Traction Control of Electric Locomotives

By:- Kishore Shinde Saideep Surve Ramindar Singh Sood

INTRODUCTION

• Driving forward of vehicle is called Traction and the system, which employs this type of mechanism is called Traction system

• classified broadly into two groups namely:

(1)non-Electric traction systems

(2)Electric traction systems

Requirements of an Ideal Traction System

• High starting pulling effort in order to have rapid acceleration.

• Equipment capable of withstanding large temporary overloads for short periods.

• The locomotive should be self contained and able to run on any route.

• Capability of withstanding voltage fluctuations and temporary interruption of supply.

• Parallel running usually more than one motor (two or four motors ) should be possible.

ADVANTAGE OF ELECTRIC TRACTION

. Cheapness. It is cheapest method of all other methods of traction.

• Cleanliness. It is free from smoke and flue gasses• Maintenance cost. Maintenance and repair cost is about

50% of steam traction system.• Starting time. It can be started without loss of time.• High starting torque. This system uses of d.c. and a.c.

series motors which has a very high starting torque. • Braking. In electric traction , regenerative breaking is

used which feeds back 40%of the energy.• Saving in high grade coal. No coal is required for electric

traction.

DISADVANTAGE OF ELECTRIC TRACTION

• Higher initial expenditure.• Failure of supply is a problem.• Additional equipments are required for

breaking purposes.• The electrically operated vehicles have to

move only on electrified track.• Interference with telegraphs and telephone

lines.

COMPONENTS OF AN A.C LOCOMOTIVE

• CATENARY - This is the overhead wire of special cross-section. • PANTOGRAPH - This is a device used for collecting current from the

catenary i.e. the over head lines.• CIRCUIT BREAKERS - The function of circuit breaker is to disconnect

the engine from the line side in case of some fault • ON LOAD TAP CHANGER - On load tap changer is used for varying the

output voltage for controlling the speed of motor • TRANSFORMER - A tap changing transformer is installed in the

locomotive for stepping down the voltage according to the requirement of traction motors

• RECTIFIERS - Semiconductor rectifiers are used for conversion of A.C power into D.C power

• SMOOTHING REACTORS - Any ripples found on the output side of the rectifier are eliminated by the smoothing reactor fitted after the rectifier.

SEPEX

Short form of SEParate EXcitement of traction motors where the armature and field coils of an electric motor are fed with independently controlled current. This has been made much more useful since the introduction of thyristor control where motor control can be much more precise.  SEPEX control also allows a degree of automatic wheel slip control during acceleration

THYRISTOR CONTROL

Schematic of AC Electric Locomotive Power System with Thyristor Control and Separately Excited DC Motors

DC Choppers

Thyristor Control Circuit for DC Supply to DC Motors

AC TRACTION MOTOR

AC Locomotives with AC Drive

Schematic of Single Phase AC Supply Powering 3-Phase AC Motors

AC Locomotives with DC Drives

Schematic of AC locomotive with Tap Changer Control of Transformer Output

DC TRACTION MOTOR

It consists of two parts, a rotating armature and a fixed field.

• The fixed field consists of tightly wound coils of wire fitted inside the motor case

• The armature is another set of coils wound round a central shaft.

• The armature is connected  to the field through "brushes" which are spring loaded contacts pressing against an extension of the armature called the commutator.

The DC Traction Motor: How it Drives the Axle

How a DC motor drives the axle through a pinion and gearwheel

DC Resistance Control

Simplified DC Traction Motor Power Control Circuit

DC Power Circuit

Schematic of Simple DC Traction Motor Power Control Circuit

Field Weakening

DC Traction Motor with Field Weakening Circuit

Braking in traction motors

• Dynamic Braking: where the motors become generators and feed the resulting current back.

• It classified into two categories: 1 Plugging

2. Rheostatic Braking 3. Regenerative Braking

• PLUGGING: Generally plugging is applied by changing the phase sequence of the three phase induction and synchronous motor

Rheostatic Braking

• The motors become generators and feed the resulting current into an on-board resistance.

• When the driver calls for brake, the power circuit connections to the motors are changed from their power configuration to a brake configuration and the resistors inserted into the motor circuit.  As the motor generated energy is dispersed in the resistors and the train speed slows, the resistors are switched out in steps, just as they are during acceleration.

Regenerative Braking

• the motors become generators and feed the resulting current back into the supply system

• a train could use its motors to act as generators and that this would provide some braking effect if a suitable way could be found to dispose of the energy.

• Trains were designed therefore, which could return current, generated during braking, to the supply system for use by other trains.

CONCLUSION

• no single motor is ideal for traction purposes. But; DC

Series Motors are most suitable for this work • Power Electronics have been resorted to in a major way as

in case of thyristor control.• Different types of braking for the traction system was

studied.