TRACTION DISTRIBUTION

This department is responsible for maintenance & operation of Overhead equipments, Power supply installations, Substation Installations & remote control to supply necessary electric power to Electric Locomotive/EMU. Traction power supplied from various Feeding post and traction sub-station is controlled by Traction Power Controller (TPC) from Remote Control Centre.

25 kV AC OHE consists of

1. Power Supply Systems2. Foundation3. Mast4. Cantilever5. Contact and Catenary Wire6. Sectioning and Sub-sectioning7. Neutral Section8. Automatic Tensioning Devices9. Schedule of Dimensions

OVER HEAD EQUIPMENT (OHE)

1. A simple polygonal type of overhead equipment is comprising of a single 65 sq. mm.size Catenary wire of Cadmium Copper and a hard drawn grooved copper Contactwire of 107 sq. mm. size suspended from the Catenary by 5 mm dia copper dropperwire spaced 9 meters apart. The OHE is supported by swiveling type Cantileverbracket assembly. A tension of 1000 kgs is given in each conductors i.e., Catenaryand Contact wire. This tension is kept constant, automatically compensating thevariations in conductor length due to change in temperature through the regulatingequipment erected at the termination of conductors, also known as AutomaticTensioning Device.

2.The Catenary wire comprises of 19 strands of cadmium copper, each strand of 2.10mm dia, with overall dia of 10.5 mm having about 80% conductivity and 65 sq. mmcross-sectional area. The contact wire is a solid hard drawn grooved electrolyticcopper of 12.24 mm dia and 107 sq. mm cross-sectional area. Total current carryingcapacity of both wires is 600 Amps. The condemning size of contact wire is 8.25mm.

3. The OHE span varies between 72 Meters and 27 Meters with a step of 4.5 M. Themaximum span of 72 M is adopted on section having wind pressure of 112.5 kgs/ M2and 75 kgs/M2 only. The span is reduced on curvature depending upon the degree ofcurvature.

4.As a standard practice, an independent mast is used to support the OHE for each trackto obtain mechanical independence Steel masts are of Four types i.e., BFB (BroadOver Head Equipments Page 7Flanged Beam), RSJ (Rolled Steel Joist) and fabricated rectangular sectional mast ofK and B type.

5.Portals are also used to serve multiple track section where space between two tracksto locate an independent mast is not adequate. There are three types of Portals in usei.e., N, O & R type. P,G and double BFB type uprights are used where trackseparation is less. All Masts & Portals are galvanized before installation.

6. Traction Mast / Portals are embedded in the concrete foundation. There are differenttype of foundations which are used according to soil pressure and location. The fivestandard types of foundations mostly used are :(a) Side Bearing (b) Side gravity (c) New Pure gravity(d) Wet Black cotton soil (e) Dry Black Cotton soil

7.A presag of 100 mm is provided on the contact wire for the maximum span of 72meters and proportionately reduced for lesser spans. Regulated OHE with 100 mmpresag is considered suitable for 160 Kmph speed operation.

8. The contact wire is staggered at support so that as the pantograph glides along thecontact wire, the contact wire sweeps to and fro across the bearing surface of thepantograph pan upto a distance of 200 mm on either side of the centre line of pan ontangent track and 300 mm on curved tracks towards the outer side. This ensuresuniform wear of the steel strips of the pantograph.

9. The electrical clearance between live part, and earthed part i.e. fixed structures ormoving load shall be maintained normally as large as possible. The minimumclearance under worst condition of temperature, wind etc are given below:(a) Minimum Vertical distance for Long duration - 250 mm Short duration - 200 mm(b) Minimum horizontal distance for Long duration - 250 mm Short duration - 200 mm

10. The OHE conductors are terminated at intervals of 1.5 kilometers and suitablyanchored. The change over is made by overlapping the conductors, normally on 3spans. The conductors height at support is so adjusted that the conductors arephysically clear from any obstruction under all conditions as well as the pantographglides over from one conductor to another smoothly without any spark. There are twotypes of overlap:(a) Uninsulated Overlap In this type of overlap the distance between two conductors is kept 200 mm and the conductors are permanently connected by jumpers to have electrical continuity.(b) Insulated Overlap

In this case, the two OHE conductors are kept apart at a distance of 500 mm. The electrical continuity at the insulated overlap is bridged by Interrupters or Isolatin Switches except at Neutral Section (SP).

11. In regulated OHE, to ensure uniform distribution of the mechanical tension in theOHE conductors, an anticreep point is installed at the midpoint of the tension lengthof OHE conductor.

12.Section Insulators are provided to insulate the OHE of one track and another track,such as at turn outs & cross over, and to separate secondary tracks and sidings fromthe main line or other sidings.

13.When the pantograph of a locomotive passes from one track to another along a crossover, current collection changes from one OHE to another. The runners do have theoverlap so that there may not be any sparking during change over.

14.Solid core Porcelain Insulators are used to support the OHE as Bracket and Stay armInsulators. For termination 9 ton insulators are used.

1.7 TRACTION SUB STATION (TSS):

Every TSS has 2 nos. traction transformer out of which one is working at a time andthe second transformer is stand by. The capacity of each traction transformer issufficient to feed its own feed zone and half of the adjoining feed zone.

1. Feeding Post (FP): To feed 25 KV traction power to OHE.

2. The section of OHE normally fed by a traction transformer.

3. Feed Length The distance for which a traction transformer will feed power in emergent conditions i.e., the distance between two adjoining FPs.

4. Over Head equipment (OHE) A system of conductors / equipments carrying traction power from traction sub station to electric locomotive. 5. Neutral Section (NS) To separate OHE of two adjoining feed posts. A short neutral section (PTFE) type is provided opposite the Traction Sub Station to avoid the need of lowering the pantograph during extended feed conditions.

6. Sectioning Post (SP) (i) To facilitate the extension of traction power from one feed zone to half of the adjoining feed zone during emergency. (ii) Parallel the UP and DN OHE in double the sections.

7. Sub-sectioning and paralleling post (SSP): (i) To sectionalize OHE. (ii) To parallel the UP and DN OHE in double line sections.

8. Sector: The section of the OHE between the FP & SP is called the sector.

9. Sub-Sector : The section of the OHE between the FP & SSP, SSP & SP is called sub-sector. This is the shortest section of the OHE which can be isolated through Remote Control by the Traction Power Controller.

10. Elementary Section (ES) : This is the shortest section of the OHE which can be isolated manually for carrying out OHE maintenance work.

Cantilever (Assembly)

It is an insulated swiveling type structural member, comprising of different sizes ofsteel tubes, to support and to keep the overhead Catenary system in position so as to facilitatecurrent collection by the pantograph at all speed without infringing the structural members. Itconsists of the following structural members.

i) Stay arm – It comprises of dia. 28.4/33.7 mm (Small) size tube and an adjusterat the end to keep the bracket tube in position. It is insulated form mast bystay arm insulator.

ii) Bracket tube – It comprises of dia 40/49 mm (large) or dia 30/38 mm(standard) bracket tube and insulated by bracket insulator. Catenary issupported form this member by Catenary suspension bracket and Catenarysuspension clamp.

iii) Register Arm – It comprises of dia 28.4 x 33.7 mm tube to register the contactwire in the desired position with the help of steady arm.

iv) Steady arm assembly : It is 32 x 31 mm BFB section made of aluminiumalloy to register the contact wire to the required stagger and to take the push up ofcontact wire. It is always in tension.

DropperA fitting used in overhead equipment construction for supporting the contact wire fromCatenary.

JumperA conductor or an arrangement of conductors for electrical continuity not under tension,which forms electrical connection between two conductors or equipments. MastA single vertical post embedded in the foundation or otherwise rigidly fixed in verticalposition to support the overhead equipment with cantilever assembly. It may be rolledsection or fabricated. The uprights of portals and TTCs are also called masts.Neutral SectionA short section of insulated dead over head equipment which separates the sectors fed by twoadjacent substations which are normally connected to different phases.Overhead Equipment (OHE)The electrical conductors over the track together with their associated fittings, insulators andother attachments by means of which they are suspended and registered in position.All overhead electrical equipment, distribution lines, transmission lines and feeders may becollectively referred to as overhead lines.PantographA collapsible device mounted on and insulated from the roof of an electric engine or motorcoach for collecting current from the overhead equipment.Over Head Equipments Page 37Return conductorA conductor which carries return current from the tracks to the sub-station in the boostertransformer system.Regulating EquipmentA device for maintaining the tension of OHE conductors constant under all ambienttemperature conditions. Note : Such OHE is called regulated OHE.Setting Distance (implantation)The horizontal distance from the nearest face of traction mast to the centre line of the track. SpanThe distance between the centre line of the adjacent supporting masts for overhead equipment/ lines.Clear span in case of portal structure, is the distance between the inner faces of portaluprights.StaggerStagger of the contact wire is the horizontal distance of the contact wire from the verticalplane through the centre of track.Section InsulatorA device installed in the contact wire for insulating two elementary electrical sections fromeach other while providing a continuous path for the pantograph without break of current.

Types of mastsOHE conductors are suspended from swiveling cantilever assembly generally erected onindividual masts.3.6.1.1 Nine types of masts are used. These are designated as 150 x 150 BFB, 200 x 150RSJ, K-100, K-125, K-150, K-175, K-200, K-225 and K-250. The first two are rolledsections and remaining seven are fabricated masts. B-series (Drg. No. ETI/C/0071) mastscan be used in lieu of K-Series masts.

Note: Sometimes 200 x 200 (8” x 8”) BFB have been imported. These are used in lieu of200 x 150 RSJ as specified in mast employment schedules.

Two Track CantileverIn the yards and sidings when the mast cannot be erected near the track to be equipped, itmay be erected span one or two tracks using a two-track cantilever. This is generally used for supporting OHE near turnouts and X-overs. These arrangements should not be used for supporting OHE of two main lines. The OHE can be supported upto a distance of 10.5 m from the upright with this arrangement.

PortalsOn multiple track sections, where adequate track centres are not available and tracks cannotbe slewed, port are used. Each portal consists of two fabricated uprights and one fabricatedboom consisting of with or without one central piece and two end pieces.3.6.3.1 Three types of portals have been standardized. ‘N’ type portal is used for clear spansof 10 m – 20 m tracks maximum). ‘O’ type portal is for clear spans of 20 m – 30 mOver Head Equipments Page 43(for 6 tracks maximum) and ‘R’ type portal with spans of 30 m – 40 m (for 8 tracksmaximum).

Mast is erected on the foundation to hold the entire static and dynamic load of the OHE.

Mast are designed to suit different application and standardized accordingly. There are three major applications namely: Independent Structures, Portal and Two/Three Track Cantilever Structures.

 Independent Structures

When structures hold OHE of one line including two/three cantilever assembly of the same elementary section. These structures are classified as RSJ (Rolled Steel Joists) and BFB (Broad Flange Beam).

RSJ Mast: It is an I or H cross-section beam. The horizontal and vertical elements are called flanges and web respectively. Beam theory shows that I shaped section is very efficient for carrying both bending and shear loads in the plane of the web. Size used is 203x152mm. The mast is further classified into A, B, C, E &H depending upon drilling hole for supporting different type of OHE equipment.

BFB Mast: The Horizontal and vertical dimensions are same in this design of mast. Sizes vary from 152x152mm to 400x400mm depending upon the load which the mast is required to carry. These masts are good for resisting bending moment but weak in arresting twisting moment. These masts are further classified into three category depending upon the drilling holes for mounting. Weight of 152x152mm size mast is 30.4kg./meter

Fabricated Mast (K-series): These masts are fabricated by channels and flats welded in K design. The dimensions across the track is fixed as 300mm and varied along the track as K100 (23.12Kg/m) , K125 (29.56Kg/m) K150 (37.25Kg/m) K175 (42.65Kg/m) K200 (48.64Kg/m), K225 (56.10Kg/m) K250 (65.11Kg/m) where the suffix indicates the dimension and weight in Kg/meter. K100 is used for mounting auxiliary transformer and K125 de-standardized.  Due to higher width they are unsuitable where minimum track center of 4.72 is available.

Independent structures having mechanical independence makes the best OHE design.

Portal Structures

Portal structures are used to accommodate OHE of many lines (2 to 8 tracks) where it is not possible to erect independent mast due to restriction of track center.

There are three types of portal namely N, O and R type. o Clear span (distance between inner face) in N type- 10-20M (4 tracks), O type

– 20-30M (upto 6 tracks), R type – 30-40M (upto 8 tracks). Portal of maximum     M has recently been designed.

o Cantilever for the extreme tracks is provided on the uprightso Cantilever on the middle tracks is provided on the drop arm suspended from

the boom.o Drop Arm

Drop arms are classified  as A (single cantilever on either or both side), B ( multiple cantilever on  side) C (multiple cantilever on both side)

Drop arms are fabricated from angles and are rod laced.

Two/three track Cantilever Structure (TTC)

This is an alternative where it is not possible to manage with mast as well as portal is difficult to erect or uneconomical.

This is generally used at turnouts and crossover, platform to provide adequate implantation (4.5m – distance between track center and inner face of mast). This can support OHE upto a distance of 10.5m from the upright. TTC is not used for supporting OHE of two main lines

TTC consists of Mast 12.21 m long 225x300mm Boom 5.0 long or 8.0m long Tie Road 20mm dia – 2 nos Drop arms : D type

 Selection of Mast

General guidelines for use of different design of mast is as follows:

Normal location and OHE on tangent Track :            BFB Mast Normal Location on curves:                                            RSJ Mast Structures with multiple OHE with anchorage:        K150, 175 Turn-out location with higher torsion stress:           K200, 250

Implantation

This is the most important dimension measuring the horizontal distance of the inner face of the mast from the track center.

As per schedule of dimensions ( popularly called SOD in Railways) prescribed, there should not be any permanent structure at distance less then 2.16m from the track center. In view of this, implantation in initial stages of electrification was fixed at 2.36m and permitted upto 2.21 with some conditions.

With the introduction of 8 wheel BOX wagon, incidence of door opening during run and hitting the OHE were reported and thus minimum implantation increased to 2.5m.

With the introduction of mechanized ballast cleaning machine, and OHE foundation interfering with the showels, it was again revised to 2.8m.