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Hkkjr ljdkj GOVERNMENT OF INDIA

jsy ea=ky; MINISTRY OF RAILWAYS

egkjktiqj, Xokfy;j & 474 005

Maharajpur, GWALIOR - 474 005

CAMTECH/E/14-15/3 Loco Transformer/1.0

March, 2015

dsoy dk;Zky;hu mi;ksx gsrq

(For Official Use Only)

MMaaiinntteennaannccee HHaannddbbooookk oonn

TTrraannssffoorrmmeerr ooff 33 PPhhaassee EElleeccttrriicc LLooccoommoottiivvee

END USER: Loco Maintenance Staff

MMaaiinntteennaannccee HHaannddbbooookk oonn

TTrraannssffoorrmmeerr ooff 33 PPhhaassee EElleeccttrriicc LLooccoommoottiivvee

QUALITY POLICY

“To develop safe, modern and cost

effective Railway Technology

complying with Statutory and

Regulatory requirements, through

excellence in Research, Designs and

Standards and Continual

improvements in Quality

Management System to cater to

growing demand of passenger and

freight traffic on the railways”.

FOREWORD

Emerging technological changes require dissemination of new technology and

induction of new maintenance practices. The three phase electric locos were inducted

quite some time back in Railway system but still there is no maintenance handbook

on transformer. The transformer is an important equipment of electric loco (like heart

in human body). The transformer needs proper maintenance for trouble free and

reliable operation of locomotives.

CAMTECH has prepared this handbook on “Maintenance of Transformer of

Three Phase Electric Locomotives” with an objective to provide comprehensive

information on the technical as well as maintenance aspects of the transformer.

I hope this handbook prove to be useful for the field staff engaged in the

maintenance of three phase electric locomotives and its transformer.

CAMTECH, Gwalior A.R.Tupe

Date: 26th

March, 2015 Executive Director

PREFACE

Transformer is an important equipment of three phase electric locomotives.

Proper upkeep of transformer is necessary to ensure trouble free operation of three

phase electric locomotives.

This handbook on “Maintenance of Transformer” of 3 phase electric

locomotive has been prepared by CAMTECH with the objective of making our

maintenance personnel aware of correct maintenance and overhaul techniques to be

adopted in the field. This handbook covers brief technical details, maintenance

practices, testing along with testing instruments required. This also covers condition

monitoring of transformer oil and model questions on the subject.

It is clarified that this handbook does not supersede any existing

provisions/guidelines laid down by Railway Board, RDSO or OEM. The handbook is

only for guidance and it is not a statutory document.

I am sincerely thankful to all field personnel who helped us in preparing this

handbook.

Technology up-gradation learning is a continuous process. Please feel free to

write tour for any addition/ modification in this handbook. We shall highly appreciate

your contribution in this direction.

CAMTECH, Gwalior Peeyoosh Gupta

Date: 26th

March, 2015 Director/ Electrical

CONTENTS

Chapter No. Description Page No.

Foreword iii

Preface iv

Contents v

Correction Slip vii

1. GENERAL 01

1.1 Introductions 01

1.2 Transformer Working Principle 03

1.2.1 EMF Equation of Transformer 04

1.3 Description of Three Phase Loco Transformer 04

1.3.1 Transformer Cooling 04

1.4 Different Parts of Transformer 07

1.5 Technical Data of Electric Loco Transformer 10

1.6 Transport of Transformer 11

1.6.1 Lifting of the Transformer 11

1.6.2 Supporting the Transformer on a Point 12

1.7 Storage of Transformer 12

1.7.1 Maintenance During Storage 13

1.9 Factors Affecting Life of Transformer 13 2. MAINTENANCE 15

2.1 Periodic Maintenance Schedules 15

2.2 Trip Inspection 16

2.3 Oil Circulating Pumps (SR & TFP) IA, IB 17

2.4 Main Transformer IC Schedule 18

2.5 Main Transformer (AOH) Schedule 19

2.6 Main Transformer (IOH) Schedule 20

2.7 Main Transformer POH Schedule 21

2.7.1 Painting Procedure 22

2.8 Procedure for Replacement of Bushings 22

2.9 Transformer Oil Check 23

Chapter No. Description Page No.

2.10 Testing of Loco Transformer 24

2.10.1 Tests 24

2.11 Testing Equipment 25

2.12 Installation of the Transformer on Locomotive 26

2.13 Check Points While Maintenance 29

2.14 Transformer Oil 31

2.14.1 Oil Specification 31

2.14.2 Purification of Transformer Oil 32

2.12.3 Condition monitoring of Transformer by Dissolved Gas Analysis 34

3. MODEL QUESTION 39

ANSWERS 45

An Approach to Equipment Failure Investigation 46 ANNEXURE – I - Reliability Action Plan (RAP) 47

ISSUE OF CORRECTION SLIPS

The correction slips to be issued in future for this handbook will be numbered as

follows :

CAMTECH/E/14-15/3 Loco Transformer/C.S. # XX date---------

Where “XX” is the serial number of the concerned correction slip (starting from 01

onwards).

CORRECTION SLIPS ISSUED

Sr. No. Date of issue Page no. and Item

no. modified

Remarks


Maintenance Handbook on Transformer of 3 Phase Electric Locomotives March, 2015

1

CHAPTER 1

GENERAL

1.1 INTRODUCTION

The transformer is a static device, which transforms power from one AC circuit to

another AC circuit at same frequency but having different characteristics. These circuits are

conductively disjointed but magnetically coupled by a common time varying magnetic field.

It can raise or lower the voltage with a corresponding decrease or increase in current.

In all the electric locomotives, limiting the value of current during starting, speed

control is achieved by supply of variable voltage to the traction motors. This variation of

applied voltage can be carried out easily by the use of transformer along with Static

Convertor provided in the locomotive.

The windings which form the electrical circuit must fulfill certain basic

requirements, particularly the di-electric, thermal and mechanical stresses imposed on it

during testing as well as in service and cater for over loads under adverse conditions.

The WAG9 transformer unit consists of the main transformer active part and two

different types of reactors, hosed in a tank.

The main transformer converts the overhead line voltage (25 kV) to the lower

operating voltages for:

traction power supply 1268V

auxiliary 1kV

The main transformer is integrated into the traction circuit between overhead line

and rail return line.

The primary current line flows from the pantograph via roof line, vacuum circuit

breaker, the roof bushing into the primary winding of the main transformer. It then flows

back to the rail via the earth return brushes on four of the six axles. And WAP5, WAP7

transformer has total load winding in addition toWAG9 transformer.

Figure 1.1 Three Phase Loco Transformer


March, 2015 Maintenance Handbook on Transformer of 3 Phase Electric Locomotives

2

Figure 1.2 Schematic Diagram of Power Circuit of 3 Phase Loco (WAG 9 , WAG 7)



3

1.2 TRANSFORMER WORKING PRINCIPLE

In general principle of working of a transformer can be expressed on the basis of law

of electromagnetic induction as following:

a. When a conductor cuts the magnetic flux or magnetic flux cut the conductor, an emf

is induced in the conductor.

b. The magnitude of this emf is proportional to the rate of change of flux.

E = -d/dt

Where, E = emf

= flux

Kinds of emf

The emf may be induced by two ways

i. Dynamically induced emf

ii. Statically induced emf.

a. Mutually induced emf

b. Self induced emf

An emf induced in a coil due to variation of flux in another coil placed near to first is

called mutually induced emf.

The emf induced in a coil due to change of its own flux linked with it is called self-

induced emf. (In case of autotransformer)

In its simplest form, a transformer consists of two conducting coils. The primary is

the winding which receives electric power, and the secondary is one which delivers the

electric power. These coils are wound on a laminated core of magnetic material.

The physical basis of a transformer is mutual induction between two circuits linked

by a common magnetic flux through a path of low reluctance as shown in fig.1.2

The two coils possesses high mutual inductance. If one coil is connected to a source

of alternating voltage, an alternating flux is set up in the laminated core, most of which is

linked up with the other coil in which it produces mutually induced emf i.e.

E = M di/dt

If the second circuit is closed, a current flows in it and so electric energy is

transferred (entirely magnetically) from first coil (primary winding) to the second coil

(secondary winding).

PRIMARY

LAMINATED CORE

SECONDARY

Figure 1.3 Ideal Transformer



4

1.2.1 EMF Equation of Transformer

Let, N1 = Number of turns in primary.

N2 = Number of turns in secondary.

m = Maximum flux in the core in webres.

f = Frequency of AC input in Hz.

v1 = Instantaneous value of applied voltage in primary winding in volts.

The instantaneous value of counter electromotive force e1, can be expressed as

e1 = - N1 d/dt volt

The counter emf e1 is equal and opposite to applied voltage v1 i.e.

v1 = N1 d/dt volt

rms value of emf induced in primary

E1 = 4.44 f N1 m

Similarly, rms value of emf induced in secondary

E2 = 4.44 f N2 m

In an ideal transformer

V1 = E1 & V2 = E2

Where V2 is the secondary terminal voltage

With the above expressions we get

E2/ E1 = N2/ N1 = K

Where K is known as voltage transformation ratio.

(a) If N2 > N1 i.e. K > 1 then the transformer is called step up transformer.

(b) If N2 < N1 i.e. K < 1 then the transformer is called step down transformer.

1.3 DESCRIPTION OF THREE PHASE LOCO TRANSFORMER & ITS PARTS

Each loco requires one transformer for feeding supply to traction converters/ traction

motors, to auxiliary converter for supplying to auxiliary machines and to supply Hotel load

of train. This transformer will consist of Primary winding, 04 Traction windings, Auxiliary

winding (BUR) and Hotel Load winding. In addition, it has a FILTER winding which is

connected on locomotive to passive filter.

The transformer tank also contains 02 series resonant chokes (one for each

converter) & 03 Auxiliary Converter double chokes (one for each of the 03 auxiliary

converters).

1.3.1 Transformer cooling

Transformer is oil cooled and external cooling of the oil is designed with two

independent oil circuits with cooling units located within the machine room of locomotives.

However, the cooling units / circuit component do not form part of transformer supply.



5

Figure 1.4 Cooling Arrangement

Figure 1.5 Layout of Winding in Transformer Tank



6

Figure 1.6 Three phase loco transformer winding diagram



7

1.4 DIFFERENT PARTS OF TRANSFORMER

i. Transformer tank fastening

Material : Aluminium

Colour : RAL-7009stain

Weight : 966 kg with lid

Identity No. : HSTN 424007

Figure 1.7 Transformer Tank Fastening

ii. Transformer main winding


Make : ABB Badodara, BHEL Jhansi,

CGL Mandideep Bhopal,

EMCO Thane Mumbai,

High volt electrical Ltd Mumbai,

Figure 1.8 Transformer main Winding

iii. SOD Winding


Make ABB Badodara, BHEL Jhansi,

CGL Mandideep Bhopal, EMCO Thane Mumbai,


Figure 1.9 SOD Winding

iv. GOD Winding


Make ABB Badodara, BHEL Jhansi, CGL Mandideep Bhopal,

EMCO Thane Mumbai,


Figure 1.10 GOD Winding



8

v. Transformer Bushing

Identity No. DT 1/250 : HSTN 310500

DT 1/630 : HSTN 310501

DT 1/1000 : HSTN 310502 DT 1/2000 : HSTN 310503

DT 1/3150 : HSTN 310504

Figure 1.11 Transformer Bushing

vi. High Voltage Bushing

Identity No. : HSTN 420783P0001

Technical Data: 18/30 kV, 800A

Supplier : Elasti mold or RDSO approved

Figure 1.12 High Voltage Bushing

vii. Temperature Sensor (Thermometer)


Technical Data : PT-100 Supplier : JUMO Stafa or RDSO approved

Figure 1.13 Temperature Sensor

viii. Overflow Valve Identity No. : HSTN 4/12/0144R

Pressure setting : 0.8 bar

Supplier : Millen Engineer or RDSO approved

Figure 1.14 Overflow Valve

ix. Transformer Main Valve


Technical Data : NW80 ND6 Supplier : Fatco or RDSO approved

Figure 1.15 Transformer main Valve



9

x. Slide of oil intake and drainage Identity No. : HSTN 422368P0001

Pressure setting : NW32/25

Supplier : Hofiman or RDSO approved

Figure 1.16 Slide of oil intake and drainage

xi Two conservator tanks including - Air dehumidifier including valve -Oil level gauge

Identity No. : HSTN Material : Aluminium

Colour : RAl 7030 stain

Volume : 137DMQ

Figure 1.17 Conservation Tanks

xii. Breather


Technical Data : EM3MA Supplier : Yogya or RDSO approved

Figure 1.18 Breather

The special features of the transformer are :-

• Transformer is mounted under slung on under frame

• Transformer is designed for feeding GTO/IGBT based Power and Auxiliary converter

load.

• Very high impedance between primary & traction windings

• 100% de-couplings between windings

• Use of continuous transposed conductor for windings

• Use of disc construction of windings

• Transformer and conservator tank of Aluminum Alloy

• Rapid action coupling between transformer and conservators in oil circuit



10

1.4 TECHNICAL DATA OF 3 PHASE ELECTRIC LOCO TRANSFORMERS (WAP5, WAP7 & WAG9)

Common Ratings for WAG9, WAP5 & WAP7 Loco Transformers

Rated voltage

Normal

Maximum

Minimum

25.0 kV

30.0 kV

17.5 kV

Frequency 50Hz ± 6 %

Cooling medium Inhibited transformer oil to IEC–296/ IS-12463

Series Resonant Choke (2SOD 240)

Inductance 0.551 mH (± 15 %), Liner to Ipeak = 1391A

Thermal current Ith 984A

Resonant frequency 100Hz

Voltage stress between terminals to earth Nominal 482 Vac , Max. 3471 V

Auxiliary Converter Choke (6GOD 120)

Inductance per PUR - choke

0A 30 mH

120A 30 mH

155A 26 mH

190A 20 mH

Frequency 100 hz

Current Rated 155A, Max. 190A

Ripple Nominal 38.6%, Max. 50.2%

Voltage to earth Rated 1153 V, Max. 2000 V

Ratings for WAG9 loco transformer

Winding Power (kVA) Voltage Current

HV 6531 25000 261.25

Traction 4 x 1449 4 x 1269 4 x 1142

BUR 334 1000 334

Filter 400 1154 347

Total weight 9450 ± 3 % kg

Ratings for WAP5 and WAP7 Loco Transformer

Winding Power (kVA) Voltage Current

HV 7475/7775 25000 299/311

Traction 4 x 1449 4 x 1269 4 x 1142

BUR 334 1000 334

Filter 400 1154 347

Hotel load 945/1245 750/960 1260/1296

Total weight 10000 ± 3 % kg



11

Weight

Unit Quantity Kg per unit Kg total

Transformer active part LOT 7500/ LOT

6500

1 5780/ 5380 5780/ 5380

Series resonant circuit recator 2 SOD 240 1 590/ 590 590/ 590

Auxiliary Converter DC-Link Reactor 6

GOD 120

1 570/ 570 570/ 570

Tank and lid 1 900/ 900 900/900

Insulation oil 1 1800/1780 1800/ 1780

Equipment 1 260/ 230 260/ 230

Total transformer unit 9900/ 9450

Expansion tank (oil level at 20°C) 2 88 176

1.5 TRANSPORTATION OF TRANSFORMER

The transformer is transported full with oil. Any oil volume changing (which is

caused by temperature variations) during the transport or storage are taken up by the

transport expansion tank which is mounted on the transformer oil.

The breather is connected to the transformer’s expansion tank. The breather should

only be removed during the installation of the transformer in the locomotive, and rectified as

soon as possible. The breather must be filled with new or dried silica gel.

1.5.1 Lifting of the Transformer

The transformer must never be lifted without its lid. Lifting points are welded to the

side of the tank for this purpose. The rope should be attached on these lifting points as

described in figure shown below. The ropes should never make a smaller angle than = 60°

with the horizontal, otherwise there is a danger that the tank will distort.

Figure 1.19 Lifting of the Transformer



12

1.5.2 Supporting the Transformer on a Point

If for any reason the transformer needs to be supported on a point, then it should

only be supported on the indicated areas shown by the arrows in the figure given below.

Figure 1.20 Support Point of Transformer

1.6 STORAGE OF TRANSFORMER

The transformer can be stored as long as required, if the maintenance is carried out

as required if it is under maintenance or ready to use. The various points for storage of

transformer is described below.

a. Storing place

The oil-filled transformer should be

stored in covered area. The storing place must

be dry and the transformer must be covered

with a lose taped plastic sheet.

Figure 1.21 Storing Place

b. Connecting flanges

All pipes, pumps and blocking valves should

be closed off using blanking flanges.

Figure 1.22 Connecting Flange

c. Expansion tank

Fix the expansion tanks in vertical position on a

higher level than the transformer’s lid. Join then with

flexible pipes with transformer in the same way as they are

installed in the locomotive. The oil level in the expansion

tank should correspond with the temperature mark.

Figure 1.23 ExpansionTank



13

d. Labels

Covering the transformer with stickers is

forbidden. If stickers need to be added then they

should be stuck on separate plates. The plates

should then be tied to the transformer using

strings (no wire).

Figure 1.24 Labels

e. Checks

After transport and installation at the storing place the transformer should be

checked for any signs of oil leakage.

1.6.1 Maintenance During Storage

a. Checks

According to the atmospheric conditions the oil level and the silica gel in the

breather should be checked every 6 months.

b. Oil level

If the oil level is lower than the equivalent temperature mark, oil can be

added by the filling cap on the expansion tank with the oil of the same quality.

Mixing with oils which have significantly different parameters should be avoided.

If the oil level is not visible at the expansion tank, the reason for the low oil

level must be found. Oil should not be added by the filling cap of the expansion tank

as long as reason has not been found.

c. Breather

If more than half of the silica gel is saturated (moisturized), then it must be

completely replaced. The old silica gel may be regenerated.

The transformer must not stay longer than 3 hours without functional breather.

1.7 FACTORS AFFECTING LIFE OF TRANSFORMER

Life of transformer is affected by the following factors:

1. Moisture

2. Oxygen

3. Solid Impurities

4. Varnishes

5. Slackness of winding

a. Effect of moisture on transformer life

Presence of moisture in oil is highly undesirable as it affects adversely the

dielectric properties of oil. The moisture present in oil also affects the solid

insulation of transformer. As paper insulation is highly hygroscopic in nature, when

transformer is filled with oil, it absorbs the moisture from oil which affects its

insulation properties as well as reduces its life. Solubility of moisture in oil increases

with increase in temperature and oxidation products of oil. When the oil in service

TFPG No. : 2027453 Make : BHEL Date of O/H : 11.05.2014



14

oxidizes, acids are formed. These acids increase moisture solubility of oil. Acids

coupled with moisture further decompose the oil forming more acids and moisture.

Thus the rate of deterioration of oil increases.

Check the colour of silica gel in each inspection and if found pink, replace or

reactivate crystals at 150 degree C. Test transformer oil for electric strength and

water content in IC schedule & POH and carry out purification with high vacuum

type transformer oil filtration plant if required. Arrest the oil leakage if any.

b. Effect of Oxygen

Oxygen may be present inside the transformer due to air remaining in oil.

The oxygen reacts and decomposes the cellulose of insulation. This forms an organic

acid soluble in oil and sludge, which blocks the free circulation of the oil. The

adverse effect of oxygen, which may be aggravated by catalytic action between hot

oil and bare copper, increase the operating temperature.

Carry out oil purification with high vacuum type transformer oil purification

plant periodically to remove atmospheric gases (air) and sludge.

c. Effect of Solid Impurities

The solid impurity present in the oil reduces its dielectric strength

considerably. A good remedy is to filter the oil periodically.

d. Effect of Varnishes

Some varnishes having oxidizing effect, react with transformer oil

and precipitate sludge on windings. Synthetic varnishes having acid

inhibiting properties, generally delay the natural formation of acid and sludge

in the oil.

e. Effect of slackness of winding

After few months of service, the transformer coils may suffer natural setting.

This may wear the conductor insulation at some places and lead to an inter-turn

failure. The coils may also get displaced under load conditions or momentary short

circuit conditions, which may result in electrical and magnetic unbalance and

produce even greater displacement. A good practice is, therefore to lift the core and

windings to take up any slackness present at the first major schedule.

Periodic maintenance of transformer is essential to ensure safety, reliability

and trouble free operation of electric locomotive over a long time period.



15

CHAPTER 2

MAINTENANCE

2.1 PERIODIC MAINTENANCE SCHEDULES

3-Phase (ABB) locomotives

Ref. : Rly. Bd. Letter No. 97/Elect(TRS)/440/18/44(3-Phase), dt. 23.02.07

Coaching Locos - WAP5/WAP7 locos

Maintenance Schedule Periodicity Duration

Trip inspection (TI) 3000 kms or one trip,

whichever is later 2 hrs

IA 90 days 4 hrs

IB 180 days 6 hrs

IC 270 days 8 hrs

MOH 18 months 6 working days

IOH

4.5 years + 6 months or

12 lakh kms. whichever is

earlier.

WAP-7 - 11 working days

WAP-5 - 20 working days

POH

9 years + 6 months or

24 lakh kms. whichever is

earlier.

28 working days

Freight Locos - WAG9/WAG9H locos

Ref. : Rly. Bd. Letter No. 97/Elect(TRS)/440/18/44(3-Phase), dt. 23.02.07

Maintenance Schedule Periodicity

Trip inspection (TI) 45 days

IA 90 days

IB 180 days

IC 270 days

MOH 18 months

IOH 6 years + 6 months or 12 lakh kms.

whichever is earlier.

POH 12 years + 6 months or 24 lakh kms.

whichever is earlier.

http://elocos.railnet.gov.in/CLW/23.02.07.pdf

http://elocos.railnet.gov.in/CLW/23.02.07.pdf



16

2.2 TRIP INSPECTION

1. OIL CIRCULATING PUMPS (SR & TFP)

Visually examine all SR & TFP oil pumps for any oil leakage

/any abnormal sound and take needful action

No leakage

2. MAIN TRANSFORMER

i Inspect the color of the silica gel. If it is pink, remove the filter

from the locomotive Blue

ii Dry the silica gel in oven at 150 degree C and replace Blue

iii

Read off the oil level on the gauge situated on the conservator.

Top up the oil as necessary and

Check for any signs of leakage

Middle strip

+/- 6”,

No leakage

iv Prismatic level gauge-clean the gauge with a dry cloth and

check for leaks

Cleaned & No

leakage

v

Examine the flanges of the pipe couplings and flexible hose that

link the transformer and conservator and check the holding

clamps.

Checked &

Found intact

vi Check/attend the condition of earthing shunts of transformer

body (As per RDSO/SMI/0248) Intact

vii Check the main TFP and its protection cover of drain cock for

damage/crack & oil leakage

Checked &

Found intact

viii Check visually the foundation bolts of transformer and nylock

nuts for proper locking

Checked &

Found intact

ix Check/attend stoochi coupling pipes of conservator for proper

layout and fitment and attend for any leakage

Intact/ No

leakage

x Check VPTFP and VPSR for oil leakage on RH. No leakage

xi Examine the HV bushing for sings of damage, burning etc.

Replace if defective. Ensure RTV on base.

Checked /

Replaced

xii Check the oil leakage from TFP bushing No leakage

3. OIL COOLING UNIT CASING WITH RADIATOR

i Examine flange joint for sign of cracks, oil leakage and

loose/missing screws Checked/ intact

ii

Remove all dust, dirt and debris from the radiator chamber via

the machine room access cover (using vacuum cleaner) in case

of less air flow booking

Cleaned

iii Visually check the oil cooler radiator for any oil leakage /

external damage from top and bottom

No leakage/No

damage



17

2.3 IA, IB SCHEDULE.

1 OIL CIRCULATING PUMPS (SR & TFP) IA,IB.

i Visually examine all SR & TFP oil pumps for any oil leakage

/any abnormal sound and take needful action

Normal

ii Check the mechanical support fasteners of all four oil pumps Normal

2. MAIN TRANSFORMER

i

ii Inspect the colour of the silica gel. If it is pink, remove the filter

from the locomotive

Blue

iii Dry the silica gel in oven at 150 degree C and replace Blue

iv Read off the oil level on the gauge situated on the conservator.

Top up the oil as necessary and


Middle strip

+/- 6”

No leakage

v Prismatic level gauge-clean the gauge with a dry cloth and

check/attend for leaks

Cleaned & No

leakage

vi Examine/attend the flanges of the pipe couplings and flexible

hose that link the transformer and conservator

Checked &

Found intact

vii Check visually the foundation bolts of transformer and Nylock

nuts, for proper locking

Intact

viii Check the condition of earthing shunts of transformer body (As

per RDSO/SMI/0248)

Intact

ix Visually inspect & clean the electrical connection to the

insulator and condition of insulator for crack

Intact

x Visually inspect the condition of oil cooling metallic pipes,

check/attend for leakage / damage & check all fixing clamps

Intact /

No leakage

xi Check/attend stuchi coupling pipes of conservator for proper

layout and fitment and attend for any leakage

Intact/ No

leakage

xii Examine the HV bushing for signs of damage, burning etc.

Replace if defective. (Ensure RTV on base)

Examined

xiii Check the availability of hosepipe over the oil pipe

compensator.

Checked

xiv Check the main TFP and its protection cover for damage / crack

& oil leakage. (RDSO/TC/076)

No crack / No

leakage

xv Check the oil leakage from TFP bushing. No leakage



18

2.4 IC SCHEDULE.

1 OIL CIRCULATING PUMPS (SR & TFP)

i. Visually examine all SR & TFP oil pumps for any oil

leakage / any abnormal sound and take needful action

Normal

ii Check the electrical connections of all four oil pumps Normal

iii Check the mechanical support fasteners of all four oil

pumps.

Normal

2. MAIN TRANSFORMER

i Perform the sample test on transformer oil.

Check specific value of BDV, DGA, moisture and acidity.

30 kV (serviceable

oil)

ii If BDV value falls below 30KV/ DGA gases more,

oil centrifuging to be done

Done

iii Inspect the color of the silica gel. If it is pink, remove the

filter from the locomotive

Blue

iv Dry the silica gel in oven at 150 degree C and replace Blue

v Read off the oil level on the gauge situated on the conservator. Top up the oil as necessary and


Middle strip +/- 6”

No leakage

vi Prismatic level gauge-clean the gauge with a dry cloth and

check for leaks

Cleaned & No

leakage

vii Examine the flanges of the pipe couplings and flexible hose

that link the transformer and conservator

Checked & Found

intact

viii Visually inspect & clean the electrical connection to the

insulator and condition of insulator for cracked, flashed

mark & ensure red marking.

Intact

ix Check visually condition of foundation bolts of transformer and Nylock nuts for proper locking

Intact

x Check / attend the condition of earthing shunts of transformer body (As per RDSO/SMI/0248)

Intact

xi Visually inspect the condition of oil cooling metallic pipes,

check for leakage / damage & check all fixing clamps

Checked Intact

found no leakage

xii Examine the HV bushing for sings of damage, burning etc.

Replace if defective. Ensure RTV on base.

Checked / Replaced


compensator

OK

xiv Check the main TFP and its protection cover for

damage/crack & oil leakage. (RDSO/TC/076)

Checked & Found

intact

xv Check the oil leakage from TFP bushing No leakage

xvi Check/attend stoochi coupling pipes of conservator for

proper layout and fitment and attend for any leakage

Intact/ No leakage

xvii Check the deformity of TFP drain cock cover guard, if

deformed, replace it.

Checked / Replaced



19

2.5 MAIN TRANSFORMER (AOH) SCHEDULE

1. MAIN TRANSFORMER (AOH)

i Perform the sample test on transformer oil. Check specific

value of BDV and moisture, acidity & DGA. OK

ii Oil centrifuging to be done. And used separate plant for

different transformer oil. & check oil as per SMI 158. 72 Hrs.

iii Replace the silica gel with new crystals Blue

iv Read off the oil level on the gauge situated on the

conservator. Top up the oil as necessary and

check for any signs of leakage

Middle strip +/-

6”

No leakage

v Prismatic level gauge-clean the gauge with a dry cloth and

check for leaks Cleaned &

No leakage

vi Visually inspect the high voltage cable at the main

transformer connection for damage or oil contamination.

Replace the cable if damaged or if contaminated with oil

OK


that link the transformer and conservator Checked & Found

intact


insulator and condition of insulator for crack & Red marking

to be done.

Intact

ix Check visually condition of foundation bolts of transformer

and Nylock nuts for proper locking Intact

x Check / attend the condition of earthing shunts of transformer

body (RDSO/SMI/0248 dated 22.11.2007) Intact


check for leakage / damage & check all fixing clamps and

also check the drain cock, isolating cock for oil leakage &

clean it.

Checked /

Intact /

No leakage/

cleaned


Replace, if defective. Checked &

Cleaned


compensator. OK

xiv Check the main TFP and its protection cover for

damage/crack & oil leakage. (RDSO/TC/076) Checked & Found

intact

xv Check the oil leakage from TFP bushing No Leakage

xvi Examine the bushing for signs of damage, burning etc.

Renew if defective. Clean off all deposits and dirt from the

insulators

Checked &

Cleaned

xvii Check conservator foundation welding and conservator stand

bolts for tightness & ensure provision of double nut Intact

xviii Check / attend Stoochi coupling pipes of conservator for

proper layout and fitment and attend for any leakage Intact



20

2.6 MAIN TRANSFORMER (IOH) SCHEDULE

1. MAIN TRANSFORMER (IOH)

i Perform the sample test on transformer oil. Check specific

value of BDV and moisture, acidity & DGA. OK

ii Oil centrifuging to be done. And used separate plant for

different transformer oil. & Maintenance oil as per SMI

158.

72 Hrs.

iii Replace the silica gel with new crystals. Blue.

iv Read off the oil level on the gauge situated on the

conservator. Top up the oil as necessary and check for any

signs of leakage.

Middle strip +/- 6”.

No leakage.

v Prismatic levels gauge-clean the gauge with a dry cloth and

check for leaks.

Cleaned & No

leakage.

vi Visually inspect the high voltage cable at the main

transformer connection for damage or oil contamination.

Replace the cable if damaged or if contaminated with oil.

OK.


that link the transformer and conservator.

Checked & Found

intact.


insulator and condition of insulator for crack.

Intact.

ix Check foundation bolts of transformer with proper torque

and Nylock nuts for proper locking. Intact.

x Check / attend the condition of earthing shunts of

transformer body (RDSO/SMI/0248 dated 22.11.2007)

Intact.


check for leakage / damage & check all fixing clamps. And

also check the drain cock, isolating cock for oil leakage &

clean it.

Checked Intact

found no leakage.


Replace if defective & ensure red marking.

Checked & Cleaned.


compensator.

OK.

xiv Check the main TFP and its protection cover for damage /

crack & oil leakage. (RDSO/TC/076)

Checked & Found

intact.

xv Check the oil leakage from TFP bushing. No Leakage

xvi Examine the bushing for signs of damage, burning etc.

Renew if defective. Clean off all deposits and dirt from the

insulators.

Checked & Cleaned.

xvii Check conservator foundation welding and conservator

stand bolts for tightness & ensure provision of double nut.

Intact.

xviii Check/ Attend Stoochi pipes of conservator for proper

layout and fitment and attend for any leakage.

Intact.

xix Replace all rubberized cork sheet and bushing oil seal &

gasket as per TC-76.

Done



21

2.7 MAIN TRANSFORMER POH SCHEDULE

Figure 2.1 Lifting of Transformer Winding

01 Visually inspect the electrical connections, earthing cable, bushing and insulators on

the main transformer for cracks, chips and evidence of impact damage. Renew if

defective. Clean the connectors and replace any damaged chipped or cracked

insulators.

02 Test oil sample for BDV, DGA, acidity and other lab tests. DGA to be done as per

RDSO SMI (RDSO/SMI/138 & OEM Doc. Dt. 27th Nov. 1995).Incoming oil test.

03 Check any leakage sign of oil from bushing, tank, pipe line, oil gauge

If any attend the same/replased.

04 Visually inspect the condition of oil cooling metallic pipes, check for leakage /

damage & check all fixing clamps. Ensure instructions contained in RDSO‟ s letter

no. EL/3.2.1/3-Ph dated 30.07.09 for arresting oil leakages cases.”

05 Examine the flanges of the pipe couplings and flexible hose that link the transformer

and conservator.

06 Maintenance of assembly of electrical terminal of traction winding bushing 2U1-

2V1, 2U2-2V2, 2U3-2V3 & 2U4-2V4 in indigenously manufactured transformers

type LOT 6500/7500 used in 3-phase drive locomotives type WAG9/WAP5.(

RDSO/ELRS/SMI/0228 dt. 13.08.02)

07 Replace all sealing gaskets including tank cover gasket.

08 Replace all rubberized cork sheet.

09 Replace all TFP bushings rubber seals

10 Cleaned the transformer winding & tank with filtered transformer oil.

11 Fit the tank & bushing cover with new gasket

12 Fit the all bushings, safety valve, temperature censer, gate valve, drain cock with

new gasket.

13 Dry out the windings moisture in vacuumed drying plant & fill the filtered oil.

14 Carry out Insulation Resistance test and Tan delta test.

15 Check the winding resistance, inductance and continuity test , ratio test of the

windings.

16 Replace Transformer foundation bolts and bushing nuts.& Tighten with proper

torque.

17 Prismatic level gauge –Clean the gauge with dry cloth to check for leaks. If any

attend it.

18 Replace the silica gel , in clean & attended breather assembly.

19 Replace the transformer oil. .

20 Conduct centrifuging of the oil (Use separate plant, the shell DIALA-DX oil should

not be mixed with any other type of transformer Oil).

21 Check the oil level on the gauge situated on the conservator. Top up if required and

any sign of leakage.

22 Finally cleaned & paint the transformer with accessories.



22

2.7.1 Painting Procedure

Cleaning the affected area

Using sand paper or a sander to smooth down and clean the affected area, a smooth

transition to the intact paintwork must be made. Cover the area with primer by including the

intact paint work out side.

Top coating (Painting of transformer)

Once the primer has been applied, wait at least 6 hours to apply the top coating. It

can be applied by painting, rolling or spraying. The drying time at room temperature of

about 20°C is 6 hours; at temperatre of 60°C it is 1 hour.

Primer Two component epoxy resin

Coating Two component polyurethane paint

2.8 PROCEDURE FOR REPLACEMENT OF BUSHINGS

Removal of bushings

The gaskets and the washers outside of the transformer can be replaced without

removing the transformer lid. The oil level has to be decreased to 50mm from the lower side

of the lid. Once the electrical terminals has been removed, the fixing nut can be untightened.

Assembly

Clan the contact surface before assembling, No oil or glue must be applied on the

gaskets. Fit the gaskets with the insulator and the corresponding washers on the bolt. Before

tightening the fixing nut make sure that the inner insulator mates on the positioning wedge.

Once the bushing has been assembled, tighten the fixing nut with a dynamometer

(tightening torque). To ensure the tightness of the gasket, retighten the nut a few hours later.

The oil level must be topped off to normal level, Use the filling system for this reason. The

transformer has to be vented after oil filling.

Gaskets of lid

In order to avoid leakages

between the upper frame of the tank

and the lid, the fixing bolts must be

tightened with the following

tightening torque. It has to be

applied on the nut where accessible.

Figure 2.2 Gaskets of Lid



23

2.9 TRANSFORMER OIL CHECK

Taking oil samples

Only clean and dry sample containers should be used. These containers must not

contain any traces of cleaning fluids. Before taking oil samples, clean the draining valve on

the transformer; 5 litres of oil should then be drained off; after that the sample container

should be rinsed using roughly ½ litre of oil. The oil sample must be protected from light.

The following are recommended as sample containers:

- glass bottles made out of dark-coloured glass, with a polished glass stopper.

- Tinned steel cans with a screw top.

- Clear glass bottle which should be covered with an opaque cover after the sample

has been taken.

The oil sample should be at least 2 litres. For laboratory tests, 5 litres are required. If an

oil sample is required to determine the amount of water gas or air content, then special

vacuum bottles should be used. In such a case we recommend that we should be notified

about the preparation of bottles and suction equipment.

Checking for any solid impurities in the oil.

A test tube should be filled with the oil sample and held up against a light source. If

there are any solid impurities in the oil, then the oil from which the sample comes should be

filtered.

Simple test for water content

This is done using the so-called ‘Spatter-test”, i.e. the oil sample heated in the test

tube up to 105-110°C. If there is any water in the oil then this will be noticeable if the oil

cracles, snaps or bubbles. If the oil is overheated then the presence of water is falsely

indicated; the upper temperature should therefore not be exceeded.

Dielectric strength (IEC test)

In accordance with the IEC standard 156 (which also complies with the Swiss

standard), this test should be performed using 12.5mm ball electrodes with a diameter of

2.5mm or with the half – ball electrodes (so-called VDE Kalloten) also with a diameter of

2.5mm. The oil sample (temperature 15-25°C) should be slowly poured (to avoid air

bubbles) into the clean test container; the test should be carried out immediately. The

voltage should be increased evenly up to break down at a rate of 2 kV/second; this should be

carried out 6 consecutive times. After each time the space between the electrodes must be

free of traces of breakdown; use a clean and dry glass rod (diameter 2mm) and move it

slowly in-between the two electrodes. All six break down voltages should be noted and the

arithmetic average calculated (i.e. the sum of the individual values divided by six). None of

the individual values should lie more than 15% below the average value, otherwise the test

must be repeated using a new oil sample.



24

2.10 TESTING OF LOCO TRANSFORMER

2.10.1 Tests

Following common tests to be carried out in the transformer either in case of failure or

during overhauling in oil filled conditions.

a. Insulation resistance test.(Meggering)

b. Continuity test

c. Winding resistance test

d. Ratio test

e. Winding inductance test

a. Meggering

Check the insulation resistance of windings. It should be minimum 2100 M ohms.

Primary to earth by 2.5 kV megger.

Secondary to earth by 1 kV megger.

Primary to secondary by 2.5 kV megger.

Primary to BUR. by 2.5 kV megger.

BUR. to earth by 1 kV megger.

Secondary to BUR. by 1 kV megger.

Primary to H.L. by 2.5 kV megger.

H.L. to earth. by 1 kV megger.

GOD Terminal. to earth. by 1 kV megger.

SOD Terminal. to earth. by 1 kV megger.

b. Continuity Test

Check the continuity of the following windings with the multimeter:

Primary winding

Secondary windings

BUR winding

H.L. winding.

SOD. winding.

GOD. winding.

c. Winding Resistance Test

SN WINDING RESISTANCE VALUE

LOT-6500 LOT 7500

1 Primary winding

2 Secondary

windings

3 BUR

winding

4 H.L.

winding.

5 SOD. winding

6 GOD. winding



25

d. Ratio Test / Polarity Test.

Apply 230V a.c. supply to the primary winding of the transformer across 1U –

1V and check the voltage appearing at the following terminals.

1 And 2V1 2V1 & 2U2 Sorted 23.35 V

4 2U3 & 2U4. 2V3 & 2U4 Sorted 23.35 V

5 2U1 & 2U2 2V1 & 2V2 Sorted 0 V

6 2U3 & 2U4 2V3 & 2V4 Sorted 0 V

e. Winding inductance test

SN WINDING INDUCTANCE VALUE

LOT-6500 LOT 7500

1 Primary winding

2 Secondary windings

3 BUR winding

4 H.L. winding.

5 SOD. winding

6 GOD. winding

2.11 TESTING EQUIPMENT

LIST OF TESTING INSTRUMENTS

Sr.No. Instrument Make / Model No. Range/Capacity

1 Power Analyzer Yokogawa / WT 330 or similar As per manual

2 100 KV HV Test set SEV or similar 100 KV, 100 mA

3 100 KV Motorised Oil Test Set SEV or similar 0-100 KV

4 Ratio meter (TR100) Fifty Hertz / TR100 or similar --

5 Digital Micro ohm meter Prestige / PE-17RP or similar As per manual

6 Digital Megger Megger Co. or similar 5KV

7 Digital Frequency meter Prestige or similar 200 HZ

Power analisor Megger Voltage Ratio Meter

Oil BDV Tester 100 kV HV SET Micro Ohm Meter



26

2.12 INSTALLATION OF THE TRANSFORMER ON LOCOMOTIVE

During assembly in the locomotive, the main valves of the transformer stay closed.

Lift the transformer slowly under the under frame of the locomotive. Make sure that the two

centering pins fit in the corresponding hole.

The transformer has 4 fixing points each with 4 bolts. So that the bolts are relived of

any strains caused by share forces in the horizontal and vertical directions, a centering pin is

provided on two diagonally opposite fixing points. The fixing plates are covered with a layer

of paint to prevent corrosion which could between aluminium and steel.

The mounting surfaces are made in such a way that the exchange of the transformer

is guaranteed; tolerances have been taken into account.

Assemble the hot dip galvanized washers under the supports when assembling the

bolts. Tighten the fixing bolts with 675 Nm.

a. Fitting of Oil Piping

Before removing the blanking flanges make sure that all blocking valves are

closed. They stay closed during the whole installation.

Special care must be taken to ensure that all pipes, pumps and coolers have been

thoroughly cleaned and flushed with insulation oil before one proceeds with

assembling.

b. Fitting of the angled connector

Before the angled connector can be fitted onto the bushing, the bushing must

be properly cleaned. No dirt should be trapped in the connection. To allow easy

fitting, the bushing should be slightly greased with silicon. When mounting the

angled connector care should be taken that no air is trapped inside. The connector

can be vented using a nylon thread on the bushing, which is pulled out when the

angled connector is fitted.

c. Electrical Connections

The electrical terminations of the bushings have to be carried out in a way,

that the nut 11.1 stay accessible to be re-tightened.

Electrical connections must not be numb. They should be made flexible so

that the bushing isn’t stained. Cable connections should be made with a loop, for

bars use flexible ribbon to connect them

on the bushing.

When assembling the electrical

connections, make sure that the nut 11.1

does not become loose. Keep a distance

of min. 3 mm between the 2nuts. After

assembling of the connection re-tighten

the nut 11.1. The tightening torque for

each type of bushing is indicated in the

table given below

Figure 2.3 Electrical Connection



27

Tightening torque and max. horizontal load for DIN bushings

DIN type Drawing no. D Section (mm2) M F

Bolt Extern.

DT 1/250 HSTN 310 500 M12 74.5 84.3 10 50

DT 1/ 630 HSTN 310 501 M 20 220 245 30 60

DT 1/1000 HSTN 310 502 M 30 x 2 596 621 65 80

DT 1/2000 HSTN 310 503 M 42 x 3 1150 1210 150 100

d. Earthing Terminal Fitting

In order to avoid discharges and unwanted failures, all metallic parts inside

and outside the transformer are earthed. The earthings of the transformer active part

and the reactors are connected with each other via the tank.

The marked earthing terminals have to be connected to the locomotive’s

earthing terminals.

Figure 2.4 Inside Earthing Figure 2.5 Outside Earthing

e. Filling the remaining oil

Once the transformer has been installed in the locomotive and all piping

connections to the heat exchanger and the pump have been made, it is necessary to

fill the remainder of the cooling system with oil. The oil used must comply with the

relevant specifications. Casting doubt on, an oil test has to be carried out.

The transformer main valves should only be opened when all pipes and the

heat exchanger have been filled with oil and vented. No air should enter the

transformer assembly from the piping or the heat exchanger.

f. Filling with oil barrel

The barrel with the insulation oil has to be brought on a higher level than the

lid of the transformer, join the oil barrel with a flexible pipe to the draining tap (13.1/

13.3). All apparatus must be cleaned and free of dirt and moisture . Fit a silica

breather to the barrel’s breather port.

g. Filling with pump

The oil filling system, which should be suitable to a standard oil barrel

standing vertically, must not exceed a flow of 5litre/min and it must contain a no

return valve. All apparatus must be cleaned and free of dirt and moisture. Fit a silica

gel breather to the barrel’s breather port. Fit the filling system with a flexible pipe to

the draining tap (13.1/13.3). Start pumping and drive any air out of the filling

system.



28

h. Venting the pipe work and heat exchangers

Make sure that there isno air in the filling hose. Crack open the drawing tap

(13.1/13.3). Open the venting tap (13.2) on the heat exchanger until oil runs out.

Close venting tap (13.2) and draining tap (13.1/ 13.3). Repeat this procedure on the

opposite side. Connect the filling hose to the draining tap (13.4/ 13.6) and vent the

pipe with venting screw (13.5) on the heat exchanger.

If during the filling process a change of barrel is required, stop pumping

before air is drawn into the system. Close the venting and the filling tap, change the

barrel, run the pump and drive any air out of the filling system. Continue filling.

Figure 2.6 Transformer Layout in the Loco

i. Oil pumping

Before the pump is put up into action, make sure that the pumps, piping and

heat exchanger are filled with oil. Never start the pump without oil.

j. Checking the direction of rotation

Remove the screw plug (14.1) and push the head face on the shaft of the

rotation indicator (14.2). The rotation direction of the pump is correct when the

rotation indicator turns in the same direction as the arrow. After completing the

check, refit the screw plug (14.1)

Figure 2.7 Transformer Layout in the Loco



29

k. Venting

Once all pumps, pipes and heat exchangers are filled up with oil, the

transformer main valves can be opened. Secure the valves in open position. To drive

any remaining air out of the system, put the two oil pumps in operation for 30

seconds. Let the whole system resting during 30 minutes. Connect the filling system

to one of the draining taps, put it into action and crack open all vent plugs (15.1) on

the transformers lid until oil leaks out. Repeat this procedure until the total breathing

of the system. Adjust the oil level in the expansion tank after.

Figure 2.8 Transformer Assembly Venting Layout

2.13 CHECK POIINTS WHILE MAINTENANCE

a. Oil Level Check

The oil level in the expansion tank has to be checked each time beore

switching on the transformer and in case of non use at least every 6 months. The oil

level in the expansion tank must be equal to the corresponding temperature mark on

the sight glass (17.3)

b. Oil Level beneath the corresponding temperature mark

In case of the oil level is under the corresponding temperature mark, oil can

be added directly by the filling plug on the expansion tank. The oil used must

comply with the relevant specification.

c. Oil level not visible on the sight glass

If the oil level isn’t visible on the sight glass (17.3), the transformer must not

be switched on. The oil must not be toped off by the filling plug on the expansion

tank. One have to control the distance between the lid and the oil level in the

transformer. For this reason open one of the vent plug on the transformer lid and

measure the distance between the upper side of the plug and the oil level. If the

distance is lower than 100mm the oil can be topped off by the draining valve of the

transformer or the pipes between transformer and heat exchanger. The transformer

has to be vented after.



30

If the distance between upper side of the plug and the oil level is more than

100mm then the level can only be topped off under vacuum conditions. For this

reason the transformer must be removed from the locomotive and put in a vacuum

oven.

d. Oil level above the corresponding temperature mark.

If the oil level is above the

corresponding temperature mark, oil can

be drained by the draining valve on the

transformer.

Figure 2.9 Expansion Tank

e. Silica Gel Breather

According to the atmospheric conditions, the colour of the silica gel should

be checked roughly every six months. When more than half of it is pink (saturated

with water), then it should be replaced. The saturated silica gel can then be dried out.

Put it in an oven and increase the temperature slowly min 115°C to max. 150°C.

Keep the temperature until the silica gel turns blue again. Silica gel should not be

dried-up in sun light as because of insufficient heat only the outer layer gets dried up.

However, this process should not be repeated too many times; after a while

the silica gel appears to be not so effective, probably due to the ingress of dirt.

Figure 2.10 Silica Gel

f. Leakage of expansion tank

Whenever breather, silica gel colour more than half got pink (saturated with

water)

Bad Condition

Good Condition



31

2.14 TRANSFORMER OIL

The transformer unit is filled with 2000 kg of mineral oil. The oil serves as a

cooling and insulating agent.

2.14.1 Oil Specification

Ref. no Characteristic Unit Value Test method

00001 Ident. Text -- Insulation oil T1

00002 Ident no. -- NBT 402614P0201

01000 Description -- The insulation oil T1 is a pure

mineral product without any

additive; it is used in transformer

and switch gear.

01120 Density at 20°C g/ml 0.895 ISO 3675

DIN 51757

01500 Delivery instructions -- ZN 02125

01800 Documentation -- ZLC – documentation and QZ

HSTC 419458

05100 Colour -- Pale yellow to yellow

07900 Special properties -- The oil is not cloudy and is free of

solid particles and water

26350 Pour point

IEC class IA

IEC class IIA

°C - 30

- 45

ISO 3016

ASTM D 97-66

DIN 51597

29300 Flash point in a

enclosed crucible

°C 130 ISO2719

ASTM D 93 – 66

DIN 51758

22500 Thermal expansion

coefficient

K-1

Standard NB

214200

31300 Dielectric loss factor

tan at 90°C 50 Hz

-- 0.005 IEC publ. 247-1978

VDE 0370/ 12.78

35300 Break-down voltage kV 50 IEC publ. 156

43700 Interface tension mN/m 40 ASTM D 971-50

45100 Cinematic viscosity

At + 20°C

At + 40°C

At – 15°C class IEC

IA

At – 30°C class IIA

mm2/s 25

11

800

1800

ISO 3104

51370 Corrosive sulphur

content

-- None DIN 51353

55100 Neutralisation value mgKOH/g 0.03 IEC Publ. 296-1978

55350 Aniline point °C 80 ISO 2977

DIN 51775



32

2.14.2 Purification of Transformer Oil

Figure 2.11 Purification of Transformer Oil

The object of oil purification is to remove all contaminants such as water, carbon

deposits, dirt, sludge, dissolved moisture and gases. The most important quality to be

preserved is the di-electric strength, which is affected by the presence of moisture.

The insulating materials used in the winding are hygroscopic by nature and therefore

moisture is absorbed through defective breathers, gaskets and addition of untreated make up

oil. It is essential to remove these impurities by purifying the oil when the dielectric strength

goes below the permissible limits.

The purification plant should be capable of removing dissolved air/ moisture in the

form of free and finely dispersed water vapour and moisture in solution, sludge and fibers,

gases, carbonaceous products formed due to arcing and drum scale or any other solid

particles from insulating oil.

The plant should be capable of purifying the rated capacity of transformer oil to the

following parameters in maximum three phases.

a. Suspended impurities – maximum 1 micron particle size.

b. Water content – from 100 ppm to less than 5 ppm

c. Gas removal – from fully saturated i.e. 10 to 12% by volume with air/gas

down to less than 0.25%

d. Acidity correction – with addition of clay filters the neutralization index should go

down from 0.5 to 0.05 mg KOH/ gm

of oil.

e. Dielectric strength – Minimum 60 kV

f. Dissipation factor of

oil/ tan delta at 90°C – 0.002

The switching ON & OFF of the heater groups should be thermostatically controlled

so that the temperature of the oil during treatment is not be permitted to rise above 60°C.

Operating vacuum should be better than 1 torr.



33

Filtration of EHV grade oil to be carried out at a vacuum level of 98% at a

temperature of 60 degree C and of inhibited oil at a pressure of 0.15 torcillie at a

temperature of 60 degree C, provided the specific resistance is within limits. Filtration

should continue till such time the oil is completely dried. Check the filtered oil sample for

electrical strength and water content and if these parameters are within the limits, the oil is

fit for use and if not, repeat filtration till electric strength and water content are within limits.

Water content in Oil

Test : Water content (PPM)

Test method : As per IS:335-1983

Periodicity : IC/ AOH/ IOH/ POH

Permissible limit : 35 PPM (Max.)

Requirement of new oil : 25 PPM (max.)

Figure 2.12 Water content test set

Acidity in Oil

Test : Total Acidity



Permissible limit : 0.5mg KOH/gm (Max.)

Requirement of new oil : 0.03mg KOH/gm (Max.)

Figure 2.13 Acidity Test Set

Oil breakdown voltage

Test : Electrical Strength (Break down voltage)



Permissible limit : 30KV (rms)(min.)

Requirement of new oil : 60 KV (rms)

Flash point

Test : Flash point

Test method : As per IS: 1448-1970

Periodicity : IOH/ POH

Permissible limit : 125 deg. C (Min)

Requirement of new oil : 140 deg. C (Min)



34

INSULATION RESISTANCE DURING DRYING OUT

Readings of temperature and insulation resistance should be recorded every two

hours, from commencement until the full operation is completed. If these readings are

plotted on a graph, the appearance will be as shown in fig.

It is observed that there are four distinct stages:

A. Initially the insulation resistance drops down to a low value because of rise in

temperature of the oil up to about 60 degree C.

B. Insulation resistance will continue to remain at a low level despite temperature being

maintained at a high level until most of the moisture from the windings and oil has

been driven out.

C. The insulation resistance will thereafter rise gradually and level off, indicating that all

moisture has been driven out and the drying out operation has been completed. At

this point oil circulation should be discontinued.

D. As the oil cools off, the insulation resistance will rise much above the leveling off

point at the end stage (C). This is because the insulation resistance value doubles for a

fall in temperature of about 10°C to 15°C.

2.14.3 Condition Monitoring Of Transformer by Dissolved Gas Analysis

Test : Dissolve gas analysis

Test method : As per SMI 138


Permissible limit : As per SMI 138

Requirement of new oil : --

Figure 2.15 DGA Analysis Set (A)

Figure 2.14 Insulation Resistance Graph

INS

UL

AT

ION

RE

SIS

TA

NC

E I

N M

EG

OH

MS

TE

MP

ER

AT

UR

E



35

A. Introduction

In order to detect incipient faults in the transformer and to arrest

deterioration/ damage to the transformer insulation, gases dissolved in the

transformer oil are detected, analysed and preventive measures adopted.

Gas Chromatography method is used for detection of the dissolved gases and

identification of incipient faults. The most significant gases generated by

decomposition of oil and deterioration of paper insulation on the conductor are

hydrogen, methane, ethane, ethylene and acetylene. The quantities of these gases

dissolved in transformer oil vary depending upon the type and severity of the fault

conditions.

B. Sensitivity Limits

Gas Chromatography apparatus should be able to detect the following

minimum concentration of dissolved gases:

Hydrogen : 5 ppm

Hydrocarbon : 1 ppm

Carbon oxides : 25 ppm



36

Figure 2.16 DGA Gas Extraction System



37

C. Establishment of Reference Values/ Bench Marks

To establish a reference value/ bench mark, gas as generated from initial

sample of oil from each healthy transformer should be collected. Results of the

analysis are taken as a reference value/ benchmark. Results of later periodic analysis

are compared with the benchmark for each transformer.

D. Establishment of Norms

The contents of various dissolved gases in the transformer oil vary with

design and operating conditions. It is desirable that the values of concentration of

gases of healthy transformers of different age groups are to be gathered by the

Railways concerned to evolve suitable norms. However, as a starting point, the

permissible concentrations of dissolved gases in the oil of a healthy transformer are

given below as guidelines:

Gas Less than 4 years

in service (ppm)

4-10 years in

service (ppm)

More than 10 years

in service (ppm)

Hydrogen (H2) 100/150 200/300 200/300

Methane (CH4) 50/70 100/150 200/300

Acetylene (C2 H2) 20/30 30/50 100/150

Ethylene (C2 H4) 100/150 150/200 200/400

Ethane (C2 H6) 30/50 100/150 800/1000

Carbon dioxide (CO2) 3000/3500 4000/5000 9000/12000

E. Diagnosis of Fault

Basic Diagnosis of DGA is based upon the quantities of gases generated.

Types of gases in excess of norms produced by oil decomposition/ cellulosic

material depend upon the hot spot temperature produced by faults.

Characteristics of gases associated with various faults are as under:

Methane (CH4) Low temperature hot spot

Ethane (C2 H6) High temperature hot spot

Ethylene (C2 H4) Strong over heating

Acetylene (C2 H2) Arcing

Hydrogen (H2) Partial discharge

Carbon dioxide (CO2) Thermal decomposition of paper insulation

Carbon monoxide (CO)

F. Word of Caution

To start with the diagnosis, it is necessary to be satisfied that measured gas

concentrations are significant and high enough to warrant diagnosis, because some

amount of gases will always be there due to normal operating conditions without any

fault but it can be sufficient to be misleading. The reasons for the situation are:

Gases formed during the refining processes and not completely removed by oil

degassing.

Gases formed during drying and impregnating the transformer in sheds/

workshops.



38

Gases formed in the event of previous faults and not completely removed from

the oil-impregnated insulation before being refilled with degassed oil.

Gases formed during repairs by brazing, welding, etc.

G. Procedure for Fault Diagnosis

Obtain the results of concentration of various gases in terms of microlitre (ppm).

Compare the concentrations with sensitivity limits. These should be at least ten

times the sensitivity.

If it exceeds sensitivity limits, compare with benchmarks.

If it exceeds benchmarks, compare concentrations with norms depending upon

age and design of transformer.

If one or more gases are above norms, compare with the last sample results; if

increase is sufficient, obtain a check sample.

If the check sample confirms the results, calculate the rate of increase of gas. If

rate of increase is more than 10% per month, it is considered rapid and warrants

immediate further investigations including lifting of core and internal inspection.

If the gas production rate is medium, i.e., less than 10% per month, sampling

frequency to be increased from quarterly to monthly.

Take a planned shut down for further investigation.

*****



39

Figure 2.17 Typical Arrangement in a Gas Chromotograph



40

Dissolve Gas Analysis (DGA)

Do’s

1. Give sufficient time for stabilization.

2. Replaced the saptan after every 15 injection

3. Check sapton before start the equipment.

4. Keep standby colomn.

5. Use stabilization electricity with proper earthing.

6. Flush the syringe after each injection.

7. While fire use proper fire extinguisher.

8. Check all leakage before testing.

Don’ts

1. Don’t start TCD before opening of gas.

2. Don’t increase filament current out of safe limit.

3. Don’t excess gas flow in column.

Figure 2.18 Sample Strip Chart

Recording



41

CHAPTER 3

MODEL QUESTIONS

3.1 OBJECTIVE

1. Before starting work on faulty circuit it should be ensured that

a. The faulty circuit has been isolated from power supply and earthed.

b. The worker is capable to do the work.

c. The connections are not approachable.

d. None of the above.

2. One can protect himself from electric shock by wearing hand gloves of good.

a. Conducting material

b. Insulating material

c. Semiconductor material

d. Any of the above.

3. Which of the following are safety precautions?

a. Don’t touch live wire or equipment with bare hands.

d. Before switching on DJ, see no one is working inside loco.

c. Use insulated melting and hand gloves.

d. All of the above.

4. Which material is recommended as fire extinguisher in electrical cases?

a. Carbon tetra chloride

b. Carbon dioxide

c. Sulphur hexafluoride

d. Any of the above.

5. The BDV of transformer oil should be

a. 20kV

b. 30kV

c. 40kV

d. 50kV

6. The colour of moisturized silica gel is

a. Pink

b. Blue

c. Yellow

d. Green



42

7. The material filled in breather of transformer is

a. Silicagel

b. Sulphuric acid

c. SF6

d. Mineral oil

8. The protective device to internal fault in a transformer is

a. Current relay

b. Bucholz

c .Lead

d. Silicon steel

9. Three phase Loco Transformer Tank & Lid made of material.

a. Iron

b. Copper

c. Stainless Steel

d. Aluminium

10. Which of the following is not the function of transformer oil

a. Cooling of winding and core.

b. Providing additional insulation

c. Media for are quenching

d. Provides inducting coupling

11. Transformer oil should be free from

a. Odour

b. Gases

c. Temperature

d. Moisture

12. The short circuit test of a transformer gives

a. Copper loss at full load

b. Copper loss at half load

c. Iron loss at any load.

d. Sum of iron loss and copper loss.

13. The type of oil, which is suitable as transformer oil is

a. Crude oil

b. Organic oil

c. Mineral oil

d. Animal oil

14. Transformer is an example of

a. Current transformer

b. Potential transformer

c. Auto transformer

d. All of the above



43

15. The colour of fresh transformer oil is

a. Pale yellow

b. Dark brown

c. Blue

d. Colourless

16. The purpose of conservator tank in a transformer is to

a. Monitor oil level

b. Top up the oil

c. Both a & b above

d. None of the above.

17. The saturated silica gel can be dried out in the oven at the max temperature until

silica gel turn blue again.

a. 60°C

b. 160°C

c. 150°C

d. 115°C

18. The oil sample container should be rinsed sample oil quantity

a. ½ Ltrs.

b. 1 Ltrs.

c. 2 Ltrs.

d. 1½ Ltrs.

19. The oil sample are require to test.

a. 2 Ltrs.

b. 3 Ltrs.

c. 4 Ltrs.

d. 5 Ltrs.

20. Dielectric strength of oil should be performed using 12.5 mm ball electrodes with a

gap of-

a. 04mm

b. 05mm

c. 2.5mm

d. 03mm



44

3.2. FILL IN THE BLANKS

1. Transformer is a ………….device

2. G-9 Loco transformer has…………….windings

3. G-9 Loco transformer has………………..tank

4. G-9 Loco Required variable voltage is achieved by the use of ……….………….

5. An emf induced in a coil due to variation of flux in another coil is called……

6. The coils of a transformer are wound on a …………core of ………….material

7. The conductors used in HV and LV windings of loco transformer are…………

8. In G-9 Loco The primary side is protected from the voltage surges by means of

………….placed on the roof of the locomotive.

9. The auxiliary winding is protected from sudden rises in voltage by means of

………………connected across the winding.

10. Ingress of moisture is prevented by means of …………….

11. The complete cooling arrangement includes……….., ………..and…………..

12. The oil pump and the cooler are connected to the conservator by…………………

13. The breather is attached to ………………and contains……………

14. Pink colour of silica gel indicates……………..

15. The colour of transformer oil become dark brown, it indicates presence of ……

……

16. Operating vacuum of transformer oil purification plant shoul be ………….

17. DGA stands for …………………..

18. Transformer must never be lift without its……………….

19. Oil BDV Test six consecutive reading should not lie more then……

20. The lifting ropes should not make a smaller angle then….with the horizontal.

3.3 SAY ‘TRUE’ OR ‘FALSE’

1. Transformer transforms power from one AC circuit to another AC circuit, at same

frequency.

2. Transformer can raise or lower the voltage.

3. Transformer can raise or lower the frequency.

4. Two circuits in a transformer linked by a common magnetic flux through a path of

low reluctance.

5. In case of step up transformer, the transformation ratio will be more than one.



45

6. Constructional features of a loco transformer are more or less same other power

transformer.

7. 25 kV condenser/ cable head bushing is mounted on the top of the tank cover.

8. The cooling arrangement of the loco transformer is force oil forced air type.

9. In G-9 Loco the complete cooling equipment is mounted on the cover of the loco

transformer.

10. In G-9 Loco spring-loaded safety valve is fitted to the top of the conservator.

11. Presence of moisture in transformer oil is highly desirable.

12. The oxygen present in transformer reacts with insulation and forms an organic

acid.

13. The solid impurities present in insulation oil strengthen its dielectric strength as

well as insulation of windings.

14. The slackness of winding is desirable factor to create electrical and magnetic

unbalance of the coils.

15. Meggering is done to check the insulation resistance of the windings.

16. The tightening torque of the bolts of tank and lid must be 70 Nm.

17. To arrest the oil leakage from bushing RDSO has recommended to use ISI make

gaskets.

18. Bushing gaskets to be replaced as per TC- 076.

19. New M.S. hardware may be used in transformer flange joints fitting.

20. Periodic maintenance of transformer is essential to ensure safety, reliability and

trouble free operation of Locomotives.

ANSWERS

3.1- 1 (a), 2 (b), 3 (d), 4 (b), 5 (d), 6 (a), 7 (a), 8 (a), 9 (d), 10 (d), 11 (a),

12 (a), 13 (c), 14 (d), 15 (a), 16 (c), 17 (c), 18 (a), 19 (d), 20 (c).

3.2- 1- Static, 2- 04, 3-Aluminium Alloy, 4-GTO or IGBT, 5-Metual Induction,

6- Leminated, Silicon Steel, 7-Continuous Transposed Cu Conductor,

8- Lightening arrester, 9-RCL Damping, 10-Air dehumidifire,

11- Radiator & Blower, 12-oil Pipe, 13-Conservator, Silicagel, 14-Humid

15- Acid & Impurties, 16-1Torr, 17-Incipien fault, 18-Lid, 19-15%, 20-60°.

3.3- 1-T, 2-T, 3-F, 4-T, 5-T, 6-T, 7-T, 8-T, 9-F, 10-T, 11-F,

12-T, 13-F, 14-T, 15-T, 16-T, 17-F, 18-T, 19-F, 20-T.



46

AN APPROACH TO EQUIPMENT FAILURE INVESTIGATION A. On Failure Aspects

1. Occurrence

2. Date of occurrence

3. Past similar occurrences if any

4. Analysis of failure i.e. why did it happen?

5. Whether the rate of failure is worse than other installations?

B. On Maintenance Aspects

1. Whether schedule maintenance & required testing have been carried out on the

failed equipment as per norms stipulated?

2. Does the frequency of maintenance require change?

3. Was the work properly supervised?

4. Was any RDSO modification required to be done?

5. Is any modification possible to avoid failure?

C. About Staff

1. Is the quality of work done satisfactorily?

2. Is the skilled staff properly trained to carry out the work?

3. Is the SMI available with them?

4. Are proper tools available with the staff?

D. About Material

1. Is the material received from approved source?

2. Whether the material is as per approved specification?

3. Can a better material be used?

E. About Testing

1. Is the testing equipment available?

2. Could testing procedure be improved to weed out the failures?

3. Whether testing equipment are calibrated?

F. General Points

Whether following points were checked / performed properly?

1. Proper contact

2. Clearances

3. Capacity

4. Proper contact pressure

5. Crack detections

6. Cleaning

7. Proper connections/alignment

8. Cross checks/super checks



47

ANNEXURE – ‘I’

Reliability Action Plan (RAP)

Condition monitoring of loco transformer by Dissolve Gas Analysis. (RDSO/SMI/138 &

OEM Doc. Dt. 27th Nov. 1995).

Replacement of bushing gaskets during IOH inspection.( ELRS/TC/0076 dt. 17.09.2002).

Maintenance of transformer oil in service.(RDSO/ELRS/SMI/158 dtd. 19.01.95).

Maintenance of assembly of electrical terminal of traction winding bushing 2U1-2V1, 2U2-

2V2, 2U3-2V3 & 2U4-2V4 in indigenously

manufactured transformers type LOT 6500/7500 used in 3-phase drive locomotives type

WAG9/WAP5.( RDSO/ELRS/SMI/0228 dt. 13.08.02)

Ensuring tightness of stuchi coupling, base plate and conservator tank foundation bolt

during overhauling. As per OEM guidelines & present

practices followed by shed.

“Ensure instructtions contained in RDSO’s letter no. EL/3.2.1/3-Ph dated 30.07.09 for

arresting oil leakages cases.”



48

REFERENCE

1. ABB Maintenance manual.

2. Electrical Technology Books.

3. RDSO SMI 138, 158

4. RDSO MS 0228.

5. RDSO TC - 076

6. Details collected from various field units (Shed and workshop).

7. Details collected from M/s High voltage Electrical Ltd. , Mumbai

6. Suggestions received during the seminar held on 30.10.2014 organised by

CAMTECH/ Gwalior.



49

To upgrade maintenance technologies and

methodologies and achieve improvement in

productivity, performance of all Railway

assets and manpower which inter-alia would

cover reliability, availability, utilisation and

efficiency.

If you have any suggestions and any specific Comments

please write to us.

Contact person : Director (Elect.)

Postal Address : Indian railways

Centre for Advanced

Maintenance technology,

Maharajpur, Gwalior.

Pin code – 474 005

Phone : 0751 – 2470740

0751 – 2470803

E-mail : [email protected]

Fax : 0751 - 2470841

OUR OBJECTIVE

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