Abstract:
The invention used devices that change in length as a function of temperature to mitigate sag in a suspended line. The devices have actuators which change in length as a function of temperature. This change in length is transferred to a linkage mechanism, such as a cog or disc, which amplifies the change in length and changes it to rotational motion that tensions the suspended line. Therefore, the same change in temperature that causes the suspended line to sag will cause the device to actuate a rotary motion that reduces line sag.

Description:
FIELD OF INVENTION 
     This invention relates to mechanical devices for holding electrical transmission lines to towers and the like, and more specifically to such devices that can automatically compensate for changes in transmission line sag caused by changes in ambient temperatures. 
     DESCRIPTION OF THE PRIOR ART 
     Transmission power lines are electrical lines that typically carry high voltage, e.g., 230 KV. For reasons of safety, such lines are suspended well above ground level, typically from towers or the like. FIG. 1 shows towers 10 and 20 that suspend a power line 30. (Although in practice the towers will have extension arms and will carry several lines, for ease of illustration, FIG. 1 has been simplified.) Power line 30 is suspended from towers with insulating devices 40, for example ceramic or glass and rubber and fiberglass insulators whose length can range from a few inches, such as six inches, to over fifteen feet, such as twenty feet, depending on the voltage in the line and the environment. 
     Power lines, which are generally supported by transmission towers, cover large distances. Due to the force of gravity, power lines intrinsically tend to sag. This initial sag increases with line temperature because the conducting material of which the line is made expands as line temperature increases, effectively lengthening the line. A small increase in line length produces a large, and potentially hazardous increase in sag. For example, for a line with a 300 foot tower spacing and an all aluminum conductor, a temperature increase of 30° F., for instance the temperature change between winter and summer months, which causes a 1.4 inch increase in line length, will increase the sag by about 2.2 feet. 
     Increase in line temperature may be due to a number of factors including increased ambient air temperature, decreased wind flow over the line and increased current flow through the line. Sagging power lines create fire hazards and other public safety issues due to ground clearance. 
     Such sag is indicated in FIG. 1 by the phantom-line version of power line 30, 30&#39; which represents the power line&#39;s position at a temperature of T 1 , such that temperature T 1 , is greater than temperature T 0 . The distance from the sagging line to the ground is represented by y. The extent of the sag is indicated by the distance Dy between the power line 30 and the phantom power line 30&#39;. H is the height of the towers and Dx is the span length. Such sag can reduce the clearance between ground and the transmissions lines. The problem of sagging power lines is well known to the electric power industry and is associated with problems which are hazardous and which are both time consuming and expensive to rectify. Sagging power lines pose an electrocution hazard to persons and vehicles and can lead to interruption in power supply and are known to cause hugely destructive and expensive forest and brush fires. 
     It is not known in the prior art how to truly effectively cope with thermal line sag. Present techniques to compensate for such sag include (i) Shortening the distance between adjacent towers to reduce span length and thus reduce line sag; this is shown in FIG. 1A wherein Dx&#39; is shorter than Dx and wherein Dy&#39; is shorter than Dy. (ii) Erecting taller transmission towers to accommodate line sag; this is shown in FIG. 1B in which H&#39; is greater than H and y&#34; is greater than y. (iii) Retro-fitting existing towers to increase height and (iv) Limiting electrical current load capacity to compensate for increased ambient temperature. 
     Seasonal and time of day changes in ambient air temperature are the most significant contributor to changes in line sag. To compensate for increased ambient air temperature during warm summer months or warm days, electric utilities must often reduce current conducted by the power lines at the very time when demand may be highest, e.g., to power air conditioners. Such current limitation may be in the 30% range during summer months, which results in economic losses to the power utility due to inability to meet demand. Needless to say, erecting higher and/or more closely spaced towers represents a further economic cost to the power utility. 
     There is a need for a device that can be used to retain transmission power lines to towers or the like, which device can automatically compensate for changes in ambient temperature to reduce thermal sag in the associated power lines. Preferably such devices should be inexpensive to fabricate, inexpensive to install, and substantially maintenance free. 
     The present invention discloses such a device, and a method for reducing sag caused by temperature increase in suspended electrical transmission wires. 
     FIG. 2 shows a representation of the sag mitigation invention 50 installed on transmission towers 10 and 20 from which the power line 30 is suspended. y&#39;&#34; is the distance between the line and the ground and is unchanging despite varying ambient temperatures. As above, Dx is the distance between the towers and H is the height of the towers. 
     SUMMARY OF THE INVENTION 
     This invention relates to an automatic mechanical device that counteracts axial expansion and hence sagging of suspended lines, such as those used in overhead electric transmission lines, due to ambient temperature increases to keep the profile of the line and hence its sag constant and independent of ambient temperature changes. This device works on the same principal as the axial thermal expansion mechanism of the line but reverses its impact on the sag. That is, as ambient temperature increases (or decreases) so does the line length and its sag, however, same ambient temperature change will increase (or decrease) the length of an actuator which can be a rod made of a material with high thermal expansion coefficient or a hydraulic or a pneumatic device whose length changes with temperature change. The change in actuator length is amplified and transferred through a series of mechanical linkages comprising of lever-type devices or cogs or gears or alike to contract (or extend) the line connections to the device such that the increase (or decrease) in line length is compensated for. 
     One skilled in the art will see that the invention may take many different embodiments, some of which are set out below, depending on the arrangement of structural elements. But each embodiment does the same thing, mitigates line sag, in essentially the same way, by mechanically amplifying and transferring the thermal expansion of a coupling member or actuator to pull in the slack in a suspended line. 
     The objects and advantages of the invention include, but are not limited to: 
     (i) provision of a means of mitigating power line sag which is considerably cheaper than current means; 
     (ii) provision of a means of mitigating power line sag which is automatic and self-adjusting such that the same change in ambient temperature that causes the line to sag will concomitantly cause the invention to act to mitigate the line sag; 
     (iii) provision of a means of mitigating power line sag without the necessity of retrofitting transmission towers to make them taller; 
     (iv) provision of a means of mitigating power line sag which will allow new transmission towers to be spaced at greater intervals than is presently necessary, thereby facilitating the erecting of fewer transmission towers; 
     (v) provision of a means of mitigating power line sag which will allow the building of shorter transmission towers than is presently necessary; 
     (vi) provision of a means of mitigating power line sag without reducing line current (ampacity). 
     (vii) provision of a means of mitigating power line sag which is inexpensive to manufacture and is essentially maintenance-free. 
    
    
     Other features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail, in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a generic power line transmission system according to the prior art showing the problem of line sag; 
     FIG. 1A depicts a generic power line transmission system according to the prior art wherein the problem of line sag has been mitigated by shortening the distance between adjacent towers to reduce span length and thus reduce line sag; 
     FIG. 1B depicts a power line transmission system according to the prior art wherein the problem of line sag has been mitigated by erecting taller transmission towers to accommodate line sag; 
     FIG. 2 depicts a generic power line transmission system in which the power line is suspended by an embodiment of the present invention, being a sag-compensating device; 
     FIG. 3 shows a side view of the invention comprising a coupling member or actuator attached to a reverse-scissor device; 
     FIG. 4 shows a side view of an alternate embodiment of the invention comprising a coupling member or actuator attached to a reverse-scissor device, said reverse-scissor device being coupled to a normal-action scissor device; 
     FIG. 5 shows an alternate embodiment of the invention comprising a coupling member or actuator attached to a series of disks; 
     FIG. 6 shows an alternate embodiment of the invention comprising a coupling member or actuator mounted parallel to an insulator, the actuator being coupled to a rotatable disk via a toothed cog coupling that transfers the axial extension of the actuator to the disk; 
     FIG. 7A shows an alternate embodiment of the invention comprising an actuator mounted within the hollow core of an insulator, connected eccentrically to a shaft such that expansion of the actuator will cause rotation of the shaft. 
     FIG. 7B is a view from the bottom of FIG. 7A. 
     FIG. 7C is a view along section 7C--7C of FIG. 7A. 
     FIG. 8A shows an alternate embodiment of the invention comprising an actuator mounted within the hollow core of an insulator, said actuator being connected to a plate or disk via a linkage system or a skewed gear system such that the axial expansion of the actuator is amplified and is translated through 90° to the connected disk to cause rotation. 
     FIG. 8B is a view from the top of FIG. 8A. 
     FIG. 8C is a view along section 8C--8C of FIG. 8A. 
    
    
     DESCRIPTION OF THE INVENTION 
     A linkage mechanism system that connects the tower to suspended lines to one or more coupling members or actuators amplifies and transfers the axial change in length of actuators, caused by temperature changes, to its line contacts. This device is connected to the tower at its tower contact from which the SLiM device is suspended. The actuator is made of a material with high thermal coefficient of expansion and a high compressive modulus of elasticity such as a metal alloy such as a steel alloy or a composite material such as carbon fiber or glass fiber or a combination composite or an alectrically non-conducting metal-filled plastic. The actuator can also be a hydraulic or pneumatic piston-tube device that comprises a fluid or gas filled vessel made of the aforementioned materials, and filled with a fluid or gas with high thermal expansion bulk modulus (such as a hydrocarbon liquid such as diesel fuel or a gas such as Nitrogen) such that the expansion of the fluid or gas within the vessel will cause the piston to move outwards. The linkage system consists of a series of linkage devices such as lever type devices such as scissors or reverse-scissors or cogs or disks or gears or a combination of lever-type devices and cogs and disks and gears. The linkage device may be packaged in an electrically non-conducting manner to electrically isolate the tower and the tower contact from the suspended lines and line connectors. The components of the linkage device are made of a metal alloys such as steel alloys or a composite material such as carbon fiber or glass fiber or a combination composite or an alectrically non-conducting metal-filled plastic or a ceramic or glass or rubber or a plastic or a wood or a combination of the aforementioned materials. 
     This invention operates automatically responding to the same ambient temperature changes that cause the suspended lines to sag. That is, as ambient temperature changes, so does the length of the actuator or actuators. The axial dimensional change of the actuator or actuators is amplified and transferred through a linkage mechanism device to the suspended lines at its line connectors opposing the change in the length of the suspended line caused by the same ambient temperature change. 
     Various Embodiments 
     FIG. 3 shows a typical embodiment of the invention. A reverse-scissor device 60 is shown having first arms 70 and second arms 80 that may be straight or arched or bent, and that are pivotally attached to each other by a scissor hinge 90. The scissor hinge 90 may serve as the tower contact from which the sag mitigator is suspended. The scissor arms and the scissor hinge may be made of a metal or a metal alloy or ceramic or glass or glass or a carbon composite material or a glass fiber composite material or a strong plastic or wood or some other material with high strength and rigidity. Each arm has a proximal end 100 and a distal end 110. The distal portion of each arm (the distance from the hinge to the distal end of the arm) is longer than the proximal portion of each arm (the distance from the hinge to the proximal end of the arm). The distal end of each arm is attached to the power line 120 being carried and may be insulated by insulators 130 which may be made of an electrically insulating material such as fiberglass, ceramic or glass, rubber or plastic. The proximal ends of the arms are opposably connected to each other by an actuator 140. The actuator 140 is made of a material with a high coefficient of thermal expansion and a high compressive modulus of elasticity, such as a metal alloy such as a steel alloy or a composite material such as carbon fiber or glass fiber or an electrically non-conducting metal-filled plastic. The actuator is thermally-affected such that its length intentionally increases as a function of ambient temperature. The arm geometry and coupling is such that as ambient temperature increases, the actuator length increases, which causes the distal ends of each reverse-scissor arm to approach each other. As the distance separating the distal ends is thus shortened, slack in the power line is taken in, and sag is reduced. In this fashion, thermal sag in the line is passively compensated. The overall size of the device may be from a few inches, such as six inches to over fifteen feet, such as twenty feet in length depending on the voltage carried in the line and the amount of sag to be mitigated. 
     The invention operates automatically, responding to the same ambient temperature changes that cause the power line to sag. In the embodiment shown in FIG. 3, an increase in ambient temperature will cause thermal expansion in the coupling member or actuator 140 which will increase in length. The expansion of the actuator is proportional to the change in ambient temperature. The increase in length of the actuator 140 will force apart the proximal arms 110 of the reverse-scissor component 60. The reverse-scissor component is hinged such that the movement of the proximal arms 100 will be amplified in the longer, distal arms 110 of the reverse-scissor component. The distal arms of the reverse-scissor component will thus be forced together. The movement of the distal arms of the reverse-scissor component will draw in the attached power line 120, taking up the slack in the line. 
     FIG. 4 shows another embodiment of the invention which uses one or more normal-action scissor devices 150 connected to one or more reverse-scissor devices 60. In this embodiment, the proximal ends of the reverse-scissor arms 110 are opposably connected to each other by a coupling member or actuator 140 as described above. The distal reverse-scissor arms 100 are attached to the proximal ends of the normal-action scissor arms 160 by hinges 180. The normal-action scissor device has first arms 190 and second arms 200 that may be straight or arched or bent, and that are pivotally attached to each other by a scissor hinge 220. The scissor hinge 220 may serve as the tower contact from which the sag mitigator is suspended. The normal-action scissor arms and the normal-action scissor hinge may be made from a material as listed for the reverse-scissor arms. The distal ends of the normal-action scissor arms contact the power line to be carried and may be insulated by insulators 130 which may be made of an electrically non-conducting material such as fiberglass, ceramic or glass, rubber or plastic. 
     In this embodiment, shown in FIG. 4, as ambient temperature increases, the actuator 140 length increases. The increase in length of the actuator 140 will force apart the proximal arms 110 of the reverse-scissor component 60. The reverse-scissor component is hinged such that the movement of the proximal arms will be amplified in the longer, distal arms 100. The distal arms of the reverse-scissor component will thus be forced apart. The end of each distal arm of the reverse-scissor component is attached to the proximal arm 160 of a normal-action scissor component 150. The movement of the distal arm of the reverse-scissor component 100 transfers force to the proximal arms 160 of the normal-action scissor component 150, forcing the proximal arms together. The normal-action scissor component is hinged by a hinge 210 such that the movement of the proximal arms 160 will be amplified in the longer, distal arms 170. The distal arms of the normal-action scissor component will thus be forced together. The movement of the distal arms of the normal-action scissor component will draw in the attached power line 120, thus taking up the slack in the line. 
     An alternate embodiment of the embodiment described in FIG. 4 may use any number of normal-action scissor and reverse-scissor devices, linked together, as described above, in such a way as to amplify the axial expansion of the actuator so as to draw in the slack in the line. 
     FIG. 5 shows another embodiment. This alternate embodiment relies on the same principal of thermal expansion and amplification of movement as the above embodiments, but uses rotating disks to transmit and amplify the movement of the coupling member or actuator so as to draw in the slack of the power line. In this embodiment each end of the coupling member or actuator 140 is connected at or close to the circumference of one of a pair of first disks 220. Each first disk may be made of a metal or a metal alloy or ceramic or glass or a carbon composite material or a glass fiber composite material or a strong plastic or wood or some other material with high strength and rigidity. Each first disk is mounted at its central axis to an immovable support 230, such as flat metal or ceramic or glass plate attached to the transmission tower, said mounting allowing rotational freedom of movement of the disk. The actuator 140 is connected to the disks in such a way that when the rod increases in length (due to thermal expansion) it produces a force upon the first disks 220, forcing the first disks to rotate, each in a different direction. Each first disk 220, is attached centrally on the side of each second disk 240, also made of a material as listed for the first disk, such that each first disk lies flat against each second disk, each pair of attached disks having the same axis of rotation, but with the second disk 240 having a greater diameter than the first disk 220. The power line 120 contacts each second disk at or near its rim. The configuration of the actuator and the disks is such that expansion of the actuator will cause the disks to rotate through about 90°, causing each point of attachment to move upward in an arc, towards the other, tightening the power line and reducing the slack. 
     An alternate embodiment of the invention comprises a variation of the above embodiment but uses a series of interlocking toothed disks as gears to amplify the movement of the actuator rod. The number of disks or gears may be increased to increase amplification of the movement of the actuator caused by thermal expansion. 
     FIG. 6 shows another embodiment comprising a suspension member 250 which is insulated by insulators 130, made of an electrically non-conducting material such as fiberglass, ceramic or glass, rubber or plastic. The suspension member 250 has a first end 260 and a second end 270, said first end 260 contacts some part of the transmission tower (not shown). A disk 280 is mounted upon the second end of the suspension member 270 such that the flat surface of the disk is parallel with the long axis of the suspension member and such that the mounting is at center of the disk, allowing rotational movement of the disk 280. A power line 120 to be carried is attached at two places on the rim of the disk. The disk 280 may be made of a metal or a metal alloy or ceramic or glass or a carbon composite material or a glass fiber composite material or a strong plastic or wood or some other material with high strength and rigidity. A toothed cog 290 is securely mounted against the disk 280 at the center of the disk such that when the cog turns so does the disk. An actuator 140 having a first end 300 and a second end 310, is attached parallel and along side the suspension member 250 such that the first end of the actuator 300 is immovably attached to some part of the suspension member, perhaps half way along the length of the suspension member. The second end of the actuator 310 is free to elongate by thermal expansion and has a toothed edge 320 that interlocks with the cog 290. As the actuator increases in length it causes the cog to rotate which in turn causes the disk to rotate thereby tightening the power line and reducing the slack. The overall size of the embodiment, from the first end of the suspension member to the bottom of the disk, may be from a few inches, such as six inches to over fifteen feet, such as twenty feet in length. 
     In this embodiment, as shown in FIG. 6, thermal expansion of the actuator 140 will force the cog 290 to rotate. Rotation of the cog will cause the concomitant rotation of the disk 280 such that the power line 120 will be drawn up, reducing slack in the line. 
     An alternate embodiment of the embodiment described in FIG. 6 uses a skewed gear mechanism or a series of hinged connections, rather than a toothed actuator and toothed cog, to facilitate transfer of force from the actuator to the disk. 
     FIGS. 7A-7C show another embodiment whereby an actuator 330, having a first end 340 and a second end 350 is centrally located within the hollow core of a hollow insulator 360, said insulator having a first end 370 and a second end 380, said first end 370 being attached to some part of a transmission tower (not shown) and said second end 380 being forked. The first end of the actuator 340 is immovably attached within the hollow core of the first end of the insulator 370. The second end of the actuator 350 attaches eccentrically to a rotatable shaft 390, said rotatable shaft being mounted in a plane perpendicular to the length of the actuator rod, and being rotatably mounted between the two forks of said second end of said insulator 380 such that an increase in length of the actuator 350 will exert an eccentric force on the rotatable shaft 390 causing the shaft to rotate. One or more disks 400 are immovably attached to the shaft such that the such that the shaft forms an axle which when rotated, causes the disks to rotate. A power line 120 to be carried is attached to the disks 400 such that when the disks rotate, the power line is drawn up and the slack in the line is reduced. 
     In this embodiment, as shown in FIG. 7, thermal expansion of the actuator 350 exerts an eccentric force upon the shaft 390, which is rotatably mounted between the forks of the second end of the insulator 380. As the shaft rotates, it causes the concomitant rotation of one or more disks 400. The power line is attached at or near the circumference of these disks such that when they are caused to rotate, the power line is drawn up and slack is reduced. 
     FIGS. 8A-8C show another embodiment whereby an actuator 410, having a first end 420 and a second end 430 is centrally located within the hollow core of a hollow insulator 440, said insulator having a first end 450 and a second end 460, said first end 450 being attached to some part of a transmission tower (not shown). Said first end of said actuator having immovably attached at its end a first skewed toothed cog 470. Said first skewed toothed cog 470 cooperating with a complimentary second toothed cog 480. Said second skewed toothed cog is immovably attached to a rotating plate 490. Said rotating plate is held in place by the bottom section 500 of said second end of said insulator 460. A Bearing plate 510 lies between said rotating plate 490 and said bottom section 500 of said second end of said insulator. Said rotating plate 490 attaches to a power line to be carried 120. In this embodiment, as the actuator increases in length due to thermal expansion, the first 470 and second 480 skewed toothed cogs communicate such that the second skewed toothed cog is forced to rotate, thereby causing the rotating plate to concomitantly rotate, thereby drawing in the power line and reducing slack in the line. 
     An alternate embodiment differs from the afore-mentioned embodiments only in that the actuator is replaced with a hydraulic or pneumatic piston-tube that comprises a fluid-filled vessel, such as a tube, one end of which is closed and the other end of which accommodates a piston, slidably mounted in the vessel such that an expansion of the fluid (such as a hydrocarbon liquid such as diesel fuel, or a gas such as Nitrogen) within the vessel will cause the piston to move outward. In this manner, the hydraulic or pneumatic piston-tube will respond to an increase in ambient temperature in the same way as the actuator rod, exerting force on members so as to ultimately cause the slack in a power line to be reduced. 
     An alternate embodiment differs from the afore-mentioned embodiments only in that the coupling member or actuator or piston-tube is clad in a heating jacket. The heating jacket may comprise an insulated electric heating element, with current being supplied from the power line. The heating element will be heated in proportion to the current being carried in the line. This heating effect will cause the actuator or piston-tube to expand, reducing slack in the line and so counteracting the sag effects due to heating of the power line due to increased current flow in the power line. 
     An alternate embodiment differs from the afore-mentioned embodiments in that the arms or disks carrying the power line are caused to move by the action of a powered motor, such as an electric motor, thereby reducing line sag. 
     SUMMARY, RAMIFICATIONS AND SCOPE 
     Accordingly, it will be apparent that the invention will automatically counteract the effects of line sag caused by thermal expansion of the line and will allow the building of fewer, shorter towers and will reduce the cost of retrofitting existing towers and will allow the transmission of higher currents during times of peak electricity demand. 
     The invention provides a means of mitigating power line sag which is considerably cheaper than current means; it provides a means of mitigating power line sag which is automatic and self-adjusting such that the same change in ambient temperature that causes the line to sag will concomitantly cause the invention to act to mitigate the line sag;; it provides a means of mitigating power line sag without the necessity of retrofitting transmission towers to make them taller; it provides a means of mitigating power line sag which will allow transmission towers to be spaced at greater intervals than is presently necessary, thereby necessitating the erecting of fewer transmission towers; it provides a means of mitigating power line sag which will allow the building of shorter transmission towers than is presently necessary; it also provides a means of mitigating power line sag without reducing line current (load). 
     Additionally, the invention is a relatively simple mechanical device, reducing the cost of manufacture and also reducing the probable need for maintenance. The invention is equally applicable to any suspended line, not just to a line carrying electric power. 
     The specificities in the above description should not be construed to limit the scope of the invention, but rather as examples of possible preferred embodiments. The sizes of the components may vary depending on the size of the tower to which the invention is fitted and the size of the voltage being carried in the power line. The materials used to construct the components may be as suggested above or may be any other materials with suitable mechanical and electrical properties. In the embodiments that involve scissor components, the arrangement and number of scissor components may be varied to change amplification of movement or to decrease stress on the individual components. In the embodiment using a gear or disk system, the arrangement or number of gears may likewise be varied. The actuator may be made of a number of substances which expand in response to increasing temperature such as metal alloys but may be made from other substances such as composite materials such as carbon fiber, glass fiber, or an electrically non-conducting metal-filled plastic and the like. 
     Thus, since numerous modifications and alternate embodiments will readily occur to those skilled in the art, the scope of the invention should not be limited by the afore-mentioned illustrative embodiments, but should be determined by the appended claims and their equivalents.