Electric Traction System.ppt

Suresh Kamble,Electrical Dept.GPA
Block Diagram of A.C Locomotive
1. Overhead Contact wire
3. Circuit breaker
4. On-load tap changer
2. Pantograph
7. Smoothing choke
5. Transformer
8. D.C . Traction motor
Trolley Wires or Contact wire
Trolley wire or Contact wire
Trolley Wires or Contact wire
Contact wire
Trolley Wires
The trolley wire or contact wire must be suspended with
the minimum of sag
so that it remains practically horizontal.
So that the contact between the wire & current collector
may be maintained at high speeds.
This is achieved by which the trolley wire(contact wire) is
supported by another wire known a the “catenary” or
The catenary construction are different types
1. Single catenary construction.
2. compund catenary construction
Single catenary construction
Contact wire
Fig. Single catenary construction
A steel wire with seven or more strands supports the trolley wire
by means of droppers clipped to catenary & trolley wire at
equidistant horizontal intervals.
The span of catenary wire 45 to 90 metres with a sag of
from 1 to 2 metres for straight track.
Single catenary construction
Single catenary construction
The distance of droppers is between 3 to 5 metres
curved track the spans of shorter length are employed.
Such construction provides for speed upto 120 kmph.
 It is relatively cheaper.
 Less maintenance.
 Single catenary construction is considered suitable for
most light Weight a.c. system.
 Suitable for secondary routes where traffic density is
low & operating speeds are low.
Compound catenary construction
Catenary or messenger wire
Loop wire
Trolley wire
Fig. shows compund catenary construction
Employed for heavy current i.e where traffic density is high.
It consist of three wires.
1.The upper wire is catenary wire, which is insulated from the
supporting structure
2. The another wire known as intermediate catenary, is
supported by droppers clipped to both wires.
3. Third wire i.e trolley wire.
Compund catenary
Trolley wire is suspended from intermediate catenary by solid
wire loop droppers which are to slide vertically on the
intermediate wire & fixed the trolley wire.
The purpose of intermediate catenary, besides increasing the
current carrying capacity, is to provide for more uniformity in
The compound catenary is used on lines where speed ranges
is 190 to 224 kmph.
Current Collector
Current Collector
Current Collector
The current in the overhead
system is collected with the
help of sliding contact collector
mounted on the roof of the
The main requirement of current collector is that it should keep
Continuous contact with trolley wire at all speeds.
There are three types of current collector
1. Trolley collector
2. Bow collector
3. Pantograph collector.
Trolley Collector
Fig. Trolley wire section
1888 on a double wire conductor tramway.
This collector is used for Tramways & trolley buses & is
mounted on the roof of the vehicle contact with overhead wire.
It is made either grooved wheel or a sliding shoe carried at
the end of a light trolley pole attached to the top of the vehicle
& held in contact with overhead wire by means of a spring.
Trolley Collector
Experimental trolley bus in Berlin in 1882
1989 trolleybus design
The trolley collector is suitable for low speeds upto 32 kmph
Beyond this speed there is risk of its jumping off the overhead
contact wire particularly at points & crossing.
Bow Collector
Trolley Bus
Fig. Bow collector
It consist of two roof mounted trolley poles at the ends of which
is placed a light metal strip or bow, about 1 metre long for
current collection
Bow Collector
Collector strip is made of soft material
like copper, aluminum or carbon.
It never wear instead of trolley wire
as it is easy to replace collection
strip than trolley wire.
The bow collector also operates in the trailing position.
Hence, it requires provision of the either duplicate bows or
an arrangement for reversing the bow for running in the
reverse direction.
Bow collector is not suitable for railway work where speeds
up to 120 kmph and currents upto 3000A
Pantograph Collector
Fig show a diamond type single pan pantograph
Fig show a actual diamond type pantograph
The main function is to maintain link between overhead contact
wire & power circuit of the locomotive at varying speeds in
different climate & wind conditions on varying stiffness of
overhead equipments.
Pantograph Collector
A positive pressure has to be maintained at
all Times to avoid loss of contact & sparking.
But pressure must be as low as possible in
order to minimize wear of overhead contact
Fig show a pantograph collector
 It consists of a pantograph framework of steel tubing.
 The contact portion consists of a pressed steel pan fitted with
renewable copper wearing Strips which are forced against the
overhead contact wire by the upward direction of pantograph
 The pantograph can be raised or lowered from cabin by air cylinders.
Desirable Characteristics of Traction motor
The main requirements of electric motors used for traction work
1. Electric characteristics:
High starting torque
Simple speed control
Possibility of electric braking
Capacity of withstanding voltage fluctuations
Capability of withstanding temporary interruption of supply
Overload capability
Parallel running
Desirable Characteristics of Traction motor
2. Mechanical features:
Robustness & ability to withstand continuous vibrations.
ii. The weight of the traction motor should be minimum in
order to increase the pay load capacity of the vehicle.
iii. The traction motor must be small inn overall dimensions.
iv. The traction motor must be totally enclosed type,
to provide protection against dirt, dust, water, mud etc.
Traction motor
None of the motors can have all the desirable characteristics.
Some of the motors which finds application in traction are:
1. D.C series motors.
2. Single phase A.C series motors
3. Repulsion motors.
4. Three-phase Induction motors
5. Linear Induction motors
Suitability of D.C series motor for Traction
1. D.C series motor develops high torque at low speeds
& low torque at high speeds. This is the exactly the
requirement of traction units.
2. The field flux varies as the armature current, as in the
case of series motor, torque corresponding to the
given armature current. Therefore, is independent of
line voltage & thus unaffected by the variations in the
line voltages.
3. Commutating properties of series motor are also very
good as increases in the armature current as a result
of heavy load torque results in the decrease of
armature speed. This reduces the magnitude of e.m.f
induced in the coils under going commutation which
helps in achieving sparkless current collections
Suitability of D.C series motor for Traction
5. In case of dc series motor , upto 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.
6. Speed of dc series motor can be controlled by various methods.
7. Because of low time constant of field in case of series motor,
the field flux dies away in very short time the result back emf of
the motor cease with temporary interruption of supply.
Therefore, there is inrush of initial current on temporary
interruption of supply
Suitability of D.C series motor for Traction
8. The dc series motor is simple & robust in construction.
9. The dc series motor, owing to its characteristics, is most
suitable for urban & suburban services where high rate of
acceleration is essential.
Draw back
The main drawback of dc series motor are commutation
Which restricts speed, current & voltage. Therefore is a
risk of flash over & the brush gear requires considerable
Suitability of single phase a.c series motor for Traction
1. For a given KW rating ac series motor is 1.5 to 2 times in size &
weight of the corresponding dc series motor.
2. The construction cost of an ac series motor is much more than
of a dc series motor.
3. 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.
4. A.C single phase motor are not suitable for urban & suburban
services, it requires high acceleration.
However, single phase motors are extensively used for main
lines services.
Suitability of single phase a.c series motor for Traction
5. 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.
6. However, single phase ac series motor have better performance
on reduced supply frequency says 25 Hz. The higher frequency
results in higher leakage reactances & hence a relatively poor
power factor.
7. The maximum operating voltage for these motors is limited
to 400 volts
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.
Suitability of Three phase Induction motor.
With the development of thyristorised inverter circuits,
it has now been possible to invert the supply and obtain
a variable frequency supply which could be used for the
3- phase Induction motor & a very smooth speed control
can be obtained.
Power supply Arrangement
Since Indian Railways have decided to adopt 25kv, 50 Hz supply system
Following arrangements of power supply to various substations exist on Indian Railways
1. Power is purchased from supply authorities who are responsible
for the operation & maintenance of 132/110 kv transmission lines
& grid substations upto 25 kv out - going terminals of substation.
However 25 kv feeder circuit breaker is controlled from remote
control centre by traction power controller. This arrangement
enables railway authorities to pay full attention to operate &
maintain traction service which is their prime responsibility.
2. All the 132 kv & 25 kv equipments of substation is owned,
installed operated & maintained by the supply authorities.
However 25 kv circuit breaker are owned, installed, operated
& maintained by the railway authorities.
Power supply Arrangement
To have better control & expeditions execution of electrification
Programme, it was considered necessary that the railways should
own , install, operate &maintain all the 132/110 kv equipments
at the substation.
Supply authorities will give only voltage supply of 132/110 kv at
the substation
Constituents or Parts of Power supply system
Various elements of power supply system are:
1. Sub-station.
2. Feeding posts.
3. Sectioning & paralleling posts.
4. Sub-sectioning & paralleling posts.
5. Sub-sectioning posts.
6. Elementary sections.
Fig. layout of a typical traction sub-station.
Feeding post

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