ELECTRIC TRACTION By Mohammad Mukheem Basha ASSISTANT PROFESSOR

ELECTRIC TRACTION By Mohammad Mukheem Basha ASSISTANT PROFESSOR (EEE) NSAKCET

SYSTEMS OF TRACK ELECTRIFICATION Composite systems: Ø Efforts has been made to combine the advantages of dc/ac and 3 -phase/1 -phase systems and composite systems have been evolved. Ø The single phase ac systems is preferable from the viewpoint of the distribution and contact wire system. Ø It can be converted into either three phase ac or dc at low voltage in the locomotive. Composite system classification: At present there are two composite systems: Ø Kando system or single phase to three phase system. Ø Single phase ac-to-dc system

Kando system or single phase to three phase system: Ø In this system single phase high voltage ac system is employed for distribution purposes and three phase induction motors for getting the necessary motive power. Ø This have the advantage of low cost of single phase overhead distribution system together with desirable characteristics of three phase induction motors. Ø Voltage used for distribution network: 15 k. V at 50 Hz.

WHATS INSIDE THE LOCOMOTIVE : Ø The locomotive carries a phase converter for converting 1 -phase supply into 3 -phase supply at relatively low frequency. Ø The development of SCR used as inverter has made possible to get variable low frequency supply(1/2 to 10 Hz) at which induction motor develops high starting torque without drawing excessive current from the system and speed control is also conveniently obtained by varying the supply frequency.

SINGLE PHASE AC-TO-DC SYSTEM: Ø In this system the advantages of the two systems are combined together by employing high voltage ac single phase system for overhead distribution and dc series motors for the necessary drive so that high efficiency of the ac distribution system is obtained together with the desirable characteristics of dc series motors. What's inside the locomotive: Ø The locomotive carries transformer and converting machinery to step down the voltage and convert into dc.

Ø Voltage employed for overhead distribution system: 25 k. V at 50 Hz Ø This system is adopted in all the areas of major traffic density on main lines. Ø It has been decided to adopt this system of traction for track electrification in our country and this is being installed on sections which are electrified

INTRODUCTION Definition: Act of drawing or state of being drawn; propulsion of vehicle is called the traction. (Action of drawing or pulling something over a surface, especially a road or track) and the system of traction involving the use of electricity is called the electric traction system.

Various systems of traction • • • Steam engine drive Internal combustion engine drive Diesel electric drive Battery electric drive Straight electric drive

Classification of traction They are classified broadly into two groups i. The traction systems which do not involve the use of electricity at any stage and called the non -electric traction systems such as steam engine drive, internal combustion engine drive etc. ii. The traction systems which involve the use of electricity at some stage or the other, and called the electric traction systems such as diesel electric drive , straight electric drive

Electric traction classification Systems of electric traction may further be subdivided into two main groups: 1. The group consisting of vehicles which receive electric power from a distributing network fed at suitable points from either a central power station or substations suitably spaced such as tramways, trolley buses, electric railways etc. This group is further sub classified into: Ø Systems operating with dc such as trolley buses, tramways railways. Ø Systems operating with ac, such as railways. 2. The group consisting of self contained locomotives such as diesel electric trains and ships, petrol electric trucks and lorries, battery driven road vehicles. This group is further sub classified into: Ø Diesel electric trains and ships Ø Petrol electric trucks and lorries. Ø Battery driven road vehicles

Direct steam engine drive Ø The steam engine drive used to be widely employed for railway work. Ø In this type of drive , the reciprocating steam engine is invariably used for getting the necessary motive power because of Ø Its inherent simplicity , simplified maintenance, the simplicity of connections between the cylinders and the driving wheels and easy speed control.

Ø Type of locomotive: - Self contained(not tied to any route). ADVANTAGES: Ø It causes no interference to the communication lines running along the track. Ø The capacity is very high in comparison to direct internal combustion engine drive, and battery electric etc. Ø Initial investment required is low in comparison to that of electric drive as no overhead structure , distribution system and power generation is required. Ø It is cheap for low density traffic areas and in initial stages of communication rail.

DRAWBACKS: Ø Adequate supplies of feed water at regular intervals is required. Ø The overload capacity of steam locomotive is limited. Ø Steam locomotive cannot be put into service at any moment as time is required for steam raising. Ø Owing to smoke, steam engine drive cannot be employed for underground railways.

Steam electric drive Ø A few locomotives employing steam turbine for driving a generator used for supplying current to electric motors have been built for experimental purposes. Ø Such locomotives have not been put into general use because of some mechanical difficulties and complicatios.

Internal combustion engine electric drive Ø In this drive the reduction gear and gearbox are eliminated as the diesel engine is to drive the dc generator coupled to it at a constant speed. Ø This type of drive has found considerable favour for railway work and locomotives of this type are becoming widely used.

ADVANTAGES: Ø No modification of existing track is required for conversion from steam to diesel engine. Ø Initial cost is low as no overhead structure distribution system and equipment is required. Ø It can be put into service at any moment. Ø The locomotive and train is self contained unit and, therefore, it is not tied to any route.

DISADVANTAGES: Ø Its overload capacity is limited as diesel engine cannot be overloaded. Ø Life of the diesel engine is comparatively shorter. Ø Running and maintenance costs are more.

Petrol Electric Traction Ø This system has been used in heavy lorries and buses. Ø Due to electric conversion it provides a very fine and continuous control which makes the vehicle capable of moving slowly at an imperceptible speed and creeping up the steepest slope without throttling the engine

Battery electric drive Ø In this drive the locomotive carries the secondary batteries which supply power to dc motors employed for driving the vehicle. Ø Such drive is well suited for frequently operated service such as for local delivery of goods in large towns with maximum daily run of 50 -60 km, shunting and traction in industrial works and mines. Ø Battery vehicles are started by series-parallel grouping of batteries-in parallel for starting and running at the speed up to half maximum speed and in series for running at full maximum speed.

ADVANTAGES: Ø Battery driven vehicle is easy to cntrol and very convenient to use. Ø Low maintenance cost and absence of fumes.

DISADVANTAGES: Ø Major limitation of this type of drive is the small capacity of the batteries and the necessity for frequent charging, speed range is also limited.

ELECTRIC DRIVE: Ø The drive of this type is most widely used. Ø In this system of traction the vehicle draws electrical energy from the distribution system fed at suitable points from either a central power station or substations.

ADVANTAGES: Ø It is the cleanest of all other types of systems of traction. Due to this only it is ideally suitable for the underground and tube railways. Ø The electric locomotive can be put into service immediately. Ø It has got advantage of rapid acceleration and braking retardation.

DISADVANTAGES: Ø The greatest disadvantage of electric traction is that it involves a heavy initial expenditure for the power supply system and, in the case of tramways, for the track rails and electrical return system, in addition to the cost of vehicles, depots, etc. Ø Failure of power supply for a few minutes may paralyze the whole system. Such occurrence is, however, rare nowadays due to increased reliability of power supply. Ø Electric traction system is tied up to only electrified routes.

Ideal traction system requirements Ø High starting tractive effort in order to have rapid acceleration. Ø Self contained and compact locomotive or train unit so that it may be able to run on any route. Ø Equipment capable of withstanding large temporary overloads. Ø Minimum wear on the track. Ø Braking should be such that minimum wear is caused on the brake shoes, and if possible the energy should be regenerated and returned to the supply during braking period. Ø Equipment required should be minimum, of high efficiency, and low initial and maintenance cost. Ø No interference to the communication lines running along the track. Ø Easy speed control. Ø It should be pollutions free.