ELECTRICAL TRACTION SYSTEM

—Introduction :

Electrical traction means the electrical systems related with the

train. E.g. Electrical supply system, electrical motors (drives),

signaling systems, various controls and equipment etc.

Different drives can be used for traction (e.g. steam engine drive,

diesel engine drive, electric drive)

—1.Electric Traction - 1881:

After many decades of satisfactory performance, the steam engines were to give way to more modern locomotives.  The year 1881 saw the birth of the first electric Railway run by a German Engineer Werner Van Siemens using both the rails to carry the current.  Finding this a little too dangerous, Siemens soon adopted the overhead electric wires.  Electric locomotives today raun on Rail roads in many countries.

2.Diesel Traction - 1912:

The diesel engine was invented in the year 1893, by a young German Engineer, called Rudolf Diesel.  But it was only nineteen years later, that the first Diesel locomotive came into existence. 

Since then, diesel traction has grown from strength to strength.  Over 89,000 Diesel locomotives have been built in the world so far, the General Motors, USA alone contributing to as many as 56,000 Locomotives.

—3.Block diagram of A.C. Electric Locomotive :

—Overhead equipment collects current through sliding contact by means of pantograph.

—Tap changer is used to vary the output voltage by which speed of traction motors can be controlled. Transformer is used to reduce high voltage of OHE to the utilization level.

—Air circuit breaker is provided on the roof of the locomotive and its main function is to disconnect the locomotive from high voltage supply.

—4.—Desirable characteristics of traction

motors :

—1). Suitable speed torque characteristic – speed torque characteristic of traction motor should match with the requirement of traction duty

—2). Parallel running – More than one motors are required for  traction purpose, therefore, these motors should be capable of operating in parallel for  which they should have identical characteristics.

—3). Overload capacity – Motor selected for traction purpose should have sufficient overload capacity.

—4). High efficiency – Motor selected for traction duty should have high mechanical and electrical efficiency.

—5). Speed control – Simple speed control facility

should be there to control the traction motor

—6). Accessibility of electric braking – Rheostatic and regenerative braking should be easily possible with the traction motor

—7). Voltage fluctuations – Traction motors should be capable of withstanding voltage fluctuations without any harmful effect on their performance.

—5.Braking:

Generally braking is classified into two types in the traction.

A). Electrical braking.

Plugging

Rheostatic or dynamic braking.

Regenerative braking.

B). Mechanical braking.

Compressed air brakes

Vacuum brakes

Hydraulic brakes

—6.Requirements of braking:

1. The braking should be simple and reliable in action

2. The braking should be smooth so as to avoid damage of  goods.

3. Maintenance needs should be minimum.

4. The braking force applied to each axle should be proportional to axle load so as to obtain uniform deceleration.

—7.Power supply for electric traction :

—Electric trains in India first introduced in Bombay sub urban services in 1925 and in madras in 1931. at that time  the system adopted was 1500v dc.

—

— In earlier days many of the systems used for electrification of railways in India and other countries such as America, France Hungary etc.

8.—High voltage ac supply

Arrangement of power supply in India are as follows:

1). The power is purchased from the authorities who are        responsible for the operation and maintenance of 220/132 transmission lines up to 25 kv outgoing terminals of substations. How ever  25 kv ckt breaker  is controlled from remote control center by Tpc.

2). The 220/132 kv equipment is maintained by the transmission authorities and 25 kv breakers are owned and maintained by the railway authorities.

9.—Requirements/Characteristics of an ideal traction system :

1). Speed control should be easy.

2).The locomotive should be capable to run on any route.

3). It should have rapid acceleration at start.

4).The wear and tear of brake shoes and track should be      minimum.

5). Braking should be possible without excessive wear on brake shoes,

6). It should have sufficient overload capacity for short periods.

7). Interference with the communication lines should be as low as possible.

8). Correction cost and running cost should be as low as possible

10.Loco Transformer:

 
1. This is a main transformer of locomotive. The 25 KV single phase AC power supply of OHE is fed to the winding of regulating transformer through main bushing. The winding is equally divided into 32 taps. These taps are connected to tap changer.

11.Traction transformer:

There are two traction transformer connected in parallel of same rating for the purpose of reliability the rating of transformer  are as follows

Capacity          : 25 KV.

Frequency       : 50 Hz

taps on HT      : 32 taps

cooling            :forced oil & air

12.—Arno Converter :

Arno converter is a device which convert single phase AC in to three phase AC.

The three phase supply needed for the three phase induction motors which used in blowers, exhausters an oil pumps. To supply three phase power to three phase induction motors arno converter is used.

Arno converter is rotating device.

—13.Transmission Path :

Under ground telecommunication trunk cable is provided for transmitting the signals from and to the Remote Control Centre (RCC) and the controlled Remote Terminal Units (RTU). Three pairs of conductors (one pair for send one pair for receive and the third as spare) from this cable are made available for remote control operation.