EE3029D Electric Power Utilization
MODULE 01
Reference Books:
1. Taylor E Openshaw, Utilisation of Electric Energy, Orient Longman,1986.
2. J B Gupta, Utilization of electric power and electric traction, S K Kataria & Sons, 2002.
Course Plan and Evaluation Policy
Mid Semester Test Portion: Portions covered before Mid Semester Test
Mid Semester Test Mark: 30 Marks.
Assignments: 20 Marks.
End Semester Examination Portion: All portions covered in the course
End Semester Examination Marks: 50 Marks.
Grading: Relative
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Indian Railways
Pantograph
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Indian Railways
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Speed-Time Curve
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Speed-Time Curve
Schedule speed can be obtained from average speed by including the duration of stops. For a given distance
between stations, higher values of acceleration and retardation will mean lesser running time and,
consequently, higher schedule speed. Similarly, for a given distance between stations and for fixed values of
acceleration and retardation, higher crest speed will result in higher schedule speed. For the same value of
average speed, increase in duration of stops decreases the schedule speed.
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Speed-Time Curve
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Speed-Time Curve
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Tutorial
Question 1
A suburban train runs with an average speed of 36 km/h between two stations 2 km apart. Values of
acceleration and retardation are 1.8 km/h/s and 3.6 km/h/s. Compute the maximum speed of the train
assuming trapezoidal speed/time curve.
Question 2
A train is required to run between two stations 1.5 km apart at a schedule speed of 36 km/h, the duration of
stops being 25 seconds. The braking retardation is 3 km/h/s. Assuming a trapezoidal speed/time curve,
calculate the acceleration if the ratio of maximum speed to average speed is to be 1.25
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Tutorial
Question 3
A train runs between two stations 1.6 km apart at an average speed of 36 km/h. If the maximum speed is to
be limited to 72 km/h, acceleration to 2.7 km/h/s, coasting retardation to 0.18 km/h/s and braking
retardation to 3.2 km/h/s, compute the duration of acceleration, coasting and braking periods. Assume a
simplified speed/time curve.
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Tractive Effort
The tractive effort (Ft) is the force developed by the traction unit at the rim of the driving wheels for moving the unit
itself and its train (trailing load). The tractive effort required for train propulsion on a level track is
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Tractive Effort
Fa = force required for giving linear acceleration to the train
If M is the dead (or stationary) mass of the train and a its linear acceleration, then Fa = Ma
Since a train has rotating parts like wheels, axles, motor armatures and gearing etc., its effective (or accelerating) mass
Me is more (about 8 − 15%) than its stationary mass. These parts have to be given angular acceleration at the same
time as the whole train is accelerated in the linear direction. Hence, Fe = Mea
(i) If Me is in kg and α in m/s2, then Fa = Me a newton
(ii) If Me is in tonne and α in km/h/s, then converting them into absolute units, we have
Fa = (1000 Me) × (1000/3600) a = 277.8 Me a newton
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Tractive Effort
Fg = force required to overcome the effect of gravity
In railway practice, gradient is expressed as the rise (in metres) a track
distance of 100 m and is called percentage gradient
When M is given in tonne, then
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Tractive Effort
Fr = force required to overcome resistance to motion
Train resistance comprises all those forces which oppose its motion. It consists of mechanical resistance and wind
resistance. Mechanical resistance itself is made up of internal and external resistances. The internal resistance comprises
friction at journals, axles, guides and buffers etc. The external resistance consists of friction between wheels and rails
and flange friction etc. Mechanical resistance is almost independent of train speed but depends on its weight. The wind
friction varies directly as the square of the train speed.
If r is specific resistance of the train i.e. resistance offered per unit mass of the train, then,
Fr = M.r newton
( r is in newton per kg of train mass and M is the train mass in kg)
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Tractive Effort
expression for total tractive effort becomes
Ft = Fa ± Fg + Fr = (277.8 a Me ± 98 MG + Mr) newton
Please remember that here M is in tonne, a in km/h/s, G is in metres per 100 m of track length (i.e. % G) and r is in
newton/tonne (N/t) of train mass.
The positive sign for Fg is taken when motion is along an ascending gradient and negative sign when motion is
along a descending gradient.
Power Output from Driving Axles
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Tractive Effort
Tractive effort transferred to the driving wheel is
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Tutorial
Question 1
A 250-tonne motor coach driven by four motors takes 20 seconds to attain a speed of 42 km/h, starting
from rest on an ascending gradient of 1 in 80. The gear ratio is 3.5, gear efficiency 92%, wheel diameter 92
cm train resistance 40 N/t and rotational inertia 10 percent of the dead weight. Find the torque developed
by each motor.
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Series-Parallel Starting
With a 2 motor equipment ½ the normal voltage will be applied to each motor at starting as shown in Fig. (Series
connection) and they will run upto approximate ½ speed, at which instant they are switched on to parallel and full
voltage is applied to each motor. Rs is gradually cutout, with motors in series connection and then reinserted when
the motors are connected in parallel, and again gradually cut-out.
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Series-Parallel Starting
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Series-Parallel Starting
The main difficulty with series parallel control is to obtain a satisfactory method of transition from series to parallel without
interrupting the torque or allowing any heavy rushes of current. In shunt transition method, one motor is short circuited and
the total torque is reduced by about 50% during transition period, causing a noticeable jerk in the motion of vehicle.
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Series Parallel Control by Bridge Transition
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Series Parallel Control by Bridge Transition
Advantage of this method is that the normal acceleration
torque is available from both the motors, through - out
starting period. Therefore acceleration is smoother,
without any jerks, which is very much desirable for traction
motors.
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Series Parallel Control
Time during which motors are in series
Time during which motors are in parallel.
Back e.m.f. Eb of each motor, in series operation
Back e.m.f. Eb of each motor, in parallel operation
Energy lost when motors are connected in series
Energy lost when motors are connected in parallel=
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Tutorial
Question 1
Two motors of a motor coach are started on series - parallel system, the current per motor being 350 A
(Considered as being maintained constant) during the starting period which is 18 sec. If the acceleration
during starting period is uniform, the line voltage is 600 V and resistance of each motor is 0.1 ohm.
Find
(a) the time during which the motors are operated in series.
(b) the energy loss in the rheostat during starting period.
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Electrical Braking
Both electrical and mechanical braking is used. Mechanical braking
provides holding torque. Electric Braking reduces wear on mechanical
brakes, provides higher retardation, thus bringing a vehicle quickly to
rest.
Rheostatic Braking
Equalizer Connection Cross Connection
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Electrical Braking
Regenerative Braking with D.C. Motors
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Tutorial
Question 1
The following data refer to the speed-current and torque – current characteristics of a 600 V d.c. series traction
motor.
Current, amperes : 50 100 150 200 250
Speed, kmph : 73.6 48 41.1 37.3 35.2
Torque, N-m : 150 525 930 1,335 1,750
Determine the braking torque at a speed of 48 kmph when operating as self excited d.c. generator. Assume resistance
of motor and braking rheostat to be 0.6Ω and 3.0 Ω respectively.
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Indian Railways
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Indian Railways
▪ Feeding Post (FP)
▪ Sectioning and Paralleling Post (SP)
▪ Sub-Sectioning and Paralleling Post (SSP)
▪ Sub-Sectioning Post (SS)
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Indian Railways
Feeding Post (FP):
It is a supply control post, where the incoming feeder
link from grid substation are terminated. Each feeder
supplies the OHE on one side of the feeding post
through interrupters controlling supply to the
individual lines. Thus, for a two track line, there will
be four interruptors at each feeding post.
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Indian Railways
A Sectioning and Paralleling Post (SP) is a part of the railway electrical distribution network that provides
power to electric trains. The SP includes two paralleling interrupters that parallel the OHE of up and down
tracks.
A Sub-Sectioning Post (SS) is
a railway installation that is
similar to a Sub-Sectioning
and Paralleling Post (SSP)
but without the ability to
parallel the up and down
tracks. SSs are rarely used.
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Indian Railways
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For further tutorials and other topics,
Refer Class Note and Reference Books
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