FIELD OF THE INVENTION
The present invention relates to a method of incorporating neutral section in the round/bored tunnel. More specifically, the invention relates to a time saving and cost effective method of incorporating neutral section in a tunnel with circular cross section by creating a niche in the tunnel and housing the neutral section within to meet the clearance requirements.

BACKGROUND OF THE INVENTION
In an urban environment, metro train service provides an economical and convenient option for people to travel long distances in considerably less time. However, there are several challenges to create an infrastructure to support a metro train service in a city. In an urban environment space is one of the major constraints that decides route and placement of the metro track. As the urban development does not support creation of new infrastructure above the ground due to adverse factors such as dense population, availability of space, availability of electrification system and time allotted for construction and completion.
The major requirements for creating a metro train service include laying tracks, powering the metro rail and metro rails. The laying of track for the metro train service requires a lot of planning, resources and efforts. A very ingenious way of avoiding these adverse factors is usually constructed through overhead bridges and underground tunnels to avoid conflict.
Although, the tracks provide a life line for the metro, but the real soul to run these metro rails require powering the metro rail. The 25kV electrification system, in India, powering the metro train services is usually supplied through a continuous conductor running along the track such as overhead lines. The electric power is usually generated in three phases with each having a phase shift of 120°and in an AC traction system comprising of different traction sections, there is a possibility of two different traction sections being fed by different phases of power supply. In such condition, to avoid the risk of, out of phase supply mixing, for traction sections with different feeder stations, there is need to keep the sections isolated from each other. Therefore, a neutral section is created, which is preferably an earthed section. Neutral sections are constructed to provide isolation to different traction supply feeds and to provide development of arc/flashover as the voltage difference may be higher than the normal system voltage, if the traction sections are on different phases.

Generally, the neutral section in underground tunnels is provided in a tunnel constructed through cut and cover method to account for the required clearances to be maintained for separation of different power supply sections in a neutral section. The cut and cover method involves temporary acquisition of land, massive excavation followed by a durable covering to support the overhead construction and subsequent restoration of excavated area which takes around 6-8 months in construction. Also, the neutral section has to be at a location which is 250m away from the platform of a metro station and at a location preferably with zero gradients, no curves, no signal and no cross over. The main drawback in construction of neutral section through cut and over method is the time taken which is at least 6-8 months apart from the issues related to acquisition of land in a dense area of city and the high cost of construction.

Accordingly, there is a need of developing improved and cost effective technology for providing neutral sections in the AC traction system for metro train tracks to reduce the time taken for construction.

Further, there is a need to create neutral section in the traction systems wherein the tunnels are constructed through boring machines which are circular and has less area to install these neutral sections, as any major dig could destabilize the whole structure by creating fault lines, leading to collapsing of the structure.

OBJECT OF THE INVENTION
The main object of this invention is to provide a method of incorporating an overlap type neutral section in a round/bored tunnel.
Yet another object of the present invention is to create sections in the round/bored tunnel to house at least one neutral section.
Yet another object of the present invention is to create sections in the round/bored tunnel to house at least one neutral section accommodating at least one neutral section ensuring the required safety clearance for effective functioning of the neutral section.
Yet another object of the present invention is to provide sections in the round/bored tunnel to house at least one neutral section accommodating at least one neutral section ensuring the required safety clearance for effective functioning of the neutral section using a cost effective method.

Yet another object of the present invention is to provide sections in the round/bored tunnel to house at least one neutral section accommodating at least one neutral section ensuring the required safety clearance for effective functioning of the neutral section using a time saving method.

Yet another object of the present invention is to sections in the round/bored tunnel to house at least one neutral section accommodating at least one neutral section ensuring the required safety clearance for effective functioning of the neutral section to prevent out of phase supply mixing in a 25kV AC traction system.

Yet another object of the present invention is to provide sections in the round/bored tunnel to house at least one neutral section accommodating at least one neutral section ensuring the required safety clearance for effective functioning of the neutral section at a distance of approximately 250m from the platform of a metro station.

Yet another object of the present invention is to provide sections in the round/bored tunnel to house at least one neutral section accommodating at least one neutral section ensuring the required safety clearance for effective functioning of the neutral section at a distance of approximately 250m from the platform of a metro station at a location preferably with zero gradient, with no curves, no signal and no cross over(s).

Yet another object of the present invention is to provide sections in the round/bored tunnel to house at least one neutral section ensuring the required safety clearance for effective functioning of the neutral section having 1m to 1.6m long sections in the ceiling of round/bored tunnel to house neutral section.

Yet another object of the invention is to accommodate neutral sections in considerably less installation space.

SUMMARY OF THE INVENTION
The present invention provides a time and space saving method of incorporating neutral sections in the 25kV AC traction system within the round/bored tunnel through minor modifications which also ensure all the safety clearances required for making effective neutral sections.

In the main embodiment of the present invention the method of incorporating neutral section comprises of constructing/excavating a tunnel with circular cross section approximately 5.6 m to 5.8 m in diameter using tunnel boring machines; creating at least a 1 m to 1.6 m long, at least 1211 mm wide and 70 mm deep niche or section in the ceiling of round/bored tunnel; incorporating at least one neutral section in the niche created in the ceiling of the tunnel such that it is at least at a distance of 250 m from the platform of a metro station at a location away from stop signals and shall be on a tangent track and on level to the extent possible.

Further, the neutral section is capable of preventing mixing of two supplies which are not in the same phase. In an AC traction system it is highly undesirable to mix two out of phase supplies as they may result in arc/flashover as the voltage difference developed between the traction sections with different phase supplies may be higher than the normal system voltage. Furthermore, an arc catcher along with an arc chute is provided which usually comprises of a stack of insulated earthed parallel metal plates to confine the arc and prevent it from causing damage to civil structure.

In another embodiment of the present invention, the tunnel with circular cross section is bored using tunnel boring machines. The bored tunnel is approximately 5.6 m to 5.8 m in diameter to house the track, metro train, overhead equipments for electrification and at least a neutral section which is housed in the section created in the ceiling of the round/bored tunnel. The time spent in boring tunnel utilizing boring machines is considerably less than the time spent in cut and cover method of construction.

In yet another embodiment, materials used for the construction of neutral section in round/bored tunnel are as follows: - plurality of drop arms with galvanized iron (GI) supports at a distance specified as per layout attached to the tunnel using plurality of fasteners such as, but not limited to like chemical fasteners, mechanical fasteners, etc., at least one rear bracket arm fastened to drop arms by means of such as, but not limited to like bolts, rivets, etc., at least one 25 kV insulator with specified BIL level and creepage distance attached to the provided rear bracket arm by means of plurality of bolts, at least one stagger arm connected to the insulator which will in contact with the aluminium conductor securing contact wire and have arc horn which will discharge the static charge to the arc catchers which usually comprises of a stack of mutually insulated parallel metal plates to confine the arc and prevent it from causing damage to the conductor rail system and the civil structures. Further, earthing clamps are assembled with the drop arm.
In yet another embodiment, the overlaps are placed in a longitudinal distance of 10 to 15 meters with necessary traction equipment assembly. The present design is with 3 to 5 overlaps running 3 to 5 meter parallel with an electrical clearance gap of at least 400 mm at each overlap.
In yet another embodiment, the stagger arm assists in maintaining the air gap of 400 mm.

In yet another embodiment, the static charge will be transferred via arc horns to the arc catchers which usually comprises of a stack of mutually insulated parallel earthed metal plates to confine the arc and prevent it from causing damage to the conductor rail system and the civil structures.
In yet another embodiment of the invention, electrostatic charge of the pantograph will be discharged and the complete train should come to neutral so that during charging from the other phase supply, the electrical system of rolling stock does not get tripped.

In yet another embodiment, in order to avoid any tripping/flashovers, the central part of the conductor rail section in multiple overlap rail section is earthed for making the pantograph potential free during changeover of supply phase from one source to the other.
Hence, the proposed method of incorporating neutral section in round/bored tunnel effectively reduces the time taken for its construction as now there is no need to use cut and cover method for incorporating neutral sections.

BRIEF DESCRIPTION OF THE DRAWING
The object of the invention may be understood in more details and more particularly description of the invention briefly summarized above by reference to certain embodiments thereof which are illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate preferred embodiments of the invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective equivalent embodiments.

Fig. 1 elucidates a perspective view of the cut and cover section for incorporating neutral section in the AC traction system;
Fig. 2 elucidates a perspective view of the round/bored tunnel with plurality of niche created to house the neutral section;
Fig. 3 elucidates another perspective of the round/bored tunnel;
Fig. 4 elucidates a conductor rail arrangement of the round/bored tunnel with overlap neutral section space in the circumference of the tunnel;
Fig. 5 elucidates a perspective view of the round/bored tunnel with a niche at the top of the circumference of the tunnel;
Fig. 6 elucidates a perspective view of a conventional conductor rail arrangement with overlap neutral section space in the circumference of the tunnel;
Fig. 7 elucidates a cut-out view of the niche formed in a round/bored tunnel at the top of the circumference of the tunnel and showing details of its steel reinforcement layout;
Fig. 8A and 8B elucidates the general arrangement of different embodiments in an overlap neutral section of the round/bored tunnel with a niche at the top of the circumference of the tunnel.

DESCRIPTION OF THE DRAWINGS
The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough, and will fully convey the scope of the invention to those skilled in the art.
Fig. 1 elucidates a perspective view of the cut and cover section for incorporating neutral section in the AC traction system. Traditionally, the cut and cover method of construction is utilized to account for the required clearances to be maintained for separation of different power supply sections in a neutral section.
Fig. 2 elucidates a perspective view of the round/bored tunnel wherein at least one niche or section is created to house at least one neutral section. The bored tunnel with circular cross section comprises of at least one arc chute along with the overhead equipment, at least one arc catcher, at least one niche to house at least one neutral section. A tunnel approximately 5.6 m to 5.8 m in diameter is bored using the tunnel boring machines wherein at least a section is created which is 1m to 1.6 m long, at least 1211 mm wide and 70 mm deep to house the neutral section. The arc chute further comprises of a stack of mutually insulated parallel metal plates to confine the arc and prevent it from causing damage.
Fig. 3 elucidates another perspective of the round/bored tunnel with plurality of niche created on the ceiling of the round/bored tunnel to incorporate the neutral sections.
Fig. 4 elucidates a conductor rail arrangement 104 of the round/bored tunnel 100 with overlap neutral section space 105. In overlap type neutral section 105 arrangement of multiple overlaps is created in the conductor rail arrangement 104. The overlaps are placed in a longitudinal distance of 10 to 15 meters with necessary traction equipment assembly. The present design is with 3 to 5 overlaps running 3 to 5 meter parallel with an electrical clearance gap of at least 400 mm at each overlap. The gap is created in the installation arrangement of conductor rail arrangement 104 for the segregation of the different power supplies from different substations.
Fig. 5 elucidates a perspective view of the round/bored tunnel 100 wherein a 1211 mm wide and 70 mm deep niche 101 is created in the ceiling of the round/bored tunnel 100 which houses at least one neutral section 105 such that it is 250 m away from the platform of metro station to ensure clearance requirements for functionally effective neutral section. The static charge will be transferred via arc horns 102 to the arc catchers 103 which usually comprises of a stack of mutually insulated parallel metal plates to confine the arc and prevent it from causing damage to the conductor rail system and the civil structures. The overlaps are provided with the electrical clearances of minimum 400 mm and electrostatic discharge gap ranging from 800 mm to 3000 mm depending upon the layout of the neutral section. All the arc catchers 103 are to be earthed with the running earthing system. The stagger arm 106 is provided to maintain the air gap of 400 mm.

Fig. 6 elucidates a perspective view of a conventional conductor rail arrangement with overlap neutral section space in the circumference of the tunnel. In order to implement this type of neutral section in underground tunnels complying with minimum static and dynamic electrical clearances, construction of cut and cover type tunnel was opted for during the initial phases of metro construction as it was not feasible to accommodate neutral section in round/bored tunnels. This involved the planning of neutral section where the area of the neutral zone is accessible from the ground so that cut and cover construction can be done. Further it resulted in extra cost and 6-8 months delay in construction of cut and cover tunnel. Since availability of land is a constraint in the metro construction, especially in dense urban clusters cut and cover construction was a major bottleneck in locating a neutral section on an underground stretch.
Fig. 7 elucidates reinforcement design details for construction of niche in the bored tunnel segments. After studying various round/bored tunnels construction scenarios, feasibility of providing the neutral section in round/bored tunnel was explored. It was concluded that the multiple overlap type neutral section for 25 kV traction systems can be provided in the round/bored tunnels with provision of construction of niche as per the drawing and providing the same arrangement in the length of neutral section.
Fig. 8A and 8B elucidates the general arrangement of different embodiments in an overlap neutral section of the round/bored tunnel 100 with a niche 101 at the top of the circumference of the tunnel 100. Details provided are in general and may vary depending upon the location, length and design of tunnel section of the round/bored tunnels. The preferred materials used for the construction of neutral section 105 in round/bored tunnel 100 comprising plurality of drop arms 108 with galvanized iron (GI) supports 107 at a distance specified as per layout attached to the tunnel 100 using plurality of fasteners such as, but not limited to like chemical fasteners, mechanical fasteners, etc., at least one rear bracket arm 109 fastened to drop arms 108 by means of such as, but not limited to like bolts, rivets, etc., at least one 25 kV insulator 110 with specified BIL level and creepage distance, attached to the provided rear bracket arm 109 by means of plurality of bolts 113, at least one stagger arm 106 connected to the insulator 110 which is in contact with the aluminium conductor 111 securing contact wire 112 and have arc horn 102 which discharges the static charge to the arc catchers 103 that usually comprises of a stack of mutually insulated parallel metal plates to confine the arc and prevent it from causing damage to the conductor rail system and the civil structures. Further, earthing clamps 115 are assembled with the drop arm 108.
Many modifications and other embodiments of the invention set forth herein will readily occur to one skilled in the art to which the invention pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

We claim:
1. A system for incorporating an overlapping neutral sections in a conductor rail arrangement 104 within a round/bored tunnel, comprising :
plurality of drop arms 108 with galvanized iron (GI) supports 107;
at least one rear bracket arm 109 fastened to at least one drop arms 108;
at least one insulator 110 with specified BIL level and creepage distance attached to the provided rear bracket arm 109 by means of plurality of bolts 113;
at least one stagger arm 106 connected to the insulator 110 in contact with the aluminium conductor 111 securing contact wire 112 and arc horn 102 for discharge of static charge to the arc catchers 103, further comprises of a stack of mutually insulated parallel metal plates to confine the arc and prevent it from causing damage to the conductor rail system and the round/bored tunnel;
earthing clamps 115 which are assembled with the drop arm 108; and
plurality of conductor rail arrangement,
wherein,
the neutral section 105 have at least 3 to 5 overlaps running 3 to 5 meter parallel with an electrical clearance gap of at least 400 mm and with electrostatic discharge gap of 800 mm to 3000 mm at each overlap;
the stagger arm 106 assist in maintaining the air gap of 400 mm; and
the arc horns 102 transfers the static charge to the arc catchers 103 comprising a stack of mutually insulated parallel metal plates to confine the arc and prevent it from causing damage to the conductor rail system and the civil structures.
2. The system as per claim 1, wherein enables electrostatic charge of the pantograph to discharge and the complete train should come to neutral so that during charging from the other phase supply, the electrical system of rolling stock does not get tripped.

3. The system as per claim 1, wherein plurality of drop arms 108 with galvanized iron (GI) supports 107 are at a distance specified as per layout attached to the tunnel 100 using plurality of fasteners such as, but not limited to like chemical fasteners, mechanical fasteners, etc.

4. The system as per claim 1, wherein rear bracket arm 109 fastened to drop arms 108 by means of such as, but not limited to like bolts, rivets, etc.

5. The system as per claim 1, wherein the central part of the conductor rail arrangement 104 is earthed for making a pantograph potential free during changeover of supply phase from one source to the other in order to avoid any tripping/flashovers.

6. The system as per claim 1, wherein overlapping neutral sections in a conductor rail arrangement 104 within a round/bored tunnel is incorporated in the 25kV AC traction system.

7. A method of incorporating neutral section in round/bored tunnel comprises of following steps:
constructing/excavating a tunnel 100 with circular cross section approximately 5.6 m to 5.8 m in diameter using tunnel boring machines;
creating at least a 1 m to 1.6 m long, at least 1211 mm wide and 70 mm deep niche 101 or section in the ceiling of round/bored tunnel; and
incorporating at least one neutral section 105 in the niche created in the ceiling of the tunnel 100 such that it is at least at a distance of 250 m from the platform of a metro station at a location with no curves, no signal, no cross over and zero inclination for functionally effective neutral section.

8. The method as claimed in claim 7, wherein the neutral section 105 have at least 3 to 5 overlaps running 3 to 5 meter parallel with an electrical clearance gap of at least 400 mm and with electrostatic discharge gap of 800 mm to 3000 mm at each overlap.