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 400030, 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, the and 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 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 length 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 pulley, according to one embodiment of the present invention; and
[0012] FIG. 3 illustrates a schematic view of the cam pulley with a drum, a rope and a spring, 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” 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 plate. The two side plates are attached to two respective sides of the base plate such that the two side plates are in parallel to each other. The device further comprises a spring mounted at the base plate. The device also includes a cam pulley mounted between the two side plates. Further, the overhead contact wire is coupled to the cam pulley. In an example, the cam pulley is a variable radius pulley. The radius of the cam pulley may be set to vary along a circumference of the cam pulley according to an expected variation in a length of the overhead contact wire.
[0020] 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 to be installed to maintain a constant tension in the overhead contact wire. The cam pulley rotates to compensate a variation in a length of the contact wire. The rotation of the frustum pulley 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 cam pulley rotates to wind the increased length over it and the rotation of the frustum pulley actuates the spring 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 parallel to two respective sides of the base plate 106, a spring 110 mounted at the base plate 106 and a cam pulley 112 mounted between the two side plates 118-1, 118-2. The device 100 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, and a drum 116 mounted on the first shaft 114. The drum 116 is mounted on the first shaft 114 such that the first shaft 114 rotates along with a rotation of the drum 116. The device 100 also comprises second shaft 118 rotatably mounted between the two side plates108-1, 108-2 and perpendicular to the two side plates 108-1, 108-2. In an example, the cam pulley 112 is mounted on the second shaft 118 such that the second shaft 118 rotates along the rotation of the cam pulley 112. The cam pulley 112 is mounted on the second shaft 118 perpendicular to the two side plates 108-1, 108-2 or walls of the casing 104. The device 100 further comprises a rope 120 wound over the cam pulley 112 and the drum 116 such that a first end 120-1 of the rope 120 is

connected to the overhead contact wire 102 and a second end 120-2 of the rope 120 is connected to the spring 110. The spring 110 is mounted at the base plate 106 perpendicular to an axis of the spring 110 through other end. In an example, the spring 110 may be a tension spring.
[0023] 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 spring 110, the cam pulley 112 or the drum 116.
[0024] 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 in the middle 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 near the curved vertex end of both of the two side plates 108-1, 108-2 to allow holding of the second shaft 118 in it. The device 100 may further include bearings 122 installed between the two holes and their corresponding shafts for smooth rotation of the first and second shafts 114, 118. 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.
[0025] FIG. 2 illustrates a schematic view of the cam pulley 112, according to one embodiment of the present invention. The cam pulley 112 is a circular disc with its radius varying during 360-degree rotation to define a cam profile. Thus, the radius of the cam pulley 112 varies along a circumference of the cam pulley 112. The length of a perimeter of the cam profile is designed such that in one rotation, the cam pulley 112 should

wound/unwound a predefined length of the overhead contact wire 102.
Thus, the radius of the cam pulley 112 depends on an expected the
maximum variation in length of the overhead contact wire 102 to be compensated.
[0026] In an example, the cam pulley 112 and the drum 116 comprises spiral groove 124 over respective surfaces of the cam pulley 112 and the drum 116. The rope 120 follows the spiral grooves 124 over the cam pulley 112 and the drum 116. The drum 116 with spiral grooves 124 is mounted on the first shaft 114. The drum 112 is a hollow cylinder with the spiral grooves 124 over its surface. The spiral grooves 124 over the respective surfaces of the cam pulley 112 and the drum 116 corresponds with a shape and size of the rope 120. A width of the base plate 106 and a distance between the two parallel side plates 108-1, 108-2 is defined by a width of the drum 116. The distance between the two side plates 108-1, 108-2 should be such that the drum 116 can be easily mounted between them on the first shaft 114 without touching the two side plates 108-1, 108-2 and is free to rotate.
[0027] In an example, the rope 120 is wound over the cam pulley 112 and the drum 110 such that the drum 116 rotates in relation to a rotational motion of the cam pulley 112. Further, as described above the first end 120-1 of the rope 120 couples the overhead contact wire 102 to the cam pulley 112 and a second end 120-2 of the rope 120 is connected to one end of the spring 110. The rope 120 is attached with the overhead contact wire 102 from its first end 120-1 and then the rope 120 is wrapped over the spiral groove 124 of the cam pulley 112 and then it is wrapped over the drum 116 for several turns and the second end 120-2 of the rope 120 is attached with the spring as shown in FIG. 3. The device 100 may further include a rope guide to guide the rope 120 as the drum 116 rotates preventing slipping of the rope 120 from the drum 116. The rope guide may also be provided with locking arrangement to lock the rope 120 in the spiral grooves 124 of the drum 116.

[0028] As described above, the dimension of the cam pulley 112, a radius of the drum 116 and a number of turns of the rope 120 on the drum 116 is designed as per the requirement of the overhead contact wire 102 length to be compensated. For example, depending on 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 radius of the cam pulley 112, the radius of the drum 116 and the number of turns of the rope 120 on the drum 116 are determined such that the additional length can be wrapped over the cam pulley 112 in case of an expansion in the length or the contraction in the length can be compensated by releasing the rope 116 from the cam pulley 112 and the drum 116.
[0029] The spring 110 is attached to the base plate 116, such that the axis of the spring 110 is perpendicular to the base plate 106 and its one end is free to be coupled to the rope 120. In one embodiment, the device 100 may further include a support pipe 126 mounted perpendicular to the base plate 106 at a location where the spring 110 is mounted, such that the spring 110 is supported from inside during operation of the device 100. The support pipe 126 allows the spring 110 to be pushed over it and get attached to the base plate 106 in such a way that the spring 110 is supported from inside and will not buckle during operation of the device 110.
[0030] In an example, the wrapping of the rope 116 over the drum 116 utilizes the tension amplification principle which is defined by Euler-Eytelwein equation. The equation relates the tension of the two ends 116-1, 116-2 of the rope 116.


where
- Tload is a load force or a tension required to be maintained at an 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 rope and the cam pulley 112; and
- ϕ is the total effective angle of contact in radians (one complete turn corresponds to ϕ = 2π radians).
[0031] Interaction of frictional forces & tension leads to different tension on either side of the drum 116. 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 116. Most of the force required to hold the overhead contact wire 102 which has to be kept in tension, is provided by the rope 120 over drum 116 system. The rope 120 wrapped over the cam pulley 112 and the spring 110 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 rope 120 over the cam pulley 112 and the drum 116 allows to provide similar force which was previously provided by bulky springs. This system 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.
[0032] In an example, the number of turns on the drum 116, the coefficient of friction, the cam pulley 112 profile and the stiffness of the spring 110 and their dimensions are designed as per the requirements of the force needed for holding the overhead contact wire 102 in constant tension.
[0033] In an example, to compensate the variation in length of the overhead

contact wire 102, the cam pulley 112 and the drum 116 rotate to wind or release the rope 116 over the cam pulley 112 and the drum 116, and the spring 110 is compressed or expended. For instance, during day hours or summer season, if there is an expansion in 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 spring 110 may get compressed to rotate the drum 116 and the cam pulley 112, which wraps some length of the rope 120 thereby pulling the overhead contact wire 102 and maintaining constant tension in it. Similarly, in winter season, if the overhead contact wire 102 contracts, the spring 110 may expand and rotate the drum 116 and the cam pulley 112 with some length of the rope 120 being released such that the overhead contact wire 102 remains in the predefined tension.
[0034] In an example, the device 100 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 pulley 112, a radius of the drum 116 and a number of turns of the rope 120 on the drum 116 of the device of the present invention.
[0035] 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 120, the drum 116, the cam pulley 112 system and the spring 110 to utilize tension amplification principle gives constant tension in the 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.
[0036] 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.
[0037] 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 in parallel to each other;
a spring 110 mounted at the base plate 106;
a cam pulley 112 mounted between the two side plates 108-1, 108-2, wherein the overhead contact wire 102 is to couple to the cam pulley 112,
wherein the cam pulley 112 rotates to compensate a variation in a length of the overhead contact wire 102, the rotation of the cam pulley 112 actuates the spring 110 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 a drum 116 mounted on the first shaft 114 such that the first shaft 114 rotates along with a rotation of the drum 116.
3. 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 wherein the cam pulley 112 is mounted on the second shaft 118 such that the second shaft 118 rotates along the rotation of the cam pulley 112.
4. The device 100 as claimed in claim 3, wherein the device 100 comprises a rope 120 wound over the cam pulley 112 and the drum 116 such that the drum 116 rotates in relation to a rotational motion of the cam pulley 112, and wherein a first end 120-1 of the rope 120 is to couple the

overhead contact wire 102 to the cam pulley 112 and a second end 120-2 of the rope 120 is connected to one end of the spring 110, the spring 110 being mounted at the base plate 106 perpendicular to an axis of the spring 110 through other end.
5. The device 100 as claimed in claim 1, wherein a radius of the cam pulley 112 varies along a circumference of the cam pulley 112, and wherein the radius depends on an expected maximum variation in the length of the overhead contact wire 102 to be compensated.
6. 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 pulley 112 and the drum 116 rotates to wind or release the rope 120 over the cam pulley 112 and the drum 116, and the spring 110 is respectively compressed or expanded.
7. The device 100 as claimed in in any one of the preceding claims, wherein the cam pulley 112 and the drum 116 comprises spiral groove 122 over respective surfaces of the cam pulley 112 and the drum 114, and wherein the rope 120 follows the spiral groove over the cam pulley 112 and the drum 116.
8. The device 100 as claimed in any one of the preceding claims, wherein the device 100 comprises a support pipe 124 attached to the base plate 106 at a location where the spring 110 is mounted, such that the spring 110 is supported from inside during operation of the device 100.
9. The device 100 as claimed in any one of the preceding claims, wherein the spring 110 is a tension spring.