traction-3.pptx

TRACTION

1. MODULE-3 CURRENT COLLECTING EQUIPMENTS

2. System of Supplying Power in Electric Traction DC System :- In this system DC series motors are used for getting the necessary motive power. The operating voltage is from 600V to 750V for urban and suburban service, and from 1500V to 3000V for main line railway service. The driving motors receiving power from distribution system which is fed from substations suitably spaced.

3. The spacing of substations depends upon the operating voltage and the traffic density of the route. For urban and sub urban railway where the operating voltage is 600V the substations are spaced 3 to 5km apart and for main line railways having operating voltage of 1500 to 3000V they may be spaced 15 to 40km. Substations receive AC power from a 3phase high voltage transmission lines and convert it into dc by means of converters. These system is better suited for urban and suburban services where starting and stopping are frequent.

4. Single Phase AC system:- In this system AC series motors are used for getting the necessary motive power. The operating voltage is from 1500 to 2500V at 25Hz, which is stepped down on the locomotive to low voltage suitable for supplying to 1 phase AC series motor by means of a step down transformer carried on the locomotive. The spacing of substation is 50 to 80km because of low current requirement at high voltage. The substations receive power from high voltage transmission lines and step down the voltage to required value and change the supplying frequency through frequency converter. Low frequency operation of AC series motor improve its commutation ,power factor and efficiency ,also reduce transmission line reactance and hence the voltage drop.

5. 3. Three phase AC system:- In this system 3 phase induction motors operating at 3000V to 3600V at 25Hz are used for getting the required motive power. The 3 phase induction motors are simple and robust in construction and have a high operating efficiency and property of automatic regenerative braking without requiring any additional equipment. However, the induction motors have few drawbacks such as low starting torque, high starting current and absence of speed control. The distribution system consist of two overhead wires and track rail for the third phase. The substations receive power from high voltage transmission lines and step down the voltage to required value and change the supplying frequency through frequency converter. This system is used in some hilly areas where output power require is high and regeneration on large scale is possible.

6. 4. Composite System :- There are two composite systems: 1 phase to 3phase system or Kando system Single phase AC to DC system 1 phase to 3phase system or Kando system In this system 1phase high voltage AC system is used for distribution purpose and 3phase induction motors for getting the necessary motive power. The voltage used for distribution network is 15000V at 50Hz The locomotive carries a phase converter for converting1phase supply into 3phase supply at a relatively low frequency. At low frequency, induction motor develops high starting torque without excessive current.

7. b) 1phase to DC system In this system high voltage AC 1phase system for overhead distribution and DC series motors for the drive is used, so that high efficiency of the AC distribution system is obtained together with the desirable characteristics of DC series motors. Locomotive carries transformers and converting machinery to step down the voltage and convert into DC. The voltage used for overhead distribution system is 25KV at normal frequency of 50Hz.

8. Conductor Rail System (Third Rail) In this system electric supply is collected from an insulated rail running parallel to the track at a distance of 0.3 to 0.4m from the running rail, return being through the running rail. In majority of conductor rail systems current collection is from the top surface of the rail but in certain system, current collection is from sides or under side of conductor rail. Under side contact is more protective against accidental contact. Conductor rails have low resistance and not as much hardness as track rail. To reduce the voltage drop at joints, conductor rails are bonded together by copper conductors rivetted or welded to the rail. Current is collected by steel shoes, necessary contact pressure being obtained by gravity in the case of top contact and by means of springs in case of side and under side contact.

9. Conductor rail system is suitable for heavy current collection-top contact system for voltages up to 750V and side contact system up to 1200V.

10. Current Collectors : The collection of current from overhead contact wire is called the current collection gear. Main requirement of a collection gear is that it should, under no circumstances, leave the contact of OHE. Contact wire in all practical installation is never perfectly horizontal. It rises and falls depending upon the weight of the contact wire, and distance between droppers. Also contact wire comes very low under bridges and tunnels and rises high over public crossings. Depending upon the speed of the electric vehicle, collection gear has to rise and fall with the help of springs in order to maintain the contact with OHE

11. Cable Collector : It is used specially at place where range of operation is small and where it is hazardous to have current collection from overhead wire by other means such as in gassy mines. It consist of a long cable which pays out or winds up on a power driven reel carried on the locomotive when it travels into or out of working place for collection work. Pole Collector or Trolley collector : It is universally used with tram ways and trolley buses. This consist of a grooved gun metal wheel or grooved slider shoe with carbon insert attached to the end of a long pole provided on the top of the vehicle.

12. Necessary upward pressure for the pole and current collector is achieved by means of springs. Trolley collector has to operating in trailing position. The main draw back of trolley collector is that it has to be rotated through 180 for reversing the direction of motion of the vehicle. Another draw back is that there is poor contact between the wheel and trolley wire, this gives rise to high current density which result in heavy arcing.

13. Bow Collector : It is also used for collecting the current with tram ways. It consist of light metal strip of 0.6 or 0.9m wide pressing against the trolley wire and attached to the frame work mounted on the top of the vehicle. Provision of metal strip enable vehicle to run at higher speeds without the risk of leaving the contact of trolley wire. Trolley wire is accuratly located above the track at the centre line of the track with about 15cm stagger to give uniform wear of the strip and prevent formation of groove on it. Bow collector has always to run trailing just like trolley collector. It therefore require either provision of duplicate bows or an arrangement of reversing the bows for motion in the reverse direction.

14. Pantograph Collector : By using Pantographs high current collection capacity and high speed operation can be achieved. It is used in railways. Main function of pantograph is to maintain a link between the overhead system and power circuit of the locomotive at varying speeds in different climate and wind conditions. A positive pressure has to be maintained at all times to avoid loss of contact and sparking, yet this pressure must be low as possible to ensure minimum wear of contact wire. Pantographs are mounted on the top of the vehicle and usually carry a sliding shoe for contact with the overhead line. Material used for pantograph is often steel with sometime sliding shoe of copper or bronze inserted.

15. Types of Pantograph : There are basic two forms of pantographs namely Diamond Type Faiveley Type 1 . Diamond Type: It consists of pressed steel channel section fitted with renewable collector strips and supported at the apex of a pentagonal tubular frame work. Collection strips are forced against the contact wire by upward action of pantograph spring. These strips slide along the contact wire as the train moves. The collector strip material and the contact pressure are such as to ensure minimum wear of the contact wire.

16. Collector material must have long life and be capable of collecting high powers required without local overheating. On DC overhead system, it is usual to collect current through a metal collector strip which requires some lubricating medium such as grease containing graphite. Difficulty of lubricating is overcome by the use of metallized carbon which has self lubricating property and also it has high current collecting capacity and it is mechanically strong. Unlike metal conductors which wear increase with increasing force, carbon wears electrically and reduces wear as contact improve. For max. electrical efficiency the contact pressure with carbon collector strip should be high. For 25KV AC OHE, since current to be collected is small, single pan pantograph will sufficient. For 1500V DC system where current collection may range upto 2500A two pan pantograph may be used

17. Faiveley Type It consists of a sub-frame or base, articulated system, pneumatic control system including throttle valve, two raising springs and four insulators. The base is made up of welded sections and houses two ball bearings on which is made up of welded sections and houses two ball bearings on which is carried the articulated system. Rubber stops are provided to limit the folding of the articulated system at the lower part. When compressed air is admitted in the control cylinder, piston compresses the holding down springs and slotted rod gets translatory motion which permits horizontal spindle to rotate under the action of upsprings . The pantograph then rises until collector touches the OHE.

18. The articulated system then stops and piston completes its stroke. Opening of the control cylinder to atmosphere causes piston to return under the force of holding down spring and lowering of the articulated system. Methods of rising and lowering of Pantograph Pantograph may be raised or lowered from cabin by any of the following methods. Air raised gravity lowered Air raised spring lowered Spring raised air lowered

19. In air raised pantographs, failure of air pressure would make locomotive inoperative as in the case of leakage of air, there will occur continuous loss of air with the possibility of reduction of contact pressure. A catch is usually used to prevent bouncing of pantograph and its need for constant pressure to keep it in lowered position in case of air lowered type pantograph.

20. Module - 4 SIGNALLING AND SUPERVISORY CONTROL

21. Requirement of signalling system Signals are the devices which are used to control the movements of trains. The following are the requirements of an signalling system. It should not possible to display safe indication unless the entire portion of the track governed by the signal is clear and safe. Failure of any component of signalling system should give danger indications. There must be the provision for automatic application of brakes to the train (if the driver ignore the danger signal)

22. Different types of signals The signals used in indian railway classified into the following thee types: Fixed signals Semaphore signals Colour light signals Hand signals (used when fixed signals fail) Detonating signals (used in foggy weather to indicate the locality of a signal to the driver of approaching train. These signals are on the rail.

23. Colour light signals , 3 and 4 – Aspects of Colour light signals Electric trains can handle heavy traffic only when it is associated with automatic signalling. Automatic signalling also reduces the train delays and increases the track capacity and increases safty . Working of automatic signalling is based upon providing adequate distance between two trains running on same line in the same direction. This is achieved by the use of track circuit which control the position of automatic signals.

24. Advantages of colour light signals Economy Simplicity of indication to drivers Better ability to deal with traffic of varying speed. Simple and easier in operation and control Increased line capacity. Let us consider a section of traction line between two successive signal boxes S1 and S2 as shown in figer Let x = distance between two signal boxes d = braking distance from home signal P = emergency braking distance S = sight distance l = train length V = train speed C = line capacity expressed as number of trains handled per second

25. h = ( l + P + x + d + s) Head way H = h/v = ( l+P+x+d+s )/v Line capacity C = 3600/H = 3600 v/( l+P+x+d+s ) when x = d at which point distant signal become coincident with the home signal This is a case of three aspect signalling, then C = 3600 v/ (l+P+2d+s) With three aspect light signalling, occupation of signalling section in advance gives red aspects on signal which indicates stop or danger, yellow aspects which means caution be prepared to stop at next signal, green aspects indicates proceed.

26. In case of high speed trains, three aspect light signalling is unsafe. Therefore four aspect signalling ; Red, Yellow, Green and Yellow is used. Ocupation of only first or second section in advance will give red or yellow indication as in three aspect signalling. Occupation of third section in advance will give yellow which is the indication of preliminary caution; be prepared to pass the next signal at restricted speed. The capacity of a four aspect signalling system is C = 3600V/(l+P+s+3/2d)

27. COPARISON OF 3 ASPECT &4 ASPECT SIGNALLING 3 Aspect Signalling Red , yellow ,green are used Capacity of line is more C = 3600V/(l+P+s+2d) Driver will receive one warning before red Signal post required is less 4 aspect Signalling Red , yellow, yellow-yellow, green are used Capacity of line is much more C = 3600V/(l+P+s+3/2d) Driver will receive two warning before red Signal post required is less

28. Track circuits (DC track & AC track) Signalling system use track circuit. The track circuit perform the following functions. When a train is on the track circuit after the home signal it should indicate stop signal for the second train to come into that section To indicate the presence of train on sections out of view of signal. D.C track Circuit D.C track circuit is used for non electrified lines and is not recommended for use in place where fear exists for the circulation of stray currents. D.C track circuit consists of a portion of track insulated from the rest of the track by means of specially insulated rail joints. These insulated rail joints are obtained by placing fibre piece in between adjacent rail ends.

29. Track relay is connected across two rails of insulated track at the start end and a D.C source along with regulating resistance across the very same rails at the other end. When track is not occupied by train circuit is completed through track relay and current flows. This leads to the energisation of the relay and its armature being attracted, closes its contacts thereby performing the required functions of operating indicator in a signal cabin and working up the signal. When track is occupied by train, a circuit parallel to the relay coil is established by train wheel and axles. This reduce the magnitude of relay current, it will de-energies and its contacts are opened, it indicate unsafe or dangerous condition. If battery failure or break in rail bonds occurs, this will de-energies the relay thereby indicating danger.

30. A.C Traction Circuits: Main advantage of a.c track circuit is that its working can be made absolutely immune from the effects of stray currents. In case of railway electrification it is easier and cheaper to instal and maintain a.c track circuits than d.c track circuits. In case of areas where electrification exists and where track current is to be carried by both the rail, it is necessary to instal impedance bonds. The function of impedance bonds are : To provide a path of low resistance for traction currents to pass through insulated track. To provide a path of high impedance for a.c signalling currents between insulated track. To keep the signalling current restricted to the insulated track circuits.

31. Impedance bond consists of two windings of low resistance Two ends of the windings and mid point are brought out for external connection. In the case of d.c traction, currents flow in opposite direction in each half of the windings, if the traction current from each rail is equal, there will be no resultant flux in the core. In the case of unbalance current in the rails, the core will get saturated specially when reluctance of magnetic path is low. Impedance bond offers a path of high impedance to signalling currents only when magnetic path remains unsaturated. To prevent attainment of magnetic saturation air gap is provided in the magnetic circuit. In the case of a.c traction there is no need to provide air gap in the core of impedance bond.

32. This is because in case of unbalancing, one of the coil will carry more current than the other haif and this will induce e.m.f in the other coil which will tend to equalise the current. If the impedance of the bond to a.c signalling currents is less, it will draw more magnetising currents, it costitute high load on the track transformer. To over come this resonated type of bonds are used.

33. Advantages of Remote control It is easy to supervise all functions of the individual posts in a route from one central control station. It is possible to complete co-ordination over the entire system. Human errors are avoided. Correct and rapid supervision about the execution of instructions are possible. It enables to carry out switching operations quickly and positively. Remote control is safe and economical

34. System of Remote Control : Remote control system, used on sections employing electrification at 25KV 50Hz, operate on transmission of voice frequency signal. In this system, coded d.c pulses carrying intelligence are made to modulate carrier currents at voice frequency ranging from 420 to 2460Hz. Within this range of frequencies, with 120Hz separation, we get 18 channels. This enables 18 stations to be controlled at a time with one pair of wires. Remote control system using voice frequency signals avoids magnetically induced disturbances from transient currents of switching operations. This system of control is used on a.c electrified tracks. Remote control system using d.c control signals and transmitting them directly on the supervisory line is used on track electrified with d.c . this is because there is no risk of any induced emf being produced and its consequent maloperation .

35. Remote control system using voice frequency signals uses two pairs of conductors. One pair carries tele commands from the remote control centre to the controlled post and another pair carries tele signals from the controlled post to the remote control centre. Each pair of conductors can control maximum upto 18 stations. In order to limit the build up of longitudinal induced voltages on account of induction effects of 25KV a.c traction, Isolating transformers are provided on cable circuits carrying both paires of conductors at interval of 10-15km. As a result of dielectric and resistance losses taking place in the cable, line attenuation takes place which is made good by voice frequency repeaters at interval of 30 to 50km.

36. D.C Versus voice frequency Signalling: The advantages of V.F signalling over d.c signalling are Within the V.F range of 420 to 2460 Hz and with 120Hz separation, at least 18 channels can be provided. Signal attenuation of the order of 0.3 db per km takes place in the cable. With V.F signalling repeater stations with amplification of 14 d.b can be employed at interval of about 45 to 50km. This is more advantage. With d.c signalling there is considerable degree of interference and cross talk over adjacent conductors. V.F operation is free from such disturbance.

37. Remote control system Equipment and Network On Indian railway three different types of remote control equipment are used: Siemens of Germany Mors of France Indian Telephone industries, india (I.T.I) A remote control centre equipment consists of Control panel with mimic diagram and control desk. Remote control witching equipment. Frequency modulated voice frequency telegraph(FMVFT) equipment Power supply for control room

38. similarly controlled post equipment consists of : F.M.V.T equipment Remote control switching equipment Power supply at the post. Mimic Diagram : Power supply arrangement for the overhead 25KV traction is shown in remote control centre on small scale on what is called mimic diagram. Every equipment of the station which is to be remote controlled such as circuit breaker, interruptor etc. is represented on the mimic diagram by a control discrepancy switch (DS). The tele -command for closing or tripping of circuit breaker or interruptor is transmitted by actuating the discrepancy switches.

39. When discrepancy switch is in line with the busbar, it represents closed position for circuit breaker and when right angles to it ,this gives open position. There is built in lamp inside the central indicator bar of every discrepancy switch. When this lamp of discrepancy switch glows, it indicate a discrepancy between the position of the discrepancy switch and the actual position of the apparatus it represents. Certain non-remote controlled apparatus like substation isolators are represented by hand operated dummy switch which are different from discrepancy switch. The electrified tracks are represented on the mimic diagram by milky white perspex strips. Indication lambs are provided for each section of catenary so that when the catenary voltage fails, the lambs provided in the corresponding section on the mimic diagram light up and become fully illuminated.

40. Control Desk For TPC This panel is located centrally with respect to the whole of the mimic diagram of the remote control centre and is provided with various telecommunication facilities such as loud speaker, telephone from TPC circuit, traction loco control circuit and emergency control circuit. Control desk is also provided with two alarm cancellation keys, one to acknowledge and cancel any alarm telesignal arriving at the control centre and the second for acknowledging the alarm of low voltage condition of the battery of the control centre for which buzzer is provided on the desk

41. Remote control switching Equipment Pulse generator Send selector Receive selector Check circuit, send and receive Indication circuits The main purpose of above equipment is to generate and send coded information for execution of any command at the controlled station and also receive coded information from the controlled station to the remote control centre.

42. The F.M.V.F.T : This equipment provide 18 two way frequency modulated voice frequency telegraph (FMVFT) channels for operation over four wire circuite . The send unit for each channel consists of an oscillator modulator, an amplifier and send filter. On the output side of send filters, individual channels are grouped together and connected to trans-amplifier and then to cable lines through 150:1120 tapping transformer. Out of four wires, two are utilised for telecommands and two for telesignals . Due to this reason same frequency can be used in the two circuits This enables simultaneous transmission of the command impulses from control room to various controlled stations over the send pair of wires and receiving the indication impulses from the controlled posts to the control room over the receive pair of wires

43. Power supply A 24V supply is obtained from a battery provided with suitable battery charger. This supply is required for switching equipment, FMVFT equipment and all the visual and audible alarm indications of the remote control centre. Controlled station Equipment: It consists of F.M.V.F.T equipment, remote control switching equipment and power supply. F.M.V.F.T equipment at controlled station serves the purpose of sending and receiving the coded information over the allotted telegraph channel In addition to 24V d.c supply is required as at remote control centre, 110/72V d.c supply is required for the operation of high voltage circuit breakers or interruptors . For this purpose battery of appropriate voltage is required along with suitable battery charger

44. Train lighting System of train lighting: Power requirement of a train can be met with in following different ways: By axle driven generators in conjuction with batteries By a separate generator driven by diesel prime mover installed either on the under frame of the coach or in separate power van Special Requirements of train lighting: D.C dynamo used in traction is of totally enclosed and of rugged construction so that road dust and jerks have no effect on its working Since dynamo has to operate in parallel with battery, it is essential that its polarity should not change with the change in the direction of rotation of dynamo It should give constant output at varying speed

45. Method of Obtaining Unidirectional Polarity Figer shows the dynamo has rocker arm mounted on the shaft,friction tight. For the movement of armature clockwise, X terminal of the rocker arm will be positive and Y terminal will be negative. Rocker arm being friction tight, will move in the direction of armature rotation. This will make X terminal to touch brush P1 and Y to touch brush N. This gives out side polarity of supply as shown. If direction of rotation is now made anti clockwise, X brush will have negative polarity and Y brush will have positive polarity. Due to anticlockwise rotation of shaft, terminal X will now touch N1 and Y terminal will touch P. Once again outside polarity remains unchanged.

46. Single Battery System : Figer shows a single battery system and is the cheapest among all axle generation system When the generator is driven above certain speed auto cut in switch will operate and dynamo will be supplying the light load as well as charging the batteries through lamp resistance. When speed falls below cut out value, auto cut in switch will disconnect that dynamo and the lamp resistance will be short circuited. Now batteries will be supplying the load directly. Main drawback of this system is that the insertion and cutting out of the resistance cause lamp flicker. By use of automatic voltage regulator in conjunction with dynamo this effect can be eliminated

47. Double Battery and Parallel Block System : In double battery system, half of the batteries, connected directly across the dynamo terminals, get charged and the other half of the batteries are connected to the lamp load and also dynamo terminals through lamp resistance. The value of lamp resistance is such that this battery just floats across the lighting mains and helps to keep the voltage steady across the lamp terminals. This battery is therefore also called regulating battery.

48. Railway coach Air Conditioning The following are the requirements of railway coach air conditioning : Supplying of clean fresh air at a controlled uniform temperature. Providing it on a train that travels through areas of widely differing climate during its journey, for heating as well as for cooling The operation of the equipment from power generated, stored and controlled on the train

49. Types of Installation The air conditioning installations in coaches are of the following two types: The conventional distributed installation, which has the compressor, condenser and liquid receiver on the under frame, the air conditioning unit in the roof space above the ceiling and the control panel in a cupboard in the luggage compartment. The compartment type installation is similar to above one except that no equipment is installed above the ceiling. It is of the semipackaged type serving one or more individual compartments. The refrigeration unit is mounted on the underframe , but the blower fans, filters, evaporator and temperature controls are all housed in a metal cabinet in the compartment.

50. Air Conditioned Rolling Stock Indian Railway have provided air conditioning equipments on the following types of coaches. Fully air conditioned coaches. Partially air conditioned coaches Refrigerated fish/parcel van. Air cooled parcel vans. Ambulance ward cars. III class chair cars (deluxe) Miscellaneous coaches such as Presidents twin car Air conditioned tourist car Inspection carriage.

51. Air Conditioning Equipments On Coaches Air conditioning equipments used on railway carriages can be broadly divided into three parts. Mechanical equipments comprising mainly the drive for power generation Refrigeration equipments and accessories for cooling and heating Electrical equipments for power generation and control of the air conditioning equipments and accessories