FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention: A DEVICE FOR MAINTAINING CONSTANT TENSION IN AN
OVERHEAD POWER LINE FOR ELECTRIC RAILWAYS
2. Applicant(s)
NAME NATIONALITY ADDRESS
RAYCHEM RPG PVT. LTD Indian 463, Dr Annie Besant Road, Worli, Mumbai, Maharashtra, India
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it
is to be performed.

FIELD OF THE INVENTION
[001] The present invention relates to overhead power lines for electrical railways and more particularly, to devices for maintaining constant tension in an overhead power line for electric railway.
BACKGROUND OF THE INVENTION
[002] A railway electrification system supplies electric power to railway train engines and trams. Power is supplied to moving trains with a continuous overhead conductor running along a track that is usually suspended from poles or towers along the track or from structure or tunnel ceilings. An overhead line is designed on the principle of one or more overhead wires situated over rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a high-voltage electrical grid. Electric train engines collect their current from overhead lines using a device such as a pantograph which presses against an underside of a lowest overhead wire, i.e., contact wire.
[003] The length of the overhead line wires tends to change throughout the day by the expansion and contraction of the wire material mostly due to daily cyclic temperature variation and sometimes due to seasonal temperature variations. For example, the length of the wire increases during the day when the temperature is high, which causes increased sagging of the overhead power line. Similarly, the during evening (dusk to dawn) the temperature is lower, and it may cause contraction and over tensioning of the wires which is also undesirable. The wires need to be at a predefined tension maintaining substantially straight configuration with a predefined tolerable sag. If the sag of the line increases, then it may come down and the pantograph may not connect with it at required pressure. Similarly, if the

wire shrinks and the sag disappears and the line goes above the required height, then pantograph may fail to establish contact with the line at some locations. These factors cause the contact loss and negatively affect the current-collecting capability the pantograph. It also induces increased strain on the line which may cause the breakage of overhead contact lines, which leads to operational faults of the overhead contact lines. The moving pantograph causes mechanical oscillations in the OHE (overhead equipment) line (catenary and contact wire) during normal operation, but the wave must travel faster than the train to avoid producing standing waves that would cause disconnect between the wire and the pantograph which may further cause sparking and sometimes breakage. To avoid this, overhead line wires are kept in mechanical tension because tensioning the line makes waves travel faster and prevents other losses.
[004] Several methods and devices are available in art to compensate for the variation in length of the conductor due to thermal expansion and shrinkage of conductor material because of ambient temperature changes. In one method, several dead weights are attached at the end of the wire by means of a pulley system, such that when the length of the line increases due to expansion in summer, and it sags between the two towers, the dead weights pull the line due to gravity and makes the line tight again removing the sag. Similarly, in winter when the line shrinks, the dead weighs move upwards and compensate for the additional length of cable needed, thereby maintaining the cable as tight. Though this method compensates for length variation of the line, however this method fails to maintain the predefined tension as constant in the line which is one major requirement to supply power to the electrical railway engine effectively. Similarly, it requires a large space to install which may be a constraint in some places such as long tunnels.
[005] In other method, spring is also used along with above mentioned

dead weight system. In another method a spring is used along with hydraulic or compressed gas cylinder, however this system is prone to problems due to fluid/gas leakage and requires maintenance frequently.
[006] In view of the limitations inherent in the available devices and method for maintaining constant tension in an overhead power line for electric railways, there exists a need for an improved device which overcomes the disadvantages of the prior art and which can be used in a simple, cost effective, reliable, secure and environmentally friendly manner.
[007] The present invention fulfils this need and provides further advantages as described following.
BRIEF DESCRIPTION OF THE DRAWINGS
[008] The advantages and features of the present invention will become better understood with reference to the following more detailed description taken in conjunction with the accompanying drawings in which:
[009] FIG. 1 illustrates a schematic view of a device for maintaining constant tension in an overhead contact wire for electric railways, according to one embodiment of the present invention;
[0010] FIG. 2 illustrates a schematic view of the device comprising a telescopic casing, according to one embodiment of the present invention;
[0011] FIG. 3 illustrates a schematic view of a cam pulley, according to one embodiment of the present invention;
[0012] FIG. 4 illustrates a schematic view of a polymeric spring used in the device, according to one embodiment of the present invention; and

[0013] FIG. 5 illustrates a schematic view of a rod and tube assembly used in the device, according to one embodiment of the present invention.
[0014] Like names refer to like parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE DRAWINGS
[0015] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details.
[0016] As used herein, the term ‘plurality’ refers to the presence of more than one of the referenced item and the terms ‘a’, ‘an’, and ‘at least’ do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
[0017] Reference herein to “one embodiment” or “another embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention.
[0018] The terms “power line” or “line” or “wire” or “cable” or “conductor” or “contact wire” interchangeably used in the present description, conveys the

same meaning and all refer to the same object.
[0019] A device to maintain a constant tension in an overhead contact wire for electric railways is described in the present subject matter. In an embodiment, the claimed invention overcomes the above-described problems associated with the conventional systems available for maintaining constant tension in an overhead power line for electric railways.
[0020] In accordance with an embodiment of the present subject matter, a device to maintain a constant tension in an overhead contact wire for electric railways includes a telescopic casing that comprises a base plate and a top plate. The telescopic casing further comprises a spring mounted between the top plate and the base plate. The device further includes at least two cam pulleys mounted on the base plate and rotatably connected to each other. Further, the overhead contact wire is coupled to the at least two cam pulleys. In an example, the at least two cam pulleys are variable radius pulleys (also termed as cam). The radius of each of the at least two cam pulleys is set to vary from a minimum value to a maximum value according to an expected variation in a length of the overhead contact wire.
[0021] The variation in length of the overhead contact wire in turn depends on temperature variations in a geographical region where the contact wire is running overhead a railway track and the device is going to be installed to maintain a constant tension in an overhead contact wire. The at least two cam pulleys rotate to compensate a variation in a length of the contact wire. The rotation of the at least two cam pulleys actuates the spring to generate a reaction force which maintains the constant tension in the contact wire. For instance, when the length of the overhead contact wire increases during day hours, the at least two cam pulleys rotate to compensate/wind the increased length over it and the rotation of the at least two cam pulleys expands the spring to generate a reaction force which maintains the constant tension in the overhead contact wire.

[0022] The above and other features, aspects, and advantages of the subject matter will be better explained with regard to the following description and accompanying figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter along with examples described herein and, should not be construed as a limitation to the present subject matter. It is thus understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and examples thereof, are intended to encompass equivalents thereof. Further, for the sake of simplicity, and without limitation, the same numbers are used throughout the drawings to reference like features and components.
[0023] According to an embodiment of the present invention, FIG. 1 illustrates a device 100 for maintaining constant tension in an overhead contact wire 102 for electric railways. The device 100 comprises a telescopic casing 104 formed of two hollow cylinders closed at respective one end and engaging with each other from their respective open ends, a spring 106 mounted between the two closed ends of the telescopic casing 104, a shaft 108 mounted perpendicular to an axis of the telescopic casing 104 at one closed end of one of the hollow cylinder of the telescopic casing 104, at least one constant radius pulley 110 mounted on the shaft 108, at least one internal wire 112 wound over one of the constant radius pulley 110 at one end and connected to the closed end of the other cylinder of the telescopic casing 104, at least two cam pulleys 114-1, 114-2 mounted parallel to the at least one constant radius pulley 110 such that the at least two cam pulleys 114-1, 114-2 and the at least one constant radius pulley 110 rotate with each other when there is rotational motion in the shaft 108. The overhead contact wire 102 or catenary or other wire of the railways which is to be kept in constant tension and compensated for length

variations is connected to the device 100 by the at least two cam pulleys 114-1, 114-2. In an example, the overhead contact wire 102 may be coupled to the at least two cam pulleys 114-1, 114-2 through a rope or a wire running over the at least two cam pulleys 114-1, 114-2. The overhead contact wire 102 may be coupled to a support structure which may in turn be connected to the rope running over the at least two cam pulleys 114-1, 114-2. For example, two ropes wound over the two cam pulleys 114-1, 114-2 may be coupled to a triangular structure following the top plate at two different ends of the triangular structure. The overhead contact wire may be connected to the third end of the triangular structure.
[0024] The telescopic casing is formed of two hollow cylinders: a first hollow cylinder 116 and a second hollow cylinder 118 as shown in FIG. 2. The first hollow cylinder 116 is closed at one end using a base plate 120 and the second hollow cylinder 118 is closed at one end by a top plate 122. The first and the second hollow cylinders 116, 118 are telescopically engaged with each other from their respective open ends, such that the first hollow cylinder 116 moves axially inside the second hollow cylinder 118. The spring 106 is mounted between the base plate 120 and the top plate 122, such that the spring 106 gets expanded or compressed when there is a relative axial movement between the first and second hollow cylinders 116, 118 of the telescopic casing 104. The telescoping casing is provided so that a variability in load requirement during an expansion or a contraction in length of the overhead contact wire 102 can be accommodated. Addition or subtraction of spring 106 can be done based upon the load requirement. The telescopic casing 104 is provided with sealing arrangements at exposed portions to protect the spring 106 inside it from external factors like dust, water to avoid corrosion. As described above, the shaft 108 is mounted on the base plate 120 perpendicular to the axis of the telescopic casing 104 and the shaft 108 connects the at least two cam pulleys 114-1, 114-2 to each other. Further, at least one constant radius pulley 110 is mounted on

the shaft 108 parallel to the at least two cam pulleys 114-1, 114-2. Owing to these features, the at least one constant radius pulley 110 and the at least two cam pulleys 114-1, 114-2 rotate with each other in relation to a rotational motion of the shaft 108.
[0025] In an example, the top plate 122 includes attachments to secure the at least one internal wire 112 with it from inside the telescopic casing 104. The base plate 120 includes arrangement to mount the shaft 108, at least one constant radius pulley 110 and the at least two cam pulleys 114-1, 114-2 over it from outside the casing 104. The base plate 120 further includes support brackets 124 which helps to mount the device 100 on a pole or wall or any support structure.
[0026] As described above, the at least one internal wire 112 is tightly wrapped or wound over the at least one constant radius pulley 110 through one end and connected to the top plate 122, such that when there is a relative axial motion between the first hollow cylinder 116 and the second hollow cylinder 118, the at least one constant radius pulley 110 rotates about the shaft 108 to wind or unwind the internal wire 112 over it. Similarly, in relation to a rotational movement of the at least two cam pulleys 114-1, 114-2, when the at least one constant radius pulley 110 rotates, the internal wire 112 winds or unwinds over it to move the top plate 122 towards or away respectively from the base plate 120 thereby respectively compressing or expanding the spring 106 inside the casing. As described above, the cam pulleys 114-1, 114-2 are mounted parallel to the constant radius pulleys 110 towards outer end of the shaft 108 and rotate along with the constant radius pulley 110 as the shaft 110 rotates.
[0027] The spring 106 acts as an actuator in the device 100 to store the energy and discharges it whenever it is required. Stiffness and sensitivity of the spring 106 is calculated after considering the number of cycles to which

the device 100 may be subjected in its life time. The spring 106 is adapted to generate an elastic reaction which is variable as a function of the variation of the length of the overhead contact wire 102. The spring 106 is connected to the overhead contact wire 102 via the at least two cam pulleys 114-1, 114-2, which are adapted to convert the elastic reaction of the spring 106 into a substantially constant tension force or reaction force applied to the overhead contact wire 102 regardless of its length, within a preset length variation range.
[0028] Referring to FIG. 3 that illustrates a schematic diagram of the cam pulley 114-1, 114-2, according to one embodiment of the present invention. The cam pulley 114-1, 114-2 is a variable radius pulley with the radius changing along its circumference from a minimum radius Rmin to a maximum radius Rmax. The minimum and maximum radius Rmin, Rmax of the at least two cam pulleys 114-1, 114-2 are designed as per the requirement of the variation in length of the overhead contact wire 102 to be compensated. For example, depending on the temperature variations in a geographical area where the overhead contact wire 102 is installed, the maximum expansion and contraction of the material of the overhead contact wire 102 and its dimensions are used to calculate the maximum length of the overhead contact wire 102 to be compensated and then the maximum and minimum radius Rmin, Rmax of the cam pulley 114-1, 114-2 are determined such that the additional length can be wrapped around the cam pulley 114-1, 114-2 or the contraction in the length can be compensated.
[0029] In an example, each of the at least two cam pulleys 114-1, 114-2 includes a pointer (not shown in figure) over a circumference of the respective pulley to set an angle of rotation of the respective cam pulley at an initial installation of the device so as to provide a predefined tension to the overhead contact wire. Thus, the pointer indicates the angle of rotation of the cam pulley 114-1, 114-2 from a pre-decided reference. The angle is

dependent on the variation in length, i.e., maximum and minimum additional length of the overhead contact wire 102 required to be compensated from a minimum temperature to a maximum temperature. The device 100 is calibrated for different temperatures by determining the required length to be compensated and then calibrating the angle of the cam pulley 114-1, 114-2 for that length. In an example, the length of the overhead contact wire to be compensated (i.e., ΔL) for a variation in temperature (ΔT) can be calculated using the formula ΔL=α.L. ΔT, where L is the original length of the overhead contact wire 102 and α is a coefficient of thermal expansion which depends on a material of the overhead contact wire 102.
[0030] When the device 100 has to be installed for the first time at a location, the calibration table is used to rotate and fix the cam pulleys 114-1, 114-2 at that angle so as to provide the required tension to the overhead contact wire 102. When there is any variation in temperature later, for instance, an increase in temperature during summer causes the overhead contact wire 102 to increase in length, then the cam pulleys 114-1, 114-2 rotate to wind the extra length over it, this also rotates the constant radius pulley 110 and unwinds the internal wires 112 over it thereby pushing the top plate 122 away from the base plate 120. This in turn expands the spring 106 and the reaction force generated by this helps to maintain a substantially constant tension in the overhead contact wire. The spring force generated is defined by the below formula:

Where,
T = Tension in the overhead contact wire θ = Angle of rotation of the cam pulley

R0 = Minimum radius of the cam pulley, at θ=0
r = radius of the constant radius pulley
R = Radius of the cam pulley at particular angle ‘θ’
F = Spring force
x = Deflection of spring
k = stiffness of spring
[0031] The spring 106 may include Metallic Bellows, Polymer Spring, Light weight spring etc. The spring 106 may include a plurality of springs 106 connected in series and the telescopic casing 104 with two cylindrical structure provides the device 100, modularity to adjust the telescopic casing 104 to accommodate more number and different size of spring 106.
[0032] In one embodiment of the device 100, the spring 106 is a polymeric spring 400 as shown in FIG. 4. The polymeric spring 400 is made of a polymer whose composition comprising natural or synthetic rubber with additives, accelerators, inhibitors and other components used as per the properties desired of the spring 106. The polymeric spring 400 may be made in cylindrical, polygonal, tapered, spiral and hybrid shapes with solid/ hollow designs. In one preferred embodiment of the present invention, the polymeric spring 400 is of substantially cylindrical shape with concave tapered sides as shown in FIG. 4. In another embodiment of the present invention, the polymeric spring may be reinforced with metallic rods to provide needed strength.
[0033] Referring to FIG. 5 that illustrates a tube 502 and rod 504 assembly used in the device 100, according to one embodiment of the present invention. The tube 502 and rod 504 are telescopically connected to each other at one end and their other respective ends are connected to the base plate 120 and the top plate 122. The tube 502 and rod 504 assembly is adapted to move telescopically with the axial movement of the telescopic

casing 104 of the device 100. The tube 502 and rod 504 assembly may be used to provide strength to a hollow polymeric spring 400 and prevent its bulging when polymeric spring 400 is compressed.
[0034] The device 100 of the present invention may provide advantages as below:
- Provides constant tension to overhead contact wire 102 throughout the cycle of temperature variation
- Combination of the cam pulley and the constant radius pulley to give constant tension in cable
- Highly sensitive to load variation
- Very light weight when used with compression spring like polymer spring/ diaphragm bellows/ gas springs
- Reduced weight < 250 150 kg
- Reduced Footprint – Compactness due to polymer spring
- Universality – Cater to various load requirement of railways Metro and can also be used for bridges and marine applications
Further the use of polymeric spring may provide following advantages:
- Weight reduction upto 50% and compressibility under heavy load application upto 60%
- Less Corrosion for Longer Life
- Field Repairable Assemblies: Safe and convenient installation of track tensioning springs makes this system field repairable
- Achieved Stable Geometries with higher compressibility/ spring functionality and reduced bulging
- Polymer based spring – for reduced manufacturing cost
- Heavy duty Metal/Composite spring replacement by Stable & Functional Elastomeric/ Polymeric/ Hybrid Spring for economical and material savings applications.

[0035] Although a particular exemplary embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized to those skilled in the art that variations or modifications of the disclosed invention, including the rearrangement in the configurations of the parts, changes in steps and their sequences may be possible. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as may fall within the spirit and scope of the present invention.
[0036] It is to be noted that the present description is for the provisional application and it may undergo changes in the terminology, drawings, explanation and details of different components, steps, compositions, material definitions, process details etc. without departing from the spirit or scope of the present invention during filing of the complete specification.

I/We Claim:
1. A device 100 to maintain a constant tension in an overhead contact
wire 102 for electric railways, the device 100 comprising:
a telescopic casing 104 comprising a base plate 120, a top plate 122 and a spring 106 mounted between the top plate 122 and the base plate 120; and
at least two cam pulleys 114-1, 114-2 mounted on the base plate 120, wherein the least two cam pulleys 114-1, 114-2 rotatably connected to each other, and wherein the overhead contact wire 102 is to couple to the at least two cam pulleys 114-1, 114-2,
wherein the at least two cam pulleys 114-1, 114-2 rotate to compensate a variation in a length of the overhead contact wire 102, the rotation of the at least two cam pulleys 114-1, 114-2 to actuate the spring 106 to generate a reaction force to maintain the constant tension in the overhead contact wire 102.
2. The device 100 as claimed in claim 1, wherein the telescopic casing 104 comprises a first hollow cylinder 116 closed at one end by the base plate 120 and a second hollow cylinder 118 closed at one end by the top plate 122, the first hollow cylinder 116 and the second hollow cylinder 118 being telescopically engaged with each other from their respective open ends such that the first hollow cylinder 116 moves axially inside the second hollow cylinder 118.
3. The device 100 as claimed in claim 1, wherein the device 100 comprises a shaft 108 mounted on the base plate 120 perpendicular to an axis of the telescopic casing 104, wherein the shaft 108 connects the least two cam pulleys 114-1, 114-2 to each other.
4. The device 100 as claimed in claim 3, wherein the device 100

comprises: at least one constant radius pulley 110 mounted on the shaft 108 parallel to the at least two cam pulleys 114-1, 114-2, and wherein the at least one constant radius pulley 110 and the at least two cam pulleys 114-1, 114-2 rotate with each other in relation to a rotational motion of the shaft 108.
5. The device 100 as claimed in claim 4, wherein the device 100 comprises an internal wire 112 wound over the at least one constant radius pulley 110 through one end and connected to the top plate 122 from inside the telescopic casing 104 through other end, such that the at least one constant radius pulley 110 rotates about the shaft 108 to wind or unwind the internal wire 112 over the at least one constant radius pulley 110 in relation to axial movement of the first hollow cylinder 116 inside the second hollow cylinder 118.
6. The device 100 as claimed in any one of the preceding claims, wherein in relation to a rotational movement of the at least two cam pulleys 114-1, 114-2, the at least one constant radius pulley 110 rotates and winds or unwinds the internal wire 112 over the at least one constant radius pulley 110 to move the top plate 122 towards or away respectively from the base plate 120 thereby respectively compressing or expanding the spring 106 inside the telescopic casing 104.
7. The device 100 as claimed in any one of the preceding claims, wherein the spring 104 includes metallic bellows, polymer spring, light weight spring.
8. The device 100 as claimed in anyone of the preceding claims, wherein a radius of each of at least two cam pulleys 114-1, 114-2 varies along a circumference of the corresponding cam pulley 114-1, 114-2 from a minimum radius Rmin to a maximum radius Rmax, and wherein the minimum

and the maximum radius Rmin, Rmax depends on the variation in the length of the overhead contact wire 102 to be compensated.
9. The device 100 as claimed in any one of the preceding claims, wherein the base plate 120 includes a support bracket 124 to mount the device 100 on a support structure.
10. The device 100 as claimed in any one of the preceding claims, wherein each of the at least two cam pulleys 114-1, 114-2 includes a pointer over a circumference of the respective cam pulley 114-1, 114-2 to set an angle of rotation of the respective cam pulley 114-1, 114-2 at an initial installation of the device 100 so as to provide a predefined tension to the overhead contact wire 102, the angle of rotation being dependent on the variation in length of the contact wire 102 to be compensated.