3. INTRODUCTION TO DIESEL SHED RATLAM
Diesel Shed Ratlam(M.P.) is established on 1
may 1967. It is awarded with ISO 9001-2000 and ISO
14001-1996 certificate firstly in western railway. It is
located on main line between Delhi and Mumbai. Shed
is a place where maintenance and repair of locomotive
is done. As on today ,the shed has holding of 140
diesel locos.
The entire diesel shed is divided into mainly
two sections :
(1) Mechanical Section
(2) Electrical Section
4. LOCOMOTIVE AND ITS TYPE
Locomotive is an automatic device
which kept on steel frame having ability to run on
rails and has power to pull passenger as well as
goods trains.
Locomotives are of three types :
(1) Steam Locomotive
(2) Diesel Electric Locomotive
(3) Electric Locomotive
5. (1) STEAM LOCOMOTIVE
Steam locomotive played a key role
during development and golden age of railroading.
Steam locomotive is a self contained power unit
consisting of a steam engine , a boiler with fuel and
water supplies. Superheated steam is admitted to
the cyllinders by a suitable valve arrangement and
the pressure on the pistons being transmitted
through main rod to the driving wheels. The
superheated steam is controlled by a throttle.
6. Steam locomotive has been replaced in developed
nations by electric locomotives and diesel- electric
locomotives because of following disadvantages of
steam locomotive :
(a) It has strictly limited overload capacity.
(b) It has very low thermal efficiency of about 6-8%
because installation of a condenser on locomotive is
very difficult.
(c) It is available for hauling work for about 60% of its
working days, remaining 40% being spent in preparing
for service, in maintence and overhaul.
7. (2) DIESEL ELECTRIC LOCOMOTIVE
Diesel electric locomotives were introduced firstly
in united states in 1924 and have become the most
widely used type of locomotive. It was introduced for
first time in India in 1958.
Diesel electric locomotive has electric drive in
form of traction motors driving the axles and controlled
with electronic controls. It differs from electric
locomotives principally in that it has its own generating
station instead of being connected to a remote
generating station through overhead wires. The
generating station consists of a large diesel engine
coupled to dc generator that provides power to traction
motors. These motors drive the driving wheels.
9. Advantages: (a) It provides high starting
acceleration in comparison to steam locomotive.
(b) It is more efficient than a steam locomotive.
Disadvantages: (a) It is costlier than either steam or
electric locomotive for same power.
(b) Life of diesel engine is shorter comparatively.
(c) Regenerative braking cannot be employed though
rheostatic can be.
(d) Overload capacity is limited because diesel
engine is a constant output prime mover.
10. (3) ELECTRIC LOCOMOTIVE
Electric locomotives generally have two or
more dc or ac motors. In these locomotives , power
is collected from an electric trolley which is running
on an overhead wire. The overhead wire can carry
both types of supply ac as well as dc. Indian railway
also uses both types of supply systems :
(a) AC system- 25 kv single phase 50 hz ac supply
(b) DC system- 1500 V dc supply
Only western zone and central zone of
railway
uses dc system.
12. Advantages: (a) It does not produce any smoke and
flue gases, so it is most suited for undergrounds
trains.
(b) The maintenance cost of electric locomotive is
lower than steam locomotive.
(c) Traction motors used in it have very high starting
torqe.
(d) Regenerative braking is used for ac systems.
(e) An electric locomotive can be started in a moment
but a steam locomotive takes about 2 hours to
heat.
13. Disadvantages: (a) Electric traction has high initial
cost of laying out overhead electric supply system.
(b) Power failure for few minutes can cause traffic
dislocation for hours.
(c) Communication lines which usually run parallel to
the power supply lines suffer from electrical
interference.
(d) Electric locomotive can be use only on those
routes which have been electrified.
14. DC SYSTEM OF RAILWAY ELECTRIFICATION
In dc system with overhead catenary, dc
traction motors are supplied 1500 V DC by
catenary. In overhead electrification systems,
electricity is supplied through an overhead system
of suspended cable which is known as catenary.
Indian Railway uses catenaries of constant tension
type. At one end of each section of catenary the
cable connects to a pulley by going over this ,is
terminated by hanging a weight. Catenary wires are
usually made of copper alloys such as cadmium-
copper which has high tensile strength of 63 kg per
sequare mm.
15. For transmission of 1500 V DC by overhead
wire, substations are made and they are located 40
km apart with each other. These substations
receive power from 132 kv ,3-phase network. At
these substations, this high-voltage 3-phase supply
is converted into low-voltage 1-phase supply with
help of Scott-connected 3-phase transformers. Next
this low voltage ac is converted into 1500 V DC by
using suitable rectifiers. The dc supply so obtained
is fed to dc traction motors via suitable contact.
16. Advantages of dc system over 1-φ ac system:
(a) DC system does not cause electrical interference with
overhead communication lines.
(b) DC motors are better suited for frequent and rapid
acceleration of heavy trains than ac motors.
(c) DC train equipment is lighter, less costly and more
efficient than similar ac equipment.
(d) When operating under similar conditions, dc trains
consumes less energy than 1-φ ac train.
Disadvantage: Only one disadvantage is the necessity
of locating ac/dc conversion substations at short
distance apart.
17. TRACTION MOTOR
(1) Description: The traction motor is a four pole
DC series motor in which field winding is connected
in series with armature. It is a forced ventilated
machine arranged for axle mounting on sleeve
bearing. Transverse movement is limited by the
flanges of axle suspension bearing. An electric
locomotive as well as diesel-electric locomotive in
indian railway contain six dc traction motors at
once.
18. (2) Construction: The armature core is made from
high permeability silicon steel stampings and these
stampings are separated by thin coating of varnish
as insulation with each other. The armature is lap
wounded with 100% equalization.
The commutator is built up with hard
drawn silver bearing copper segment which are
insulated with micanite segment. After the
commutator is statically and dynamically seasoned
to insure stability ,the complete armature is
dynamically balanced.
19. The high permeability cast steel magnet
frame is machined to insure alignment of the end
shields, pole bores & axle way bores. The main
poles are built from steel laminations.
There are four brush holder per motor, each
carrying 3 split carbon brushes. Each brush holder
is carried on two insulated support pins.
The armature is supported on grease
lubricated roller bearing. Bearing assemblies are
sealed type, so necessity of lubrication in about 2
or 3 years.
20.
21. (3) Rating: A traction motor has following
ratings:
Voltage - 285 volts
Current - 980 ampere
Speed - 360 rpm
Power - 248 kw
22. (4) Principle: When a current carrying conductor is
placed in a magnetic field, a force is exerted on it
and direction of force is determined by fleming’s left
hand rule. In a dc motor, dc supply is provided to
field winding. As a result, unidirectional magnetic
field is produced and magnetic field lines cut the
rotor conductors which carry current equal to field
current. Since the conductors are on circumference
of rotor, force acts in tangential direction to the
rotor. Thus a torque is developed on the rotor and it
starts to rotate.
23. (5) Operation: To understand the operation of a
traction motor, three transition panels are studied.
Transition panels perform transition events. These
events correspond to field weaking and changing
the connections of traction motor. Three transition
panels are performed at three different speeds –
First transition at 30 km/hr speed
Second transition at 50 km/hr speed
Third transition at 80 km/hr speed
24. When 1500 V dc supply is provided to circuit
of traction motors, a large current flows through
armature of motor as it is connected in series with
field. As a result armature, armature begins to
rotate and a back emf is generated which opposes
the main supply voltage. ( back emf Eb =
PφNZ/60A
Eb α N )
As speed increases, back emf also
increases and it offers resistance to flow of
generated current to traction motors. Hence for
increasing the speed , the supply voltage must
increase but it is not
25. possible to increase supply above 1500 V.
Therefore, when speed is reached at 30 km/hr, first
transition panel is switched on. Now a parallel
combination of two series connected traction
motors is under operation and resistance is
connected in parallel with the field of motors to
refuse back emf.
Now speed increases beyond 40 km/hr
and back emf again starts increasing rapidly. So
second transition panel is switched on at speed of
50km/hr. After second transition, all six motors run
in parallel
26. without resistance parallel to field of motors.
No longer back emf is controlled by
second transition panel as speed increases beyond
70 km/hr, so third transition panel is switched on at
speed of 80 km/hr. By this transition, resistances
are connected parallel with field of motors in circuit
of second transition to reduce back emf.
27. (6) Speed-Torque characteristic:
The speed Vs torque characteristic of dc series
traction
motor with a constant votltage
supply is shown on right side.As
the speed decreases, torque
for motor increases sharply. As
load is removed from motor,
speed increases sharply. Hence
it must have a load connected.
28. (7) Braking: Dynamic or rheostatic braking is
employed for electric locomotives. During the time
of braking, traction motors are disconnected from
supply and is connected to a dynamic resistance.
Now traction motors are acted as traction generator
because kinetic energy is converted into electrical
energy. The direction of current is reversed during
this period as before braking. Field current also
reverses as field winding is connected in series with
armature. Hence connections of field winding
should be changed such that current flows in it in
should
29. be changed such that current flows in it in same
direction as before braking. The output of generator
is given to grid resistance and it dissipates power
as heat. Due to friction between wheel and track, a
opposite torque is developed. As a result,
locomotive stops.
If connections of field winding is not
revesed, no braking will occure.
Dynamic resistance must be less than
critical resistance otherwise generator will not be
self exciting.
