Electric Traction


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Electric Traction Basic, Traction Types, advantages, control for traction.

zunaib ali
uet atd campus, Electronic Engineering Department

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Electric Traction

  1. 1. ELECTRIC TRACTION Group Members Muqadsa Iftikhar (03) Zunaib Ali (09) Tayyaba Saleem (24) Zenab Fazal (34) Ayaz Khan (43)
  2. 2. Introduction- Traction Driving forward of vehicle is called Traction and the system, which employs this type of mechanism is called Traction system. classified broadly into two groups namely: (1)non-Electric traction systems (2)Electric traction systems
  3. 3. Electric Traction- The system which use electrical power for traction system i.e. for railways, trams, trolleys, etc. is called electrical traction. OR Electric traction means a locomotion in which the driving force is obtained from electric motors. Electric traction will continue to play a dominant role in the Railway since it is an environmentally clean technology compared to diesel traction and also its running cost is low. There are many advantages of electric traction over other forms of locomotion.
  4. 4. Ideal Traction System (i) Maximum tractive effort should be exerted at starting in order to have rapid acceleration. (ii) Equipment should be capable of overloads for short periods (iii) The wear caused on the track should be minimum (iv) Braking should be possible without excessive wear on the brush (v) Capability of withstanding voltage fluctuations and temporary interruption of supply. (vi) Parallel running usually more than one motor (two or four motors ) should be possible.
  5. 5. Advantages of Electric Traction Cheapness. It is cheapest method of all other methods of traction. Cleanliness. It is free from smoke and flue gasses Maintenance cost. Maintenance and repair cost is about 50% of steam traction system. Starting time. It can be started without loss of time. High starting torque. This system uses of d.c. & a.c. series motors, which has a very high starting torque. Braking. In electric traction , regenerative breaking is used which feeds back 40%of the energy. Saving in high grade coal. No coal is required for electric traction.
  6. 6. Disadvantages of Electric Traction (i) High initial expenditure (ii) Failure of supply is a problem (iii) Electrically operated vehicles have to move only on electrified track (iv) For braking & control, additional equipments required (v) Interference with telegraphs and telephone lines.
  7. 7. System Of Track Electrification (i) D.C. Systems (ii) A.C. Systems (a) Three phase A.C. system (b) Single phase standard frequency system (c) Single phase low frequency system (d) Single phase to three phase system [Kondo system] e.g 600V dc is given to tramways and trolley buses.
  8. 8. Track System Classification In general following electric traction systems exist : • AC 3 phase 3.7 kV system • AC single phase 15/16 kV -161/25 Hz • AC single phase 20/25 kV - 50/60 Hz • DC 600 V • DC 1200 V • DC 1.5 kV • DC 3 kV.
  9. 9. Advantages & Disadvantages of A.C. System Over D.C. System Advantages 1. Light overhead catenary 2. Saving in sub-stations 3. More flexibility 4. Lesser equipment used & easy to maintain 5. Starting efficiency 6. Cheap as far as cost for fixed installation Disadvantages 1. Single-phase A.C. system imposes Unbalancing effect 2. Produces interference with telecommunication lines
  10. 10. Electric Locomotives
  11. 11. Block Diagram Of an A.C. Locomotive
  12. 12. Auxiliary Equipment Catenary - This is the overhead wire of special cross-section. Pantograph - This is a device used for collecting current from the catenary i.e. the over head lines.
  13. 13. Auxiliary Equipment Cont… Circuit Breakers - The function of circuit breaker is to disconnect the engine from the line side in case of some fault On Load Tap Changer - On load tap changer is used for varying the output voltage for controlling the speed of motor Transformer - A tap changing transformer is installed in the locomotive for stepping down the voltage according to the requirement of traction motors Rectifiers - Semiconductor rectifiers are used for conversion of A.C power into D.C power Smoothing Reactors - Any ripples found on the output side of the rectifier are eliminated by the smoothing reactor fitted after the rectifier.
  14. 14. Independent Control- SEPEX Short form of SEParate EXcitement of traction motors where the armature and field coils of an electric motor are fed with independently controlled current. This has been made much more useful since the introduction of thyristor control where motor control can be much more precise.
  15. 15. Thyristor Control Schematic of AC Electric Locomotive Power System with Thyristor Control and Separately Excited DC Motors
  16. 16. DC Choppers Thyristor Control Circuit for DC Supply to DC Motors
  17. 17. DC Resistance Control Simplified DC Traction Motor Power Control Circuit
  18. 18. Parallel Motors - DC Resistance Control Schematic of Simple DC Traction Motor Power Control Circuit
  19. 19. DC Traction Motor It consists of two parts, a rotating armature and a fixed field. • The fixed field consists of tightly wound coils of wire fitted inside the motor case • The armature is another set of coils wound round a central shaft. • The armature is connected to the field through "brushes" which are spring loaded contacts pressing against an extension of the armature called the commutator.
  20. 20. The DC Traction Motor: How it Drives the Axle How a DC motor drives the axle through a pinion and gearwheel
  21. 21. AC Motor Traction Schematic of Single Phase AC Supply Powering 3-Phase AC Motors AC Locomotives with AC Drive
  22. 22. AC Motor Traction Schematic of AC locomotive with Tap Changer Control of Transformer Output AC Locomotives with DC Drives
  23. 23. Braking Characteristics If any electric motor is to be stopped, electric supply to it is disconnected. In this way, the motor shall take long time to stop, as the motor shall continue to rotate due to inertia. Some braking system must be used so that it stops within the pre-determined short time. A good braking system must posses the following features (i) It should be fast and reliable. (ii) The braking force must be capable of being controlled (iii) Kinetic energy of the rotating parts of the motor and its driven machine must be suitably dissipated & suitable means must be provided.
  24. 24. Advantages & Disadvantages of Electric Braking Advantages (i) It is quite fast (ii) It is quite cheap as far as maintenance part (iii) Higher speed can be maintained (iv) Heat produced during braking is not harmful (v) It is free from fires and is smoother Disadvantages (i) It can stop the motor but it cannot hold it stationary. (ii) It cannot be applied to all motors (iii) Its initial cost is very high.
  25. 25. Types Of Electric Braking Dynamic Braking: where the motors become generators and feed the resulting current back. It classified into three categories: 1. Plugging 2. Rheostatic Braking 3. Regenerative Braking PLUGGING: Generally plugging is applied by changing the phase sequence of the three phase induction and synchronous motor
  26. 26. Rheostatic Braking • The motors become generators and feed the resulting current into an on-board resistance. • When the driver calls for brake, the power circuit connections to the motors are changed from their power configuration to a brake configuration and the resistors inserted into the motor circuit. As the motor generated energy is dispersed in the resistors and the train speed slows.
  27. 27. Regenerative Braking • The motors become generators and feed the resulting current back into the supply system • A train could use its motors to act as generators and that this would provide some braking effect if a suitable way could be found to dispose of the energy. • Trains were designed therefore, which could return current, generated during braking, to the supply system for use by other trains.
  28. 28. Conclusion •No single motor is ideal for traction purposes. But; DC Series Motors are most suitable for this work •Power Electronics have been resorted to in a major way as in case of thyristor control. •Different types of braking for the traction system was studied.
  29. 29. Thank You