Railway Electrification Survey PDF

RAILWAY ELECTRIFICATION SURVEY 2.0 PURPOSE OF RAILWAY ELECTRIFICATION Electric power contact lines are provided as overhead conductors over running Railway Lines to provide energy to electrically driven Railway locomotives or to train sets. As compared to diesel locomotives, whose p...

RAILWAY ELECTRIFICATION SURVEY 2.0 PURPOSE OF RAILWAY ELECTRIFICATION Electric power contact lines are provided as overhead conductors over running Railway Lines to provide energy to electrically driven Railway locomotives or to train sets. As compared to diesel locomotives, whose power is limited by the permissible axle load and the moving dimensions for accommodation of the diesel engine, the contact lines permit almost unlimited power at the disposal of the electrically driven vehicle. Higher power permits heavier trains to achieve higher speeds. Electric Multiple Units provide fast commuter services with quick reversal at with main line trains, the Electric Multiple Units offer least interference to the latter due to the EMU’s high acceleration rates. The major advantages of electric traction are, economy in operation and maintenance, saving in consumption of scarce diesel oil and increased through put of traffic. The capital cost for provision of fixed installation required for electric traction is found adequately remunerative for routes having high levels of traffic. 2.1 RAILWAY ELECTRIFICATION WORKS 2.1.1 Main works These consist of : 1. Provision of most economic reliable electric contact system to continuously supply power to the moving electric rolling stock. 2. Power Supply Arrangements. 3. Provision of switches to regulate the flow of power along with the electric protective gear. 4. Monitoring and remote control of power supply. 5. Immunization of signalling and the trackside telecommunication circuits against electromagnetic and electrostatic induction effects of 25 KV, 50 HZ, single phase traction power supply. 6. Modernization of signalling and telecommunication. 7. Provision of maintenance and operation facilities for electric traction. 2.1.2 Discipline wise Division of Works Different Engineering disciplines take up their portion of the work which form components of Electrification works. These are given below: a) Electrical i) Provision of Overhead Equipment, booster transformers and return conductor. Over Head Equipments Page 10 ii) Provision of Power Supply Equipment, transmission lines, traction substations, and installation of Power Supply Control Posts. iii) Remote Control of the Power Supply Equipment. iv) Electric Locomotive maintenance facilities. v) Ancillary Works of modification to the existing power supply arrangements on the route to immunize the system against induced voltages due to the traction current and provision of power supply at new points. vi) Liasion with Electricity Authorities to modify their power line crossings to suit 25 KV ac traction. vii) Consequential electrical works for electrification and air-conditioning of service buildings and staff quarters. b) Signal and Telecommunications: i) Provision of colour light signals and immunization of the signalling installation against induction effects of 25 kV ac traction power supply system. ii) Provision of underground cables for the Railway’s telecommunication lines and provision of additional traction control circuits. iii) Liaising with the Department of Telecommunications for modification of their circuits to immunize them against induced voltages due to traction current. c) Civil Engineering: i) Yard remodeling, slewing of tracks, sidings and oil track works. ii) Construction of loco sheds, service buildings and staff quarters. iii) Modification to overline structures such as overbridges, flyovers, through girder bridges, as well as to tunnels, platform shelters and water columns to suit 25 kV ac clearances. 2.1.3 Choice of system of Power Supply: Before designing the Power Supply arrangements and the type of overhead equipment of a section, a choice is required to be made whether conventional 25 kV system is to be adopted or 2 X 25 KV Auto Transformer system is to be adopted. This choice depends upon a number of factors viz. the sections to be provided with booster transformers and return conductor as demanded by the Department of Telecommunications, the demand of power for the volume and type of the traffic and suitable location available for traction substations. 2.1.4 Coordination of Works Railway Electrification, being a multi-disciplinary project work, needs close coordination amongst electrical, signalling & telecommunications and civil engineering disciplines. It further needs coordination with outside agencies such as Power Supply Authorities, the Department of Telecommunications, the Revenue officials as well as with the Open Line organization or whose section the work is to be taken up. Accordingly the organization for Railway electrification coordinates works Over Head Equipments Page 11  of all the disciplines and the agencies from inception to completion including support services to the open line in early stages of electric traction over the section. 2.2 SELECTION OF ROUTE FOR ELECTRIFICATION 2.2.1 Main Consideration Railway Electrification, being in the nature of major improvement to the infrastructure of a section, is taken up basically on routes having high density of traffic. Short spurs of, or those lines which interconnect the electrified lines, which improve the mobility of the rolling stock are also taken up for electrification. 2.2.2 Financial Evaluation As Railway Electrification entails capital expenditure, the sanction to the project is subject to Cost Benefit Analysis (CBA) through Discounted Cash Flow (DCF) technique. Two scenarios are considered, one under diesel traction, and the other under electric traction, for the given volume of traffic forecast on the section over a long enough period of time such as 30 years after the energization of the section for electric traction. The cash outflows under the two scenarios are discounted at the approved rate of 12% over the life of the project (taken as 35 years, about 5 yeas for construction and 30 years thereafter of operation). If the total of the stream of the annual discounted cash flows for electric traction is found to be lower than that for diesel traction, the project is considered as remunerative and desirable for approval. Sometimes an Economical analysis is also called for such as when funding by an International Aid Agency viz. the World Bank or Asian Development Bank is proposed. Although the Economic analysis is also carried out on the same DCF technique, the inputs and the outputs reflect the Social Costs and benefits, and the discount factors chosen may also be different, being dependent upon funds available for investment for future benefit against those required for immediate consumption and as decided by say, the Planning Commission. The investment in electric traction is found remunerative on account of : i. Lower fuel-costs ii. Less number of locomotives iii. Lower operating costs iv. Lower locomotive maintenance costs. as compared to diesel traction of the given traffic. The traffic level in Gross Million tonne per route kilometer per annum at which the minimum acceptable rate of returnis obtained is called the “Break Even Level” of traffic density. Over Head Equipments Page 12 2.2.3 Past policy on Electrification a) Early Years At the end of the 19th century electricity was in widespread use for running trams in North America and Europe, being found more economic than their haulage by horses. By 1930s on the Railway systems electric traction was in different parts of the world over short high density main line or suburban sections. The system of supply was usually 1500 V dc although some sections at 600 V dc or 750 V dc with third rail system were also adopted. The Copper Catenary was heavy and complex Rectifier substations were required to be located at close intervals. The cost of electrification was high. In India, also, by 1930 the suburban sections of Bombay and Madras were electrified at 1500 V dc. There were only two main line sections on electric traction, being Bombay to Pune and from Kalyan to Igatpuri, the electrification being beneficial in drastically increasing the throughout of traffic over these two sections, both having 1 in 37 gradient over the Western Ghats. The traction required reversing stations to negotiate, such steep inclines. There being no Extra High voltage grid system in the country or adequate generating capacity, the entire power for these electrified sections were generated and transmitted by the then Great Indian Peninsular Railway to its traction substation. b) Post World War – II Scenario After India’s Independence electrification of Howrah-Burdwan section on 3000 V dc was taken up and was completed in 1958. In the meanwhile in 1955 the French National Railway (SNCF) who had perfected the system of Electrification on 25 kV ac, demonstrated its advantages at the International conference of the International conference of the International Union of Railways (UIC) at Lille in France. The major advantages of 25 kV ac 50 Hz single phase was a light Overhead Equipment, simple transformer substations located far apart feeding power to rectifier locomotives having tap changer control giving greatly improved adhesion characteristics. But the adjacent signalling and telecommunications circuits needed immunization from the electro-magnetically induced voltages due to traction currents. This called for modification to these circuits and to their terminal equipment, but in the process gave an opportunity to improve and upgrade these equipment. This system was more reliable and on the whole cheaper to construct and to maintain. The ac locomotives could haul heavier loads and gave better acceleration than dc locomotives. However, such a system was dependent upon power supply from Extra High Voltage (132KV) grid system having adequate short circuit capacity required for supplying the extent of single phase traction loads. Weighing the advantages of this system and the fact that 132 kV grid system was also in the process of being set up in the country, Indian Railways in the year 1957 decided to adopt 25 kV ac 50 Hz single phase system for all future Railway Electrification schemes, as well as to convert the system of 3000 V dc traction recently established in Howrah Burdwan section of Eastern Railway and the one existing at 1500 V dc on the suburban metre gauge section of Madras on Southern Railway, to this system for uniformity. For the initial stages the technical collaboration of SNCF was taken. Choice of 25 kV ac single phase system at industrial frequency (50Hz) gave a large drive towards main line electrification of the coal and iron ore routes serving the steel plants located on the Eastern and South Eastern Railways was carried out. To cater for the suburban commuter traffic of Sealdah Division of Eastern Railways was carried out. To cater for the suburban commuter traffic of Sealdah Division of Eastern Railways so far on stream traction, these routes on the Over Head Equipments Page 13 Division were Electrified. Electrification of Igatpuri-Bhusawal section of Central Railway and Tambaram-Vilupuram (metre gauge) section of Southern Railway, was also taken up. c) Corporate Plan of Indian Railways Indian Railways, in their first Corporate plan for the period 1974-89, identified the Broad Gauge trunk routes interconnecting the four major metropolitan cities viz. Calcutta, Madras, Bombay and Delhi which should ultimately be electrified, having high potential for growth of traffic, along with other high density coal and ore carrying routes. d) Accelerated electrification The Arab-Isreal wars of the 1970s highlighted the strategic nature of Petroleum and their scarcity value. Further the sharp ioncrease in the cost of oil in the period from 1973 to 1980 and increasing outflow of India’s foreign exchange for importing petroleum and its products spurred the Government of India in 1980, to take a policy decision to accelerate the pace of Railway Electrification. The target was to achieve an electrification programme of energizing 1000 route kilometer per year. Though this was not achieved, a rate of hitherto 150 to 200 km of energization was increased to a rate of 500 to 600 km per year from 1985 onwards. Electrification of complete route rather than section has been, thereafter, planned. By 1992 Electrification of Delhi-Calcutta, Calcutta-Bombay, Delhi-Bombay, and Delhi- Madras was completed. The Overhead Equipment and the Power Supply on some of the electrified routes are being strengthened to cater to goods train loads of 9000 tonne. By march 2009 a total of 18942 km are electrified. 2.2.4 Present Policy on Electrification The successive Corporate Plans of Indian Railways generally identify the routes most suitable for electrification. Following considerations dictate the priority or electrification of a route. a) high traffic density b) extension of an electrified route on short spur or interconnection of two electrified routes to improve rolling stock mobility, and c) passenger commuter sections. Availability of requisite power supply at reasonable rates is a basic condition combined with availability of adequate short circuit power of tap for the single phase traction power needs. The zonal Railways and the Railway Board maintain section wise traffic density figures as a part of their statistics. With this as the base and the anticipations of future traffic the highest traffic density routes which are not electrified are short listed. After making a list of such routes and short listing them in order of their operating benefits, priorities for electrification are finalized by the Ministry of Railways in consulation with the Planning Commission. Over Head Equipments Page 14 2.3 SURVEY FOR ELECTRIFICATION 2.3.1 General After having narrowed down the choice of routes which may be considered for electrification, it is essential to further examine the chosen route in detail for its suitability for electrification in following aspects: a) The feasibility of electrification viz. availability of power supply, suitability of the terrain and of the overline structure (or their amenability to modifications) to suit the electrical clearances, and of terminal yards to be able to provide lines for change of traction. b) A realistic assessment of the cost of the project. c) The financial viability of the investment. To ascertain the above details a route is surveyed for Railway Electrification. The survey may either be a ‘Reconnaissance Survey’ or a detailed Foot by Foot, ‘Cost-cum- Feasibility Survey’ as the circumstances call for. 2.3.2 Reconnaissance Survey This is a rapid survey examining the salient and vital points, leaving the details to be worked out in the extensive Foot by Foot Survey. The survey covers the following items. a) Assessment of existing traffic forecast of projected traffic, both for goods and passenger, including special requirements such as plans for running Superfast passenger trains or / and of heavy haul goods trains. b) Availability of Electric Power. c) Details of the section covering the terrain, the terminal yards, the signal and telecommunication installation and the volume of work involved in modification to overline structures and the over bridges to suit ac traction. This is normally done by a joint inspection by the officers of the concerned disciplines biz, electrical, civil engineering, and signal and telecommunications using motor trolley or an OHE inspection car. d) An idea of the lengths of the route to be equipped with booster transformers and return conductor, involving a preliminary discussion with Department of Telecommunications. e) The information collected by this rapid survey yields a fairly accurate idea of the volume of electrification work content. For obtaining an estimate within 10 to 20% of its cost. Unit costs derived from a recently completed project on cost per unit of work, or per route of track km. As most applicable, are applied to the quantities of the component works estimated, and the project cost is worked out. Based on the latest cost of inputs, of fuel electric energy, specific fuel or energy consumption and other Over Head Equipments Page 15  operating and maintenance norms derived from statistical data, a rate of return is worked out. The feasibility for electrification, its cost and its remunerativeness so worked out gives adequate information based on which the project can be sanctioned. However, if the competent authority desires to examine the project more closely, then a detailed cost-cum- feasibility survey has to be taken up. This survey has to be included in the programme for surveys and sanctioned in the annual works Programme b the Railway Board and a separate organization set up to conduct it. Such a situation may arise for example, when the cost of inputs have altered radically and the traffic density forecast on the route is not very much above the ‘break even’ level. 2.3.3 Cost-cum-Feasibility Survey A multi disciplinary Survey Team is formed expressly for carrying out the detailed survey. This survey organization finalises the wiring plan, conducts foot by foot survey of the route and prepares the survey plans followed by the prepagging and pegging plan. The team examines the clearances on the route to suit 25 KV ac 50 Hz single phase system and suggests modifications wherever required. By liasing with power supply authorities and the Department of Telecommunications, it also examines in detail the availability of power and the quantum of protection required by involved and the cost implications to be worked out. Based on these the financial viability of the work is examined. Finally all these details are incorporated in the Project Report and the Abstract Estimate which is placed before the competent authority for sanction of the Railway Electrification project. On sanction of the project the drawings prepared and the estimates made are used for calling of tenders and finalisation of schedule of quantities. Accurate foot by foot survey, and carefully finalised designs prepared by a survey organization is the cornerstone of a successful Electrification Project. 2.4 FOOT BY FOOT SURVEY 2.4.1 General In order to prepare the designs of Overhead Equipment Layout forming the basis of the Project construction work a detailed foot survey of the route proposed for Electrification is taken up. This survey forms the basis of Survey Sheets. These sheets are prepared to scale, the longitudinal scale being 1:1000 in open route and 1:500 within station limits and in yards. The sub-scale chosen for cross-sections is 1:200. On these sheets the OHE structures and anchor, foundations are marked according to the Principles for OHE Layout Plans and Sectioning Diagrams for 25 KV ac Traction. Document No. ETI/OHE/53, issued by RDSO. These plans, called prepegging plans are then vertified at site and modified to site conditions and finalised. The final plan thus issued is called the Pegging Plan, and forms the basis for estimation of quantities, the cost estimates and for schedule of quantities to tenders for OHE construction Contracts. Bonding and Earthing plans and plans for modifications of power distribution lines at stations and yards are also prepared based on these survey plans. Preparation of accurate detailed survey plan, therefore, cannot be overemphasized. Over Head Equipments Page 16 2.4.2 Field Book A Surveyor’s field book is required to be maintained in which all the details obtained during the survey should be entered. These details are transferred to field sketches. Such sketches are then sent to the Drawing Office to enable preparation of Survey plans. The entries in the field book should be dated and progress in accordance with increasing chainage. Details entered should include important features along the track and their offset from the centre line of the nearest track. The chainage of location where embankment changes to level ground, or level ground to cutting or vice versa should be recorded as these are essential in ascertaining the soil bearing pressure, required for design of foundations for OHE structures. Continuous features, such as, Track centres, width of cess, offsets to continuous running drains, fences or pipes, cables; either on surface or buried underground, should be recorded at 50 m intervals on open route and at 25 m intervals in yards and within station limits. Cross section of the route at intervals of 250 m should be measured and recorded. 2.4.3 Important Features to be noted These are: a) Track centres between all tracks. b) Track structure i.e. type of sleeper, depth of ballast, width of cess, embankment, level of cutting. The programme of track works such as re-sleepering with prestressed concrete sleepers, deep screening of ballast or rail renewal works, which affect the track levels and / or alignment, should also be ascertained and noted. c) Details of cross section every 250 m d) Type and condition of soil every 250 m and at geologic discontinuities. e) Buried water mains, and cables and their runs alongside and across tracks. f) Signal cabins and location boxes, signal wires, point rods, cranks and signal cables. g) Signals: Main Routing, Shunt; their type and track for which meant. h) Buildings, huts, platforms, other structures such as columns for overbridges, abutments of road overbridges. i) Platform shelters, their profile across tracks, height and distance of columns, and edges of shelters from adjacent track. j) Turnouts, crossovers, and diamond crossings, their deviation numbers viz. 1 in 8.5. 1 in 12 or 1 in 16 chainage of the fouling boards / marks, track centres at toes of turnouts and at the fouling boards / marks. k) Water columns, ash pits and steam blowdown pits. l) Fueling points for Diesel locomotives. Over Head Equipments Page 17  m) Metallic circuits (electric, low or high tension, signal, or telecommunications) running parallel to tracks and their distance from adjacent track centres. n) Fencing: Metallic or otherwise, running along tracks, chainages of their beginning and end, and their distance to adjacent track at regular intervals; their type of construction. o) Overhead wire crossings of tracks Telecommunications (Railway or belonging to Department of Telecommunications); signalling and power including their ownership, their voltage and clearances from each track crossed, if the voltage of the power line is 33 KV or above the angle of crossing and also the location of two adjacent supports on either side of the tracks. p) Overline structures such as Road overbridges. Flyovers, foot overbridges and signal gantries: their vertical clearances from each track spanned, and horizontal distances of their support columns or abutments form the adjacent tracks, if the overline structure has smoke baffle plates, the clearance to the lowest member of the structure should be recorded. A sketch of the cross-section across the tracks giving the leading dimensions is required to be prepared. q) Curves: Whether right hand or left hand as seen in the direction of increasing chainage; the degree of curvature, and the chainage of tangent points both at the beginning of transition and of main curves. Versines in mm are taken every 50 m with nylon cord for the entire curve. The super-elevation as found at site should be recorded. Actual versines measured at site may be different depending upon the disturbance the track has suffered since its last realignment. r) Level crossings, their chainages, and location of gate lodges, whether manned or unmanned and location of gate signals, if an. Special note should be made of level crossings on important roads or those giving access to main roads (this is useful during construction and subsequently for maintenance). s) Locations of gradient posts and signal location marker posts. t) Culverts and bridges: Chainage of their abutments, piers, trolley and man refuges, whether culverts or long bridges. If so whether deck type or through girder type. For through girder types the head room of entry portals. Sketch showing plan and elevation of the piers and the entry portals are also required. Location of alignment of water mains, cables and open wires running on the bridge structures should also be noted. u) Tunnels; their chainages and profile, whether lined or unlined, location of trolley and man refuses, areas with extensive water seepage, arrangements of water drainages, and location of drains. v) Identification and extent of Exposed Locations: Areas where full wind effects are likely to be encountered by OHE structures and termed ‘Exposed locations’ should be noted down. These are generally encountered on approach embankments to long bridges and on them, high bare grounds and in valleys subject to funnel effect of wind. Over Head Equipments Page 18  w) Identification of polluted locations: Areas, adjacent to factories and power stations having high ambient pollution particles should be identified and recorded. 2.4.4 Field Survey: To ensure accuracy only steel tape or fibre glass / plastic coated tape should be used for measurements. Yellow paint or crayon marks should be marked on the web of the rail along which measurements have been made every 25 m. on curves the chainage should be taken along the outer rail of the middle track when there are odd number of tracks. If there are even number of tracks the chainage should be taken along the inner rail of the first track outside the centre line of the group of tracks. At the point of start ‘zero’ chainage is taken. While proceeding along the tracks the features detailed in paragraphs 2.4.2 and 2.4.3 are recorded indicating their chainages and offset distances. When the next kilometer post is reached, the closing chainage distance to the km post is recorded. Chainage distance with respect to the new km post is commenced afresh. Thus chainages are taken from one km post to the next. 2.4.5 Overline Structure The headroom available under an overline structure is an important parameter, the design of OHE under it being governed by this parameter. It is necessary to mark the track level on the adjacent support column with yellow paint and use this reference mark to measure the headroom. This reference point is essential to be made permanent, since alteration to the level by permanent way gang subsequent to survey may radically affect the solutions to provide adequate electrical clearance which are found after a detailed study subsequent to field survey. Accordingly, all locations under overline structures where change in the track level by more than 50 mm may cause reduction in clearance of OHE from such structure or of the height of contact wire above the rail, need a special investigation by the field survey team. 2.4.6 Soil Characteristics The survey of soil characteristics ever 250 m should also include its type and a bearing pressure capacity. Samples of the soil should be collected and sent to a soil mechanics test laboratory to obtain the type of soil and its bearing pressure. This information is required to be recorded on the survey sheet. 2.4.7 Curve Realignment While measuring versines on curves if it is found that the figures are not uniform as should be found for a circular curve of that degree it may be necessary to have it examined by the open line permanent way engineers and get the curves realigned prior to finalisation of designs of OHE. Similarly, the super-elevations may also be adjusted to the designed values. This will ensure that the OHE designs have been appropriately made for the designed track layout minimizing subsequent adjustments during operation of the services. Over Head Equipments Page 19 2.4.8 Proposal to alter the track geometry During the survey it is essential to obtain from the open line details of work on the track which may alter the track geometry and which may be taken up earlier than the anticipated programme of electrification such as a) Provision of prestressed concrete steepers, resulting in raising of track level. b) Realignment of curves for higher speeds, resulting in longer transition curves and higher super-elevation. c) Easing of gradients. d) Remodelling of yards, and doubling works. e) Replacement of lower speed turn-outs to higher speed turn-outs. 2.4.9 Programme of Improvement to track structure As OHE is erected to suit the track, alteration to the erected OHE to follow the changed track geometry subsequently becomes difficult and expensive. It is therefore, necessary for the open line to complete the works for improvement to track structure prior to taking up the OHE work. The Survey Plans should, wherever possible, indicate the existing track layout as well as the altered location with respect to the existing track after improvement. Details of such improvements should be invariably obtained through joint inspection with open line officials during foot by foot survey. 2.4.10 Field Sketches The data recorded in the field books by the surveyor should be promptly transferred to field sketches as the survey proceeds so as to ensure full details are recorded and another visit to the site for items left out is obviated. In the basic form the field sketch sheet may contain pre-lined vertical and horizontal lines. The vertical lines may each denote distances of 50 m on open route and 25 m in yards and station limits. The horizontal lines may represent centre line of tracks. Major yards having more than five to six lines may need special sketches to be made as required to suit the geographical conditions. Each sheet may contain details for 250 m of track and have at least one cross-section of the route. All details should be neatly recorded, as this forms the basic document for preparation of the survey sheet. All distances should be in metre and the versines in milli-metre. 2.4.11 Survey Sheets The preparation of survey sheets in the drawing office proceeds serially as the field sketches are received there. These should be prepared in sheets of standard metric sizes with top sheet having the standard proforma, legend, and letter sizes. These are contained in RDSO’s Specification No. ETI/OHE/25. The drawings should be on tracing and in ink to permit reproduction. Over Head Equipments Page 20 2.5 PREPARATION OF PREPEGGING AND PEGGING PLANS 2.5.1 GENERAL Prepegging plans are prepared on the survey sheets in accordance with the ‘Principles for OHE Layout Plans and Sectioning Diagrams for 25 KV ac Traction’ issued by RDSO. The aim is to provide the most economical support arrangement for the Catenary system, being technically sound for the maximum traction current expected. The maximum speed envisaged, and the maximum number of pantographs expected in a span. The prepegging plan is superimposed in soft pencil on a print of the survey sheet. After a number of trials, the best plan providing for least number of structures, called the ‘Prepegging Plan’, is got ready for check at site for its feasibility. This plan is sent to site for marking out the location of structures and anchors on the adjacent rail. A joint inspection of the site is then conducted, by Electrical (OHE designs). Civil, and Signal & Telecommunications engineers. During the inspection the plan is verified, and if required, modified to suit the field conditions. At this time the Civil and the Signal and Telecommunications engineers also make out their plans for track slewing, shifting of drains, pipes, or signal point rods, cranks etc to make way for the foundations for the OHE structures and their anchors. The site verified plan is then finalized as ‘Pegging Plan’ and is available for use for tendering for the contract for field work and for estimation of quantities. On award of the contract for field work, the pegging plan is once verified by the contactor jointly with project electrical (OHE) engineer prior to taking up the field work. The plan actually followed for field work, incorporating further details of type of structures used, the style of the cantilevers used, the stagger of the OHE conductors, the run of wires, portal spans as well as the setting distances of the structure legs becomes the ‘OHE layout plan’. This plan is the record to be kept for proper maintenance of the equipment after commissioning. The prepegging and the pegging plans are finalised in series in increasing chainages without leaving an gap in between. There may be exceptions over sections where yard remodeling, doubling or an other work involving insertion of turnouts and crossovers are contemplated but not taken up or not marked at site. The field party of the survey organization takes up site marking and assists in the verification of the plan. 2.5.2 Particular Specification Prior to commencement of work on prepegging plan, the site conditions and the specific design of the equipment to be adopted needs to be finalised. Based on these parameters known as particular specifications the various details of the designs are adopted. 2.5.2.1 Meteorological conditions a) The maximum, the minimum and the mean ambient temperatures: The mean temperature adopted over the entire Indian subcontinent is 35 Degree C. A range of 15 Degree C to 65 Degree C as the minimum and the maximum is adopted for India except the northern plains having colder winters for which the range adopted is 4 Degree C to 65 Degree C. For unregulated OHE a contact wire height at supports of 5.65 m is adopted for the former range of temperatures and of 5.75 m for the latter range of temperatures. The Over Head Equipments Page 21 contact wire height of regulated OHE is uniformly kept at 5.60 m at supports. The extreme temperature variations dictate the limit of the length of the OHE conductors from the anticreep central mast to the balance weight anchor mast, the movement of the balance weights on the masts due to thermal expansion and contraction of conductors being limited as also to limit the swing of the bracket assemblies nearer the balance weights. For both the temperature ranges a maximum distance of 750 m from anticreep to the balance weight anchor mast is prescribed, inside long tunnels the temperature ranges are much lower and, therefore, advantage may be taken of this fact for specially designing the passage of OHE through them by minimizing the number of anticreeps and balance weight anchors. b) Wind Speed Zone It is to be ascertained from IS 875 as to in which zone area the section to be electrified falls. This dictates the maximum permissible span to be adopted and the relevant employment schedule to be adopted for the design of structures and foundations. c) Identification of ‘Exposed Locations’ As ascertained during foot by foot survey (refer paragraph 2.4.3 (V) the exposed locations which are likely to have maximum severity of wind velocity, which are identified on the survey sheets, should have maximum spans reduced by 4.5 m below the maximum permissible for the section as determined for item (b) above. 2.5.2.2 Design Parameters The design parameters and the type of equipment to be adopted is required to be specified in regard to the following: a) Choice of Portals or Individual masts at stations and on multitrack (more than two tracks) sections: Whether portals spanning all the wired tracks are to be provided or individual masts should be provided, if the track centres permit. Whether headspans are to be used for yard lines, and if so, where? b) Sections of open route and yard lines where regulated / unregulated OHE is to be used. c) Choice of the type of OHE for : i) Main lines – Whether conventional copper conductors or an other material is to be taken into consideration. ii) Sidings and yards – whether conventional OHE with catenary and contact wires is to be used or tramway type of equipment is to be used. For tramway type, whether the equipment is to be regulated or not. d) Booster transformers and return conductors : The decision jointly arrived at with the Department of Telecommunications, of the sections over which these are to be provided. e) Decision to use 2 x 25 kV AT system. A decision jointly arrived at with the open line Railway whether this system is to be adopted: if the Department of Telecommunications require Booster transformers and return conductor over the concerned section, their consent Over Head Equipments Page 22 to the use of this system in lieu of the provision of booster transformers and return conductors is also necessary. f) Finalisation of track slewing plans for yard or secondary lines to locate OHE structures in the identified lanes. 2.5.2.3 Movement of Over dimensional consignments (ODC) The minimum height of the contact wire under heavy overline structures is normally kept such that class ‘C’ over dimensional consignments of Height 4.92 m can be moved at unrestricted speed with electric locomotives. At heavy overline structures such as through girder bridges, road over bridges or tunnels having low clearances, and where modifications may not be feasible or the cost excessive a decision may have to be taken in regard to their passage such as : a) Whether adequate clearance may be provided to move with electric locomotive at restricted speed. b) Whether the ODC can be diverted through another line not spanned b the overline structure. c) Whether the ODC can be diverted through another line not overline structure can be nominated to move the ODC with electric locomotive. d) Whether ODC can be moved with ‘power off’ on OHE b a non electric engine, ensuring only adequate physical clearance. e) Or, whether the ODC should not be permitted under the overline structure, nominating an alternative route through which ODCs should be diverted. A suitable solution may need a careful examination of the extent f modifications, the cost; feasibility and the time frame for carrying out the modifications. 2.5.3 Principles of Prepegging Plans It is essential to be conversant with ‘Principles for Layout Plans and Sectioning Diagrams for 25 kV ac Traction’, Document No. ETI/OHE/53 issued by RDSO before attempting preparation of a prepegging plan. Some important principles, however, are brought out in the following paragraphs for read reference. 2.5.3.1 Span Lengths Span lengths are chosen in multiples of 4.5 m. The shortest span adopted is 22.5 m and the longest, depending upon the particular specification of the wind speed zone and the type of equipment, being a maximum of 72 m. The difference between two consecutive spans should not exceed 18 m to ensure compatible flexibility over the adjacent spans. Non standard span lengths are permitted only if special conditions do not permit choice of standard span sizes, such as while locating on bridge structure. The maximum span lengths as permitted by the location should be aimed at. On tangent track this is the maximum permissible depending upon the particular Over Head Equipments Page 23  specification of the section. On curves, turnouts and crossovers, the span lengths are lower, being governed by the maximum permissible stagger of the contact wire at the structure and in the middle of the span; this limitation being guided by the design consideration of pantograph contact surface its sway and blow-off of OHE conductors in wind. As a general rule the maximum stagger at a structure should not exceed 300 mm on curves and 200 mm on tangent track. Mid span staggers should also not exceed the figures prescribed by RDSO. 2.5.3.2 The Setting Distance (Implantation) of Structures The setting distance to be provided are : a) For individual masts carrying one OHE: i) On tangent track Standard 2.80 m Minimum 2.36 m (*Note: In special circumstances, with prior approval of the Chief Electrical Engineer of the Railway) ii) On curves Degree of curve Radius of curve in m Setting distance in m Inside Curve Zero to 1/2° Above to 3500 3.20 1/2° to 3/4° 3500 to 2350 3.35 3/4° to 1/2° 2350 to 1150 3.55 1 1/2° to 6° 1150 to 300 3.60 Outside Curve Zero to 2 >1 = to 875 2.80 Above 2 less than 875 2.95 b) For a Portal upright or a headspan leg or a mast carrying more than one OHE the setting distance adopted should not be lesser than 3.00 m c) Lower setting distances permissible on curves: If the stipulated standard setting distances mentioned in subparagraphs (a) and (b) above cannot be obtained, lower setting distances upto a minimum may be adopted as found out from following reckoning: To the minimum setting distance as permitted in the schedule of fixed structure as provided in the ‘Schedule of Dimensions, 1676 mm Gauge’, a slewing allowance of 150 mm should be added; to this a curve allowance for the degree of curve should be added. The curve allowance for different degrees of curves and for different speed potentials are given in the ‘Schedule of Dimensions, 1676 mm Gauge’ and in tables I, II, and III of RDSO’s Document No. ETI/OHE/53: Principles for Layout plans and Sectioning Diagrams for 25 kV ac Traction. Over Head Equipments Page 24 2.5.3.3 Location of obligatory structure There are certain features along the track, within a few metre of which an OHE structure should be provided. These are, for example, at turnouts and crossovers or adjacent to overline structures. These OHE structures are called ‘Obligatory structures’. While commencing a prepegging plan it is most convenient to commence from an obligatory structure at a turnout or a crossover. An OHE structure should be located within 2 m of the theoretical centre of a turnout. If this is found not feasible, as an exception the structure may be located farther away. The maximum distance from a centre of a turnout that a structure can be located is indicated in Table 2.5.2. In all cases, the contact wire staggers at structures and at mid spans should be verified during site verification of the prepegging plan. During the verification the location of the section insulator, if required to be provided in the span should also be fixed. The span under an overline structure should not exceed 54 m to limit the amount of push up of Catenary by the upward thrust of the pantograph; also the structures supporting the OHE should be more or less equidistant from the centre line of the overline structure to ensure maximum clearance between the overline structure and the OHE conductors. Passage of OHE under heavy overline structures having restricted clearance has to be designed specially through a “profile study”. Such a study fixes the location of OHE structures, the span lengths to be adopted under and adjacent to the overline structure along with the contact wire gradient and the encumbrances at the supports. Table 2.5.2 Maximum permissible distance from OHE support to Centre of Turnout No. of Turn- Distance from centre of turn-out to Maximum distance permissible out from centre of turnout to the OHE structure, towards Toe (m) Nose (m) Toe (m) track Nose (m) track separation = separation = 150 mm 700 mm 1 in 8 1/2 11.15 14.30 5.72 4.20 1 in 12 15.15 20.15 7.00 6.10 1 in 16 20.10 26.85 9.60 7.50 1 in 20 23.75 33.50 10.70 10.50 Over Head Equipments Page 25 Over Head Equipments Page 26  This is based on the fact that on a turn out, although the contact wire for the main track is, appropriately placed for the pantograph of a locomotive running at speed, it is the contact wire for the turn out that should always be within appropriate stagger (=300 mm at support and the appropriate mid-span stagger for the turn out span). The curvature on the turn out requires staggers of 300 mm in all cases towards the main track. Further, there should be a minimum horizontal separation, between the two contact wires, of 50 mm and a maximum of 200 mm at support to ensure non- interference between two OHEs and smooth change over of contact wire for the pantograph of the locomotive negotiating the turn out. This is possible if the obligatory structure at a turn out is located at any point between the track separation of 150 mm and 700 mm, irrespective of the number of the turn out, as would be clear from the Figure 2.5.1. 2.5.3.4 Location of OHE structures in advance of a Signal: OHE structure should not be located nearer than 10 m behind and 30 m in advance of a signal. For proper visibility of a signal, a larger setting distance is given to a few OHE structures in advance of a signal. For Semaphore signals a larger setting distance is required for 5 OHE structures, with the one immediately in advance having a minimum setting distance of 3.05 m, followed by the next one at 2.9 m and the next three consecutive structures having a minimum setting distance of 2.75 m. For colour light signals, the minimum setting distances are regulated upto 600 m in advance of the stop signals and upto 300 m in advance of a signal with route indicators. On curved track, depending upon the topography and curvature, the structures should be so located as to ensure the best continued visibility of signals. In such cases the setting distances and the lanes for location of OHE structures should be fixed by a joint field inspection of Electrical (OHE designs) engineer with the Signal Engineer. 2.5.3.5 The location of overlaps The insulated overlaps are located at the appropriate sites selected for the subsectioning and paralleling posts (Neutral sections are required to be provided at the sectioning and at feeding posts), the locations for the manually operated isolating switches, and for the booster transformers stations, all of these having been finalized in the sectioning diagram earlier. Having located the insulated overlaps the uninsulated overlaps are inserted ensuring longest tension lengths, the effort being to have minimum number of overlaps in the section. There is a limit of 750 m between the anticreep central mast to the corresponding balance weight anchor mast at the overlap for regulated OHE. This limits the tension lengths to 1500 m maximum. For unregulated OHE no anticreeps are required and the maximum tension length of conductors is increased to 2000 m. In case the insulated overlap is on a curve having a radius of 5000 m or sharper (0.35 degrees) a 4 span overlap becomes necessary with a central overlap OHE structure having two brackets at different elementary sections. To ensure satisfactory clearance between the brackets the distance from anticreep to the centre of the 4 span insulated overlap is limited to 600 m. In view of the problem of maintaining appropriate clearances at the overlap central mast and need to take power block on two elementary sections for maintenance of such overlaps, location of insulated overlaps on curves should be avoided as far as possible. The tension lengths Over Head Equipments Page 27  at conventional overlap type of neutral section and at short neutral section are limited to 600 m or less. The overlaps should be also so adjusted that their location at a station does not result in use of three bracket structures. If, adjustment of the uninsulated overlaps between the predetermined location of insulated overlaps results in having a tension length 750 m or lower (600 m if adjacent to 4 span insulated overlap or adjacent to a 41 m neutral section), a half tension length of OHE, having one end as fixed termination may be adopted, omitting the anticreep. 2.5.3.6 Location of Section Insulator The total weight of the section insulator including the weight of the two insulators on the OHE and the copper runners is 55 kg. to accommodate the two insulators for both the conductors and to permit the locomotive pantograph to glide over the two runners of the section insulators there is a requirement of a minimum dropper length of 450 mm, and a maximum permissible stagger of 100 mm at the location of the section insulator. Since the maximum encumbrances at the OHE structure is limited to 1.4 m, this imposes a limit to the sag and therefore, the distance of the section insulator from the nearest OHE support. This limit is given in Table 2.5.3 below. In view of the limit of 100 mm of stagger, this should be achieved by adjusting the staggers at the adjacent OHE structures during site verification of the prepegging plan. Table 2.5.3 Maximum permissible distance of section insulator from nearest OHE structure, having 1.4 m encumbrances of the span, applicable for regulated OHE with 107 mm2 contact wire and 65 mm2 catenary at 1000 kg tension in each Weight of section insulator = 55 kg All dimensions in m Span 72.0 67.5 63.0 58.5 54.0 49.5 45.00 < 45.0 Distance 7.7 8.1 9.4 12.3 13.5 15.0 18.2 No limit At a turnout the section insulator assembly should be located beyond the Nose of Crossing with runners facing away from the centre of turn out. It is a good design practice to locate the OHE mast towards the Nose so as to make the span over the turnout short permitting wider latitude in location of the section insulator and having adequate latitude in selection of suitable staggers at the structures in order to achieve the stagger of contact wire below 100 mm under the section insulator. 2.5.3.7 OHE at a turnout On main running lines the OHE of the turnout should have overlap type of equipments. On secondary lines this may be crossed type to reduce the cost. The turnout OHE taking off from the main line should be regulated and have both, the contact wire and the Catenary. The OHE for a secondary line taking off from a loop line may be either unregulated or tramway type. Three backet assemblies at a turnout Over Head Equipments Page 28  structure should be avoided as adjustments to the OHE are difficult. As mentioned in paragraph 2.5.2.3 above, in this effort overlap multicantilever OHE supports should be suitably located away from turnout structures. 2.5.3.8 OHE at Special locations: a) Adjacent to overline structures: Prior to preparation of OHE prepegging plan in vicinity of a heavy overline structure the clearance study should be completed. In case of restricted clearances the profile drawing should be prepared in advance for incorporation in the OHE prepegging plan. b) On long bridges The spans on long bridges are dictated by the location of the piers on which the OHE structures are located, therefore, these are usually non standard. On through girder bridges the OHE may have to be supported on specific members of the trusses, as such the design of OHE on such a bridge may be finalized subsequently, without delaying the finalization of the prepegging over the rest of the route. However, the feasibility of location of the OHE support must be established in advance during the survey. c) In tunnels: The design of OHE in tunnels require careful study. The spans are required to be kept short as it becomes difficult to obtain adequate headroom for large encumbrances. Unless the tunnel is long, anticreeps and overlaps should not be located inside the tunnel. For long tunnels one method to avoid the anticreep is to erect unregulated OHE, the seasonal temperature variations inside the tunnel being limited, provided there are permanent speed restrictions inside the tunnel imposed due to civil engineering considerations; the effort being to avoid imposition of speed restriction on account of OHE only. In sum a detailed examination of the local conditions is required before finalizing the design of OHE inside a tunnel. 2.5.4 Provision for Remodelling Yard remodelling works may be in progress or proposed on the route. Doubling works may also be in progress. If the electrification works is expected to be taken up either after remodelling or has to take in account such remodelling, so as to conveniently modify the OHE when such remodelling is taken up, the design for OHE should take into account such works in the prepegging plan. Accordingly the proposed locations of toes of turnouts and alignment of the new track should be jointly examined by the civil engineer in charge of the track construction works and the OHE design electrical engineer, so as to obtain the most economic plan involving least amount of traffic block for carrying out the remodelling work both for the track and for the OHE when the plan is finalized. The toes of the turnouts and the alignment of the proposed tracks are marked out on the ground with permanent bench marks. These are incorporated in the survey sheet. The special arrangements to be provided for in the prepegging and subsequently in the pegging plans including in the phase plans, if any, should be noted in the finalized plans. Over Head Equipments Page 29 2.5.5 Preparation of prepegging plans The drawings should be of standard size and follow the standard orientation of the top sheet and the direction of progress. For this purpose provision contained in RDSO’s Specification No. ETI/OHE/25 may be followed. The exercise for preparation of the prepegging plan should commence as an exercise in soft pencil on a print of the survey sheet. It may begin from an obligatory structure of a turnout on the main line and structures marked according to the guide lines. Adjusting the location of structures, to minimize their number, and those of the location of the overlaps, anticreeps and anchors to the most suitable locations may need a number of exercises. At stations where portals are not to be used, main and loop line cantilevers may be located in an umbrella fashion on a common mast, provided they are on the same elementary section. Number of brackets on a mast, the anchors, return conductors, earth wires, and 25 kV feeders should be clearly marked. After the trials, when the plan is considered satisfactory the structure numbers and their chainages are marked out. This plan is now transferred to the inked tracing of the survey sheet, but in SOFT PENCIL, so as to erase and incorporate the changes, if required, after site verification of the plan. To confirm the feasibility of the plan during site verification the prepegging plan should include the following details: a) Anchors – Balance weight, fixed termination, and anticreep for OHE, 25 kV feeders, return conductors and earth wire. b) Anticreep central masts – indicating thereon the number of spans and distance in metre to the balance weight anchors. c) Multiple cantilevers –0 for overlaps, turnouts and out of run wires. d) Overlaps – insulated, uninsulated or neutral section, the insulated overlaps being at the location selected for the supply control post, manually operated isolating switch or for booster transformer. e) Conductors – OHE return conductors 25 kV feeders and earth wires. The length of the OHE span is to be recorded in the middle of the span. f) Section insulators – for sectioning or for neutral sections: the distance to the nearest mast should be recorded. g) Signals – existing as well as those to be installed. h) Auxiliary transformer (25/0.230 kV) stations – for stations, signal cabins, intermediate block signal huts and level crossings. At least two prints of the prepegging plan, thus made ready are furnished to the survey civil and S&T engineers who are required to attend the site inspection for verification of the plan. 2.5.6 Marking at site On receipt of the print of the prepegging plan at site, the field subordinate marks the locations of the structures and anchors in yellow paint on the web of the rail adjacent to the shown location of the OHE structure or anchor 7.5 m away from the OHE structure alongside, structure numbers and their chainages are also marked. During marking out the locations on web of the rail, simultaneously, obstructions, if any to the location of structures or anchors, found at site should be recorded on the print. Further at the location of structure the following measurements are taken and recorded on the print for : Over Head Equipments Page 30  a) track centres, b) width of the cess, if in a cutting distance to the drain and its width and to the edge of the slope, c) turnouts: distance of the structure location from the toe of the switch and track separation at the location, d) drains, point roading underground, pipeline or cables running along the route distance from the adjacent track to be checked if located in the same lane in which the structure locations are proposed, e) versines in mm of span for the tracks on curves and of turnouts and crossovers, f) signals: distance to the nearest OHE structure location, g) powerline, signal or telecommunication crossings: distance along the track from the nearest structure location, h) obstruction, if any, for location of structures as shown in the prepegging plan. Marking out the prepegging plan at site gives one more opportunity to the survey team to verify ground conditions and incorporate changes, if any, since the original survey. After marking out the locations of structures on rails and incorporating other details as required, one copy of ‘as marked’ plan is returned to the OHE design office. One copy is retained by the field subordinate as his copy. 2.5.7 Joint field inspection In the OHE design office the ‘as marked’ plan is carefully examined and the plan is modified, taking into consideration the ground conditions viz. obstructions or excessive versines on curves or at turnouts or inadequate track centres for location of a structure. This revised prepegging plan is now ready for Joint Field Inspection. Copies of this plan is distributed to the civil and signal and telecom engineers of the Survey organization. A programme of joint inspection of the site is now made by the Electrical (OHE designs) engineer with the concerned civil and S&T engineers. The Officials must be of adequate level so as to take decisions on the spot during the inspection in regard to modifications, if any, required to be done to the civil engineering or S&T installations at site. The S&T official should have with him the finalized plan for the proposed colour light signals. Modifications, such as, diversions of drains, pipelines, trolley or man refuges, or slowing of tracks to obtain adequate track centres, or shifting of point rodding alignments or of cranks for locating OHE structures are recorded for their compliance. All overhead crossings of Signal and telecommunications circuits including those belonging to the DOT are specifically taken note of, so as to either divert them or cable them well before commencement of OHE construction work. Any power line crossing should confirm to the Regulations for Power Line Crossings of Railway Track. If it does not, the owner of the crossing will have to be advised to modify the crossing to confirm to the Regulations contains Over Head Equipments Page 31  some of the important provisions of the Regulations for Power Line Crossings of Railway Tracks for ready reference. Based on the decisions taken during the joint inspection the OHE layout is finalized. This plan is now termed the ‘Pegging Plan”. 2.5.8 The Pegging Plan The location of OHE structures and of anchors, being final, are now inked over in the tracing of the original Survey Sheet. Vital details at the location of structures, such as the track centres and measured cess widths; spans of portals; versines of spans on curves, at turns outs and at crossovers are recorded on the plan. This pegging plan forms the basis for estimation of quantities of work and of materials, based on which the tender schedules are finalized. 2.5.9 The OHE Layout Plan This pegging plan is further completed in stages as the construction work proceeds. Finally when the construction work is over, the final plan, called the OHE layout plan contains the details of run of conductors, showing both ‘in run’ and ‘out of run’ contact wires, setting distance of each structure and its type, the type of portal and span of its boom, the staggers of the contact wire and any other special features which may be required to be given such as reference to a profile drawing for passage of OHE below an overline structure. There is usually a time gap between preparation of pegging plan which indicates the milestone of conclusion of the survey, and the OHE layout plan, prepared during construction by the contractor, who commences the work after further verifying the pegging plan. On completion of the work the contractor finishes the OHE layout plan as “As completed” plan for handing over to the maintenance organization. 2.5.10 Modifications to Railways electrical overhead distribution lines The overhead distribution lines running on platforms or in yards need to be checked for the quantum of electromagnetic and electrostatic induction from the 25 kV ac 50 Hz single phase traction currents. During the survey, drawings should be also made of the power distribution lines indicating their separation distance from the centre line of the track to be electrified and the arrangement of feed, whether in the middle or at the end to ascertain the extent of parallelism, on receipt of the survey sheets in the electrical design office the voltage rise due to electromagnetic induction and the discharge current due to electrostatic induction in the distribution lines are checked in accordance with the formula obtained form SNCF. If the induction effects are found to be beyond permissible limits, the distribution lines would need to be modified to bring down the effect to be within safe limits, the distribution lines would need to be modified to bring down the effect to be within safe limits and plans are accordingly made. 2.5.11 Bonding and Earthing plans All metal work adjacent to electrified lines have electro-magnetically induced voltages, which increase in proportion to their length, such as metallic or platform shelters running parallel to tracks. Other metal work open to public such as the foot overbridges and platform columns may also pick up hazardous voltages either Over Head Equipments Page 32  induced or by accidental contact with the live OHE. Rails of the track carry heavy traction currents in vicinity of feeding posts or at other locations where some rails are taken up for track circuits, these locations may pose hazard to the permanent way gang. Accordingly plans for suitable earthing and bonding of the metal work adjacent to track, breaking the long fencing in smaller electrical section, and providing safe passage of traction currents through rails by providing longitudinal and transverse bonds for running rails of electrified tracks are made. All OHE structures are bonded to the non track circuited rail through structure bonds, or if such a rail is not available to an earth wire run on the OHE structures, the earth wire being broken up electrically in parts and each part individually earthed. Accordingly bonding and earthing plans are made for the entire route o be electrified in accordance with the Code for bonding and Earthing. Document No. ETI/OHE/71 issued by RDSO. This plan, however, needs to be made only at the stage of construction activity. 2.5.12 Progress Chart To monitor the progress of survey, preparation and finalization of the plans, conduct soil tests and do the clearance studies under overline structures a progress chart is essential. Over Head Equipments Page 33