AC And DC How it operate actually

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2. CONTENTS
Introduction
• What Is Electric Traction?
• A Brief History To Electric Traction
• Requirements of Ideal Traction Systems.
• Types and Examples of Traction Systems.
Electric Traction
Systems
• Types of Electric Traction Systems
• Advantages of Electric Traction
• Disadvantages of Electric Traction
AC/DC Traction
System
• Auxiliary equipment's
• Types of Electrification
• Braking
Other Diverse
Topics
• DC Traction
• AC Traction
• Composite Systems
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4.  Electric Traction involves utilization
of electric power for traction
systems i.e., for railways, trams,
trolleys etc.
 For traction purposes mostly 3-
Phase Induction motors and d.c
series motors are used and both
have high starting torque,
prevailing requirement for the high
speed acceleration.
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5. EXAMPLES OF TRACTION SYSTEMS
 Railway electrical locomotives
 Battery driven road vehicles
 Petrol, diesel trucks and busses
 Tramways and Tramcars
 DC electrical trains and small ships
 Diesel trains and ships
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6. REQUIREMENTS OF IDEAL TRACTION SYSTEMS
 High starting tractive effort to have rapid acceleration.
 Minimum wear on the track.
 Easy speed control.
 Minimum equipment and maximum efficiency.
 Withstanding of large temporary loads.
 Self contained and compact locomotive.
 No interference with the other systems like communication
 Pollution free environment 6

7.  Italian Railways were the first in the world to
introduce the electric traction.
 The world's first AC locomotive in Valtelina,
northern Italy (1898–1902).
 Power supply: 3-phase 15 Hz AC, 3000 V (AC
motor 70 km/h).
 It was designed by a Hungary company.
 The 106 km Valtellina line was opened on 4
September 1902.
A Brief History to Electric Traction
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8. Electric Traction
Systems
Direct Electric power
Locomotives
Self-contained
Locomotives
AC Driven DC Driven Petrol Electric Driven Battery Driven
Diesel Electric Driven 8

9. SYSTEMS OF TRACK
ELECTRIFICATION
DC SystemComposite System AC System
Single Phase System Three Phase System
Single Phase Three Phase System Single Phase DC System9

10.  D.C Series Motors- Develops high torque at low speeds and low torque at high speed,
exact requirement of the traction units.
 Torque is independent of the line voltage and thus unaffected by the variations in the line
voltage.
 Single phase A.C Series Motors- Starting torque is lower than dc series motor due to poor
power factor at starting
 This motor has surpassed the d.c series motor in terms of size, weight cost for the same
rating.
 Maximum operating voltage is limited to 400 Volts.
 Three Phase Induction Motors- Provides constant speed operation, developing low starting
torque drawing high starting current and complicated control networks makes it
unsuitable for electric traction work.
 Automatic regeneration is the main advantage in electric traction with this motor.
TRACTION MOTORS
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12. DC traction units use direct current drawn
from either a conductor rail or an overhead
line.
The most popular line voltages for overhead
wire supply systems – 1500V DC and 3000V
DC.
600V DC–750V DC volt range used for third
rail systems (a means of providing electric
power to a railway train, through a semi-
continuous rigid conductor placed alongside
or between the rails of a railway track and
that additional rail is called conductor rail)
DC TRACTION
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14. SUITABILITY OF D.C SERIES MOTOR FOR TRACTION
D.C series motor develops high torque at low
speeds & low torque at high speeds. This is the
exactly the requirement of traction units.
In case of dc series motor , up to the point of
magnetic saturation, torque developed in
proportional to the square of the current.
Therefore, dc series motor requires
comparatively less increased power input with
the increase in load torque. Thus the series
motor are capable of withstanding excessive
loads.
Speed of dc series motor can be controlled by
various methods. 14

15. DC ELECTRIFICATION SYSTEM
DC traction system use the DC supply drawn
from the conducting rail or overhead supply
system.
The operating voltage is from 600 to 750
volts for tramways and for many suburban
railways and from 1500 to 3000 volts for
main line railways.
DC electric motors employed are for getting
the necessary driving power usually from
series motors.
Compound motors are used in favour for
tramways and trolley busses where
regenerative braking is desired 15

16.  Expensive substations are required at frequent intervals and the overhead
wire or third rail must be relatively large and heavy.
 The low-voltage, series-wound, direct-current
 Motor is well suited to railroad traction, being simple to construct and easy
to control.
 Low overall efficiency
 Bulk and size restrictions
 Undesirable requirements for periodic maintenance inspection and
replacement
Disadvantages of DC
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18. AC Traction units draw alternating
current from an overhead line.
Typical Voltages Used are:-
 15 kV AC, 16⅔ Hz (16.7 Hz)
 25 kV AC, 50 Hz (Currently used in India)
 25 kV AC, 60 Hz
Fewer substations are required
and the lighter overhead current
supply wire can be used
Reduced weight of support structure
Reduced capital cost of electrification
AC TRACTION
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19. COMPONENTS OF AN A.C LOCOMOTIVE
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20. AC ELECTRIFICATION SYSTEM
 AC electrification can be done in different
ways
Single Phase System
Three Phase System
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21. SINGLE PHASE SYSTEM :-
In this distribution system is 15000v
to25000v at 6.67hz or 25hz and was
stepped down to 300-400 suitable
for supplying single phase motors.
Distribution system is supplied with
substations at spacing of 50 to 80
km because of high current
requirements
For longer economic transmission
the voltage level is extended further
and transmitted longer distances
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22. Change in supply frequency is necessary because of best
performance of ac series motors at low frequencies.
Low frequency operation of series motor increases communication,
efficiency, power factor .
Low frequency operation of the overhead lines reduces the line
reaction and hence the voltage drop directly.
AC single phase system is adopted where overhead construction is
main important and where rapid acceleration and retardation is not
that important like sub-urban areas.
SINGLE PHASE SYSTEM :-
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23. • In this system 3-phase induction motors operating at 3000 to 3600 volts and
normal frequency of 6.67hz are employed.
• 3 phase induction motors have maximum efficiency and property of automatic
regenerative braking without requiring any additional equipment.
• They have low starting torque
and need high starting currents,
absence of speed control.
• These are implemented in
hilly areas and where the
regenerative braking and high output power is required.
THREE PHASE SYSTEM :-
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24. SUITABILITY OF A.C SERIES MOTOR FOR TRACTION
The construction cost of an ac series motor is much more easier
than of a dc series motor.
The starting torque of a.c single phase motor is lower than that
of dc series motor due to poor power factor at the start.
The speed of an ac series motor may be controlled efficiently by
taps on a transformer. Which is not possible in case of a dc series
motor.
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25. SUITABILITY OF THREE PHASE INDUCTION
MOTOR FOR TRACTION
It has simple & robust construction.
 Trouble free operation.
 Less maintenance.
 High voltage operation consequently requiring reduced amount of current.
 Automatic regeneration are the main advantages of 3-ph. Induction motor
for traction.
But due to their flat speed- torque characteristics, constant speed operation,
developing low starting torque, drawing high starting current, complicated
speed control systems they are not suitable for electric traction work.
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26. ADVANTAGES & DISADVANTAGES OF A.C. SYSTEM OVER D.C. SYSTEM
ADVANTAGES:-
1.Light overhead catenary
2.Saving in sub-stations.
3.More flexibility and high efficiency
4.Lesser equipment used & easy to maintain
5.Cheap as far as cost for fixed installation
DISADVANTAGES :-
1.Single-phase A.C. system imposes Unbalancing effect
2.Produces Interference with telecommunication lines
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27. SYSTEM ELECTRIFICATION
• CATENARY
• PANTOGRAPH
• CIRCUIT BREAKERS
• ON LOAD TAP CHANGER
• TRANSFORMER
• RECTIFIERS
• SMOOTHING REACTORS 27

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30. suspended with minimum of sag so that contact between the trolley wire and
current collector can be maintained at higher speeds.
Trolle
y Wire
Trolley wire or contact wire

31.  Provided for speeds upto 120kmph
 Span of catenary wire 45-90 m and sag of 1-2m.
 Relatively Cheaper
 Less Maintenance
 Suitable where traffic density and operating speeds are low.
Single Catenary Construction Compound Catenary Construction
 Provided for speeds ranges 190-
224kmph
 Additional wire called intermediate
wire is used to increase current
carrying capacity i.e., to have
increased traffic density.
The trolley wire wire is supported by another wire known as catenary.
Two different types of Catenary construction can be used
CATENARY
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32. SYSTEM OF TRACK ELECTRIFICATION
Current Collector- Current from the
overhead wire is collected with the
help of sliding contact collector
mounted on the roof of the vehicle.
Three types of Current collector
Trolley Collector
Bow Collector
Pantograph Collector
Current
Collector
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33. Trolley Collector- Used for Tramways and trolley buses, held in contact
with overhead Wire by spring. Suitable for low speed up to 32kmph
Bow Collector- It uses a light metal strip or bow about 1 m long for
current collection.
 Not suitable for railway work
 Requiring speed of 120kmph and higher.
 Requires reversing arrangement of the bow
Pantograph Collector- Main function is to maintain the link between
overhead contact wire and power circuit of the locomotive at varying
speeds in different climate and wind conditions
 This can be lowered or raised from cabin by air cylinders.
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34. PANTOGRAPH DESIGN
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37. ADVANTAGES OF ELECTRICAL TRACTION SYSTEMS
It is the cheapest method of traction systems.
Pollution free and clean environment.
Maintenance and repair cost are very less compared to other traction systems
like steam engine traction.
Starting and control of the electrical traction system is very fast and can be
done without loss of time.
This traction uses AC or DC series motors which provide very high starting
torque.
Braking or stopping of this system can be done in very less time and less
energy usage.
Carriage of fuel (coal , oil) is not needed. 37

38. DISADVANTAGES OF ELECTRICAL TRACTION SYSTEMS
High initial expenditure
Extra equipment is required for braking
Failure of electrical supply is a major problem
The electrified tracks are needed for running the electrical
locomotives
Interference with communication systems (telephone or telegraph
) is a problem
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40. REFERENCE
• UTILIZATION OF ELECTRIC POWER AND ELECTRIC TRACTION – J.B
GUPTA
• WWW.WIKIPEDIA.COM
• WWW.ELECTRICAL4U.COM
• WWW.IRFCA.ORG
• WWW.RAILWAY-TECHNICAL.COM
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