Traction Ppt.pptx - 123SeminarsOnly by jianglifang


									          Power System-III
          Assistant Professor,
           EEE Department,
             K L University,
      Vaddeshwaram, Vijayawada,
        Andhra Pradesh-522502
        Mobile No:9989743653
What is Traction?
The act of drawing or pulling, as by an elastic or
 spring force.
Traction refers to the maximum frictional force that
 can be produced between surfaces without slipping.
TRACTION is resulting from a specific
 FRICTION coefficient (i.e. friction between rubber
 and ground) combined with area of ground covered
 by the tire – FOOTPRINT combined with vehicle
 WEIGHT pressing a tire onto the ground.
TRACTION is a resistance between tire and
           Why do we need traction?
Well, that question comes up every once in a
  while. Its a good question?
 If our feet do not find a surface with good grip
  (traction) our legs and feet could not move us
 Same story for a car - if the ground would not
  provide enough resistance (traction) the force
  generated in the engine would not be able to move
  the car forward.
 The scenario is quite simple. The more traction can
  be made available the more torque can be
  generated       to     move      more       weight.
     Requirements of an IDEAL Traction System
The following are some of the important requirements
  of the driving equipment used for traction purposes:
 The coefficient of adhesion(sticking) should be high
  so that high tractive effort at start is possible and
  rapid acceleration of the train can be obtained.
 It should be possible to overload the equipment for
  short periods.
 The wear(consume by use) caused on the shoes,
  wheel tires and the track should be minimum.
 It should be possible to use regenerative braking so
  that on descents it should be possible to generate
  energy and feed back to the supply system.
 It should be pollution free.
                  Traction System
 1. Non-Electric Traction System: Does not use
 electricity at any stage. Ex: Steam Engine Drive,
 Internal Combustion Drive.
 2. Electric Traction System: If electric supply is
 used for driving a locomotive, the system is
 known as electric traction.
Involves use of electricity at some stage or other.
 Ex: Battery Electric Drive, Diesel Electric Drive,
Electric traction is the most efficient of all other
 systems and is going to be the future system to be
 adopted by almost all countries of the world.
         Types of Electric Traction
 Vehicles which receive electric power from a
   distribution network fed at suitable points from either
   a central power station or substations suitably spaced.
 It is further subdivided into
 1) Systems operating with d.c. such as trolley buses,
   tramways and railways.
 2) Systems operating with a.c. such as railways.
 The group consists of self contained locomotives i.e.
   they generate their own power.
It is further subdivided into
 1) Diesel electric trains and ships
 2) Petrol electric trucks and lorries
 3) Battery driven road vehicles

 The diesel electric locomotive uses a diesel engine to drive an electric
  generator, which then supplies the current to traction motors, which are
  geared directly to the locomotive's wheels.
 In India, the diesel locomotives were introduced in 1945 for shunting
  purposes on broad gauge section and in 1956 for main line services on
  medium gauge section. The diesel electric locomotives employed in
  practice are of the following types:
 1. Main line diesel electric locomotive having engines of output not
  exceeding 1500 kW and speeds of 160 kmph.
 2. Shunting diesel electric locomotive having an engine of 225 to 375
  kW output and speed between 25 to 50 kmph.
 3. Diesel electric multiple units stock of which each motor has an engine
  of 135 to 150 kW output and train is capable of having speeds between
  80 to 110 kmph.
 4. Diesel electric rail car having an engine of 75 to 450 kW output which
  may operate as a single car or car with one or more trailer coaches.
 In diesel electric system used for traction, electric motors are used for
  driving the locomotive which are fed by a d.c. generator driven by diesel
  engine mounted on the same locomotive as shown by the schematic
  diagram in fig.1
           ADVANTAGES                           DISADVANTAGES
 The initial investment required is low     Its overload capacity is limited.
  as compared to direct electric traction
  since there is no need of overhead         The life of the diesel engine is
  structure distribution system and
  equipments.                                 comparatively shorter.
 Due to its higher acceleration and         In addition to motor generator
  retardation, the schedule speed over a
  given route will be higher.                 set, special cooling system is
 It can be put into service at any           required for cooling the diesel
  moment since hardly any time is             engine also.
  required to start up the engine and put
  it on duty.                                Its running and maintenance
 The power loss in speed control is very     costs are high.
  low because it can be carried out by
  field control of generator.                For the same power output,
 Its overall efficiency is higher than       diesel electric locomotive is
  that of steam locomotive about 25%.         costlier than steam or electric
 There is no interference with the
  adjoining communication lines.              locomotive.
 Since a diesel electric locomotive is a    Regenerative braking cannot be
  self contained unit and does not
  requires any overhead structure hence       used with such types of drives.
  it can be used on any route.
                        ELECTRIC LOCOMOTIVE

 It is the most widely used traction system in which the vehicle draws
  electrical energy from a distribution system fed at suitable points from a
  central power station or substation.
 In India both AC and DC type of electrified train systems operate today.
 1500 V DC based train system is mostly operating in Mumbai area. It is
  being converted to 25 kV AC system. Rest of the India where routes are
  electrified mostly operates under 25 kV AC overhead wire.
 The electric locomotives are of two types
 A.C. locomotive
 D.C. locomotive
 In case of d.c. locomotive d.c. motors are used for traction. The fig.1
  shows a schematic block diagram of d.c. locomotive.
 It basically consists of a step down transformer, a full wave rectifier with
  filters and d.c.motors. The fig.2 shows an a.c. type electric locomotive.
 The following are the advantages and disadvantages of electric system:
 Since electric motors are used as the drives , the system is clean and
  pollution free. Starting torque is high, so high acceleration is possible.
  Speed control is very simple. Braking is simple and efficient. Electric
  braking is used in this case which is superior to mechanical braking used
  by steam and diesel locomotives. It is possible to apply regenerative
  braking which has the following advantages
 Above 80% of energy spent during ascent(upward movement) is
  pumped back during descent.
 Less maintenance of brake shoes, wheels, tyres and rails on account of
  less wear and tear.
 An electric locomotive requires much less time for maintenance and
  repairs than a steam locomotive; and hence can be kept in service for
  95% or more of the working day if desired.
 Its maintenance and repair cost is about 50 % of that of steam
 The electric locomotive can be put into service immediately whereas
  steam locomotive requires about two hours getting up steam and be
  ready for service.
 The centre of gravity of electric locomotive is lower than that of steam
  locomotive due to which it is able to negotiate curves at comparatively
  higher speeds.
 The most important factor against electric traction is
  high capital outlay on overhead supply system.
  Therefore, unless heavy traffic is to be handled electric
  traction becomes uneconomical.
 Power failure for few minutes can cause disruption of
  traffic for hours.
 The electric traction system is tied to electric routes
  only. Hence it cannot be used on any of the routes.
 In case of A.C. traction the communication lines
  running along the track experience considerable
  interference from power lines. The communication
  lines therefore must either be removed away from the
  track or replaced by special expensive cables (this
  increases the capital cost outlay by 15%)
    What are the voltages used for electric traction in India?
 Voltages used are 1.5kV DC and 25kV AC for mainline trains.
 Calcutta had an overhead 3kV DC system until the '60s.
 The 1.5kV DC overhead system (negative earth, positive catenary) is used
  around Bombay (This includes Mumbai CST - Kalyan, Kalyan - Pune,
  Kalyan - Igatpuri, Mumbai CST - Belapur - Panvel, and Churchgate -
 Conversion to 25kV AC has already been done on the Titwala-Kasara
  section; next to be converted are Khapoli-Vangani, Vangani-Thane, and
 The Madras suburban routes (Madras-Tambaram in the '60s, extended
  later to Villupuram) used to be 1.5kV DC until about 1967, when it was
  converted to 25kV AC (all overhead catenary supply).
 The 25kV AC system with overhead supply from a catenary is used
  throughout the rest of the country.
 The Calcutta Metro uses 750V DC traction with a third-rail mechanism
  for delivering the electricity to the EMUs.
 The Calcutta trams use 550V DC with an overhead catenary system with
  underground return conductors. The catenary is at a negative potential.
 The Delhi Metro uses 25kV AC overhead traction with a catenary system
  on the ground-level and elevated routes.
                 System of Track Electrification
Presently, following four types of track electrification systems are available:
 Direct Current System: DC at 600-750 V is universally employed for tramways in urban
   areas and for many suburban railways while 1500-3000 V dc is used for main line railways.
   Low voltage dc system is undoubtedly superior to single phase ac system for heavy
   suburban services.
 (1) Single Phase AC System: In this system ac series motors are used for getting the
   necessary motive power. The voltage employed for distribution network is 15 to 25 Kv at
   162/3 or 25 Hz, which is stepped down on the locomotive to a low voltage (300 to 400 V)
   suitable for supplying to single phase ac series motors.
 (2) Three Phase AC System: In this system 3-phase induction motors operating at 3300 to
   3600 V systems consist of two overhead wires and track rail for the third phase and receives
   power either directly from the generating station or through the transformer substations.
 (3) The Composite Systems: Such systems incorporate good points of two systems while
   ignoring their bad points. Two such composite systems presently in use are:
 A. Single Phase To Three Phase System or Kando System: In this system single phase hv
   ac system is employed for distribution purposes and 3-phase induction motors for getting
   the necessary driving power in order to have the advantage of low cost of single phase
   overhead distribution system together with the desirable characteristics of 3-phase induction
   motors (at low frequency 3 phase induction motor develops high starting torque without
   excessive current). Speed control is also conveniently achieved by varying the supply
   frequency. This system is likely to be developed in future.
 B. Single Phase To Direct Current System : This system combines
  the advantages of hv ac distribution system and dc series motors for
  traction. The voltage used for overhead distribution system is 25 kv
  at normal supply frequency of 50 Hz. The locomotive carries
  transformer and converting machinery to step-down the voltage and
  convert into dc. This system of track electrification using 25 kv, 50
  Hz, single phase ac supply has been adopted for all future track
  electrification in India. The advantages of such a system are light
  overhead catenaries owing to lower currents, less number of
  substations (usually spaced at 50-80 km distances), flexibility in the
  location of substations, simplicity of substation design, lower cost of
  fixed installations, higher adhesion coefficient and higher starting
  efficiency. The draw-backs of this system are unbalancing effect on
  the supply and interference to telecommunication circuits.
  Fortunately both of these undesirable effects can be minimized.
                          Typical Railway Services
S.No    Parameter of        Urban or City Service     Sub-Urban         Main Line
        Comparison                                     Service           Service

1      Acceleration       1.5-4Kmphps               1.5-4Kmphps       6-8Kmphps
2      Retardation        3-4Kmphps                 3-4Kmphps         1.5Kmphps
3      Max. Speed         120Kmph                   120Kmph           160Kmph
4      Distance           1Km                       1-8Km             >10Km
       between stations

                                                                     Long         free
5      Special remarks Free running period is Free           running running       and
       if any          absent and coasting period period is absent coasting period
                       is small.                  and       coasting s. Acceleration
                                                  period is long.    and       braking
                                                                     periods are small
 A train is to be run most optimally as for as possible.
 for this it is necessary to know the speed time curves so that it
  is possible to find out what energy must be supplied to the train
  to perform a particular job.
 The slope at any point of the curve gives the acceleration or
  retardation of the train at that instant of time.
 The area between the curve and the time axis up to a certain
  time gives the distance covered by the train till that instant of
 Positive slope-Acceleration; Negative slope-Retardation.
 (i) Acceleration while notching up or constant Acceleration:
  During this period of run (0 to t1), Rst is gradually cut off so
  that the motor current is limited to a certain value and the
  voltage across the motor is gradually increased.
 (ii) Speed curve running: From t1 to t2, the current starts
  decreasing with the increase in speed.
 (iii) Free running(t2-t3):This period occurs when
 the power output from the driving axels balances
 the rate at which energy is expended against the
 resistance to motion.
 (iv) Coasting period(t3-t4): At the end of free
 running period , supply to the motors is cut off and
 train is allowed to run under its own momentum.
 (v) Braking period(t4-t5):At the end of coasting
 period, brakes are applied to bring the train to
Crest Speed, Average Speed And Schedule Speed
 Crest speed is the maximum speed (Vm) attained by a
  train during the run.
 Average speed is the mean speed from start to stop i.e.
  the distance covered between two stops divided by the
  actual time of run is called the average speed.
 Schedule speed is the ratio of distance covered
  between two stops and total time of run including the
  time of stop.
 The schedule speed of a given train when running on
  a given service (i.e. with a given distance between
  stations) is affected by (i) acceleration and braking
  retardation (ii) maximum or crest speed and (iii)
  duration of stop.
Direct Current Motor Control
 DC Motors:
For a DC motor, Torque
    T=0.1592Φ[Z Ia /A]P N-m =KΦIa
 For shunt motor: Φ is constant for a constant
 supply voltage, so, the torque is directly
 proportional to the current drawn by the motor.
For series motor: Φ α Ia, therefore T α I2.
 Eb=V-Ia r= ΦZNP/60A
 N=(60A/ΦZP)(V-Ia r)
  the Berlin Exhibition of 1879. The short line
  was about 600 yards long, and current was
  drawn from a third rail between the track
  which acted as the return to the dynamo. The
  locomotive hauled a maximum of some thirty
  passengers at a speed of about four miles an
  hour. This historic illustration shows one of the
  earliest trainloads of passengers, seated upon
  three carriages.

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