5Trolley WiresThe trolley wire or contact wire must be suspended with the minimum of sagso that it remains practically horizontal.So that the contact between the wire & current collector may be maintained at high speeds.This is achieved by which the trolley wire(contact wire) is supported by another wire known a the “catenary” or “Messenger”The catenary construction are different types1. Single catenary construction.2. compund catenary construction
6Single catenary construction DroppersContact wireFig.Fig. Single catenary constructionA steel wire with seven or more strands supports the trolley wireby means of droppers clipped to catenary & trolley wire atequidistant horizontal intervals.The span of catenary wire 45 to 90 metres with a sag offrom 1 to 2 metres for straight track.
8Single catenary construction contd……… The distance of droppers is between 3 to 5 metrescurved track the spans of shorter length are employed.Such construction provides for speed upto 120 kmph.AdvantagesIt is relatively cheaper.Less maintenance.Single catenary construction is considered suitable formost light Weight a.c. system.Suitable for secondary routes where traffic density islow & operating speeds are low.
9Compound catenary construction Catenary or messenger wireIntermediatecatenaryDropperLoop wireTrolley wireFig. shows compund catenary constructionEmployed for heavy current i.e where traffic density is high.It consist of three wires.1.The upper wire is catenary wire, which is insulated from thesupporting structure2. The another wire known as intermediate catenary, issupported by droppers clipped to both wires.3. Third wire i.e trolley wire.
10Compund catenary Contd… Trolley wire is suspended from intermediate catenary by solidwire loop droppers which are to slide vertically on theintermediate wire & fixed the trolley wire.The purpose of intermediate catenary, besides increasing the current carrying capacity, is to provide for more uniformity inElasticity.The compound catenary is used on lines where speed rangesis 190 to 224 kmph.
12Current Collector contd….. The current in the overheadsystem is collected with thehelp of sliding contact collectormounted on the roof of the vehicle.The main requirement of current collector is that it should keepContinuous contact with trolley wire at all speeds.There are three types of current collectorTrolley collectorBow collectorPantograph collector.
13Trolley CollectorFig. Trolley wire section1888 on a double wire conductor tramway.This collector is used for Tramways & trolley buses & ismounted on the roof of the vehicle contact with overhead wire.It is made either grooved wheel or a sliding shoe carried atthe end of a light trolley pole attached to the top of the vehicle& held in contact with overhead wire by means of a spring.
14Trolley Collector contd…. Experimental trolley bus in Berlin in 18821989 trolleybus designThe trolley collector is suitable for low speeds upto 32 kmphBeyond this speed there is risk of its jumping off the overheadcontact wire particularly at points & crossing.
15Bow CollectorTrolley BusFig. Bow collectorIt consist of two roof mounted trolley poles at the ends of whichis placed a light metal strip or bow, about 1 metre long forcurrent collection
16Bow Collector contd….Collector strip is made of soft materiallike copper, aluminum or carbon.It never wear instead of trolley wireas it is easy to replace collectionstrip than trolley wire.The bow collector also operates in the trailing position.Hence, it requires provision of the either duplicate bows or an arrangement for reversing the bow for running in the reverse direction.Bow collector is not suitable for railway work where speeds up to 120 kmph and currents upto 3000A
17Pantograph CollectorFig show a diamond type single pan pantographFig show a actual diamond type pantographThe main function is to maintain link between overhead contactwire & power circuit of the locomotive at varying speeds indifferent climate & wind conditions on varying stiffness ofoverhead equipments.
18Pantograph Collector contd……. A positive pressure has to be maintained atall Times to avoid loss of contact & sparking.But pressure must be as low as possible inorder to minimize wear of overhead contactwire.SpringFig show a pantograph collectorIt consists of a pantograph framework of steel tubing.The contact portion consists of a pressed steel pan fitted withrenewable copper wearing Strips which are forced against theoverhead contact wire by the upward direction of pantographsprings.The pantograph can be raised or lowered from cabin by air cylinders.
19Desirable Characteristics of Traction motor The main requirements of electric motors used for traction workElectric characteristics:High starting torqueSimple speed controlPossibility of electric brakingCapacity of withstanding voltage fluctuationsCapability of withstanding temporary interruption of supplyOverload capabilityParallel running
20Desirable Characteristics of Traction motor contd……. Mechanical features:Robustness & ability to withstand continuous vibrations.The weight of the traction motor should be minimum inorder to increase the pay load capacity of the vehicle.The traction motor must be small inn overall dimensions.The traction motor must be totally enclosed type,to provide protection against dirt, dust, water, mud etc.
21Traction motor D.C series motors. Single phase A.C series motors None of the motors can have all the desirable characteristics.Some of the motors which finds application in traction are:D.C series motors.Single phase A.C series motorsRepulsion motors.Three-phase Induction motorsLinear Induction motors
22Suitability of D.C series motor for Traction D.C series motor develops high torque at low speeds & low torque at high speeds. This is the exactly the requirement of traction units.The field flux varies as the armature current, as in the case of series motor, torque corresponding to the given armature current. Therefore, is independent of line voltage & thus unaffected by the variations in the line voltages.Commutating properties of series motor are also very good as increases in the armature current as a result of heavy load torque results in the decrease of armature speed. This reduces the magnitude of e.m.f induced in the coils under going commutation which helps in achieving sparkless current collections
23Suitability of D.C series motor for Traction contd.... 5. In case of dc series motor , upto the point of magnetic saturation,torque developed in proportional to the square of the current.Therefore, dc series motor requires comparatively less increasedpower input with the increase in load torque. Thus the series motorare capable of withstanding excessive loads.6. Speed of dc series motor can be controlled by various methods.7. Because of low time constant of field in case of series motor,the field flux dies away in very short time the result back emf ofthe motor cease with temporary interruption of supply.Therefore, there is inrush of initial current on temporaryinterruption of supply
24Suitability of D.C series motor for Traction contd.... 8. The dc series motor is simple & robust in construction.9. The dc series motor, owing to its characteristics, is mostsuitable for urban & suburban services where high rate ofacceleration is essential.Draw backThe main drawback of dc series motor are commutationWhich restricts speed, current & voltage. Therefore is arisk of flash over & the brush gear requires considerablemaintenance.
25Suitability of single phase a.c series motor for Traction For a given KW rating ac series motor is 1.5 to 2 times in size &weight of the corresponding dc series motor.2. The construction cost of an ac series motor is much more thanof a dc series motor.3. The starting torque of a.c single phase motor is lower than thatof dc series motor due to poor power factor at the start.4. A.C single phase motor are not suitable for urban & suburbanservices, it requires high acceleration.However, single phase motors are extensively used for mainlines services.
26Suitability of single phase a.c series motor for Traction contd… 5. The speed of an ac series motor may be controlled efficientlyby taps on a transformer. Which is not possible in case of adc series motor.6. However, single phase ac series motor have better performanceon reduced supply frequency says 25 Hz. The higher frequencyresults in higher leakage reactances & hence a relatively poorpower factor.7. The maximum operating voltage for these motors is limitedto 400 volts
27Suitability of Three phase Induction motor for Traction It has simple & robust construction.Trouble free operation.Less maintenance.High voltage operation consequently requiring reducedamount of current.Automatic regeneration are the main advantages of 3-ph.Induction motor for traction.But due to their flat speed- torque characteristics, constantspeed operation, developing low starting torque, drawing highstarting current, complicated speed control systems they are notsuitable for electric traction work.
28Suitability of Three phase Induction motor. contd… With the development of thyristorised inverter circuits,it has now been possible to invert the supply and obtaina variable frequency supply which could be used for the3- phase Induction motor & a very smooth speed controlcan be obtained.
29Power supply Arrangement Since Indian Railways have decided to adopt 25kv, 50 Hz supply systemFollowing arrangements of power supply to various substations exist on Indian RailwaysPower is purchased from supply authorities who are responsiblefor the operation & maintenance of 132/110 kv transmission lines& grid substations upto 25 kv out - going terminals of substation.However 25 kv feeder circuit breaker is controlled from remotecontrol centre by traction power controller. This arrangementenables railway authorities to pay full attention to operate &maintain traction service which is their prime responsibility.2. All the 132 kv & 25 kv equipments of substation is owned,installed operated & maintained by the supply authorities.However 25 kv circuit breaker are owned, installed, operated& maintained by the railway authorities.
30Power supply Arrangement contd….. To have better control & expeditions execution of electrificationProgramme, it was considered necessary that the railways shouldown , install, operate &maintain all the 132/110 kv equipmentsat the substation.Supply authorities will give only voltage supply of 132/110 kv atthe substation
31Constituents or Parts of Power supply system Various elements of power supply system are:Sub-station.Feeding posts.Sectioning & paralleling posts.Sub-sectioning & paralleling posts.Sub-sectioning posts.Elementary sections.
32SubstationFig. layout of a typical traction sub-station.