Download - Overhead Electrification

OHE BASICSOHE means Over Head Electrification. It consist of,

1. Catenary wire (copper cadmium 19 strands 65 sq.mm)

2. Contact wire (Hard drawn copper solid round 107 sq.mm)

3. Dropper wire is bet catenary and contact wire.( 5 mm hard drawn copper ) and supported by OHE cantilevers.

Feeding post-

Means a supply control post, where the incoming feeder lines from grid sub-station are terminated.

Neutral section-

Means a short section of insulated and dead overhead equipment which separates the areas fed by adjacent sub-stations or feeding posts.

OHE BASICS Power Block-

Means blocking of a section of line to electric traffic only.

Supply control post-

Means an assembly of interrupters, isolator switches, remote control equipment and other apparatus provided for controlling power supply to overhead equipment. It includes feeding posts, sectioning and paralleling posts and sub-sectioning posts.

Tower wagon-

Means a self-propelled vehicle which is used for the maintenance and repairs of overhead equipment.

OHE BASICSBond

An electrical connection across a joint in or between adjacent lengths of rail.

i) Bond, continuity : A rail bond used for maintaining continuity of the rail circuit at crossings and junctions.

ii) Bond, Cross – A rail bond used for connecting together two rails of a track or rails of adjacent tracks.

iii) Bond, Impedance : A special rail bond used to bridge an insulated rail joint in actrack circuited sections in areas equipped for electric traction.

iv) Bond Rail – An electrical connection across a joint between two adjacent lengths of rail as part of the track return.

v) Bond, Structure – An electrical connection between the steel work of track structures, bridge or station building, to which the traction overhead equipment is attached.

OHE BASICSCantilever (Assembly)

It is an insulated swivelling type structural member, comprising of different sizes of steel tubes, to support and to

keep the overhead Catenary system in position so as to facilitate current collection by the pantograph at all speed

without infringing the structural members. It consists of the following structural members.

i) Stay arm – It comprises of dia. 28.4/33.7 mm (Small) size tube and an adjuster at the end to keep the bracket

tube in position. It is insulated form mast by stay 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 is supported from this member by Catenary suspension bracket and Catenary

suspension clamp.

OHE BASICSCrossings

The electrically live member / conductor passing over another electrically live member /

conductor, without physical contact.

i) Power line crossing – An electrical overhead transmission or distribution line or underground

cable placed across railway tracks whether electrified or not for transmission of electrical energy.

ii) Crossing OHE – Crossing of two conductors of OHE crossing without physical contact.

OHE BASICSElectrical Clearance- The distance in air between live equipment and the nearest earthed part.

Encumbrance-The axial distance on vertical plane between the Catenary and the contact wire at support.

Feeder-A conductor connecting (a) a substation with a feeding post, or (b) a feeding post with the OHE.

Height of contact wire-The distance from rail level to the under side of contact wire.

OHE BASICSInterrupter

It is a single phase Vacuum breaker used as load switch to close the circuit on Fault, but does not open on fault. It is operated either by remote control or manually at site.

Different methods of connection of interrupters are:

a)Bridging Interrupter: An interrupter which is provided at the neutral section to extend

the feed from one substation to the overhead equipment normally fed by the other

substation in emergencies or when the latter is out of use. This normally remains in

the open position.

OHE BASICS b)Sectioning Interrupter: An interrupter which connects adjacent sub-sectors together to maintain continuity of supply. This normally remains in closed position.

c)Paralleling Interrupter : An interrupter which connects overhead equipment’s of two different tracks. This normally remains in closed position to reduce the voltage drop.

Mast

A single vertical post embedded in the foundation or otherwise rigidly fixed in vertical

position to support the overhead equipment with cantilever assembly. It may be rolled

section or fabricated. The uprights of portals and TTCs are also called masts.

Note : Pre-stressed concrete spun poles for traction overhead equipment are under

development.

OHE BASICSJumper - A conductor or an arrangement of conductors for electrical continuity not under tension, which forms electrical connection between two conductors or equipment’s.

Return conductor - A conductor which carries return current from the tracks to the sub-station in the booster transformer system.

Regulating Equipment - A device for maintaining the tension of OHE conductors constant under all ambient temperature conditions.

Note : Such OHE is called regulated OHE.

OHE BASICSSuspension Distance - The horizontal distance from the centre of the eye of Catenary suspension bracket to the face of the mast for a single cantilever assembly or the face of cross arm channel in case of multiple cantilever assembly.

Span -The 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 portal uprights.

Stagger - Stagger of the contact wire is the horizontal distance of the contact wire from the vertical plane through the centre of track.

Section Insulator - A device installed in the contact wire for insulating two elementary electrical sections from each other while providing a continuous path for the pantograph without break of current.

OHE BASICSSupply Control Post - It is general term which refers to an outdoor assembly of control gear, such as interrupters, isolators, potential transformers, auxiliary transformers, etc including remote control equipment installed in a cubicle, for controlling power supply to overhead equipment.

a) Feeding Post (FP) – It is a supply post where the incoming 25 kV feeder lines from substation are terminated and connected to the overhead equipment through interrupters.

b) Sectioning and Paralleling Post (SP) - It is the supply control post situated mid-way between two feeding posts at the neutral section and provided with bridging and paralleling interrupters.

c) Sub-sectioning and Paralleling Post (SSP) – It is a supply control post where sectioning and paralleling interrupters are provided.

d) Sub-sectioning Post (SSP) – (for single line section) : It is a supply control post where a sectioning interrupter is provided.

OHE BASICSSector - A section of Overhead equipment of a track which can be energized by closing a feeder circuit breaker at the substation.

a) Sub-sector – The smallest section of overhead equipment which can be isolated remotely by opening of interrupters.

b) Elementary Section – The smallest section of overhead equipment which can be isolated from the rest of the system by manual operations.

Tension Length - Length of conductor which is stretched between the two anchor points

Versine - The versine is the maximum offset of the rail on which spans have been measured of the curved track form the chord connecting two points, each opposite adjacent masts.

OHE BASICSElectrical Clearance

Clearance - The clearance between 25 kV live parts and earthed parts of fixed structures or moving loads shall be as large as possible. The electrical clearances to be maintained under the worst conditions of temperature, wind, etc are given below:

a) Maximum vertical distance between any live part of overhead equipment or pantographs and parts of any fixed structures (earthed or otherwise) or moving loads:

i) Long duration 320 mm

ii) Short duration 270 mm

b) Minimum lateral distance between any live part of overhead equipment or pantographs and parts of any fixed structures (earthed or otherwise) or moving loads:

i) Long duration 320 mm

ii) Short duration 220 mm

OHE DESIGN General Power Supply Diagram:General Power supply Diagram shows the basic scheme of switching station and sub-section wise. OHE DRAWINGS Pegging Plan OHE Layout Plan (LOP) Cross Section Drawings(CSD) Structural Erection Drawings (SED) Profile/Clearance Study Drawings As Erected Drawings Switching Station Drawings

OHE FOUNDATIONSFoundation Design Basis:

Foundations are designed on the basis of FBM code, type and bearing capacity of soil, shoulder width and the extent of projection above ground level.

Selection of the type and size of foundation is done from the “Volume Chart and equivalent chart for foundations”

OHE FOUNDATIONS TYPES OF FOUNDATIONS

a)Side bearing foundations or “B” type foundations - are used for masts where earth is normal and fully consolidated, the soil bearing capacity is 11.000 or 21,500 kgf/m2 and 300mm wide shoulder is available beyond the outer edge on the foundation on banks.


b)Side gravity foundations or “BG” type foundations-may be used for masts where soil bearing capacity is 8000 and 11000 kgf/m2, or adequate shoulder width is not available i.e less than 300mm beyond the edge of foundation.


c)Pure gravity foundations or “P” type foundations - are used for portals and are designed for soil bearing capacity of 8000 and 11000 kgf/m2.


d)New pure gravity foundations or “MG” type foundations may be used for masts where soil bearing capacity is 5500, 8000 and 11000 kgf/m2 or where adequate shoulder width is not available. In such cases, it should be ensured that foundation is not exposed.


e)WBC and NBC type of foundations are used in Black cotton soil. Primarily WBC foundations are to be adopted where swelling / shrinkage is not expected to take place at the founding level and NBC foundations have to be provided where swelling / shrinkage is expected to occur.

OHE FOUNDATIONS CLASSIFICATION OF FOUNDATIONS

OHE FOUNDATIONSPreparatory Works for Foundation:Ensuring of approved LOP & CSD for the particular section at site. Copy of Volume chart & Boom combination chart

Marking of location number, chainage, type of mast, implantation on rail.

Collection of Coarse aggregates (metal), Fine aggregates (sand) & Cement near to the location.

Arranging required size of shutters.

Ensuring working condition of the Vibrator & availability of other T&P’s like scroll box, shovel, spade, crow bar, pick axe, motor pan etc.

OHE FOUNDATIONS IF ROCK IS ENCOUNTERED RESORTED TO “BLASTING”

First, inform the condition to Railway representative.

Carry out joint inspection with railway representative to assess the intensity of the blasting and

obtain Railway’s approval in writing.

Chalk out a blasting programme and arrange ‘line block’ accordingly.

According to intensity of blasting, request for caution order from railway.

OHE STRUCTURESMAST - A single vertical post embedded in the foundation or otherwise rigidly fixed in vertical position to support the overhead equipment with cantilever assembly. It may be of rolled section or fabricated.6” x 6” BFB – Broad Flanged Beam (152mm x 152mm)8’’ x 6’’ RSJ – Rolled Steel Joist ( 203mm x 152mm)“B” Series Mast (B 150, B 175, B 200, B250)

SWS Masts (S1, S3, S4, S5, S6, S7, S8 & S9) AT Mast (T150)

All OHE masts are 9.50 metres in length.The Drillings for fixing various SPS will be according to the drilling schedules.

OHE STRUCTURES PORTALS - On multiple track sections, where adequate track centres are not available and tracks cannot be slewed, Portals are used. Each portal consists of two fabricated uprights and one fabricated boom consisting of with or without one central piece and two end pieces.

OHE STRUCTURES

OHE STRUCTURES METHODOLOGY FOR MAST ERECTION BY RAIL CRANEList of Mast to be erected for the km either in ascending/descenting order based on the approved OHE Layout plan to be prepared.Summary of total mast required for the KM to be mark on the schedule.Availability of mast to be verified before loading.Request for placing BFR to be given to the Customer in advance.Masts to be loaded on the BFR- type wise as per the summary of schedule.Masts should be secured on the BFR to avoid falling of structure on movement.Clean the core hole of OHE foundation from any foreign materials at least one day in advance.

OHE STRUCTURESErection:Avail the line block from railways in prescribed format request.After getting granted traffic block, start the erection as per schedule. Provide 16 mm dia 1.5 m long sling on one third length of the mast from top and lock with 5T capacity ‘D’ Shackle..Crane operator to lower the Rail crane hook near the sling of the mast.Mast lifting from BFR and placing on core hole of the foundationLean the structure away from the track and provide necessary packing & wedge.Moving the formation to next location.Note: On reaching to the erection spot one mast can be erected in 5min time with rail crane. Labour requirement: 5

OHE STRUCTURESMETHODOLOGY FOR MANUAL MAST ERECTION BY DERRICK ARRANGEMENT

Preparatory Work:List of Mast to be erected for the km/section to be prepared based on the approved OHE Layout plan.Availability of mast to be verified before making erection schedule.Shifting of mast to locations by tractor trailer or dip trolley. Mobilizing the T&P resources –Derrick, Hook chook, Manila ropes, “D” Shackles, Crow bar, Wire slings etc.For erection of 9.5m long mast 2 derrick pieces has to joined together (3mx 2nos), For erection TTU & Uprights 3 derrick pieces has to be joint together (3mx3).

OHE STRUCTURES METHODOLOGY FOR MANUAL MAST ERECTION BY DERRICK ARRANGEMENTT&P Requirement:-Extendable derrick : 1No, 1.5-2.0T capacity Hook Chook with 20 mtr long wire rope:1No,16 mm dia,25m long polypropylene rope :5Nos, Crow bar:5Nos, ’D’ Shackle (5Tonne capacity):2Nos. 16mm dia, 1.5m long sling:2Nos.

OHE STRUCTURES METHODOLOGY FOR MANUAL MAST ERECTION BY DERRICK ARRANGEMENTErection:Bring the assembled derrick near to the foundation and place parallel to the track. Lift bottom side of the derrick and place above the foundation(adjacent to core hole).Tie the poly propylene rope on four corners of the top plate of derrick.Insert the hook chook wire rope on the single sleeve pulley and place the pulley hook on the derrick where the provision has been made.Place the mast on the foundation center portion of the mast should rest on foundation and also parallel to the track.Lift the derrick by pulling the poly propylene rope and place the derrick in vertical position. Tie the ropes on four corners by driving crow bar inside the ground.Attach the hook chook on the bottom side of the derrick with the help of sling & ‘D’ Shackle.

OHE STRUCTURES METHODOLOGY FOR MANUAL MAST ERECTION BY DERRICK ARRANGEMENTErection Provide the 1.5 mtr sling on middle of the mast and attach the hook chook wire rope hook on the sling with the help of ‘D’ Shackle.Tie one poly propylene rope on top of the mast for alligning.Take load on the hook chook – Mast will get lift from the foundation.Hold the bottom portion of the mast and continue the load taking through hook chook till the mast is attaining the position of 45 to 60 degree from the top of foundation .Push the bottom side of the mast in side the core hole.Release the load of hook chook and ensure mast bottom is resting on foundation core hole.

OHE STRUCTURES METHODOLOGY FOR MANUAL MAST ERECTION BY DERRICK ARRANGEMENTErection Lean the mast toward country side and arrest the movement with wedges.Remove the hook chook , sling from the derrick.Lower the derrick by loosening the poly propylene rope carefully.Shift the T&P’s to the next location through dip trolley.Note: with 10 workers we can erect one mast in 30 min.

OHE INSULATORSIn OHE there are different types of insulators are being used.

Stay arm insulators:

These insulators are equipped with stay arm tube in cantilever, these insulators are having two different types.

Porcelain insulator ( 850 mm CD & 1050 mm CD)

Composite type insulator. (850 mm CD & 1050 mm CD)

Bracket insulators

This insulators is equipped with bracket tube in cantilever, these insulators are having two different types.

9 - ton insulators (Cut-in-insulators) In an insulated overlap the two OHEs are made electrically separated by provision of cut-in-insulators in the catenary and contact wire.In section insulator arrangement this insulator is erected in the catenary wire.In termination of wires where the platform involves, this insulators is used in the edge of the platform.

OHE INSULATORS25 KV support Insulator / Pedestal insulators This type of insulators are used in single pole isolators, double pole isolators and in bus bar arrangements.25 KV tie rod insulatorsThis type of insulators are used in single pole isolators, double pole isolators arrangements.Section Insulator:A device installed in the contact wire for insulating two elementary electrical sections from each other while providing a continuous path for the pantograph without break of current.

OHE JUMPERSJumpers:

A jumper is a conductor or an arrangement of conductors, not in tension, used for electrical connection between two conductors or equipments.

Types of Jumpers are:

a)In span Jumpers or “H” Jumpers

b)Turnout /Un-insulated overlap Jumpers or “G” Jumpers

c)Potential Equalizing Jumper of “F” Jumpers

OHE ISOLATORISOLATOR:Function of isolator is to make and break the Electrical continuity of an Elementary section. The picture shows the view of the Single Pole Isolator. In major yards where loading and unloading of materials are involved Double Pole Isolators with Earthling Heels are being used.

OHE TRANSFORMERAUXILIARY TRANSFORMERS230 V single phase power supply required for operation of substation equipment, lighting of the station yard, tunnels and working of colour light signals, is obtained through 25 kV / 230 V, 100/10/5 Kva, 50.Hz. single phase LT supply transformer.It is provided at substations feeding and switching posts, stations, block-huts and at other outdoor locations e.g. level crossings with gate signals.Capacity:LT supply transformers are of 5/10/25 kVA capacity. More than one transformer are provided at large station, yard etc.Protection:LT supply transformers are protected only by a 25 kV dropout fuse on the primary side and 63A fuse wire of 20 SWG tinned copper wire on the secondary side.

OHE TRANSFORMERSMounting arrangement:The LT supply transformer is mounted on steel platform erected on the OHE mast and connected to the 25 kV OHE through rigid aluminum bus-bar or 50 mm2 copper jumper wire.Substation LT supply:At substation, in order to provide power to single phase transformer oil centrifuging / filtration plant, 100 kVA`, 25 kV/ 230V, 50 Hz single phase transformers are provided.

OHE TRANSFORMERSBooster Transformers

Booster Transformers wherever necessary for suppression of inductive interference of P&T

communication lines running in close vicinity and parallel to 25 kV OHE may be provided

separately for each running tracks. The primary winding of the booster transformer is connected

in series with the OHE at insulated overlaps.

The Booster transformers are located at an approximately spacing of 2.66 km between each

other.

OHE TRANSFORMERSThe location of the booster transformer should be decided considering the following aspects.

a) At feeding posts and sectioning and paralleling posts the booster transformers should be located equidistant on either side so that the mid-point falls in front of these switching stations.

b) In exceptional circumstances where the booster transformers are not placed equidistant from the feeding post or sectioning post, it must be ensured that the distance of the booster transformer from FP or SP does not exceed 1.33 km.

c) The booster transformer should not be located:

In the vicinity of the stop signals to avoid bridging of insulated overlap by locomotives pantograph.

Within the station limits except for very big stations

OHE RETURN CONDUCTORSRoute

In deciding the route of return conductors the obstructions in route should be taken into consideration. Besides, adequate physical and electrical clearances should be maintained from fixed structures.

The general objectives is to run the return conductor as close as possible to the associated overhead equipment so as to secure maximum compensation. Subsidiary lines such as sidings, loops etc are not provided with return conductors

The return conductor will be normally run on the traction masts on the same side as the overhead equipment.

OHE RETURN CONDUCTORSClearance:

The static and dynamic clearance to any part of the return conductor from an earthed structure should be 150 mm and 80 mm respectively.

The clearance between the return conductor and the overhead equipment should not be less than 400 mm under the worst conditions.

At over-bridges return conductors may be run straight through, if possible, as on normal structures.

OHE RETURN CONDUCTORSReturn conductors in complicated areas:

In station areas, having complicated track layout. It may not be practicable to position the return conductor sufficiently close to the associated overhead equipment to secure the required compensation. In such cases, the route of the return conductor should be decided on the merits of each case. Care being taken to avoid running of return conductor over platforms.

Tension lengths of return conductors:

Return conductors are normally terminated at the masts where the return conductors are

connected to the rail. They may be anchored back to back at such masts.

OHE RETURN CONDUTORSConnections to booster transformers : - At all booster stations, the return conductors for each track

should be provided with a cut-in-insulator. The return conductor is connected in series with the

secondary winding of the booster transformer.

(i) The mid-point of return conductor shall be connected to the buried rail. The mid-point is defined

as a mid point between two consecutive booster transformers.

(ii) Mid-point of the return conductor before feeding posts shall be connected to the buried rail on

either side of the insulated overlap and in case of sectioning posts shall be connected on either side

of the neutral section.

OHE RETURN CONDUCTORS(iii) In exceptional circumstances, where mid-point does not fall in front of feeding posts and sectioning posts, the two rail links between return conductor and rail should be provided in front of feeding posts and sectioning post on either side of the insulated overlap / neutral section. In these cases, mid-point should not be connected to rail.

Power Quality Issues in Railway Electrification

Since the beginning of railway electrification, power quality has been a main problem in railway networks because of their special characteristics.

Many ways of power quality improvement have been investigated an applied to ac and dc traction systems through railway electrification history.


System Imbalance:-

Most trains are single phase and a single-phase load produces a current NSC as much as a PSC. If these NSCs are not attenuated, then the NSC ratio is 1, and since a traction load is large, it may harm the power system and must be compensated.

Harmonic:-

Urban dc traction systems using 12-pulse rectifiers generate large amounts of the 11th- and 13th-order harmonics, and for ac traction systems, trains use ac/dc/ac converters causing different harmonics flowing into the three-phase power system. There also may be a dc component injected into the ac system


Reactive Power:-

Modern ac converters of traction motors use pulse width modulation (PWM), which generates zero reactive power and for power quality compensators, the power factor is 1 as well.

Voltage Problems:-

The most frequent problems of voltages are associated with their magnitudes. As noted before, unbalanced currents produce unbalanced voltages.


Impacts on signaling and communication:-

Track circuits are designed to work with a special frequency that must not have any interference with the power frequency. However, in the presence of harmonics, communication signals may be affected by harmonic frequencies.

Impact on upstream network:-

Decrease utilization factor,

Malfunction of a protective system,

Incorrect operation of transmission line control system.


Power Quality Improvement methods:

Configuration based classification:-

In the first decades of the 20th century, some countries such as Italy, U.S., and Switzerland designed three-phase trains to achieve a symmetric three-phase load, which included two pantographs for two phases and running rails as the third phase.

Power Source-Based Classification:-

The delta–wye-type transformer is the most conventional in the power industry, but in case of traction application.



Equipment-Based Classification:-

There are some electric equipment for the improvement of power quality problems such as passive and active filters used for harmonic elimination.

Active power quality conditioner (APQC), and hybrid power quality conditioner (HPQC) compensate both the current NSC and reactive power as well as perform harmonic elimination.



Theory Based Classification:-

Steinmetz Law:-

A single-phase resistive load between a and b phases which is equal to G can be symmetrized by an inductive load between a and c phases equal to G/√3 and a capacitive load between b and c phases equal to −G/√3

Download - Overhead Electrification

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