ELECTRIC TRACTION SYSTEM

1. ELECTRIC TRACTION SYSTEM Presented by: AMIT RAJ ROLL NO.-09EE6406

2. Introduction Act of drawing or state of being drawn propulsion of vehicle is called tractions. There are various systems of traction prevailing in our country such as steam engine drive, electric drive. These systems of tractions may be classified broadly into groups namely 1) The traction system which do not involve the use of electricity at any stage and called as non-electric tractions system such as steam engine drive, IC engine drive etc. 2) The tractions system which involves the use of electricity at some stage and called as electric tractions. System such a diesel electric drive, electric drive etc.

3. In India electrification in tractions are conducted with three types of locomotives. 1. Using single phase A.C. series commutator motor. 2. Using D.C. motor with tapped transformer and rectifier. 3. Using phase converter and induction motors.

4. Existing Tractions System Existing tractions system uses D.C. motors. • The 25 KV over head voltage is step down to 2000 V with the help of step down transformer. • Rectifier rectifies this A.C. voltage to D.C. voltage. • This rectified D.C. voltage is used to operate the D.C. motors in existing system engine. Causes favouring the DC motors 1) D.C. series motors are less costly, however for some H.P more efficient and requires less maintenance than A.C. series motor. 2) Rail conductor system of track electrifications which is less costly with D.C. system than with A.C. system

6. Future Trends Of Tractions System There are some disadvantages of D.C. series motor used in system. 1) D.C. motors commutator which prove to failure because of vibrations and shock. This results in lots of sparking and corrosion. 2) It is hard to use a D.C. motor for regenerative braking and for this purpose extra switchgear is required, which adds to the bulks and increases the complexity of the locomotives.

7. This short coming from this overcome by using three phase A.C. motor in locomotive. Microprocessor technology and availability of efficient and compact power components have given a new technology for A.C. locomotive. • In three phase A.C. locos, the single phase input signal from overhead equipment is rectified • then three phase A.C. is generated with the help of three phase inverter, whose phase voltage and frequency can be manipulated widely. • The three phase induction motors are simple and robust in construction and have a high operating efficiency and properly of automatic regenerative braking with requiring additional equipment.

9. There are three main stages in power circuit of three phases locomotive. Input converter • A transformer section step-down the voltage from the 25 KV input. • This converter rectifies AC from catenary to as specified dc voltage using GTO thyristors. • It has filter and circuitry to provide a fairly smooth and stable dc output, at the same time attempting to ensure good power factor. • The input converter can be configured to present different power factor to power supply.

10. DC link • This is essentially a bank of capacitor and inductor or active filter circuitry to further smooth. • Also to trap harmonics generated by drive converter and traction motors. • The capacitor bank in this section can also provide a small amount of reserve power in transient situations (e.g., pantograph bounce) if needed by the traction motors.

11. Drive converter This is basically an inverter which consist of three thyristors based components that switch on and off at precise times under the control of a microprocessor. The three components produce three phase of A.C. The microprocessor controller can vary the switching of thyristors and thereby produce A.C. of wide range of frequency and voltage.

12. Advantages Of AC Motors Over DC Motors • DC motors use commutators which are prone to failure because of vibration and shock, and which also result in a lot of sparking and corrosion. Induction AC motors do not use commutators at all. • It is hard to use a DC motor for regenerative braking, and the extra switchgear for this adds to the bulk and complexity of the loco. AC motors can fairly easily be used to generate power during regenerative braking. • In addition, DC motors tend to draw power with a bad power factor and injecting a lot of undesirable harmonics into the power system. • AC motors have the advantage of a simpler construction.

13. System Of Supply 25 kV AC single phase For traction substation (TSS) the incoming EHV supply is 220/132/110/166KV through protective equipment it can be transformed by using traction transformer to 25 KV AC single phases. • Spacing between TSS is 30 KM to 40 KM depending upon the traffic (load). • To avoid load on one phase and balancing the incoming supply grid, the section TSS is divided into sub-sector through switching posts. • S.P:- Sectioning and paralleling Post. • S.S.P:-Sub-sectioning and paralleling Post.

14. Traction transformer There are two traction transformer connected in parallel of same rating for the purpose of reliability the rating of transformer are Capacity: 20,000 KVA. Frequency: 50 Hz Full load: 25 KV Preferred: 0.9 Zero load: 27 KV

15. Power supply for signaling For the purpose of signaling and reliable operation the 25 KV is converted to 240 V through auxiliary transformer by tapping 25 KV OHE at the places where needed.

16. Sectioning and paralleling post (SP) • These post are situated approximating midway between feeding posts making the demarcating points of two zones fed from different phases from adjacent substations. • At these posts, a natural section is provided to make it impossible for the pantograph of an electric locomotive or EMU train to bridge the different phase of 25 KV supply, while passing from the zone fed from one sub-station to the next one. • Since the natural section remains “dead” warning boards are provided in advance to warn and provided Remind the driver of an approaching electric locomotive/EMU to open locomotive circuit breaker (DJ) before approaching the ‘neutral section’ to coast through it and then switch ‘on’ on the other side. • Special care is taken in fixing the location of natural sections, on level tangent track far away from signals, level crossing gates etc. to ensure that the train coasts through the neutral section at a sufficiently high speed, to obviate the possibility of its stopping and getting stuck within the neutral section .

17. Sub-sectioning and Paralleling post (SSP) One and more SSPs are providing between each SP and adjacent SP depending upon the distance between them. In a double track section, normally three interrupters are provided at each SSP i.e. two connecting the adjacent sub-sectors of up and down tracks and one for paralleling the down tracks.

18. Equipments at switching sections Certain equipments are installed at various points to protect the lines, to monitor the availability of power supply and provide other facilities. These are generally as under • Lighting arrestors are provided to protect every sub-sector against voltage surges. • Auxiliary transformers are provided at all the posts and also at certain intermediate points to supply AC at 240 V, 50 HZ required for signaling and operationally essential lighting installations. To ensure fairly steady voltage, automatic voltage regulators are also there, where required. • Potential transformers are provided at the various switching stations for monitoring supply to each sub-sector. • A small masonry cubicle is provided to accommodate remote control equipment, control panel, telephone and batteries and battery chargers required for the control of interrupters and the similar equipments.

19. Control Equipments To segregate the faults and to isolate the faulty section, the circuit breaker at traction substation and interrupters at SP/SSP’s are being remotely control through remote control centre. A Remote Control Centre (RCC) is set up near the traffic control office on each division having electric traction to work in close liaison with the traffic control. The RCC includes the main control room, equipment room, uninterrupted power supply (UPS) room, remote control laboratory and battery room and is the nerve centre of the traction power control.

20. The following types of remote control equipment are mainly in use on Indian Railways at present I. Frequency modulated voice frequency telegraph (FMVFT): This equipment was in use for all electrification schemes prior to 1980. Being mainly all relay system, the equipment has become outdated although some remote control centers still continue to operate on this system. II. Supervisory control and data acquisition (SCADA) systems with microprocessor: The SCADA equipment based on state of the art technology has come into use after 1980. Considering the fast growth and development of computer based equipment, newer types with enhanced capabilities are being introduced. The SCADA equipment at the RCC is called master station while that of the controlled station is referred as remote terminal unit (RTU).

21. Remote Terminal Unit (RTU) The RTU is microprocessor based and include its associated digital input/output modules, alarm input modules, analog input modules, watch dog transducer memory modules, interposing relay summation CTs, power supply unit(s) surge resistor and other items necessary for its proper working.

22. Transmission Path Under ground telecommunication trunk cable is provided for transmitting the signals from and to the Remote Control Centre (RCC) and the controlled Remote Terminal Units (RTU). Three pairs of conductors (one pair for send one pair for receive and the third as spare) from this cable are made available for remote control operation.

23. Microwave Communication In some of the sections on Indian railways dedicated microwave channel at carrier frequency of 18 GHz has been provided for the purpose of Communication. Optical Fiber Cable Optical fiber cable has also been introduced for communication in some section of Indian railways, which is also used for Remote Control equipment. Details of interface between latest communication system and the RCC/RTU equipment may be seen in the relevant technical document.

24. UPS and Batteries at RCC • Dual stand-alone UPS system of adequate capacity to supply 240V A.C., 50 Hz single phase supply to the SCADA system at master station is provided. Both the UPS work in parallel sharing the load. • In case of failure of one the entire load is automatically taken over by the healthy UPS without affecting the working of the system. • In case of outage of both the UPS at the same time, the load of SCADA equipment is directly connected to input main though a static switch without any break. • A single battery is provided with both the UPS with adequate capacity to provide the supply to various equipments is case of failure of input for 415V A.C., 50 Hz supply.

25. Electric Locomotives Introduction Electricity is used to drive the electric locomotives. Two types of vehicles are used for electric traction. The first type of vehicle receives power from a distribution network while the second type of vehicle generates own power. In the second category comes a diesel engine electric drive. The former types of vehicle are used on ac or dc power from the overhead line.

27. Main Function Of Various Components

28. Catenary This is an overhead wire of special cross section. The catenary is supplied at 25 KV; 50 Hz supply. AC voltage is trapped from catenary by pantograph.

30. Pantograph Pantograph is a current collecting device which is mounted on both ends of locomotive roof on insulator and collect the current from Over Head Extension and supply it to power system of locomotive at various speed and different climate/wind condition smoothly.

31. Circuit Breaker The high voltage circuit breaker is special type of electro pneumatic contactor mounted on the roof of the loco. The electrical equipment of the loco is connected to or disconnected from the OHE by means of the circuit breaker.

32. Loco Transformer This is a main transformer of locomotive. The 25 KV single phase AC power supply of OHE is fed to the winding of regulating transformer through main bushing. The winding is equally divided into 32 taps. These taps are connected to tap changer.

33. Tap Changer (Graduator) • The tap changer is directly built on to the transformer. The tapings of the transformers are brought out and arranged in circular fashion on an insulated contact plate. • There are two rows of contact segments which are aligned on outer and inner circles of the contact plate. • An arm which is known as selector arm is driven by shaft at the centre of the contact plate. • Two rollers are situated at the edge of the selector arm. These rings are provided in front of the contact plate. • The centre shaft which extends outside the tap changer casing is driven by an air servomotor. • The design of the air servo motor is such that once the selector arm begins its movement, it can be stopped only at the required tap (not in between two taps). • The connection between the inner or outer ring to the transformer is being established by means of acontactor.

35. Rectifier • In electric loco mainly two silicon rectifier blocks RSI1 and RSI2 are provided for converting AC to DC. • They are bridge connected. • Continuous current rating of each block is 1000 amps.

36. Arno Converter • Arno converter is a device which convert single phase AC in to three phase AC. • The three phase supply needed for the three phase induction motors which used in blowers, exhausters an oil pumps. To supply three phase power to three phase induction motors arno converter is used. • Arno converter is rotating device.

37. Brief Data Of Arno Converter Single phase input Three phase output KVA 150 KVA 120 Volts 380 Volts 380 Amps 395 Amps 190 Due to the voltage variation the speed of the Arno is also varies so the three phase output supply is not constant but varies with the OHE voltage which is not desired. Due to this reason now a days Arno converter are replaced by solid state static converter unit which is known as SI unit.

38. Traction Motors (DC Series Motor) • The traction motor is a dc series motor, four pole or six pole, forced ventilated machine arranged for axle mounting on sleeve baring and supported on the opposite by the resilient suspension unit, transverse movement is limited by the flanges of axle. • These motors are axle hung, nose suspended type and are provided with grease lubricated roller bearings for armature as well as for suspension. • Special provision has been made in design of the motors to ensure the locomotive operates satisfactorily on flooded track, to max. Flood level of 20 cm , above rail level.

40. The main parts of motors are given below • Magnet frame armature and shields. • Brush holders and brushes. • Commutator • Armature • Stator • Armature windings • Field windings • Inter poles • Armature bearings • Axle bearing

41. Generally in locos there are six traction motors. • Three motors per bogies and each motor driving one axle directly through gears. • The motors M1 to M6 are supplied jointly by the two silicon rectifiers connected in parallel through two contactors. • Each rectifier units is connected to separate secondary winding and smoothing the current thus rectified in carried out by means of two smoothing reactors.

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