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electric traction


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it is about electrical traction and electric trains.

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electric traction

  1. 1. INTRODUCTION Driving forward of vehicle is called Traction and the system, which employs this type of mechanism is called Traction system. Electric trains are those trains which use electric traction or in general “electric power”. UTKARSH(srmscet,unnao)
  2. 2. Main types There are mainly two types of electric trains, Which are described as below- (a.)trains which use electric power to drive electric motors for the all indian electric trains. (b.)trains which use electric power to generate a magnetic field for the most advanced bullet trains. UTKARSH(srmscet,unnao)
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  4. 4. WHY ELECTRIC TRACTION? Traction System Efficiency Steam locomotive 5-7% Gas turbine electric locomotive 10% Diesel electric locomotive 26-30% Electric locomotive with thermal power plant 34-36% Electrical locomotive with Hydroelectric power plant 40-42% UTKARSH(srmscet,unnao)
  5. 5. The use of electric locomotives primarily came in order to reduce problems of smoke pollution. Though electric locomotives are more efficient than steam and diesel locomotives, electrification of railway lines is expensive. For this reason, electric locomotives are used mainly for busy passenger lines . UTKARSH(srmscet,unnao)
  6. 6. Systems of track electrification  THERE ARE BASICALLY TWO TYPES OF ELECTRIFICATION-  A.) Dc system.  B.) Single phase ac system. UTKARSH(srmscet,unnao)
  7. 7. Existing Tractions System UTKARSH(srmscet,unnao) Existing tractions system uses D.C. motors. a) The 25 KV over head voltage is step down to 2000 V with the help of step down transformer. b) Rectifier rectifies this A.C. voltage to D.C. voltage. c) This rectified D.C. voltage is used to operate the D.C. motors in existing system engine. Causes favoring the DC motors a) D.C. series motors are less costly, however for some H.P more efficient and requires less maintenance than A.C. series motor. b) Rail conductor system of track electrifications which is less costly with D.C. system than with A.C. System
  8. 8.  There are two kinds of power transmission that are used for electric locomotives. These include alternate current and direct current. Alternate current, as the name suggests, flows in more than one direction where as DC is restricted to one direction only . UTKARSH(srmscet,unnao)
  9. 9.  Alternating current has an advantage over DC current such that it can be used over large distances even through a wire that has a smaller radius. Direct current locomotives typically require wires with greater diameter and in some cases a third rail. At present, alternating current locomotives haul trains over large distances or main line areas where as DC locomotives are restricted to shorter distances. The voltage difference is also great as AC is varied between 15KV to 50KV while DC is confined to below 3KV UTKARSH(srmscet,unnao)
  10. 10.   There are different methods in which the current is transferred. One way is through a third rail and the other is through overhead wires. The third rail is most popular with DC electric systems. Examples of trains that use the third rail are usually metro rail systems but they can be found in main-line routes in southern England to provide speeds of up 100 miles per hour at 750V DC. UTKARSH(srmscet,unnao)
  11. 11. UTKARSH(srmscet,unnao) THIRD RAIL There are certain disadvantages of the third rail. The first one is that there is a safety hazard. If pedestrians were to trample on the rail, they are likely to have a shock hazard. Secondly, weather conditions such as snow can cause the system to not function
  12. 12. UTKARSH(srmscet,unnao)  Third Rail systems also have rail gaps in order to cope with excess voltage supply. For each gap, there is what is called a “substation”. These substations ensure continuity and provide voltage in the direction of propagation and are off support if one substation were to fail.  Substations also give an indication for the train to continue on its route or to halt for any reason. In cases where there may be faults along the electric lines, there are switches to stop the flow of current which means that the train must stop before entering that section
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  17. 17. MAST UTKARSH(srmscet,unnao)
  18. 18.  AC electric systems are more likely to be used overhead wires otherwise known as a catenary.  The design of the overhead wires are created such that it is held in tension horizontally and also subjected to lateral pulling such that it can accommodate for curves. UTKARSH(srmscet,unnao)
  20. 20.  In order to makeup for interference along the catenary, there are booster transformers connected at frequent intervals throughout the route. The main purpose of this is to reduce any inequality of voltages that are induced by other electric lines that run parallel to the catenary. A return wire is connected to the track such that the current returns to the transformer. Without this, there can also be a safety hazard. UTKARSH(srmscet,unnao)
  21. 21. POWER CIRCULATION  The NEXT circuits show a circuit of an electric railway system used by the Indian Railways. The current IC flows through the catenary and then enters the locomotive through the pantograph. The departing current IR returns to the main power supply through the tracks. The second circuit diagram is an example of booster transformers used in Indian Railways. Notice that the there are insulated rail joints to be sure that the current flows at the correct sections . UTKARSH(srmscet,unnao)
  23. 23. Circuits of electric locomotives UTKARSH(srmscet,unnao)
  24. 24.  , the locomotive receives its power through the pantograph from the catenary. The voltage received is decreased by a step-down transformer.  The amount of current is controlled by a device known as the “tap changer”. The “tap changer” is basically a camshaft set of operated switches and connects more sections of the transformer. The next device is the AC- DC rectifier.  The kind of rectifier used in this circuit is the bridge rectifier. It is basically an arrangement of diodes that enable the current to flow in one direction only. The capacitor is used to decrease the fluctuation of voltage. The drop of voltage from the rectifier is eliminated by the voltage drop in the capacitor UTKARSH(srmscet,unnao)
  25. 25. RECTIFIER USED IN TRAINS  Instead of using a bridge rectifier, it is possible to use a thyrister. A thyrister is a kind of diode such that it allows current to flow when it receives a command through a third terminal . UTKARSH(srmscet,unnao)
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  27. 27.  When the thyristor is used to rectify from AC to DC, the sinusoidal wave display on the voltage and time graph is confined to above the positive axis. In order to create a steady supply of voltage and smoothen the delivery, a smoothening circuit is connected. The smoothening circuit may include inductors and capacitors . UTKARSH(srmscet,unnao)
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  29. 29.  It is also possible to have AC electric locomotives with AC motors. As seen in the circuit below, there is both an AC-DC rectifier and a DC-AC inverter. The connection between the rectifier and the inverter is known as a DC link.  The DC-AC inverter is necessary in order to provide input to the 3 phase traction motors. The speed of the motor also depends on the frequency submitted towards it.  There may be more inverters connected to the DC link in other to serve other parts of the locomotive such as the compressor and cooling fans UTKARSH(srmscet,unnao)
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  32. 32. Braking: UTKARSH(srmscet,unnao) Generally braking is classified into two types in the traction.  Electrical braking.  Plugging  Rheostatic or dynamic braking.  Regenerative braking.  Mechanical braking.  Compressed air brakes  Vacuum brakes  Hydraulic brakes
  33. 33. PLUGGING  Plugging is a method of braking used in induction motors. Plugging involves interchanging the supply to two of the stator phase windings. This method is used in applications which require immediate stop applications. When the phase supply is reversed, torque is produced in the opposite direction. This leads to braking of the electric motor.  Motors which are operated this way have a plugging switch. This switch operates when the stop command is given to the motor circuit. The operation of this switch applies reverses the supply to two of the windings. When the motor comes to a complete halt, this reversed supply is disconnected. UTKARSH(srmscet,unnao)
  34. 34. DYNAMIC BRAKING  Another method of reversing the direction of torque and braking the motor is dynamic braking. In this method of braking the motor which is at a running condition is disconnected from the source and connected across a resistance. When the motor is disconnected from the source, the rotor keeps rotating due to inertia and it works as a self –excited generator. When the motor works as a generator the flow of the electric current and torque reverses. During braking to maintain the steady torque sectional resistances are cut out one by one. UTKARSH(srmscet,unnao)
  35. 35. DYNAMIC BRAKING UTKARSH(srmscet,unnao)
  36. 36. Regenerative braking  Regenerative braking takes place whenever the speed of the motor exceeds the synchronous speed. This baking method is called regenerative baking because here the motor works as generator and supply itself is given power from the load, i.e. motors. The main criteria for regenerative braking is that the rotor has to rotate at a speed higher than synchronous speed, only then the motor will act as a generator and the direction of electric current flow through the circuit and direction of the torque reverses and braking takes place. The only disadvantage of this type of braking is that the motor has to run at super synchronous speed which may damage the motor mechanically and electrically, but regenerative braking can be done at sub synchronous speed if the variable frequency source is available. UTKARSH(srmscet,unnao)
  37. 37. Loco Transformer UTKARSH(srmscet,unnao) 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.
  38. 38. LOCO TRANSFORMER UTKARSH(srmscet,unnao) There are two traction transformer connected in parallel of same rating for the purpose of reliability the rating of transformer are as follows Capacity : 25 KV. Frequency : 50 Hz taps on HT : 32 taps cooling :forced oil & air
  39. 39. ARNO-CONVERTER UTKARSH(srmscet,unnao) 1. Arno converter is a device which convert single phase AC in to three phase AC. 2. 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. 3. Arno converter is rotating device.
  40. 40. DC LINK UTKARSH(srmscet,unnao)  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.
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