ELECTRIC TRACTION SYSTEM

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

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• 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.

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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

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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.

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• 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.

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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.

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DC link

1. This is essentially a bank of capacitor and
   inductor or active filter circuitry to further
   smooth.
2. Also to trap harmonics generated by drive
   converter and traction motors.
3. 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.

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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.

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Advantages Of AC Motors Over DC Motors

1. 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.
2. 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.
3. In addition, DC motors tend to draw power with a
   bad power factor and injecting a lot of
   undesirable harmonics into the power system.
4. AC motors have the advantage of a simpler
   construction.

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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.

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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

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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.

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Sectioning and paralleling post (SP)

1. These post are situated approximating midway
   between feeding posts making the demarcating
   points of two zones fed from different phases
   from adjacent substations.
2. 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.
3. 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.
4. 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 .

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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.

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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.

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Control Equipments

• To segregate the faults and to isolate the faulty
  section, the circuit breaker at traction
  substation and interrupters at SP/SSPs 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.

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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).

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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.

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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.

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• 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.

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UPS and Batteries at RCC

1. 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.
2. In case of failure of one the entire load is
   automatically taken over by the healthy UPS
   without affecting the working of the system.
3. 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.
4. 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.

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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.

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Main Function Of Various Components
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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.

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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.

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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.

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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.

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Tap Changer (Graduator)

1. 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.
2. There are two rows of contact segments which are
   aligned on outer and inner circles of the contact
   plate.
3. An arm which is known as selector arm is driven
   by shaft at the centre of the contact plate.
4. Two rollers are situated at the edge of the
   selector arm. These rings are provided in front
   of the contact plate.
5. The centre shaft which extends outside the tap
   changer casing is driven by an air servomotor.
6. 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).
7. The connection between the inner or outer ring to
   the transformer is being established by means of
   a contactor.

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Rectifier

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

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Arno Converter

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.

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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.
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Traction Motors (DC Series Motor)

1. 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.
2. These motors are axle hung, nose suspended type
   and are provided with grease lubricated roller
   bearings for armature as well as for suspension.
3. 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.

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The main parts of motors are given below

1. Magnet frame armature and shields.
2. Brush holders and brushes.
3. Commutator
4. Armature
5. Stator
6. Armature windings
7. Field windings
8. Inter poles
9. Armature bearings
10. Axle bearing

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1. Generally in locos there are six traction motors.
2. Three motors per bogies and each motor driving
   one axle directly through gears.
3. The motors M1 to M6 are supplied jointly by the
   two silicon rectifiers connected in parallel
   through two contactors.
4. 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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