On load tap changer In A.C. locomotive transformer & Air blast circuit breaker

Content • Introduction

• Block diagram of A.C. Locomotive

• Equipment of locomotive & their function

• Advantages

• Disadvantages

Introduction Locomotives in India consist

of electric and diesel locomotives.  Locomotives are also called locos or engines.

An electric locomotive is a locomotive powered by electricity from overhead lines, an on-board energy storage device such as a chemical battery or fuel cell.

Electricity is used to eliminate smoke and take advantage of the high efficiency of electric motors.

Equipment of locomotive & their function 1) Over head conductor : This is the over head conductor running along the that

through which high voltage a.c.(22 to 25 kv) is supplied from traction substation and fed to the locomotive.

2) Pantograph : It is a current collecting device mounted on the

roof of locomotive. It collects the required power from over head

conductor & feds to locomotive.

3) Circuit breaker : The circuit breaker is a protective device for

locomotive equipments it is mounted on the roof of locomotive.

The function of circuit breaker is to make the supply ON & OFF both in normal & faulty condition.

4) Loco Transformer The 25 KV single phase AC power supply of Over

head line 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.

A tap changer is a device fitted to power transformers for regulation of the output voltage to required levels.

This is normally achieved by changing the ratios of the transformers on the system by altering the number of turns in one winding of the appropriate transformer.

It regulates motor speed by varying voltage from input side of the transformer.

5) On load tap changer :

6) Rectifier : It is a rectifying unit which converts a.c. Into d.c.

Voltage required for a.c. series motors. Instead of using a bridge rectifier, it is possible to

use a thyrister. A thyrister is a kind of diode such that it allows current to flow when it receives a command through a third terminal.

7) Smoothing reactor : The smoothing reactor is used to make a.c. ripple

free d.c. available from rectifire and pure d.c. is given to d.c. series motor better performance.

8) D.C. Motors: Two or more number of motors receives filtered

d.c. & gives out required mechanical motive power which is transmitted to train wheel by direct or geared drive.

Train wheel move the train-mass linearly on the track.

Air Blast Circuit Breaker

This operates using high velocity blast of air which quenches the arc.

It consists of blast valve , blast tube & contacts.

Blast valve contains air at high pressure.

Blast tube carries the air at high pressure & opens the moving contact attached to spring.

Air should be kept clean & dry to operate it properly.

Air Blast Circuit Breaker :

Advantages Lower running cost of locomotives and multiple

units. Higher power-to-weight ratio, resulting in, Fewer locomotives  Faster acceleration  Higher practical limit of power  Higher limit of speed     Less noise pollution (quieter operation).     Lower power loss at higher altitudes.      Lack of dependence on crude oil as fuel.

Disadvantages The main disadvantage of electric traction is that

it involves a heavy initial expenditure for the power supply system.

Power break down for a short period may paralyse the whole system.

Electric traction system is bound only to electrified routes.

Significant cost of electrification. Increased maintenance cost of the lines. Overhead wires further limit the clearance in

tunnels.

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