object of this invention is thereEore .1 ~ to alleviate this corona discharge problem. This and other -~ objects of the invention in producing suitable synthetic fiber guy means will be apparent upon reading the detailed description which follows.
Brief Description Of The Invention A guy means is provided for an elevated metallic structure. The guy means comprises a dielectric synthetic fiber rope sheathed in a moisture proof jacket. A terminal means is attached to one end of the rope for connecting the rope to the elevatecl structure. The terminal means in-cludes a potting head in which splayed fibers of the rope are encapsuled in potting material to attach the terminal means to the end of the rope. A corona discharge means is attached to the potting head and disposed annularly around the synthetic rope where the rope enters the potting head to reduce the likelihood of a corona discharge near the rope surface which may cause the rope to burn through and part. Several embodiments of the corona discharge means L2~
are disclosed, including a metal torroid connected to the . .~
potting head by an electrical conductor, a bell-mouth ex-tension of the neck of the potting head, and a bell-mouth extension of the neck of the potting head in which the inside arc of the bell-mouth is continued through substan-tially three-quarters of a circle to create a collar around the potting head neck.
Two alternative embodiments of such guy means in com-bination with a mast are disclosed. In one embodiment the guy means are directly connected to the mast. The other embodiment is an umbrella antenna in which the guy means are used to support the radiating antenna conductors in the proper array pattern.
Brief Description Of l'he Drawings For the purpose of illustrating the invention, there is shown in the drawings a ~orm which is presently pre-Eerred; it being understood, however, that this invention is not limited to the precise arrangements ancl instrumen-talities shown.
r1~ Figure 1 is a symbolic representation of a mast and guy rope combination showing symbolically the equipotential lines of force concentrated about the mast.
Figure 2 is a longitudinal cross section of a prior art terminal connector and potting head with a synthetic fiber cable potted therein.
Figure 3 is a perspective view of a prior art ter-minal connector showing symbolically the concentration of electrostatic forces on the synthetic Eiber rope.
Figure 4 is a perspective view of a terminal connec-tor according to one embodiment of the presellt invention showing symbolically the dispersion of electrostatic forces around the synthetic fiber rope.
Figure 5 is a perspective view of three alternative embodiments of a terminal connector and potting head according to the present invention.
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Figure ~a, 6b, and 6c are longitudinal sections of -~ potting heads showing the areas of corona discharge.
Figure 7 is a partial longitudinal section of a prior art potting head showing symbolically the concentra-tion of elec-trostatic forces around the neck of the potting head.
Figure ~ is a partial longitudinal section of a potting head according to the present invention showing symbolically the distribution of electrostatic forces away from the synthetic fiber rope.
Figure 9 is a longitudinal section of a terminal connector according to one embodiment of the present in vention.
Figure 10 is a longitudinal section of a terminal connector according to another embodiment of the present invention.
Figure 11 is a perspective view of a synthetic Eiber rope ancl egg-insulator means as a guy for an antenna wire on an umbrella antenna.
~ Detailed Description Of The Disclosure Referring now to the drawings wherein like numerals ;~ indicate like elements, Figure 1 shows a grounded metal mast structure 10 guyed by an array of guy ropes 12~ It is well known that the earth carries a negative electrical charge, and that the upper layers of the atmosphere carry a corresponding positive charge. In between there is created an electrostatic field of varying intensities, as indicated symbolically by the equipotential force lines El through En. As shown in Figure 1, a grounded metal mast may extend the negative earth charge several hundred feet into the air, resulting in a concentration of the lines of equipotential force around the mast 10.
Synthetic fiber ropes have been used as guy ropes.
These synthetic fiber ropes may be of the type discribed in the aforegoing background of the invention, and are gen-`.~, ~9~25~
erally desirable for the proper-ties mentioned therein. In the prior art, these guy ropes have been terminated by terminal connecting means such as terminal connector 14 in Figure 2. Terminal connector 14 is a metallic structure, and has a connector ring portion 16 to be attached to a mast by suitable means. Connector 14 also has a potting head portion 18 which is a frusto-conical structure having a narrow neck 20 opening onto a hollow frusto-conical chamber 22. The chamber 22 is closed at the wide end by a plate 24, which may be integrally formed with connector 14. Potting head 18 is used to connect a synthetic fiber rope to the terminal means 14. As shown in Figure 2, a synthetic fi~er rope 26 comprises a number of fine syn-thetic fiber strands 28 covered by a protective jacket 30.
The fiber strands 28 may be braided in either solid or hollow brald, twisted into a cable as shown in Figure 2, or laid horizontally and wrappecl with either cloth serving or other strands. The jacket 30 has heretofore been pri-marily a net-like polyester sheath although an extruded copolymer has been used.
To attach the terminal connector 14 to the rope 26, a section of the jacket 30 is cut away and one or more wind-ings of tape 32 are applied at the end of the remaining jacket. The exposed fiber strands 2~ are unwoven and splayed apart as shown by strands 34 in Figure 2. The strands 3~ are inserted through neck 20 into chamber 22, and a suitable liquid potting material is poured throuc~h an aperture (not shown) in plate 24 to fill the chamber 22. Such potting materials are well known, and may be for instance an epoxy of polyester resin. The potting material is applied in liyuid form and hardens -through chemical reaction following adittion of a hardener or catalyst.
With some potting materials heat may be applied to speed hardening. When the potting material 36 hardens, the strands 34 are encapsuled (potted) therein and the terminal connector 14 is securely joined to rope 26.
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~ eferring now to Figure 3, a synthetic fiber rope 26 is attached as a guy to mast 10 by terminal connector 1~
and a hook ring 38 which engages connector ring 16. Hook ring 38 is shown only by way of illus-tration, as there are a number of suitable means for connecting the terminal connector 14 to the mast 10.
As shown symbolically in Figure 3, the electrostatic forces represented by the equipotential lines El through En are concentrated at the point where rope 26 emerges from terminal connector 14. Masts 10, hook ring 3~ and terminal connector 14 are metal structures which are electrical con-ductors. Fiber rope 26 is a dielectric. This causes a discontinuity in conduction properties at the point where rope 26 emerges Erom connector 14 and ls accentuated by the small area and sharp corners of nec]c 20. It is in this area that a corona discharge will form if the electrostatic forces become sufficiently powerEul. This corona discharge may burn through the protective jacket and synthetic fiber strands of rope 20, and cause the rope to part under strain. The results could be catastrophic if the par~ing occurred while the mast was subjected to heavy side loads, as from heavy winds associated with thunder storms.
In Figure 4 there is shown a terminal connector 14 according to one embodiment of the present invention. It may be seen from the symbolic representation of the equi-potential lines E1 through En that the field is less concentrated around the synthetic fiber rope 26. This results from the providing of a corona discharge means 40 at the neck of the potting head. Details of the corona discharge means and an explanation of its function are set forth below.
Corona suppression devices have been used with metallic conductors. These may be in the form of corona suppression rings as shown in U.S. Patent 3,179,740, or stress relief cones as shown in UOS. Patent 3,217,091.
In these applications, the corrosion suppression devices -~L~S~
are placed at various points along the conductor to in-crease the effective diameter of the conductor and thus reduce the field intensity surrounding the conductor.
It is not believed, however, that the art has heretofore recognized the importance of preventing corona discharge on a synthetic fiber cable at the point in which the fiber cable enters a metallic terminal connector, and it is therefore believed to be novel to provide a corona dis-charge means at the neck of a potting head of a terminal connector for a synthetic fiber guy.
While any corona discharge means, such as the three embodiments shown in Fiyure 5, are far superior to the prior art terminal connector shown in Figure 2, experiments performed by this inventor indicate certain preferred em-bodiments are substantially superior to others.
Referring now to Figure 5, there are shown three embodiments, (a), (b), and (c), of terminal connectors having corona suppression means. In embodiment (a), the corona suppression means ~2 is a bell-shaped extension Oe the neck of the potting heacl. In embodiment (b), the corona discharge means is a metal torroid 4~ disposed annularly around the synthetic fiber and connected to the neck of the potting head by one or more conductors 46. In embodiment (c), the corona suppression means combines features of embodiment (a) and embodiment (b), and com prises a bell-mouth extension of the neck of the potting head in which the inside arc of the bell-mouth is continued through substantially three quarters of a circular arc to create a collar ~ around the potting head neck. More details regarding the three embodiments and the relative performance of each in preVentincJ corona damage to the fiber rope is discussed below.
Theoretical mathematical computations of field strength effects around a potting head were conducted by this inventor for the prior art potting heads shown in Figure 2 and for potting heads with a corona discharge ., -3~9~
torroid as shown in embodiment (b) of Figure 5. ~ scien-tific paper awaiting publication was written by the inven-tor. While the mathematic solutions go beyond the scope necessary for this application, the following results were indicated:
(a) Maximum electric field strength occurs at the sharp edge of the neck of the prior art potting head, as expected. The intensity of the electrical field at this point varied from 14 to 30 times the intensity of the homogenous electrical field to which the potting head was subjected, the intensity depending on the sharpness of the corner at the potting head neck.
(b) With the torroid potting head, the field inten-sity was greatly reduced, and could be varied by changing either the radial cross-section of the torroid (R in Figure 6a) or the distance of the torroid annular axis rom the longitudinal axes of the fiber rope (D in Fiyure 6a).
SpeciEically, by enlarging the torroid crosssectional raclius R, the electric field strength on the circumference oE the torroid and on the synthetic rope declined in in-verse ratio. By increasing the distance D between the torroid annular axis and the axis of the rope, the electric field strength along the rope declined, while the field strength on the inner circum~erence of the torroid in-creased.
Another variable which was studied and provded to be . . .
of great significance was the distance of the terminal connection from the mast. It was found that the electrical field strength both at the torroid and on the rope in-creased linearly with the distance of the connection from the mast.
From the above mathematical computations, two signi-ficant conclusions were drawn. First, the terminal connec-tion should be made as close to the mast as practical.
Secondly, the torroid might not be the best embodiment for corona suppression with synthetic fibers, as the electrical ,~
.~
s~
field strength on the inner dimension of the torroid in-creased when the torroid axis was moved away from the rope.
This is signiflcant in that it is desirable to have corona discharge occur, if at all, as far from the synthetic fiber rope as possible, and be directed away from the fiber.
When the axial distance D of the torroid is increased to reduce strength at the rope, the likelihood of a discharge on the inner circumference of the torroid (directed toward the rope) increased.
An experiment was conducted at the Milan Vidmar In-stitute of High Voltage Technics in Ljubljana, ~ugoslavia.
Two large flat copper plates were connected together by a short section of Phillystran, and suspended above the ground so that one plate was the upper plate and the other the lower plate of a large capacitor. The lower plate was connected to the Phillystran by a pottiny head terminal connector. The lower plate was grounded, and the upper plate connected to a high voltage generator. Measurements were made using alternating current at 50Hz, and direct current. Voltages were increased until the onset of a visible corona and then further increased until the sy-nthetic rope burned through.
Referring to Figure 6, it can be seen where the corona discharge occurred. With the prior art potting head shown in Figure 6(c), a visible corona first appeared when the field strength between the plates was approxi-mately 160kV/m. At 190kV/m the corona effect was very intense and caused breakdown. The corona appeared directly adjacent to the fiber rope as shown in the area designated Cl, in Figure 6(c). With the torroid discharge means, a visible corona occurred at 225kV~m in the area marked C2 of Figure 6(a). At 280kV/m the corona effect was very intense and caused breakdown. With the bell-mouth potting head, visible corona occurred at 280kV/m in the area marked C3 of Figure 6(b). Field strength was increased up to 375kV/m without corona occurring at any other point, and the rope was not damaged.
.~
.
At the same time as the above test, another test was conducted to determine the effect of rain water saturation on the synthetic fibers. An exposed fiber rope was im-mersed in fresh water for an extensive period of time to allow it to become Fully saturated with water. The rope became immediately conductive when voltages were applied to the upper plate. This lead to the conclusion that the net-like polyester jacket heretofore used would not be sufficient to prevent conduction in a prolonged wet period, and recommendations were made to use only the extruded solid polyurathane jacket.
The above theoretical calculation and testing indi-cated that the bell-mouth extension of the neck of the potting head would be preEerable to a torroid where sub-stantial electrical fields might be present. Elowever, for exceptionally large synthetic cables another embodiment of corona dischar~e means was devised. This is embodiment ~c) of Fi~ure 5, and is shown in more detail in Figures 8 and 10. As shown in Figure 8, the neck 21 oE the potting head 15 is extended by an outward curving surface 50 identical to the bell-mouth embodiment. However, the arc of the outward curve is carried through approximately 270, to the area 52 shown on Figure 8. This creates a large gener-ally circular collar 48 around the potting head neck.
Collar 48 has a large discharge surface, consistent with the previously mentioned mathematical predictions that increasing the cross-sectional radius of the torroid would reduce the field intensity. The collar 48 also adds struc-tural rigidly to the potting head, which may be important where a larye rope is subjected to very high tension.
Comparison of Figures 7 and 8 show the relative in-tensity of the electrical field distribution around the prior art potting head and the potting head with collar respectively. In Figure 7, a sharp peak field distribu-tion (E max) occurs at the potting head neck close to the rope. In Figure 8, field distribution is relatively uni-S~
form around the collar circumference and E max occurs onthe upper-front quadrant away from the ropeA
Referring now to Figures 9 and 10, preferred embodi-ments of terminal connectors are shown. In Figure 9, -terminal connector 14 has a bell-mouth extension 56 of the neck 20 of potting head 18, and in E'igure 10 terminal con-nector 1~ has a collar 54 around the potting head neck 20.
In both embodiments, the potting head 1~ is an hollow frustoconical chamber up to plane 60. At plane 60, top and bottom sides o~ terminal connector 14 are cut away to from parallel clevis posts 62 and 63. An aperture 64 is provided in each clevis post 62, 63 for insertion therein of a clevis pin (not shown). A ring 66 (shown in ~host lines) may be mounted directly on the mast. By placing the clevis posts 62, 63 over ring 66 and securing thereto with a pin or bolt through aperture 64, the terminal con-nection may be made as close to the mast as practical, thereby reducing the electrostatic field intensity at the point where the synthetic Eiber rope emerges from the potting head. This is consistent with the previously discussed mathematical calculations predicting that the electrostatic field intensity would increase linearly with the distance of the potting head/synthetic rope transition from the mast.
However, in at least one application the synthetic fiber guys cannot be attached close to the mast. That is . . .
the situation of an umbrella antenna in which the antenna array includes flexible conductors disposed in a ~laypole type arrangement from the mast. In those situations, the synthetic guy ropes serve to hold the antennas in the proper outstretched position relative to the mast~ In this situation the electrostatic forces may be considerable at the transition point between the conducting antenna wires and the non-conducting synthetic fibers. For this reason i~ may be necessary to introduce insulator means between the antenna wires and the synthetic rope. As :g S~
; shown in Figure 11, two ceramic egg-insulators 68, 70 connected by a metallic rope 72 are disposed between the antenna wires 74 and the terminal connector 14.
The present invention may be embodied in other spe-cific forms without depar-ting from the spirit or essential attributes thereof and, accordingly, reference should be :~ made to the appended claims, rather than to the foregoing ' specification, as indicating the scope of the invention.
. .
~i ,~
-~i
Claims (6)
1. In combination:
(a) an elevated and grounded metal mast; and (b) one or more guying means, comprising a dielectric synthetic fiber rope, terminal means attached to one end of said rope, said terminal means including a substantially continuous bell-mouth potting head in which splayed fibers of the rope are encapsulated in potting material to attach the terminal means to the rope, and corona discharge means attached to said potting head and disposed annularly around the synthetic rope where the rope enters the potting head to reduce the likelihood of a corona discharge on the rope which may cause the rope to burn in part, said terminal means further including a pair of clevis posts with an aperture therebetween for insertion of a pin, and said mast has attached thereto means for receiving in operative coupling said clevis posts and pin, whereby the synthetic fiber cable is attached in close proximity to the mast to reduce the electrostatic forces on the rope and said bell-mouth potting head withstanding corona breakdown at least up to 280kV/m.
(a) an elevated and grounded metal mast; and (b) one or more guying means, comprising a dielectric synthetic fiber rope, terminal means attached to one end of said rope, said terminal means including a substantially continuous bell-mouth potting head in which splayed fibers of the rope are encapsulated in potting material to attach the terminal means to the rope, and corona discharge means attached to said potting head and disposed annularly around the synthetic rope where the rope enters the potting head to reduce the likelihood of a corona discharge on the rope which may cause the rope to burn in part, said terminal means further including a pair of clevis posts with an aperture therebetween for insertion of a pin, and said mast has attached thereto means for receiving in operative coupling said clevis posts and pin, whereby the synthetic fiber cable is attached in close proximity to the mast to reduce the electrostatic forces on the rope and said bell-mouth potting head withstanding corona breakdown at least up to 280kV/m.
2. Apparatus as in claim 1 wherein the corona discharge means is a bell-mouth extension of the potting head in which the inside arc of the bell mouth is continued through substantially three-quarters of a circle to create a collar around the potting head.
3. For use with a dielectric synthetic fiber rope used as a guy for a mast, a terminal means for attachment to one end of the rope for connecting the rope to the structure to be guyed, comprising:
(a) connecting means comprised of a pair of clevis posts with an aperture therethrough for connecting the terminal means to the structure to be guyed;
(b) a bell-mouth potting head in which splayed fibers of the rope are encapsulated in potting material to attach the terminal means to the rope; and (c) said bell mouth corona discharge means is attached to said potting head and disposed annularly around the synthetic rope where the rope enters the potting head to reduce the likelihood of a corona discharge on the rope which may cause the rope to burn in part and dissipates the electrostatic field strength at least up to 280kV/m.
(a) connecting means comprised of a pair of clevis posts with an aperture therethrough for connecting the terminal means to the structure to be guyed;
(b) a bell-mouth potting head in which splayed fibers of the rope are encapsulated in potting material to attach the terminal means to the rope; and (c) said bell mouth corona discharge means is attached to said potting head and disposed annularly around the synthetic rope where the rope enters the potting head to reduce the likelihood of a corona discharge on the rope which may cause the rope to burn in part and dissipates the electrostatic field strength at least up to 280kV/m.
4. Guying means for an elevated metallic structure comprising a dielectric synthetic fiber rope, terminal means attached to one end of the rope for connecting the rope to an elevated structure, said terminal means including a potting head in which splayed fibers of the rope are encapsulated in potting material to attach the terminal means to the rope, a corona discharge means attached to said potting head and disposed annularly around the synthetic fiber rope where the rope enters the potting head for reducing the likelihood of corona discharge on the rope which may cause the rope to burn, said corona discharge means being a metal bell-mouth extension of the potting head in which the inside arc of the bell-mouth is continued through substantially three-quarters of a circle to create a collar around the potting head at the location where the rope emerges from the potting head.
5. Guying means in accordance with claim 4 wherein said bell-mouth extension curves outwardly before commencing with said portion of a circle.
6. Guying means in accordance with claim 4 including a solid plastic jacket around said rope and in contact with said potting material.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000375354A CA1191251A (en) | 1981-04-13 | 1981-04-13 | Synthetic fiber rope guy means |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000375354A CA1191251A (en) | 1981-04-13 | 1981-04-13 | Synthetic fiber rope guy means |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1191251A true CA1191251A (en) | 1985-07-30 |
Family
ID=4119724
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000375354A Expired CA1191251A (en) | 1981-04-13 | 1981-04-13 | Synthetic fiber rope guy means |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1191251A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011020763A1 (en) * | 2009-08-19 | 2011-02-24 | Brose Fahrzeugteile Gmbh & Co. Kg, Hallstadt | Synthetic fiber rope having load transmission element |
-
1981
- 1981-04-13 CA CA000375354A patent/CA1191251A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011020763A1 (en) * | 2009-08-19 | 2011-02-24 | Brose Fahrzeugteile Gmbh & Co. Kg, Hallstadt | Synthetic fiber rope having load transmission element |
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