Utilization of Electrical Energy

TRACTION SYSTEM

SUBJECT CONTENT
4.1 Requirements of ideal Traction System.
4.2 Traction Mechanics: Types of Services, Speed Time Curve.
4.3 Supply system: DC System, Composite System, Single Phase
ac system with low and normal frequency and 3 phase system
❑ INTRODUCTION:-
What is traction?
✓ A Traction system is that which involves the propulsion of
wheels of vehicle on a track.
(It means the system become operated on a track .)
What is electric traction?
✓ Electric traction is meant for locomotion in which the driving
(tractive) force is obtained from electric motors (called as traction
motors).
✓ It 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.
❑ REQUIREMENTS OF IDEAL TRACTION
SYSTEM:
❑ Each Traction System has its on merits or demerits. No single
system can fulfill all the ideal requirement s for traction system.
These requirements are as under :
❖ A Traction should have high starting torque or effort so that high rate
of acceleration is obtained.
❖ Traction should be as compact in size as possible.
❖ The traction system should have large over load capacity for short
duration of time.
❖ It should minimum maintenance and there should be minimum wear
and tear on the equipments and component of the system.
❖ It should have smooth braking system and it offers minimum wear on
brake shoes.
❑ TYPES OF TRACTION SYSTEM:
❑ This System become classified in two ways,

(1) Non – Electrical Traction: In non electrical traction system

electric energy is not used at any stage for its propulsion.
In Short in this system does not use electricity.
✓ Steam engine drive
✓ I.C engine drive

(2) Electrical Traction:

This system Which utilize the electric energy.
✓ Diesel engine electric drive
✓ Petrol engine electric drive
✓ Battery operated electrical drive
✓ Electric drive
❑ Steam Engine Drive:
❑ A steam locomotive is a locomotive powered by steam. The term
usually refers to its use on railways, but can also refer to a "road
locomotive" such as a traction engine.
❑ On a steam locomotive, a fire in the firebox heats water to create
steam. This steam is channeled through tubes to the steam dome, where
the engineer regulates the amount of steam that will go into the
cylinders (sort of like what a gas pedal in a car does). This steam is
channeled to the cylinders, where it pushes the connecting rods, which
turn the wheels. The used steam is then shot out of the smokestack with
the exhaust from the fire.
❑ Steam engine drive has following main
features:-
The following main features:-
1) It has simple construction.
2) Its connection between cylinders and the driving wheels.
3) It has very smooth speed control.
4) Its maintenance is simple but it requires reporting time of about 8
to 12 hours.
5) It has efficiency of about 8 to 10%.
6) It is for underground railway.
7) It is limited cruising range up to 160.
8) It is requires periodic stops for cleaning ash & gas.
9) A Reciprocating steam engine are most commonly used for
railway trains.
10) Operational dependability for fuel and water.
11) Overload capacity is very less.
12) emitting smoke ,corrosion in steel structure.
13) Low coefficient of adhesion of 0.25 which
reduce power to weight ratio.
14) Not suitable for underground railway.
15) Require high rate of repair and maintenance.
16) Require periodic stops for cleaning ash &
coals. generally 2 to 2.7 tones coal require for
one hour.
❑DIRECT I.C. ENGINE DRIVE:
❑ TO CONIT….
❖ This traction system is mostly used in road
transports.

❖ its Efficiency of about 25% at normal speed of 600

to 1000 rpm.

❖ At low speed it is uneconomical.

❖ Speed control can be obtain by gear box

arrangement.
❑ADVANTAGES OF I.C. ENGINE:-
This system has following advantages:-
1) It has low initial cost and hence it is very cheapest
drive.
2) It has very simple speed control.
3) It has very simple braking system.
4) Its efficiency is higher compared to steam
locomotive.
❑ DISADVANTAGES OF I.C. ENGINE :-
It system has following disadvantages:-
1) It has a very low overload capacity(10%)
2) It has high maintenance cost.
3) The life equipment is very less to other drives.
4) Its operation is uneconomical at other than normal
speed.
5) For heavy duty train services its operation is not
satisfactory due to gear box.
❑ PETROL ELECTRIC DRIVE:-
❑ This system is used in heavy duty trucks, buses etc..
Due to electric conversation it provides very smooth
drive and speed. It can have capability to slowly on up
gradient at an imperceptible speed and creeping up at
the slope.
❑ADVANTAGES OF PETROL DRIVE:-
❑ It has low initial cost as compared to electric traction as track
electrification is not required.
❑ It requires no modification of existing track system.

❑ As it is self contained locomotive, it can be operated on any

routed.
❑ This locomotive is available for 6 days in a week.

❑ Its maintenance cost is little high.

❑ It has higher over all efficiency of about 45%.

❑DISADVANTAGES OF PETROL DRIVE :-

❑It has limited over load capacity of about 10%.

❑Its running and maintenance cost is high.

❑Fuel crisis can affect the working of the system.

❑In this system re-generating braking is not possible.

❑ BATTERY ELECTRIC DRIVE:-
❑ In this system there is vehicle, which carries secondary cell
batteries. These batteries supply power to the driving motors.
❑ Such drive is used for small distance travel and for light duty
service.
❑ It is generally used for shunting in railway yards , mines , for
delivery of good in cities, and for transportation of parts in
industries , docks etc..
❑ It offers very easy operational control.
❑ It has a less weight.
❑ It has maximum daily run of 45 to 60 km.
TO CONTI…
❑In view of limited hour capacity, batteries are required to
charged.
❑It has advantages over IC engine drive are its low maintenance,
longer of motor and control gear.
❑There is no fumes.
❑This system is now getting importance with the use of non
concentric energy sources.
❑ DIESEL ELECTRIC DRIVE:-
❑ A Diesel locomotive is a type of railroad locomotive in which the prime
mover is a diesel engine. Several types of Diesel locomotive have been
developed, the principal distinction being in the means by which the prime
mover's mechanical power is conveyed to the driving wheels
❑ On a diesel locomotive, diesel fuel powers a 12- or 16-cylinder engine. The
energy is transformed into electricity in the generator. The electricity is then
sent to the tractive motors (located near the wheels), powering the
locomotive.
❑ Once the concept of diesel electric drive was accepted the pace of
development quickened. By the mid 20th century the Diesel locomotive had
become the dominant type of locomotive in much of the world, offering
greater flexibility and performance than the steam locomotive.
❑ Three styles of diesel locomotive body:
cab unit, hood unit and box cab.

These locomotives are operated by Pacific

National in Australia.
 ❑ ADVANTAGES:-
❑ it has a low initial cost.
❑ it requires no modification of exiting track system.
❑ in this power loss in speed control is very less.
❑ as it is self contained locomotive.
❑ this is available for service 6 days in a week.
❑ higher over all efficiency.
❑ DISADVANTAGES:-
❑ It Has Limited Over Load Capacity Of Above 10 %.
❑ Life Of Engine Is Low.
❑ This System Is Required A Cooling System.
❑ Maintenance Cost Is High.
❑ Running Cost Is High.
❑ Regenerative Braking Is Not Possible.
❑ ELECTRIC DRIVE:-
❑ In this type of drive DC series or 1-phase AC series motor or
3- phase induction motor is used in the locomotive. The motor is
fed from overhead distribution lines fed at suitable points from grid
system is controlled manner.
❑ The current from over head line conductor is connected by means
of bow collector pantograph.
❑ The torque developed by motor is utilized in propelling the train.
❑An electric locomotive works a lot like a diesel, except that it receives
electricity from an overhead centenary system or a third rail. This electricity is
then sent to the traction motors, powering the loco. Since no engine is needed
inside of the locomotive, the engine is lighter, allowing for faster starts and stops.
This makes it ideal for commuter service and high-speed passenger trains.
❑One advantage of electrification is the lack of pollution from the locomotives
themselves. Electrification also results in higher performance, lower maintenance
costs, and lower energy costs for electric locomotives.
❑ADVANTAGES OF ELECTRIC DRIVE:-
❑ This type of drive is the most neat and clean as compared to
all other types of traction system. It is ideally suitable for
underground railways.
❑ This system can offer higher rate of acceleration and
retardation. As a result the scheduled speed is also higher as
compared to any other drive. It is roughly 50 to 100 %
higher.
❑ It can offer better and efficient speed control. It can also
provide locomotion on steep gradient with slow speed.
❑ As compared to steam engine it can exert higher torque
and there fore it can handle roughly double passenger or
goods traffic.
❑ Electric trains can be operated in section according to traffic density.
❑ Its maintenance, running cost and the time required for maintenance is
comparatively low.
❑ As no reporting time is required it can be put in to service without any loss of time.
❑ It is the most economical traction system for high traffic density particularly where
electricity available is cheap.
❑ It requires less terminal space. less size of shed and smaller workshop as compares
to that for steam locomotives.
❑ As torque exerted by motor is uniform and continuous. Vibrations are minimum and
journey for passengers becomes comfortable.
❑ Electric drive is not consuming any fuel hence this fuel can be utilized in steel
industries and promote greater industrialization.
❑ This type of drive offers better coefficient of adhesion. Which reduces weight to HP
ratio of the locomotive. Improves riding qualities and reduces wear and tear of the
track.
❑ It can handle temporary over load condition.
❑ Power distribution system used for track electrification can also be used for rural
electrification with no additional cost.
❑ DISADVANTAGES OF ELECTRIC DRIVE:-
❑ Its initial expenditure is very much high, this expenditure is
mainly due to track electrification substations and
maintenance and upkeep centers etc.
❑ Failure of electric supply for few minutes can cause much
more discrepancy in its schedule and dislocation of traffic.
❑ Electric locomotive can be operated only on electrified rules.
❑ It requires to follow severe statutory regulation and rules in
electrification of trains and operation of locomotives.
❑ AC traction system cau7ses interference in the nearby
communication lines, special arrangements for suppression of
interference are to be made.
❑ Additional equipments for regenerative breaking is required
with use of DC series motor which increases the cost and
weight of locomotive.
❑ DIFFERENT ELECTRIC TRACTION SYSTEM:
❑ In electric traction again various system of track electrification are employed depending
upon the availability of power from over head network. the various system of track
electrification can be classified as follow:
SYSTEM OF TRACK
ELECTRIFICTION

A.C. SYSTEM
D.C. SYSTEM (a) Single phase low COMPOSITE
frequency a.c. System SYSTEM
(b) Single phase high (a) Kando system
frequency operated a.c. (b) AC to DC System
System
(c) Three phase a.c. system
❑ D.C. SYSTEM:-
❑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)
SR. NO. D.C. VOLTAGE DISTANCE APPLICATION
BETWEEN S/S

1. 600 V 3 TO 5 KM TRAM WAY AND TROLLY

BUS

2. 1500 V TO 3000 V 15 TO 40 KM MAIN LINE

 ❑ ADVANTAGES:-
❑ D.C. Series Motor Have Better Speed Torque Characteristics And
Smooth Speed Control.
❑ It Has Low Maintenance Cost.
❑ Capable Of Attaining High Acceleration And Retardation Rates It
Is Best.
❑ DISADVANTAGES:-
❑ This System Has High Cost Of Sub Station Due To Converting
Equipments.
❑ More No. Of Sub Station Are Required As They As They Are
Spaced At Shorter Distance.
❑ APPLICATIONS:
❑ The D.C. System Are Prefer For Urban And Sub Urban Services
And Road Transports Where Distance Between Two Stops Are Small.
❑ A.C. SYSTEM:-
❑ There Are Three Types Of A.C System:-
1.Single Phase Low Frequency
2.Single Phase High Frequency
3.Three Phase Low Frequency
❑ SINGLE PHASE LOW FREQUNCY:-

❑ 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
➢ 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
electrification
❑ APPLICATIONS:-
❑ suitable for sub urban and main line services but now
a day this system is not used anywhere.
❑ SINGLE PHASE HIGH FREQUENCY A.C.
SYSTEM:-
❑ THREE PHASE LOW FREWUENCY
A.C. SYSTEM:-
❑
❑ DRAWBACKS:-
1. Induction motors offers low starting torque and draws high
starting current. It has constant speed characteristics.
2. The centenary systems becomes much more complicated at
crossing and junction.
3. Supply frequency is changed to Hz causing extra cost.
❑ COMPOSITE SYSTEM:
❑ It is seem that no system of track electrification is so good in
all respects . the composite system combines any two of the
above system incorporates some good point of each system.
Now a days two such composite system are used:

1. Kando system
2. A.C to D.C system
❑ KANDO SYSTEM:-

 In This System 1-phase HV (25kv) At Normal Supply Frequency Is

Used To Distribute Power. The Locomotive Which Carries A Phase
Convertor Which Converts Single Phase A.C. To Three Phase A.C.
 The Three Phase Power Is Then Fed To Three Phase Induction
Motors For Getting Necessary Motive Force.
 This System Was Adopted In Hungary In 1932.
❑ ADVANTAGES:-
 Three Phase O.H. Distribution Network System Is Replaced By
SingleWire Earth Return System.
 Induction Motor Is Cheap And Robust In Construction.
❑ SINGLE PHASE A.C TO D.C:-
 In this system of track electrification single phase a.c. 25
kv,50Hz at normal frequency is fed to overhead
distribution.

 The A.C. locomotive carries transformer to step-down

high input voltage and rectifying equipments to convert
a.c. into d.c. This system is adopted in India for
electrification.

 This system becomes most popular because of various

salient advantages over other systems particularly d.c.
system.
❑ ADVANTAGES:-
 Overhead Centenary System Has Reduced Diameter.
 Due To The Higher Voltage Power Demand Is Less.
 Reduced A Size Of Line Conductor And Supporting
Structure.
 overhead equipments becomes simple, light,
economical and efficient.
 saving a substation cost.
 starting efficiency is higher.
❑ DISADVANTAGES:-
Unbalance In The Power Supply.
How to remove???......

✓ by taking traction power supply at high voltage .

✓ by using high capacity supply source.
✓ by balancing all phases for traction purpose.
Interference In The Neighboring
Telecommunication Lines.

How to remove???......

✓ by using aluminum sheathed cable.

✓ by using isolating transformer, the induced voltages are
greatly minimized.
❑ ADVANTAGES OF AC TRACTION
SYSTEMS:-
 High power-to-weight ratio than forms of traction such as diesel or
steam that generate power requiring on board prime mover.
higher power-to-weight ratio, resulting in
➢ Fewer locomotives
➢ Faster acceleration
➢ Higher practical limit of power
➢ Higher limit of speed
➢ Higher hauling capability
 No exhaust fumes or carbon emissions
 Less noise pollution (quieter operation)
 The maintenance cost of an electric locomotive is nearly 50% of that for
a steam locomotive. Moreover, the maintenance time is also much less.
 An electric locomotive can be started at a moment’s notice whereas a
steam locomotive requires two hours to heat up.
 The motors used in electric traction have a very high starting torque.
Hence, it is possible to achieve higher acceleration of 1.5 to 2.5 km/h/s
as against 0.6 to 0.8 km/h/s in steam traction.
It is possible to use regenerative braking in electric traction system. It
leads to the following advantages.
➢About 80% of the energy taken from the supply during ascent is
returned to it during descent. And presently this returned energy is
not sent back to public network but made available for other vehicles
within the network
➢Goods traffic on gradient become safer and speedier.
Since height of an electric locomotive is much less than that of a steam
locomotive, its centre of gravity is comparatively low. This fact enables an
electric locomotive to negotiate curves at higher speeds quite safely.
electric trains may be powered from a number of different sources of
energy (e.g. hydroelectricity, nuclear, natural gas, wind generation etc.) as
opposed to diesel trains that are reliant on oil.
electric trains do not have to carry around the weight of their fuel
unlike diesel traction.
A fully electrified railway has no need to switch between methods of
traction thereby making operations more efficient. One country that
approaches this ideal is Switzerland
❑ DISADVANTAGES OF AC TRACTION
SYSTEMS:-
Significant capital cost of electrification
Increased maintenance cost of the lines
Overhead wires further limit the clearance in tunnels
Upgrading brings significant cost, especially where
tunnels and bridges and other obstructions have to be
altered for clearance
Railway Traction needs immune power, with no cuts,
warranting duplication of Transmission and Distribution
systems, which obviously comes at a Premium Price.
SPEED TIME CURVES
❑ INTRODUCTION:-
 The curve drawn between Speed and Time by taken speed (in
Km/hour) on Y-axis and time (in second) on X-axis is known as
Speed Time Curve. This speed time curve provided complete
information of the motion of the train from starting to stoppage
at next station. The slop of the curve at any point gives the
acceleration at the corresponding instant of speed of train at that
instant. The area covered by the curve represents the distance
covered by the train in the corresponding time.
❑ COMPONENT OF SPEED TIME CURVES:
 The speed time curves mainly consist of four components as
follows:
 Acceleration
 Constant speed or free running
 Coasting or running without power and
 Retardation or braking
❑ THE TYPICAL SPEED TIME CURVE
FOR MAIN LINE SERVICES OF
TRAIN IS SHOWN IN FIG.
❑ ACCELERATION (O-A-B):
(I) Rheostat acceleration or acceleration while notching up or constant
acceleration (O-A):
During this period (0 to A or 0 to t1) the current is maintained
approximately constant while the voltage across motor is gradually increased by
stepping up notch of the starting resistant. During this period tractive effort
remains constant hence acceleration is also maintained constant.

(II) Speed curve running or acceleration on speed curve

(A-B or t1 to t2):
During this period (t1 or t2) the voltage across the motor remains constant
and current decreases with increase in speed according to the characteristics of
the motor and finally the current drawn by the motor becomes constant. During
this period train accelerates but the rate of increase of acceleration decreases with
increase in speed and becomes zero at the speed at which the tractive effort
developed by motor becomes exactly equal to the resistance to motion of train.
❑ CONSTANT SPEED OR FREE
RUNNING (B-C):
 At the end of acceleration period i.e. at B. the train attains the
maximum speed. During this period (t2 to t3) the train runs
with constant speed attained at B and almost constant power
is drawn.
❑ COASTING OR RUNNING WITHOUT
POWER (C-D) :
 At the end of constant speed period i.e. at C, power supply to
the motor is cut-off and the train is allowed to run under its
own momentum. The rate of decrease of speed during coasting
period is known as coasting retardation.
❑ RETARDATION OR BRAKING (D-E):-
 At the end of coasting period i.e. at D, the brakes are applied to
stoop the train at station. During this speed decreases and finally
becomes zero and the train stops.
 The curve shown in fig is also known as actual speed time curve
as a includes all the components of speed time curve and is most
suitable for main line services but for urban or city services and
sub-urban services criteria are slightly different. Hence the curve
for main line, urban and sub-urban services.
❑ TYPICAL SPEED TIME CURVES
FOR DIFFERENT TRAIN SERVICES :
Considering different criteria like rate of acceleration. rate of
retardation .maximum speed and distance between two stops the
train services can be classified into following three services :
 Main line service
 Sub-Urban service
 Urban or city service
❑MAIN LINE SERVICE:
 In main line service, the distance between two stops is more (usually more than 20
kms). In this service free running period is of longer duration. The duration for
acceleration and retardation are comparatively very small say, small fraction of total
time of run. The rate of acceleration and retardation does not affect the average or
schedule speed; hence they are of little importance. While free running and coasting
duration is more which results reduction in running time as well as power
consumption.The typical speed time curve for Main Line is shown in fig.
❑ SUB-URBAN SERVICE:-
❖ In sub-urban services, the distance between two stops is smaller than
main line services and higher then urban services (between 1 to 10
kms). Free running is not possible & coasting is of longer duration.
Total time of run is less & hence to obtain high average speed, the rate
of acceleration & retardation are to be kept high of about 1.5 to 4.0
km per hour and about 3 to 4 km per hours respectively. The typical
speed time curve is as shown in fig.
❑URBAN OR CITY SERVICE:-
 In this type of services, the distance between the two stops is
comparatively very small (say 1 km or so). The time of running is also very
small (say few minutes). The rate of acceleration and retardation are
required to be high to get higher average speed as that required in sub-
urban services. The coasting period is also small. The typical speed time
curve for urban services is shown in fig.
❑ COMPARISONS OF DIFFERENT TYPES
OF TRAIN SERVICES:-

 Following table will give comparison of characteristics

of various train services.
Sr.no Types of Acceleratio Retardatio Maximum Distance Remarks
. services n in n in speed in between
kmphrs kmphrs kmphrs stops in km

1. Main Line 0.6 to 0.8 1.5 160 More than ❖ Long free
10 km running and
coasting period.
❖ Comparatively
very small
acceleration
and braking
period.

2 Sub- 1.5 to 4.0 3.0 to 4.0 120 1 to 10 Km ❖ No free running

Urban period.
❖ Long coasting
period.
❖ High rate of
acceleration
and braking.

3 Urban or 1.5 to 4.0 3.0 to 4.0 120 Up to 1 Km ❖ No free running

city period.
❖ Small coasting
period.
❖ High rate of
acceleration
and retardation
❑TERMS RELATED TO SPEED TIME
CURVE:-
✓ Crest speed: It is the maximum speed attained by the train during run is known as
crest speed. It is denoted byVc orVm and measured in km per hour.
✓ Average speed: It is the mean of the speed from start to stop or the distance covered
between two stops divided by the actual time of run is known as average speed. It is
denoted byVa and measured in km per hour.

✓ Scheduled speed (Vs): The ratio of distance between two stops and the total time of
run including stoppage time is known as scheduled speed. It is measured in km per hour.
✓ Acceleration () : It is the rate of rise of speed in km per hour
per second.

✓Retardation () : It the rate of fall of the speed when brakes are
applied in km per hour per second.

✓Coasting Retardation (Bc): It the rate of fall of speed when

power is cut-off when train moves on its own momentum in km
per hour per second.

✓Actual time of run (T) :It the total time required by the train to
cover distance between the two stations in second.

✓Stoppage time (ts) :It the time of stoppage of train at station.

✓ Time of acceleration (t1): It the time between the train
starts for journey and reaches to a maximum speed. It is given
by
t1 =Vm / α = Maximum speed / Rate of acceleration.
✓ Time of Retardation (t3): It is the time between
applications of brake to the train stoppage or come to the
rest. It is given by
t3 = Vm /  = Maximum speed / Rate of Re tradition
❑ FACTORS AFFECTING SCHEDULED SPEED:-
(a)Effect of maximum speed:
✓Scheduled speed will increase with increase in maximum
speed.
✓ This factor is consider in case of long distance run.

(b)Effect of acceleration and braking retardation:

✓ Increase in rate of acceleration & retardation decrease in
actual time of run & increase schedule speed.
✓ Variation in acceleration and retardation will have more
effect on scheduled speed in case of short distance
compared to long distance.
TO CONTI…
(c)Effect of stoppage time:

✓ Schedule speed increase by reducing stoppage time.

✓ Stoppage time will affect more in short distance.
❑SIMPLIFIED SPEED-TIME CURVE:-
❑ It is difficult to solve numerical on typical speed time curves for

any types of services. The speed time curve for main line
services can be replaced most easily by a trapezoid shape.
Similarly the speed time curve for urban and sub urban services
can be replaced by an equivalent speed time cure.
 Actual speed time
curve(OAEBC)
Trapezoidal speed time
A E
A2 curve(OA1B1C)
B1
A1 B Quadrilateral speed time
curve(OA2B2C)
B2
Speed in km/hr

O Time in second (t) C

•OAEBC is actual speed time curve of main line service.

•OA1B1C is simplified trapezoidal speed time curve.

•OA2B2C is simplified quadrilateral speed time curve.