SUMMER INDUSTRIAL TRAINING

ON

Failures of armature coils in DC Machines

2011-12

ELECTRIC LOCO SHED, KANPUR

Submitted to :- Submitted by:-

Er. S.K. Pandey \

ACKNOWLEDGEMENT

There are many people have helped from the beginning till the completion of my project during

my industrial training visit in the Electric Loco Shed, Kanpur.

It is with a great sincerity, I convey my heartfull gratitude to my guide Supervisor, Er. Mohd.

Israr, for his excellent guidance, valuable advice and ample co-operation throughout the

training. It is a proud privilege to have availed of the opportunity of guidance.

I am thankful to Er. S.K.Pandey too, for their excellent cooperation during my training for the

proper response of the machine. I am grateful to all the railway employees, who gave their

contribution to make this report.

EC branch (final year)

Certificate

This is to certify that

has completed their Industrial Training during the academic year 2011-

2012 as partial fulfillment of B.Tech. (Electronics and communication)

course.

DATE:- Er. S.K. Pandey

SECTION ENGINEER

ELECTRIC LOCOSHED, KANPUR

History of rail transport in INDIA

History of rail transport in India

The history of rail transport in India began in the mid-nineteenth century. In 1849,

there was not a single kilometer of railway line in India. By 1929, there were

41,000 miles of railway line serving every district in the country. At that point of

time, the railways represented a capital value of some 687 millions sterling, and

they carried over 620 millions of passengers and approximately 90 million tons of

goods each year.

Under British rule

A rail system in India was first proposed in 1832 in Madras but it never materialized. In the

1840s, other proposals were forwarded to the British East India Company who governed India.

The Governor-General of India at that time, Lord Hardinge deliberated on the proposal from the

commercial, military and political viewpoints. He came to the conclusion that the East India

Company should assist private capitalists who sought to setup a rail system in India, regardless

of the commercial viability of their project.

In 1832 a proposal was made to build a railroad between Madras and Bangalore, and in 1836 a

survey was conducted for this line.

On September 22, 1842, British civil engineer Charles Blacker Vignoles, submitted a Report on

a Proposed Railway in India to the East India Company. By 1845, two companies, the East

Indian Railway Company operating from Calcutta, and the Great Indian Peninsula Railway

(GIPR) operating from Bombay, were formed. The first train in India was operational on

December 22, 1851, used for the hauling of construction material in Roorkee. A few months

later, on April 16, 1853, the first passenger train between Bori Bunder, Bombay and Thane

covering a distance of 34 km (21 miles) was inaugurated, formally heralding the birth of railways

in India. And then the first passenger railway line in North India opened from Allahabad and

Kanpur on March 3, 1859. This was followed in 1889, by the Delhi - Ambala - Kalka line.

The British government encouraged the setting up of railways by private investors under a

scheme that would guarantee an annual return of 5% during the initial years of operation. Once

completed, the company would be passed under government ownership, but would be operated

by the company that built them.

The East Indian Railway Company's Chief Engineer George Turnbull built the first railway from

Calcutta (the then commercial capital of India). It opened for passenger traffic from Howrah

station to Hooghly on 15 August 1854. The 541 miles (871 kilometres) to Benares opened to

passenger traffic in December 1862.

Start of Indian Railways

(fig above- Chhatrapati Shivaji Terminus, Mumbai is the busiest railway station in India. It

is also a World Heritage Site)

Following independence in 1947, India inherited a decrepit rail network. About 40 per cent of

the railways then passed through the newly independent republic of Pakistan. A large number of

lines had to be rerouted through Indian territory, and new construction had to be undertaken.

In 1951, the rail networks were abandoned in favour of zones. A total of six zones came into

being in 1952. As India developed its economy, almost all railway production units started to be

built indigenously. Broad Gauge became the standard, and the Railways began to electrify most

lines to AC.

In 1985, steam locomotives were phased out. Under Rajiv Gandhi, reforms in the railways were

carried out. In 1987, computerization of reservation first was carried out in Bombay and in 1989

the train numbers were standardized to four digits. In 1995 the entire railway reservation was

computerized through the railway's intranet.

ELECTRIC LOCO SHED, KANPUR

The Electric loco shed, Kanpur was established during the year 1965 for homing

11 locomotives. This shed was commissioned primarily to meet the requirement of

passenger and goods traffic over Indian railways. At present the shed has been

expended suitably to home 176 loco motives for hauling, passenger and goods

traffic.

The shed is responsible for carrying out monthly inspection schedule.

Further the unscheduled repairs to electric locos of CNB shed & other sheds are

being done as per requirements of RDSO organization & HQs instructions. All modification & special maintenance instructions, approved by RDSO & N.Rly.

Hd.Qtr., are also carried out as per the guide lines being issued from time to time.

ELECTRIC LOCO MAINTENANCE SHED

Electric Loco Shed maintains locomotive for utilization in freight and passenger

train. All the miner and major inspection are carried out in the shed on a regular

schedule specified by RDSO (Research Design Standard Organization). Monthly

schedule are done at an interval of 45 days and major schedule are carried out after

18 months.

QUALITY MANAGEMENT

Through this quality manual, ELS intents to provide a transparent quality system to

assure its customer of ELSs the capability in maintaining in electric locomotives to highest standard.

This quality manual has been written and develop in accordance with international

quality system. Standard ISO-9001:2000. The manual is used as a refreshed

document by:

Employees of ELS to practice the quality system.

Customers to have confidence in the capability of ELS to meet quality requirements on regular basis.

Internal as well as external auditors for verification of compliance of the quality system.

Different Equipments in an Electrical Locomotive

1) Pantograph

It is pneumatically operated equipment mounted on the roof for collection of current from

overhead wire.

(fig above- Assymetrical Z-shaped Pantograph)

2) Main Transformer

It is an autotransformer which is utilized for drawing various grades of voltage required for

operation of locomotive.

3) Rectifier

This unit consists of rectifier diodes connected in bridge for conversion of AC current to DC

current.

4) Traction Motor

The traction motor is one of the most important equipment in the locomotive which transmits

power to wheels for moving the trains.

IR use HITACHI (HS-15250) DC SERIES Traction Motor.

5) Auxiliary Circuit

This Circuit is three phase 415 volts which supplies current to various three phase induction

motors used for driving blowers for forced air cooling of major equipments like transformer,

rectifier, smoothing reactor and traction motor. This 3 phase line voltage is supplied by either

static converter or Rotary ARNO Converter.

6) ARNO Converter

Arno converter , is specific-duty machine for conversion of a single-phase supply into a three-

phase supply. While the electric traction supply is standardized as single-phase A.C. supply, a

three-phase supply is needed on locomotives for driving certain auxiliary equipments. The

function of the Arno converter is to convert the incoming single-phase supply in to a three-phase

supply for the auxiliaries.

ARNO Converter is of vertical construction and has a flexible mounting .The machine is of

robust mechanical construction to withstand the several vibrations encountered on locomotives.

(fig above- ARNO Converter)

7) Battery

All trains are provided with a battery to provide start up current and for supplying essential

circuits, such as emergency lighting, when the line supply fails. The battery is usually connected

across the DC control supply circuit.

8) Camshaft

Most DC electric traction power circuits use a camshaft to open or close the contactors

controlling the resistances of the traction motor power circuit. The camshaft is driven by an

electric motor or pneumatic cylinder. The sound of this camshaft stepping can be heard under

many older (pre electronics) trains as they accelerate.

9) Chopper Control

A development in electric traction control which eliminates the need for power resistors by

causing the voltage to the traction motors to be switched on and off (chopped) very rapidly

during acceleration. It is accomplished by the use of thyristors and will give up to 20%

improvement in efficiency over conventional resistance control.

(fig above- DC CHOPPER CONTROL)

10) Circuit Breaker

An electric train is almost always provided with some sort of circuit breaker to isolate the power

supply when there is a fault, or for maintenance.

11) Contactor

Similar to a relay in that it is a remotely operated switch used to control a higher power local

circuit.

12) Converter

Generic term for any solid state electronic system for converting alternating current to direct

current or vice versa. Where an AC supply has to be converted to DC it is called a rectifier and

where DC is converted to AC it is called an inverter.

13) Cooling Fans

To keep the thyristors and other electronic power systems cool, the interior of a modern

locomotive is equipped with an air management system, electronically controlled to keep all

systems operating at the correct temperature. The fans are powered by an auxiliary inverter

producing 3-phase AC at about 400 volts.

(fig above- Traction motor cooling blower motor and impeller covered by a hood)

14) Rectifier

A converter consisting of thyristors and diodes which is used to convert AC to DC. A modern

locomotive will usually have at least two, one for the power circuits and one or more for the

auxiliary circuits.

15) 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.

Voltages used for electric traction in India

Voltages used are :-

1.5kV DC and 25kV AC for mainline trains.

(fig above- Simple Cartenery feeding system)

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 DC and AC 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.

DC

ELECTRIC MOTOR

DC Electric motor

An DC electric motor converts electrical energy into mechanical energy.

Most electric motors operate through the interaction of magnetic fields and current-carrying

conductors to generate force. The reverse process, producing electrical energy from mechanical

energy, is done by generators such as an alternator or a dynamo; some electric motors can also be

used as generators, for example, a traction motor on a vehicle may perform both tasks. . Electric

motors and generators are commonly referred to as electric machines.

Electric motors are found in applications as diverse as industrial fans, blowers and pumps,

machine tools, household appliances, power tools, and disk drives. They may be powered by

direct current (e.g., a battery powered portable device or motor vehicle), or by alternating current

from a central electrical distribution grid or inverter. The smallest motors may be found in

electric wristwatches. Medium-size motors of highly standardized dimensions and characteristics

provide convenient mechanical power for industrial uses. The very largest electric motors are

used for propulsion of ships, pipeline compressors, and water pumps with ratings in the millions

of watts. Electric motors may be classified by the source of electric power, by their internal

construction, by their application, or by the type of motion they give.

The physical principle of production of mechanical force by the interactions of an electric current

and a magnetic field was known as early as 1821. Electric motors of increasing efficiency were

constructed throughout the 19th century, but commercial exploitation of electric motors on a

large scale required efficient electrical generators and electrical distribution networks.

Some devices convert electricity into motion but do not generate usable mechanical power as a

primary objective and so are not generally referred to as electric motors. For example, magnetic

solenoids and loudspeakers are usually described as actuators and transducers, respectively,

instead of motors. Some electric motors are used to produce torque or force.

(fig above- Equivalent circuit of DC Motor)

Principle of operation

In any DC electric motor, operation is based on simple electromagnetism. A

current-carrying conductor generates a magnetic field; when this is then placed in

an external magnetic field, it will experience a force proportional to the current in

the conductor, and to the strength of the external magnetic field. As you are well

aware of from playing with magnets as a kid, opposite (North and South) polarities

attract, while like polarities (North and North, South and South) repel. The internal

configuration of a DC motor is designed to harness the magnetic interaction

between a current-carrying conductor and an external magnetic field to generate

rotational motion.

Look at a simple 2-pole DC electric motor (here red represents a magnet or

winding with a "North" polarization, while green represents a magnet or winding

with a "South" polarization).

RED- North Polarization

GREEN- South Polarization

(fig above- common motor layout)

Every DC motor has six basic parts -- axle, armature, stator, commutator, field

magnet(s), and brushes. In most common DC , the external magnetic field is

produced by high-strength permanent magnets. The stator is the stationary part of

the motor -- this includes the motor casing, as well as two or more permanent

magnet pole pieces. The armature (together with the axle and attached

commutator) rotates with respect to the stator. The armature consists of windings

(generally on a core), the windings being electrically connected to the commutator.

The above diagram shows a common motor layout -- with the rotor inside the

stator (field) magnets.

DC Motor Rotation

DC electric motor-

When the coil is

powered, a magnetic

field is generated

around the

armature. The left

side of the armature

is pushed away from

the left magnet and

drawn toward the

right, causing

rotation.

The armature

continues to rotate.

When the armature

becomes horizontally

aligned, the

commutator reverses

the direction of

current through the

coil, reversing the

magnetic field.

The process then

repeats.

(fig above- DC Motor Rotation)

HISTORY OF DC MOTOR

The basic principles of electromagnetic induction were discovered in the early 1800's by Oersted,

Gauss, and Faraday. By 1820, Hans Christian Oersted and Andre Marie Ampere had discovered

that an electric current produces a magnetic field. The next 15 years saw a flurry of cross-

Atlantic experimentation and innovation, leading finally to a simple DC rotary motor. A number

of men were involved in the work, so proper credit for the first DC motor is really a function of

just how broadly you choose to define the word "motor."

Armature

An Armature generally refers to one of the two principal electrical components of an

electromechanical machinegenerally in a motor or generator, but it may also mean the pole

piece of a permanent magnet or electromagnet, or the moving iron part of a solenoid or relay.

The other component is the field winding or field magnet. The role of the "field" component is

simply to create a magnetic field (magnetic flux) for the armature to interact with, so this

component can comprise either permanent magnets, or electromagnets formed by a conducting

coil. The armature, in contrast, must carry current so it is always a conductor or a conductive

coil, oriented normal to both the field and to the direction of motion, torque (rotating machine),

or force (linear machine). The armature's role is twofold. The first is to carry current crossing the

field, thus creating shaft torque in a rotating machine or force in a linear machine. The second

role is to generate an electromotive force (EMF).

In the armature, an electromotive force is created by the relative motion of the armature and the

field. When the machine is acting as a motor, this EMF opposes the armature current, and the

armature converts electrical power to mechanical torque, and power, unless the machine is

stalled, and transfers it to the load via the shaft. When the machine is acting as a generator, the

armature EMF drives the armature current, and shaft mechanical power is converted to electrical

power and transferred to the load. In an induction generator, these distinctions are blurred, since

the generated power is drawn from the stator, which would normally be considered the field.

FAILURES of

Armature Coils in

DC machines

Failures of Armature in DC machines :-

1 Armature Earth.

2 Armature BBCR.

3 Armature Cone Burnt.

4 Armature Band Fail.

5 Armature Evolutes Burnt.

6 Roker lead cut.

7 Carbon Broken.

8 Arc Horn.

9 B. Box Insulator Broken.

10 Pinion End Shaft Broken.

11 Pinion Teeth Broken.

12 Armature Locking Bolt Broken.

13 Dirt and Corrosion.

14 Armature Windings Burnt.

Armature Earth

If armature insulation gets deteriorated or damaged or due to any short circuiting of

wires causes Armature to get Earth.

This can Damages the Armature commutator segments as large amount of current

flows through it.

Armature BBCR

In this failure mode, there were inter-turn shorts between upper and lower layer of

the Windings.

These shorts usually occur in the commutator Riser because that was the location

where the conductors in the upper and lower layer crossed each other and further

where the conductors were twisted through 90 degree for insertion in the segments

slots. Strengthening of the insulation wrapper over the layers and on individual

conductors end reduce the failure role significantly.

(fig- BBCR)

Armature Cone Burnt

In this failure mode the PTF insulation band at cone side of the motor got damaged

due to excessive temperature or due to any other cause. This causes the rotor

windings to be short circuited and hence causes failure of rotor windings.

( Fig- Cone burnt)

Armature Band Fail

In this failure, the PTFE band gets damaged due to some mishandling or rupture

inside the motor. This effects the normal operation of the armature. It should be

smooth for the uniform movement of the armature.

(fig PTFE Band)

Armature Evolutes Burnt-

In this failure, when Evolutes tubes get burnt due to some cause, the armature run

forward and hits the stator thus it damages the armature.

(fig Evolutes tubes of Armature )

Carbon Broken

In this failure if the carbon get ruptured or gets damaged then it cause the failure in

the motor as then uneven amount of current gets distributed in the armature.

To avoid this failure, carbon must be checked at regular intervals.

Carbon length must not be less than 25 mm for the normal operation of the

armature.

(fig above- Carbon brushes )

Arc Horn Broken-

In this failure, if arc horn gets broken, it causes the large surge voltage across the

Armature which results in the armature failure.

Arc horn prevents the Surge voltage.

They pass the large insulation voltage into the earth.

(fig above- Arc Horn )

B. Box Insulator Broken

In this failure, if the Brush Box insulator gets broken then it causes following

results:-

1. Brush box falls onto the armature which damages the commutator segments.

2. Current starts to flow in the body of the TM, resulting in failure.

Pinion Teeth Broken

In this failure, Broken pinion disturbs the traction movement of the loco.

As Pinion is responsible for the gear to move which provides the traction motion.

(fig above- Broken Pinion )

Armature Locking Bolt Broken -

In this failure, Armature locking bolt gets broken due to over use. This causes

armature to fall and damages the Armature pinion shaft or pinion teeth.

(fig above- Armature Locking BOLT )

Dirt and Corrosion

Armature suffers excessive heat or vibration due to accumulation of dirt and

corrosion.

Wipe, brush, vacuum or blow accumulated dirt from the frame and air passages of

the motor.

Dirty motors run hot when thick dirt insulates the frame and clogged passages

reduce cooling air flow.

Heat reduces insulation life and eventually causes motor failure.

Feel for air being discharged from the cooling air ports. If the flow is weak or

unsteady, internal air passages are probably clogged. Remove the motor from

service and clean.

Check for signs of corrosion. Serious corrosion may indicate internal deterioration

and/or a need for external repainting. Schedule the removal of the motor from

service for complete inspection and possible rebuilding.

In wet or corrosive environments, open the conduit box and check for deteriorating

insulation or corroded terminals. Repair as needed.

.

(fig above- Motors waiting for repair)

(fig above- Crane used for moving motors)

Poor or Over Lubrication

Not lubricating or poor lubrication in the bearings, when scheduled will result the

armature to run hot and damage the motor.

Over-lubrication means excessive grease and oil creates dirt and can damage

bearings.

Armature winding Burnt -

Due to over use or after long time, there may come errors in armature windings.

Armature winding may have varying resistances, at that point we remove the old

armature and isolate the problem.

(Fig. above- Front view of Armature)

Precautions -

Care of Windings and Insulation

Except for expensive, high horsepower motors, routine inspections generally do

not involve opening the motor to inspect the windings. Therefore, long motor life

requires selection of the proper enclosure to protect the windings from excessive

dirt, abrasives, moisture, oil and chemicals.

When the need is indicated by severe operating conditions or a history of winding

failures, routine testing can identify deteriorating insulation. Such motors can be

removed from service and repaired before unexpected failures stop production.

Whenever a motor is opened for repair, service the windings as follows:

Moisture reduces the dielectric strength of insulation which results in shorts. If the

inside of the motor is damp, dry the motor.

Wipe any oil and grease from inside the motor. Use care with solvents that can

attack the insulation.

If the insulation appears brittle, overheated or cracked, the motor should be re-

varnished or, with severe conditions, rewound.

Loose coils and leads can move with changing magnetic fields or vibration,

causing the insulation to wear, crack or fray.

Cleaning and Drying Windings

Motors which have been flooded because of contamination by moisture, oil or

conductive dust should be thoroughly cleaned and dried. The methods depend

upon available equipment.

A hot water hose and detergents are commonly used to remove dirt, oil, dust or salt

concentrations from armature, stators and connection boxes. After cleaning, the

windings must be dried.

CONCLUSION

CONCLUSION :-

The key to minimizing motor problems is scheduled routine inspection

and service. The frequency of routine service varies widely between

applications.

Including the motors in the maintenance schedule for the driven machine

or general plant equipment is usually sufficient. A motor may require

additional or more frequent attention if a breakdown would cause health

or safety problems, severe loss of production, damage to expensive

equipment or other serious losses.

Written records indicating date, items inspected, service performed and

motor condition are important to an effective routine maintenance

program.

From such records, specific problems in each application can be

identified and solved routinely to avoid breakdowns and production

losses.

Basic Overhaul Process:-

Disassemble motor.

Clean all parts

Inspect all metal parts for

distortion and wear.

Electrical test the armature and

field coils

Surge test

Ground test

Turn, undercut, and balance the

armature.

Test the armature and field coils

after VPI

New brushes and bearings.

Run test the motor under no load condition. .

Check the running vibration on the assembled motor .

Paint the motor.