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 WIRE OF 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 day hours when the temperature is high, which causes increased sagging of the overhead power line. Similarly, during evening (dusk to down) 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 of the pantograph. It also induces increased strain on the line which may cause the breakage of overhead contact lines, which leads to operation faults of the overhead contact lines. The moving pantograph causes mechanical oscillations in the overhead equipment (OHE) 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 overhead line wire by means of a pulley system, such that when the length of the line wire 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 wire tight again removing the sag.
[005] Similarly, during winter season when the line wire shrinks, the dead weighs move upwards and compensate for the additional length of the line wire needed, thereby maintaining the line wire tight. Though this method compensates for length variation of the line wire, however this method fails to maintain the predefined tension as constant in the line wire 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.
[006] 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. Further, the springs required are of very high stiffness value, which are huge in size and weight, thereby making the system bulky and complicated.

[007] 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.
[008] The present invention fulfils this need and provides further advantages as described following.
BRIEF DESCRIPTION OF THE DRAWINGS
[009] 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:
[0010] 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; and
[0011] FIG. 2 illustrates a schematic view of a cam, according to one embodiment of the present invention; and
[0012] FIG. 3 illustrates a schematic view of the device for maintaining constant tension without casing, according to one embodiment of the present invention.
[0013] Like names refer to like parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE DRAWINGS
[0014] 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.
[0015] 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.

[0016] 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.
[0017] The terms “power line” or “line” or “wire” or “cable” or “conductor” or “line wire” or “contact wire” are interchangeably used in the present description, all refer to an overhead power line for railways which is to be kept in constant tension either individually or in combination of other similar wires used for the similar purpose. All terms convey the same meaning, and all refer to the same object.
[0018] 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 contact wire for electric railways.
[0019] In accordance with an embodiment of the present subject matter, the device to maintain a constant tension in an overhead contact wire for electric railways includes a casing that comprises a base plate and two side plates. The two side plates are attached to two respective sides of the base plate such that the two side plates are substantially parallel to each other. The device further comprises two torsional springs mounted at the two respective side plates. The device also includes a cam mounted between the two side plates. Further, the overhead contact wire is coupled to the cam. In an example, the cam pulley is a variable radius pulley. The radius of the cam may be set to vary along a circumference of the cam according to an expected variation in a length of the overhead contact wire.
[0020] The variation in length of the overhead contact wire, as mentioned

above, in turn depends on temperature variations in a geographical region where the contact wire is running overhead a railway track and the device is to be installed to maintain a constant tension in the overhead contact wire. The cam rotates to compensate a variation in a length of the contact wire. The rotation of the cam actuates the spring to generate a force which maintains the constant tension in the overhead contact wire. For instance, when the length of the overhead contact wire increases in case of an increase in temperature during day hours, the pulley rotates to wind the increased length over it and the rotation of the cam actuates the two torsional springs which may get compressed and generate a force which maintains the constant tension in the overhead contact wire.
[0021] 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.
[0022] 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 casing 104 formed by a base plate 106 with two side plates 108-1, 108-2 attached substantially parallel to two respective sides of the base plate 106, two torsional springs 110-1, 110-2 mounted at the two respective side plates 108-1, 108-2 and a cam 112 mounted between the two side plates 108-1, 108-2. The device further comprises a first shaft 114 rotatably mounted between the two side plates 108-1, 108-2 and perpendicular to the two side plates 108-1, 108-2 of the casing 104. The cam 112 and a cam pulley 116 is mounted on the first shaft 114 such that the first shaft 114 rotates along the rotation of the cam

112 thereby rotating the cam pulley 116. The device also comprises a second shaft 118 rotatably mounted between the two side plates 108-1, 108-2 and perpendicular to the two side plates 108-1, 108-2 and a drum 120 mounted on the second shaft 118. The drum 120 is mounted on the second shaft 118 such that the second shaft 118 rotates along with a rotation of the drum 120. The device comprises a third shaft 122 rotatably mounted between the two side plates 108-1, 108-2 and perpendicular to the two side plates 108-1, 108-2 and a spring pulley 124 mounted on the third shaft 122. In an example, the two torsional springs 110-1, 110-2 are attached at two respective ends of the third shaft 122. The spring pulley 124 is mounted on the third shaft 122 such that the third shaft 122 rotates along with a rotation of the spring pulley 124. The rotation of the third shaft 122 actuates the two torsional springs 110-1, 110-2.
[0023] In an example implementation, the device 100
comprises a first rope 126 wound over the cam 112. A first end 126-1 of the first rope 126 is connected to the overhead contact wire 102 and a second end 126-2 of the first rope 126 is wrapped over the cam 112 and fixed on the cam 112. The device 100 further comprises a second rope 128. A first end 128-1 of the second rope 128 is connected to the cam pulley 116 and a second end 128-2 of the second rope 128 is connected to the spring pulley 124. The second rope 128 is wound over the drum 120 and the spring pulley 124 such that the drum 120 and the spring pulley 124 rotate in relation to a rotational motion of the cam pulley 116. In another word, the second rope 128 starting from the spring pulley 124 of third shaft 122 where it is wrapped, is wrapped with multiple turns over the drum 120 and then attached to the cam pulley 116. As mentioned above, the third shaft 122 further includes at least two torsional springs 110-1, 110-2 connected at its two respective ends which helps to keep the second rope in a predefined tension.
[0024] In an example, the base plate 106 is a rectangular plate which forms the foundation of the device 100 to mount all other components on it. One side of the base plate 106 is used to install the device 100 on a pole or flat surface. The two side plates 108-1, 108-2 are perpendicular to the base plate 106 from the two parallel sides of the base plate 106 to form the casing 104. The space between the two side plates 108-1, 108-2 is used to mount

other components of the device 100 such as the two torsional springs 110, the cam 112, the cam pulley 116, the drum 120 or the spring pulley 124.
[0025] In an example, the two side plates 108-1, 108-2 are of substantially trapezoidal shape with its one edge aligned with the base plate 106 and the opposite vertex of that edge is curved as shown in the FIG. 1. A first hole is provided near the curved vertex end of both of the two side plates 108-1, 108-2 to allow holding of the first shaft 114 in it. A second hole is provided in the middle of both of the two side plates 108-1, 108-2 along its length to allow holding of the second shaft 118 in it. Similarly, a third hole provided towards the base plate 106 end of the two side plates 108-1, 108-2, which holds the third shaft 122. The device 100 may further include bearings installed between the two holes and their corresponding shafts for smooth rotation of the first, second and third shafts 114, 118, 122. The casing 104 may be made of Aluminium or any suitable material which can withstand the weight and strength requirement of the device 100 of the present invention.
[0026] FIG. 2 illustrates a schematic view of the cam pulley 116 and cam 112, according to one embodiment of the present invention. The cam 112 mounted on the first shaft 114 is a variable radius pulley. The cam 112 is a circular disc with its radius varying during 360-degree rotation to define a cam profile. Thus, the radius of the cam 112 varies along a circumference of the cam 112. The length of a perimeter of the cam profile is designed such that in one rotation, the cam 112 should wound/unwound a predefined length of the overhead contact wire 102 which is equal to the maximum length of contact wire 102 to be compensated. The use of the cam 112 which has variable radius helps to decrease the diameter of a constant pulley, i.e., the cam pulley 116 required to achieve same length of wrapping of a rope such as the first rope 126 or the second rope 128, which eventually reduces overall weight of the device 100. The variation in the tension with respect to change in length of the overhead contact wire 102 during expansion or contraction is equally compensated by the variable radius of the cam 112. The second shaft 118 also has the cam pulley 116 mounted thereon which is a contact radius pulley. The cam 112 and the cam pulley 116 both rotate simultaneously. The first rope 126 is wound over the cam 112. The first end 128-1 of the second rope 128 is fixed over the cam pulley 116 and the second end 128-2 of the second rope 128 is wrapped

over the drum 120 on the second shaft 118 and then over the spring pulley 124 mounted on the third shaft 122 and fixed on it, such that all the three shafts rotate simultaneously.
[0027] In an example, the cam 112, the cam pulley 116, the drum 120 and the spring pulley 124 comprise grooves 130 over respective surfaces of the cam 112, the cam pulley 116, the drum 120 and the spring pulley 124. The first rope 126 follows the grooves over the cam 112 and the second rope 128 follows the grooves over the cam pulley 116, the drum 120 and the spring pulley 124. As described above, the drum120 with multiple grooves is mounted on the second shaft 118. It is a hollow cylinder with grooves 130 on its surface which corresponds with the shape and size of the second rope 128. The width of the base plate 104 and the distance between the two parallel side plates 108-1, 108-2 is defined by the width of the drum 120. The distance between the two side plates 108-1, 108-2 should be such that the drum 120 can be easily mounted between the two side plates 108-1, 108-2 on the second shaft 118 without touching the two side plates 108-1, 108-2 and is free to rotate.
[0028] As described above, the third shaft 122 has the spring pulley 124 mounted thereon in middle with two torsional springs 110-1, 110-2 at its two respective ends. The spring pulley 124 is a constant radius pulley and it may also be a spring-based pulley in one embodiment of the present invention. The torsional springs 110-1, 110-2 may be flat springs in one embodiment of the present invention. At the extreme ends of the third shaft 122, the torsional springs 110-1, 110-2 are placed which can resist the movement of the third shaft 122 and hence provide the required spring force. In an example, the specification/ weight of the torsional springs 110-1, 110-2 are so chosen that it can take load upto 2KN or more which can be amplified using the drum 120 mounted on second shaft 118 using Capstan method. The design of torsional springs 110-1, 110-2, number of turns of the second rope 128 on the drum 120 and on the spring pulley 124, material between the second rope 128 and the drum which is cylindrical in shape on the spring pulley would depend on the design calculations based on the load to be maintained. The use of the torsional springs 110-1, 110-2 provides a large

tensioning force in reduced size. This eventually reduces the overall length of the device 100 and the device 100 can be installed at places where the space is a constraint.
[0029] As explained, the first rope 126 is attached with the overhead contact wire from its first end 126-1 and then its wrapped over the groove of the cam 112 and then its gets terminated there on the cam 112 itself. The second rope 128 is connected to the cam pulley 116 through its first end 128-1 and then wrapped over the drum 120 for several turns and then the second end 128-2 of the second rope 128 is wrapped and attached on the spring pulley 124 as shown in FIG. 3. Thus, the cam 112 contains the first rope 126 which is connected with the overhead contact wire or OHE line through its first end 126-1 and get terminated there. The second end 126-2 of the first rope 126 is terminated on the cam 112 itself. In this way the first rope 126 on the cam is completely independent of the second rope 128.
[0030] In an example, the spring pulley 124 is a constant radius pulley. The device 100 may further include a rope guide (not shown in figures) to guide the second rope 128 as the drum 120 rotates preventing slipping of the second rope 128 from the drum 120. The rope guide may also be provided with locking arrangement to lock the second rope 128 in the grooves of the drum 120. Further metallic clamps may be provided to make sure that the second rope 128 does not slide out of the grooves provided on the drum 120.
[0031] As described above, the dimensions of the cam 112, the cam pulley 116, the spring pulley 124, a radius of the drum and a number of turns of the second rope 128 on the drum 120 is designed as per the requirement of the overhead contact wire 102 length to be compensated. For example, depending on the temperature variations in a geographical area where the overhead contact wire 102 is installed, a maximum expansion and a contraction of the material of the overhead contact wire 102 and its dimensions are used to calculate a maximum length of the overhead contact wire 102 to be compensated and then the dimensions such as the cam 112, the radius of the cam pulley 116, the spring pulley, the radius of the drum 120 and the number of turns of the second rope 128 on the drum 120 are

determined such that the additional length can be wrapped over the cam 112 in case of an expansion in the length or the contraction in the length can be compensated by releasing the first rope 126 from the cam 112.
[0032] The two torsional springs 110-1, 110-2 are attached on the respective ends of the third shaft 122, such that the axis of the two torsional springs 110-1, 110-2 is parallel to the third shaft 122 and both the torsional springs 110-1, 110-2 are parallel to each other. In an example, the torsional springs 110-1, 110-2 are flat springs which may be mounted on the third shaft 122 and provide the needed predefined tension force as per the requirements of the device 100.
[0033] The wrapping of the second rope 128 over the drum 120 utilizes the tension amplification principle which is defined by Euler-Eytelwein equation. The equation relates the tension of the two ends 128-1, 128-2 of the second rope 128.

where
- Tload is a load force or a tension required to be maintained at the output side of the device,
- Thold is a hold force to be applied by the spring,
- µ is a coefficient of static friction between the second rope 128 and the spring pulley or the drum 120;
- ϕ is the total effective angle of contact in radians (one complete turn corresponds to 4 = 2π radians)
- Hold or load force neither depend on the radius of the drum nor the total contact area.
- Equation valid for non-rigid & non-elastic types of rope/wire only. Equation also assumes “no sliding” between the rope and the cylinder/drum.
[0034] The overhead contact wire 102 is connected with the first rope 126, so when there is any extension or contraction in the length of the overhead contact wire 102, it pulls or contracts the first rope 126 which then rotates

the cam 112 which in reaction rotates the first shaft 114. Rotation of the first shaft in turn rotates the cam pulley 116 which in turn pulls or contracts the second rope 128. Thus, the first shaft 114 actuates the second rope 128 which is wound over the drum 120 mounted on the second shaft 118 and terminated on the third shaft 122. The second shaft 118 has the drum 120 mounted thereon and having multiple grooves which guides the second rope 128 towards the third shaft 122 where the second rope 128 gets terminated on the spring pulley 124. Any rotation of the first shaft 114 rotates the second 118 and the third 122 shafts. However, it is to be noted that the load amplification happens at the second shaft 118 using the drum 120 where the second rope 128 is wounded with multiple turns. Rotation of the third shaft 122 actuate both of the two torsional springs 110-1, 110-2 immediately and comes into action, by resisting the pull form the second rope 128.
[0035] Interaction of frictional forces and tension leads to different tension on either side of the drum 120. A small holding force applied on one side can carry a much larger loading force on the other side. The tension force increases exponentially with the coefficient of friction and the number of turns around the drum 120. Most of the force required to hold the overhead contact wire 102 which has to be kept in tension, is provided by the rope over drum system, i.e., the second rope 128 and the drum 120. The first rope 126 wrapped over the cam 112 and the torsional springs 110-1, 110-2 further adds to the force and accommodates for any variation in the force required due to expansion/contraction of the overhead contact wire 102. This first rope 126 over the cam 112, the drum 120 and the torsional springs 110-1, 110-2 allows to provide similar force which was previously provided by bulky springs. This device 100 eliminates the need of such bulky springs, dead weights and other accessories required to provide the needed force thereby making the device 100 compact and simple.
[0036] In an example, the number of turns on the drum 120, the coefficient of friction, the cam 112 profile and the stiffness of the two torsional springs 110-1, 110-2 and their dimensions are designed as per the requirements of the force needed for holding the overhead contact wire 102 in constant tension.

[0037] In an example, to compensate the variation in length of the overhead contact 102, the cam 112 and the drum 120 rotates to wind or release the first rope over the cam 112 and the second rope over the drum, respectively and the two springs are respectively compressed or expanded. For instance, during summer season, if there is an expansion in the length of the overhead contact wire 102, it has a tendency to sag, however the device 100 of the present invention will prevent it by pulling the overhead contact wire 102. The torsional springs 110-1, 110-2 may get compressed to rotate the third shaft 122 in clockwise direction which will eventually rotates the drum 120 on the second shaft 118, which wraps some length of the second rope 128 over it, thereby pulling the overhead contact wire 102 via the first rope 126 of the first shaft 114 and maintaining constant tension in it. Similarly, in winter season if the overhead contact wire 102 contracts, the two torsional springs may expand and rotate the spring pulley 124 in counter clockwise direction which will rotate the drum 120 and the cam pulley 116 making some length of the second rope 128 being released such that the overhead contact wire 102 remains in the predefined tension.
[0038] In an example, the device is calibrated for different temperatures by determining the compensation overhead contact wire 102 length required and then designing the dimension of different components such as the dimension of the cam 112, the cam pulley 116 and the spring pulley 124, a radius of the drum 120 and a number of turns of the second rope 128 on the drum 120 of the device 100 of the present invention. Based on the temperature of the ambient at the place of installation, a calculated preload will be applied to the torsional springs 110-1, 110-2 by pulling the second rope 128, so that the torsional springs 110-1, 110-2 compensates the change in tension due to expansion or contraction of contact and overhead contact wires 102. In an example, the spring design may be chosen, so that it provides only one-tenth to one-fifteenth of the load requirement as per the Eytelwin’s formula.
[0039] 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 rope 126, 128, the drum, the cam system (the cam 112 and the cam pulley 116) and the torsional springs 110-1, 110-2 to utilize tension amplification principle gives constant tension in overhead contact wire 102 with simpler spring
- Highly sensitive to load variation
- Reduced weight because of elimination of bulky springs and dead weights
- Simple Design
- Reduced Footprint – Compactness
- Universality – Cater to various load requirement of railways and Metro and can also be used for bridges and marine applications.
- Lesser number of components makes installation easier – Simpler mounting to the mast with bolts and then the first rope may directly be connected to overhead lines
- Can also be easily installed in tunnels.
- Reduced Footprint – Very Compact as compared to all the previous designs
- Scalability – Current system is scalable which increases its areas of application with respect to different types of overhead lines
- Lesser cost of installation - There is no need to arrange an auxiliary set up for counterweights
- Reduced weight (less than 110 kg)
- Compact and light weight – With introduction of the torsional springs 110-1, 110-2 at the third shaft’s ends for highest load application, there is a significant reduction in weight.
- Very light weight when used with compression spring like metallic spring/ diaphragm bellows/ gas springs
[0040] 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.

[0041] 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 casing 104 comprising a base plate 106 and two side plates 108-1, 108-2, the two side plates 108-1, 108-2 attached to two respective sides of the base plate 106 such that the two side plates 108-1, 108-2 are substantially parallel to each other;
two torsional springs 110-1, 110-2 mounted at the two respective side plates 108-1, 108-2;
a cam 112 mounted between the two side plates 108-1, 108-2, wherein the overhead contact wire 102 is to couple to the cam 112,
wherein the cam 112 rotates to compensate a variation in a length of the overhead contact wire 102, the rotation of the cam 112 actuates the two torsional springs 110-1, 110-2 to generate a force to maintain the constant tension in the overhead contact wire 102.
2. The device 100 as claimed in claim 1, wherein the device 100 comprises a first shaft 114 rotatably mounted between the two side plates 108-1, 108-2 and perpendicular to the two side plates 108-1, 108-2 and wherein the cam 112 and a cam pulley 116 is mounted on the first shaft 114 such that the first shaft 114 rotates along the rotation of the cam 112 thereby rotating the cam pulley 114.
3. The device 100 as claimed in claim 1, wherein the device 100 comprises a first rope 126 wound over the cam 112, and wherein a first end 126-1 of the first rope 126 is to couple the overhead contact wire 102 to the cam 112 and a second end 126-2 of the first rope 126 is fixed to the cam 112.
4. The device 100 as claimed in claim 1, wherein the device 100 comprises a second shaft 118 rotatably mounted between the two side plates 108-1, 108-2 and perpendicular to the two side plates 108-1, 108-2; and a drum 120 mounted on the second shaft 118 such that the second shaft 118 rotates along with a rotation of the drum 120.

5. The device 120 as claimed in claim 4, wherein the device 100 comprises a third shaft 122 rotatably mounted between the two side plates 108-1, 108-2 and perpendicular to the two side plates 108-1, 108-2 such that the two torsional springs 110-1, 110-2 are attached at two respective ends of the third shaft 122; and a spring pulley 124 mounted on the third shaft 122 such that the third shaft 122 rotates along with a rotation of the spring pulley 124, and wherein the rotation of the third shaft 122 actuates the two torsional springs 110-1, 110-2.
6. The device 100 as claimed in claim 5, wherein the device 100 comprises a second rope 128, wherein a first end 128-1 of the second rope 128 is connected to the cam pulley 116 and a second end 128-2 of the second rope 128 is connected to the spring pulley 124; wherein the second rope 128 is wound over the drum 120 and the spring pulley 124 such that the drum 120 and the spring pulley 124 rotate in relation to a rotational motion of the cam pulley 116.
7. The device 100 as claimed in claim 1, wherein a radius of the cam 112 varies along a circumference of the cam 112, and wherein the radius depends on an expected maximum variation in the length of the overhead contact wire 102 to be compensated.
8. The device 100 as claimed in any one of the preceding claims, wherein to compensate the variation in length of the overhead contact wire 102, the cam 112 and the drum 120 rotates to wind or release the first rope over the cam 112 and the second rope over the drum 120 respectively, and the torsional springs 110-1, 110-2 are respectively compressed or expanded.
9. The device 100 as claimed in in any one of the preceding claims, wherein the cam 112, the cam pulley 116, the drum 120 and the spring pulley 124 comprise grooves 130 over respective surfaces of the cam 112, the cam pulley 116, the drum 120 and the spring pulley 124, and wherein the first rope 126 follows the grooves over the cam 112 and the second rope 128 follows the grooves over the cam pulley 116, the drum 120 and the spring pulley 124.

10. The device 100 as claimed in any one of the preceding claims, wherein the two torsional springs 110-1, 110-2 are flat springs.