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POWER SYSTEMS SEMINARELECTRIC TRACTION

By MOIDEEN THASHREEF

SARANG KRISHNAMOHAMMED MUBARAK

MUNEEB PP

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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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WHAT IS ELECTRIC TRACTION?

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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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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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

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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Electric TractionSystems

Direct Electric powerLocomotives

Self-containedLocomotives

AC Driven DC Driven Petrol Electric Driven Battery Driven

Diesel Electric Driven

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SYSTEMS OF TRACK ELECTRIFICATION

DC SystemComposite System AC System

Single Phase System Three Phase System

Single Phase Three Phase System Single Phase DC System

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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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DC TRACTION SYSTEM AND ELECTRIFICATION

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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

13SCHEMATIC OF MOTOR GENERATOR SUPPLY SETUP

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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.

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DC ELECTRIFICATION SYSTEMDC 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

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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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AC TRACTION SYSTEM AND ELECTRIFICATION

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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 usedReduced weight of support structureReduced capital cost of electrification

AC TRACTION

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COMPONENTS OF AN A.C LOCOMOTIVE

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AC ELECTRIFICATION SYSTEM

AC electrification can be done in different ways

Single Phase System Three Phase System

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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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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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• 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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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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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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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 effect2.Produces Interference with telecommunication lines

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SYSTEM ELECTRIFICATION• CATENARY• PANTOGRAPH• CIRCUIT BREAKERS• ON LOAD TAP CHANGER • TRANSFORMER• RECTIFIERS• SMOOTHING REACTORS

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CIRCUIT DIAGRAM OF A TRACTION

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suspended with minimum of sag so that contact between the trolley wire and current collector can be maintained at higher speeds.

Trolley Wire

Trolley wire or contact wire

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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.

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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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 CollectorBow Collector Pantograph Collector

Current Collector

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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 bowPantograph 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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PANTOGRAPH DESIGN

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WHY USE ELECTRIC TRACTION METHOD ?

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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.

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DISADVANTAGES OF ELECTRICAL TRACTION SYSTEMS

High initial expenditureExtra equipment is required for brakingFailure of electrical supply is a major problemThe electrified tracks are needed for running the electrical

locomotivesInterference with communication systems (telephone or

telegraph ) is a problem

CONCLUSION

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REFERENCE• UTILIZATION OF ELECTRIC POWER AND ELECTRIC TRACTION – J.B

GUPTA• WWW.WIKIPEDIA.COM• WWW.ELECTRICAL4U.COM• WWW.IRFCA.ORG• WWW.RAILWAY-TECHNICAL.COM