Transformer Life Management Condition Assessment and Dissolved Gas Analysis

19/09/2006 Prepared by : VKL 1

TRANSFORMER LIFE MANAGEMENT,CONDITION ASSESSMENT

&DISSOLVED GAS ANALYSIS

By : VK LAKHIANICROMPTON GREAVES LTDMUMBAI


OUTLOOK

• MECHANISMS OF LIFE DEGRADATION PHENOMENA

• KEY DETERIORATION PROCESSES

• LIFE ASSESSMENT AND CONDITION MONITORING TECHNIQUES & RECOMMENDATIONS

• DISSOLVED GAS ANALYSIS


TRANSFORMER LIFE INVOLVES SEVERAL MECHANISMS OF

DEGRADATION


COMPONENTS OF TECHNICAL LIFE OF A TRANSFORMER

1) THERMAL LIFE

2) DIELECTRIC LIFE

3) MECHANICAL LIFE

4) LIFE OF ACCESSORIES


Thermal LifeTime to critical decomposition DP<200

Is the Life of Transformermechanical life of Aged paper?

AGED


Dielectric LifeTime span to critical reduction of dielectric margin


Mechanical weakness and Deformation under cumulative stresses

of through faults


Impairment of electromagnetic circuit


Life of OLTC


Limited life of bushings


TRANSFORMER LIFE IS TRANSFORMER INSULATION LIFE

TRANSFORMER INSULATION LIFE IS DEFINED AS PER IEC 60076-7 AS :

“TOTAL TIME BETWEEN THE INITIAL STATEFOR WHICH THE INSULATION IS CONSIDERED NEW AND THE FINAL STATE WHEN DUE TO THERMAL AGEING, DIELECTRIC STRESS, SHORT CIRCUIT STRESS, OR MECHANICAL MOVEMENT, WHICH COULD OCCUR IN NORMAL SERVICE AND RESULT IN A HIGH RISK OF ELECTRICAL FAILURE”


RELATIVE THERMAL AGEING RATE

AS DEFINED IN IEC 60076-7

“FOR A GIVEN HOT SPOT TEMPERATURE, RATE AT WHICH TRANSFORMER INSULATION AGEING IS REDUCED OR ACCELERATED COMPARED WITH THE AGEING RATE AT A REFERENCE HOT SPOT TEMPERATURE”

THE RELATIVE AGEING RATE v=1.0 CORRESPONDS TO TEMPERATURE OF 98°C FOR NON-THERMNALLY UPGRADED PAPER AND TO 110°C FOR THERMALLY UPGRADED PAPER.


LIFE OF PAPER UNDER VARIOUS CONDITIONS

121898°C

273490°C

767280°CUPGRADED PAPER

0.81598°C

1.93890°C

5.711880°CNON-UPGRADED PAPER

WITH AIR AND 2% MOISTURE

DRY AND FREE FROM AIR

LIFE YEARSPAPER TYPE / AGEING TEMP


RELATIVE AGEING RATE

(θh – 98/6)V = 2 ………….. FOR NON-THERMALLY

UPGRADED PAPER

{ 15000 15000 }{ ------------ - --------- }{ 110 + 273 θh + 273 }

V = e

…………….FOR THERMALLYUPGRADED PAPER

WHERE θh = HOTSPOT TEMPERATURE °C


RELATIVE AGEING RATES DUE TO HOT--SPOT TEMPERATURE

17.2128.014010.164.01345.832.01283.2916.01221.838.01161.04.0110

0.5362.01040.2821.0980.1450.5920.0730.25860.0360.12580

UPGRADED PAPER-V

NON-UPGRADED PAPER– V

θh °C


NORMAL INSULATION LIFE OF A WELL DRIED, OXYGEN FREE THERMALLY UPGRADED PAPER AT REFERENCE

TEMPERATURE OF 110 °C

20.55180000INTERPRETATION OF DISTRIBUTED TRANSFORMER FUNCTIONAL LIFE

17.12150000200 RETAINED DEGREE OF POLYMERISATION

15.4113500025% RETAINED TENSILE STRENGTH OF INSULATION

7.426500050% RETAINED TENSILE STRENGTH OF INSULATION

YEARSHOURS

NORMAL INSULATION LIFEBASIS


DIELECTRIC LIFE

• ‘PD’ GOVERNS THE DIELECTRIC LIFE!• PD IS A RESULT OF VOLTAGE STRESSES• VOLTAGE STRESSES ARE ON ACCOUNT OF

SWITCHING IN/OFF, LIGHTNING, SYSTEM OVERVOLTAGES

• DESIGN IS MADE FOR PD FREE CONDITION AT TEST VOLTAGE

• TEST LEVELS ARE MUCH HIGHER THAN DAY IN/DAY OUT SWITCHING CONDITIONS

• FOR NEW INSULATION THESE SWITCHING IN/OFF OPERATIONS DO NOT AFFECT THE LIFE

• IN AGED INSULATION PD THRESHOLD VALUE MAY REDUCE AND PD MAY OCCUR DURING SWITCHING IN/OUT CONDITIONS AFFECTING LIFE

• NO DATA AVAILABLE AS TO HOW MANY TIMES SWITCHING IN/OFF MAY BE PERMITTED

• INRUSH CURRENTS MAY HAVE MECHANICAL STRESSING


MECHANICAL LIFE (DUE TO SYSTEM SHORT CIRCUIT FAULTS)

• THERE IS NO CONSENSUS ABOUT HOW MANY TIMES THE TRANSFORMER CAN WITHSTAND SHORT CIRCUITS AT FULL LEVEL.

• FAILURE RATE AT KEMA AND OTHER SHORT CIRCUIT LAB IS 30% OR MORE

• THERE IS NO CONSENSUS ON AGEING DUE TO SHORT CIRCUIT

• WINDING DISPLACEMENT DO TAKE PLACE WITH EVERY SHORT CIRCUIT AND NEED BE MONITORED BY FRA


The life cycleSAFETYMARGIN

CRITICALLEVEL

FAILED

NORMAL DEFECTIVE FAULTY


Review of key deterioration processes


Deterioration processes

Moisture contaminationParticles in oil Oil oxidationPaper agingSurface contaminationImpact of oil by-products


Moisture contamination


Why Moisture management is so important for transformer life?

Moisture affects transformers both in the short and long term.Short-term risks electrical failures due to the influence of the moisture in both the

paper and the oil in the transformer, e.g.• Partial discharge• Surface creapage• Flashovers

Long-term riskThe presence of moisture in the transformer, to whatever degree,

does actually harm the insulation which is, in fact permanent damage.


What is the effect of moisture on the dielectric breakdown voltage in the

insulation?

The dielectric properties of the solid and liquid insulation arepartly influenced by the water content and temperature.

The dielectric breakdown voltage of the solid insulation decreases with increasing water content.

This occurs most noticeably after 2 to 3 percent, but usually the lower levels are considered best for complete electrical integrity.


What is bubble evolution?

Bubble evolution occurs when the transformer insulation is heated rapidly to the extent that the moisture within the paper is transformed into vapours, which move out of the paper in a bubble form.

This phenomenon can cause streaming of gas bubbles in an electrical stress field, thus creating a flashover,Under overload conditions.

Dry transformers (<0,5% water in paper) are much less susceptible to bubble evolution. Emergency loading of dry insulation at hot-spot temperatures below 180°C may be possible with little risk of bubble generation.

However, a wetter unit, with 2.0% moisture in paper, should not be operated above hot-spot temperatures of 139°C under the same conditions.


Structure of Transformer Insulation

Processes of insulation deterioration involve slow diffusion of water, gases, and aging products and therefore affect basically only the so-called thin structure


The main insulation components of a core-type transformer

Angle ring

Clamping plate

Spacer block

Paper wrap around copper wireCylinder


Insulation components. Thin structure

Turn coil, conductors (paper)Barriers (pressboard)Angle ring

Diffusion time constant – a few days-month


Insulation components. Thick structure

Support blocksStrips , SpacersClamping rings and plates

40-55% of the mass and 4-8% of the surface

Diffusion time constant – some years


Thick components absorb miserable amount of moisture

φ= 55%

Thin

Thick

50 days


Thin structure retain a large portion of the water

Thin cold structures” that operate at bulk oil temperatures is the main storage area for water which is readily available for migration between oil and cellulosic materialsAbout 10% (by mass) which is at the coldest temperature, forms “ wet” zones, where water contents can be 1 – 1.5% higher than the average value

Components of this group are the main source of high water in oil during temperature cycling


Moisture profile


What are sources of Moisture in transformers ?

Source of MoistureOnce in service a transformer is subjected to the

following sources of moisture:

external - from the atmosphere

internal - from manufacture

internal - from cellulose (paper) ageing


Free water through poor sealing is repeatable worldwide case


Accumulation of free water on the bottom core yoke


Merits & Limitations of Moisture-measurement methods

Methods usedKarl-Fisher method

On-line moisture probe

Water Heat Run testDielectric SpectroscopyReturn Voltage measurement RVM

Frequency Domain Spectroscopy]-- FDS ]

Polarization /Depolarization ] Current -- PDC ]

Simple conventional method, difficult to estimate moisture in solid insulation.

Requires proprietary algorithms to relate moisture content reading indicated by probe to moisture in solid insulation

Estimates the level of water contamination using the build-up of water content in oil with time and temperature

The measured moisture content is much higher than the other method. The interpretation is too simplistic. Does not take into account dependencies on geometry of design and oil properties.

These methods take into account geometry and oil properties into account. Better method for estimating moisture in solid insulation.


Particles in oil


Particles origin

ForeignDebris

Oil

ManufacturingDebris

Componentdelivered particles

Oil deliveredparticles


Particles mode

Cellulose fibers, iron,aluminum,copper

Manufacturing


ForeignManufacturingInstallation, Repair


Component wear out:Pumps, coolers, OLTC, contacts, cellulose

Polymers, carbonOil : oxidation pyrolysis by-products/


Type of particles

Floating in oil In solution in oilOn surface depositionMigration through paper layers


Particles microscopic analysis

Quartz

Coke

InsectFragment Paper fiber

Copper


Insulation contamination


Surface contamination


Attraction by field and Deposit conductive sediments

Oil sludge deposit

Carbon depositConductive particles deposit


Impact of corrosive oil

Originally formally non-corrosive oil becomes corrosive under effect of temperature and time

The presence of Cu2S coating (copper sulfite)On conductorOn paper facing the conductorOn free cellulose surfaces

Deposition can occur at low temperaturesTime required for test 12 weeks at 100oC, 3 weeks 120oC


Corrosive Deposits on Coils


Failures of 28 MVA ,500 kV shunt reactors due to affect of corrosive sulfur

short circuits between turnsof the disks in the upperpart of the winding

copper conductors were covered by a heavy black film

Bad cooling due to obstruction to the oil entrance


Alternative Corrosion Tests

ASTM D 1275

Copper strip 19 hours @ 140oC

IEC ( DIN 51353)

silver strip.

in air at 100°C

for 18 hours

Modified ASTM D127548 hours @ 150oC

ГОСТ 2917-76

Copper strip

3 hours @ 100oC

ABB proposal:Covered Conductor Corrosion & Depositionwrapped copper conductor bar,100°C 9-12 weeks.


Oil oxidation


Peroxide AlcoholsPhenolsFree radicals

Non-acid polarCarbonides

AldehydesKetones

Carboxyl(acids)

Product of condensation and polymerization

Sludge:Soluble

Non-soluble

Mechanism of oxidation: attack of Dissolved oxygen


Paper aging


Thermal Life is a function oftemperature, water and by-products

][36524

11

_ 27313350

yearseA

DPDPLifeExpected TStartEnd +⋅

∗•

−=

Hot spot temperature

Water & acids


Aging profile


End of life can come under 20Aging profile of 700 MVA, 420 kV, 14 years

Hot spot area


Impact of oil by-product on degradation of insulation

properties


Predominant deterioration of surface layers from oil side

Oil side

Copper side

Destruction of surfacelayers


Residue results in dielectric degradation

Insulationcondition

Stability to PD actions.Time to flashover

Surface ResistivityOhm

Pressboard with residue on the surface

Flashover immediately after rise the voltage

3·1013

Without residue

12 min 2·1014


Adsorption of oil by products results in deterioration of dielectric properties of

paper

3.910.1final

4.914.5final

0.710.010.21final

initial

initial

initial

2.30.43Creep paper

3.30.6Kraftpaper

0.14ND0.01Oil

ε20tgδ20SludgeHydrophilic

acids


Condition Assessment and Maintenance


Main maintenance modes

Reactive – reacting to problems as theyarise due to emergencies

Proactive – work programme basedon monitored data


Reactive maintenance varies from:

“If it is not broken don’t fix it”, to

Time based activities that are carried out too often, and may not be required


PROACTIVE MAINTENANCE is based on surveillance and monitoring activities:

SURVEILLANCE involves batch analysis of oil samples and planned diagnostic measurements

MONITORING involves regular measurement of data, perhaps on a continuous basis


Aims of transformer surveillance

• Predictive maintenance• Life extension• Refurbishment• Replacement strategy


Drivers to install surveillance equipment

• Need to reduce maintenance costs

• Increased use of power electronics

• Maintenance equipment inefficient for

modern electronics-based schemes


Transformer surveillance – on-line

• Oil analysis (resistivity, particles, water) • Dissolved gas analysis• Liquid chromatography• Partial discharge (electrical Lemke probe)• Partial discharge (acoustic)• Temperature (infra-red camera)• Vibration


Transformer surveillance – off-line measurements

• Recovery voltage method (RVM)• Leakage inductance• Low frequency impulse• Fourier analysis• Frequency response analysis (FRA)• Dielectric loss angle


Transformer surveillance – intrusive measurements

• Degree of polymerisation (DP index)• Winding clamping pressure• OLTC contact wear• Gel permeation chromatography• X-ray photoelectron spectroscopy


Transformer condition monitoring :

External sensors

• Temperature (tank and OLTC)

• Partial discharge (electrical and acoustic)

• Current (loading , fault levels and life history)

• Voltage (system transients)

• On-line DGA


Transformer condition monitoring :

Internal sensors• Partial discharge (waveguide and acoustic)

• Water content of oil

• Hydrogen and CH gases

• Winding temperature (point and distributed)

• Movement and vibration

• Magnetic field


Maintenance strategies

• CM - corrective maintenance

• TBM - time based maintenance

• CBM - condition based maintenance

• RCM - reliability centred maintenance


RECOMMENDATION FOR CONDITION MONITORING

1. THERMAL LIFE

1) DGA2) FURFURAL C ONTENTS3) DP4) FIBRE OPTIC HOT SPOT MEASUREMENT(NEW)5) THERMAL IMAGING

2. DIELECTRIC LIFE

1) PD2) OIL QUANTITY 3) FDS

3. MECHANICAL

1) FRA


DISSOLVED GAS ANALYSIS (DGA)OF MINERAL OIL INSULATING

FLUIDS IN TRANSFORMERS -INTERPRETATIONS


WHY DGA ?

1. INSULATING MATERIALS AT HIGHER TEMPERATURES AND AT ELECTRICAL FAULTS BREAKDOWN LIBERATE GASES.

2. DISTRIBUTION OF THESE GASES CAN BE RELATED TO TYPE OF FAULTS AND RATE OF GAS GENERATION CAN INDICATE THE SEVERITY OF FAULT :

3. OBVIOUS ADVANTAGES THAT DGA CAN PROVIDE ARE :i) ADVANCE WARNING OF DEVELOPING FAULTSii) DETERMINING THE IMPROPER USE OF UNITSiii) STATUS CHECKS ON NEW & REPAIRED UNITSiv) CONVENIENT SCHEDULING OF REPAIRSv) MONITORING OF UNITS UNDER OVERLOAD


BASICS OF DGA ?

ORIGIN OF FAULT GASES :

1) CORONA OR PARTIAL DISCHARGE2) PYROLYSIS OR THERMAL HEATING3) ARCING

- THESE THREE CAUSES DIFFER MAINLY IN THE INTENSITY OF ENERGY DISSIPATION PER UNIT TIME PER UNIT VOLUME BY FAULT.

- MOST SEVERE INTENSITY OF ENERGY DISSIPATION OCCURS WITH ARCING LESS WITH HEATING AND LEAST WITH CORONA


FAULT GASES

CLASSIFIED IN 3 GROUPS :

1. HYDROCARBONS AND HYDROGENMETHANE CH4 ETHANE C2H6ETHYLENE C2H4 ACETYLENE C2H2HYDROGEN H2

2. CARBON OXIDESCARBON MONOXIDE CoCARBON DIAOXIDE Co2

3. NON-FAULT GASESNITROGEN N2 OXYGEN 02

SOME LABORATORIES ALSO MEASURE PROPYLENE, PROPANE AND PROPYNE


FAULT GASES Vs TYPE OF MATERIAL INVOLVEDAND TYPE OF FAULT

1. CORONAA) OIL H2B) CELLULOSE H2, Co, Co2

2. PYROLYSIS LOW TEMP. HIGH TEMP.A) OIL CH4, C2H6 C2H4,H2(CH4,C2H2)B) CELLULOSE Co2 (Co) Co (Co2)

3. ARCING H2, C2H2 (CH4, C2H6, C2H4)


FAILURE ANALYSIS AND DGA

1. INSTANTANEOUS FAILURES THAT CANNOT BE PREVENTED BY DGA

-FLASHOVER WITH POWER FLOW THROUGH

2. SERIOUS FAILURES, DEVELOPING WITHINSECONDS AND NOT DETECTED BY DGA

-BROKEN OR LOOSE CONNECTION IN A WINDING WHICH LEADS TO SMALL ARC WHICH BURNS THE SOLID INSULATION


FAILURE ANALYSIS AND DGA (CONTD)

DETERIORATED CONDUCTOR INSULATION PAPER LEADING TO INTERTURN FAULT

BROKEN LOOSE OR DAMAGED DRAW ROD IN A BUSHING CAUSING SPARKING AND ARCING WITHIN TUBE

BUSHING EXPLOSION LEADING TO FIRE



3. DETECTABLE FAULTS BY DGA

3.1 WITHIN WINDING

A) SHORTING OF PARALLEL WIRES IN A BUNCH CONDUCTOR WITHIN A COMMON PAPER COVERING

B) LOST POTENTIAL CONNECTIONS TO SHIELDING RINGS, TORROIDS- FLOATING POTENTIALS, SPARKING TO GROUNDS

C) CONDITIONS OF PARTIAL DISCHARGES BETWEEN DISCS OR CONDUCTORS DUE TO CONTAMINATED LOCAL OIL-LEADING TO FLASHOVER



3.2 CLEATS AND LEADS

A) BOLTED CONNECTIONS, PARTICULARLY BETWEEN ALUMINIUM BUSBARS, IF THE SPRING WASHERS DO NOT SUSTAIN THE NEEDED HIGH PRESSURE

B) ALL GLIDING MOVING CONTACTS FORMING BAD JOINTS DUE TO AGEING



3.3 IN THE TANK

A) HEATING OF TANK PART, BOLT ETC. DUE TO MAGNETIC FIELD

B) OVERHEATING DUE TO DOUBLE GROUNDING OF THE CORE

C) DAMAGED INSULATION BETWEEN COVER SUPPORT POINT DUE TO CLOSED LOOP



3.4 SELECTOR SWITCH

A) CARBONISATION OF SELECTOR SWITCH CONTACTS AND HOTSPOT FORMATION

B) GAP BETWEEN SELECTOR SWITCH CONTACTS

3.5 CORE

A) SHORTING AT BURRS OF LAMINATIONS

B) FAILURE OF BOLT INSULATION


STANDARDS ON DGA

1.”RECENT DEVELOPMENTS IN DGA INTERPRETATION”Cigre Brochure 296,June 2006

2. “NEW GUIDELINES FOR INTERPRETATION OF DGA IN OIL-IMMERSED TRANSFORMERS” cigre Task force 15.01.01,Octr 1999

3. LIFE MANAGEMENT TECHNIQUES FOR POWER TRANSFORMERS-WG12-18,cigre br.227,2003

4. IEC PUB. 60599 (1999-03)-GUIDE TO INTERPRETATION OF DGA

5. IEEE Std.C57.104-1991 IEEE GUIDE FORINTERPRETATION OF DGA


ABBREVIATIONS USED

ALARM RATE OF GAS INCREASE

ARGI

VALUES INTERMEDIATE BETWEEN TGC AND PFGC

ALARM GAS CONCENTRATION

AGC

PRE-FAILURE RATE OF GAS INCREASE

PFGC

GAS ANALYSIS CORRESPONDING TO A FAILURE RELATED EVENT

PROBABILITY OF A FAILURE RELATED EVENT IN SERVICE

PFS

TYPICAL RATE OF GAS INCREASE

TRGI

TYPICAL VALUES OBSERVED IN 90% OF A POPULATION OF TRANSFORMERS IN SERVICE

TYPICAL GAS CONCENTRATION

TGC


RANGES OF 90% TYPICAL(TGC) VALUESFOR POWER TRANSFORMERS,in ppm (CORE FORM)

60-280COMMUNI-CATING OLTC

2-20NO OLTC

3800-14000

400-600

20-9060-280

30-130

50-150

C02C0C2H6C2H4CH4H2C2H2


RANGES OF 90% TYPICAL(TRGI)FOR POWER TRANSFORMERS, in ppm/YEAR

(CORE TYPE)

21-37COMMUNI-CATING OLTC

0-4NO OLTC

11700-10,000

260-1060

5-9032-146

10-120

35-132

C02C0C2H6C2H4CH4H2C2H2


PFGC VALUES CALCULATED ON DIFFERENT NETWORKS, in ppm

13005001800480270240LCIE-shell12006001050830340900LCIE-core15003101000700460550LCIE-hydro

9844088509934241318Labelec

9844088509934241318HQ

3000350750900400600PFGC

COC2H2C2H6C2H4CH4H2


AGC VALUES CALCULATED ON DIFFERENT NETWORKS, in ppm

10001001700340200110LCIE-shell

110070800120150240LCIE-core

1300120670240230290LCIE-hydro

956295805421194665Labelec

1700170400350120250HQ

AGC

COC2H2C2H6C2H4CH4H2


TYPICAL STRAY GASSING TEST RESULTSAT 120°C in ppm/16h OF TEST

172-10-2191088-240-61NEW VOLTESSO 35

161-15-88127-9-85OLD VOLTESSO 35

3-14-(0)138-27(0)NYNAS 10GBN

1-2-576-16-14DIALA G

41-5-(107)54-8-(60)NYTRO 11EN

4-1-(9)60-7-(25)UNIVOLT 52

0-1-(0)48-19-(147)DIALA S

1-0-250-16-27NYNAS 10 XT

0-0-(0)12-7-(0)NYNAS 10 X16-164-1616-164-16TEST DURATION, h

CH4H2


TYPICAL STRAY GASSING TEST RESULTS AT 200°C in ppm/16h OF TEST

260-32-(0)232-32-(0)45-5-(0)NYTRO 11EN

97-15-(0)147-20(0)26-2-(6)UNIVOLT 52

91-1689-16-(0)49-6-(0)DIALA S

C2H6CH4H2OIL


CALCULATED CONTRIBUTION OF STRAY GASSING TO GAS LEVELS IN TRANSFORMERS AFTER HEAT RUN TESTS, IN ppm OF H2

10-50---0.10.2UNIVOLT 5210-50--0.10.20.4DIALA D50--0.10.20.5TECHNOL 400020-0.10.20.30.5OLD VOLTESSO 35

-0.10.20.40.8NYTRO 10GBN

0.10.71.32.24.0NEW VOLTESSO 35

OBSERVED DURING HEAT RUN TESTS

8598110120140HOTTEST SPOT

TEMP °C


STRAY GASSING VS. CATALYTIC REACTIONS AND CORONA PARTIAL DISCHARGES

>0.4C2H6,CH4,H2- AT 200 °C

0.15-1H2,CH4,C2H6- AT 120 °C

STRAY GASSING OF OIL :

0.02-0.14H2,CH4CORONA PARTIAL DISCHARGES

<0.02H2CATALYTIC REACTIONS

CH4/H2GASES FORMED


RATES OF GAS FORMATION FROM PAPER, IN ppm / YEAR / kg OF PAPER / 50,000 L OF OIL

TECHNOL4000

3.57800023400

38852001230250/300°C

NYNAS 11CX

1518301223312400160°C

NYNAS 10CX

422305--0.40.30135°C

NYNAS 10CX

502204--0.30.40125°C

OIL USEDCO2/CO

CO2COC2H6C2H4CH4H2C2H2PAPER TEMP.


RECOMMENDATIONS

1. DISSOLVED GAS CONCENTRATIONS IN SERVICE

INDIVIDUAL NETWORKS ARE RECOMMENDED TO CALCULATE THEIR OWN TYPICAL VALUES OF TGC & TRGI WHENEVER POSSIBLE.

2. THERMAL STRAY GASSING OF OIL

• STRAY GASSING IN GENERAL, WILL NOT INTERFERE WITH DGA DIAGNOSES UNLESS A AVERY STRONGLY STRAY GASSING OIL IS USED OR OPERATION IS LARGELY ABOVE NOMINAL LOAD.

• HEAT RUN TESTS IN GENERAL WILL NOT BE AFFECTED BY THE STRAY GASSING OF OIL.


RECOMMENDATIONS (CONTD.)

3. GAS FORMATION FROM PAPER

• AMOUNT OF PAPER INVOLVED IN A FAULT CAN BE CALCULATED FROM GAS FORMATION RATES.

4. PARTIAL DISCHARGES

• DGA IS PARTICULARLY USEFUL TO DETERMINE WHEN PARTIAL DISCHARGES START BECOMING HARMFUL TO THE INSULATION AND DETECTABLE BY VISUAL INSPECTION.


RECOMMENDATIONS (CONTD.)

5. GAS TRAPPED IN PAPER INSULATION

• TRAPPED GASES ARE DIFFICULT TO REMOVEPARTIAL DISCHARGES

• THE ONLY WAY TO DO THAT IS BY INCREASING THE TEMPERATURE TO 60 °C DURING 1 TO 6 MONTH PERIOD FOR H2 AND HYDROCARBONS AND TO 70-90 °C DURING 3 TO 6 MONTHS FOR CO, CO2.

• ALTERNATIVE PROCEDFURE WOULD BE TO SUBJECT THE TRANSFORMER TO VAPOUR-PHASE DRYING TO REMOVE THE CONTAMINATED OIL FROM PAPER.


DGA INTERPRETATION - STATUS

• ATTEMPTS TO DIAGNOSE THE TYPE OF A FAULT FROM THE GASES EVOLVED FROM THE OIL STARTED BY BUCHHOLZ AS EARLY AS 1928.

• SEVERAL METHODS ARE IN USE FOR THE INTERPRETATION OF RESULTS

• NO SINGLE METHOD IS CAPABLE OF UNIVERSAL USE.


DGA INTERPRETATION - STATUS (CONTD.)

• TWO POINTS TO CONSIDER BEFORE PROCEEDING WITH ANY METHOD OF DIAGNOSIS.

1) RESULTS OBTAINED FROM DGA MUSTBE ABOVE THE DETECTION LIMIT OF THE INSTRUMENT.

2) THE MEASURED GAS CONCENTRATIONS ARE SIGNIFICANT


DGA INTERPRETATION METHODS

I) RATIO TECHNIQUE

• IEC 60599 RECOMMENDS USE OF 5 GASES AND 3 RATIOS.

• IEEE STD C57.104 AND ROGERS AND DORNENBURG ALSO RECOMMEND THE SAME 5 GASES. THE GASES ARE LISTED IN ORDER OF INCREASING DECOMPOSITION TEMPERATURE.


DGA INTERPRETATION METHODS (CONTD.)

II) GRAPHICAL REPRESENTATION

• CONVENIENT TO VISUALLY FOLLOW THE EVOLUTION OF FAULTS

• BASED ON CALCULATING THE RELATIVE PERCENTAGE OF 3 GASES. EACH CORNER OF A TRIANGLE REPRESENTS 100% OF ONE GAS AND 0% OF THE OTHER GAS.

• PLOTTING THE PERCENTAGE OF THE 3 GASES ON THE TRIANGLE DEPENDS ON THE AREA ON WHICH A DIAGNOSIS IS NAMED.



III) KEY GAS METHOD

• DEPENDENCE OF TEMPERATURE TO THE TYPES OF OIL & CELLULOSE DECOMPOSITION GASES PROVIDES THE BASIS FOR THE QUALITATIVE DETERMINATION OF FAULT GASES THAT ARE TYPICAL, OR PREDOMINANT AT VARIOUS TEMPERATURES.

• THESE SIGNIFICANT GASES AND PROPORTIONS ARE CALLED “KEY GAS”



III) KEY GAS METHOD (CONTD.)

• THIS TECHNIQUE PROVIDES GRAPHS FOR 4 GENERAL FAULT TYPES

• THERMAL (OIL DECOMPOSITION)• THERMAL (CELLULOSE

DECOMPOSITION)• ELECTRICAL (CORONA)• ELECTRICAL (ARCING)


DGA INTERPRETATION METHODS-CLASSICAL

1) IEC 60599

• FIRST PUBLISHED IN 1978• METHOD OF INTERPRETATION USES RATIO

TECHNIQUE AND EMPLOY 3 RATIOS

CH4 / H2C2H4/C2H6C2H2/C2H4

• INTERPRETATION OF THE RESULTS SHOULD BE CARRIED OUT IF THE GASES CONCENTRATIONS ARE ABOVE THE SIGNIFICANT LEVELS.



2) IEEE METHOD

• GENERALLY 3 TYPES OF FAULTS ARE CONSIDERED

• THERMAL• LOW ENERGY ELECTRICAL• HIGH ENERGY ELECTRICAL

• TOTAL COMBUSTIBLE GASES AND CONCENTRATION LIMITS FOR FOUR CONDITIONS ARE SUGGESTED FOR ACTIONS



2) IEEE METHOD (CONTD.)

• THE RATIOS USED FOR KEY GASES ARE SIMILAR TO IEC 60599

C2H2 CH4 C2H2_____ , ____ , _____C2H4 H2 C2H6

TO DIAGNOSE POSSIBLE FAULTS.



2) IEEE METHOD (CONTD.)

• REFERENCE IS MADE TO DORNENBURG.

• EVOLUTION OF THE GAS CONCENTRATION IS FUNCTION OF THE TIME AND AN IMPORTANT PART OF THIS STANDARD.



3) CEGB / ROGERS RATIOS

• CENTRAL ELECTRICITY GENERATING BOARD OF ENGLAND AND WALES STARTED EXTENSIVE WORK ON FAULT GAS CORELATIONS AS EARLY AS 1968.

• THE STUDY INDICATED THAT AN INCREASE IN OIL TEMPERATURE LEADS TO AN INCREASE IN THE RATIO OF UNSATURATED TO SATURATED HYDROCARBONS ESPECIALLY RATIOS C2H2/C2H4 , C2H4/C2H6.



3) CEGB / ROGERS RATIOS (CONTD.)

• THERE IS ALSO A PREDICTED INCREASE IN THE AMOUNT OF HYDROGEN PRODUCED WITH INCREASING TEMPERATURES

• 4 RATIOS USED :

CH4/H2 C2H6/CH4C2H4/C2H6 C2H2/C2H4

• ROGERS REPORTED ABOVE IN 1978.



3) CEGB / ROGERS RATIOS (CONTD.)

• THE GASES ARE USED IN ORDER OF INCREASING DECOMPOSITION TEMPERATURE

• DEPENDING UPON THE RATIO, A CODE NO. IS GIVEN.

• THE CODE NUMBER WILL LEAD TO FAULT DIAGNOSIS.

• SEVERAL SIMULTANEOUS OCCURRING FAULTS CAN CAUSE AMBIGUITY



4) SCHLIESINGER METHOD

• A RATIO TECHNIQUE, COMBINED WITH LIMIT OF GAS CONCENTRATION. COMBINATION OF RATIO AND LIMIT OF GAS CONCENTRATION WILL LEAD TO A CODE WHICH CAN BE USED FOR INTERPRETATION OF THE RESULTS.

• 5 RATIOS USED :

C2H2/H2 C2H2/C2H6 H2/CH6

C2H2/C2H6 C02/CO



4) SCHLIESINGER METHOD (CONTD.)

• DEPENDING ON THE CONCENTRATION OF THESE GASES CODES ARE EXTRACTED FROM THE TABLE.

• COMBINATIONS OF THE CODES ARE LISTED IN THE DIAGNOSTIC TABLE

• METHOD IS CAPABLE OF DISTINGUISING MORE THAN ONE FAULT.



5) DORNENBURG’S METHOD

• ORIGINAL METHOD PLOTTED THE RATIO CH4 / H2 AGAINST C2H2/C2H4 USING LOG LOG PAPER.

• THE METHOD WAS FOUND TO BE INSUFFICIENTLY DISCRIMINATIVE ALTHOUGH HAVING THE ADVANTAGE OF BEING APPLICABLE TO BUCHHOLZ GASES.

• LATER ON METHOD WAS REVISED TO USE RATIO OF MEASURED GASES



6)NOMOGRAPH TECHNIQUE

• COMBINATION OF FAULT GAS RATIO CONCEPT WITH ESTABLISHED VALUES.

• INTENDED TO PROVIDE BOTH GRAPHICAL REPRESENTATION OF FAULT GAS DATA AND TH MEANS TO INTERPRET THEIR SIGNIFICANCE.

• CONSISTS OF A SERIES OF VERTICAL LOGARITHMIC SCALES REPRESENTING THE CONCENTRATIONS OF THE INDIVIDUAL GASES.



6)NOMOGRAPH TECHNIQUE (CONTD.)

• STRAIGHT LINES ARE DRAWN BETWEEN ADJACENT SCALES TO CONNECT THE POINTS REPRESENTING THE VALUES OF KEY GAS CONCENTRATIONS.

• SLOPES OF THESE LINES ARE THE DIAGNOSTIC CRITERIA FOR DETERMINING THE TYPE OF FAULT.



7) DUVAL METHOD

• REPORTED IN 1989 BY DUVAL OF HYDRO-QUEBEC BY USING A TRIANGLE

• BASED ON CALCULATING THE PERCENTAGE OF 3 GASES :

CH4 C2H4 C2H2

• EACH CORNER OF THE TRIANGLE REPRESENTS 100% OF ONE GAS AND 0% OF THE OTHER



7)DUVAL METHOD (CONTD.)

• CONCENTRATION OF THE GASES INCREASE IN CLOCK-WISE DIRECTION.

• INSIDE OF THE TRIANGLE IS DIVIDED INTO 6 DIFFERENT AREAS.

• METHOD EASY BUT SOME WHAT BULKY.


IV) RATE OF EVOLUTION OF THE GASES

• CALCULATES RATES OF GAS GENERATION BY COMPARING RESULTS OF TWO ANALYSES AND DATES OF THE ANALYSIS.

• SINCE VOLUME OF THE OIL REMAINS CONSTANT, RELATIVE CHANGES IN FAULT GAS CONCENTRATIONS OVER TIME MAKES POSSIBLE THE CALCULATION OF THE RATE OF EVOLUTION OF THE GASES.


V) KEY GASES

• TECHNIQUES RELATES EACH INDIVIDUAL GAS TO A PROBABLE FAULT

• H2 IS PRODUCED BY TWO MECHANISMS :

• AT LOW TEMPERATURE ASSOCIATED WITH PD

• AT ELEVATED TEMPERATURE PRODUCED BY FRACTIONATION OF THE OIL.


V) KEY GASES (CONTD.)

• C2H2 IS ASSOCIATED WITH HIGH ENERGY DISSIPATION.

• LOW MOLECULAR WEIGHT HYDROCARBON WHEN PRODUCED TOGETHER WITH H2, INDICATES PYROLYSIS.

• A FAULT DOES NOT PRODUCE A SINGLE UNIQUE DECOMPOSITION PRODUCT


V) KEY GASES (CONTD.)

• PATTERN OF COMBINATION OF GASES PRODUCED IS UNIQUE FOR EACH OF THE 3 MAIN TYPES OF FAULT.

• ARCING PRODUCES ALL FAULT GASES.

• PYROLYSIS PRODUCES ALL EXCEPT ACYLENE.


DGA INTERPRETATION SCHEMES

• DGA INTERPRETATION SCHEME OF ABB • ASINEL DGA INTERPRETATION SCHEME (SPAIN)• KEMA DIAGNOSTICS OF DGA• LABELEC DGA INTERPRETATION SCHEME (PORTUGAL)• LABORELEC DGA INTERPRETATION SCHEME (BELGIUM)• DGA INTERPRETATION SCHEME OF LCIE (FRANCE)• DGA INTERPRETATION SCHEME OF SLOVENIA• NATIONAL GRID DGA INTERPRETATION SCHEME (UK)• RWE ENERGIE DGA INT. SCHEME (GERMANY)• SIEMENS TRAFO UNION DGA SCHEME (GERMANY)• CBI&P GUIDELINES


DGA INTERPRETATION METHODS (CONTD.

DISADVANTAGES :

SEVERAL SIMULTANEOUSLY OCCURRING FAULTS CAN CAUSE AMBIGUITY IN ANALYSIS.

ADVANTAGES :

RATIOS ARE INDEPENDENT OF BOTH THE OIL VOLUME AND THE CHOICE OF CONCENTRATION UNITS


DGA INTERPRETATION

A) NEW GUIDELINES - CIGRE TASK FORCES15.01.01/.03

1. KEY RATIOS

KEY RATIO NO.1 C2H2 / C2H6 (ACETYLENE/ETHANE)INDICATION : ELECTRICAL DISCHARGEFAULT IF > 1

KEY RATIO NO.2 H2 / CH4 (HYDROGEN/METHANE)

INDICATION : PARTIAL DISCHARGEFAULT IF > 10


DGA INTERPRETATION (CONTD.)

KEY RATIO NO.3 C2H4 / C2H6 (ETHYLENE / ETHANE)INDICATION THERMAL FAULTIF > 1

KEY RATIO NO.4 Co2 / Co

INDICATION CELLULOSE DEGRADATION>10 OVERHEATING OF CELLULOSE< 3 DEGRADATION OF CELLULOSE BY ELECTRICAL FAULT(TO CONFIRM BY FURFURAL ANALYSIS, IEC 61198)



KEY RATIO NO.5 C2H2 / H2 (ACETYLENE/HYDROGEN)

INDICATION : INTANK TAPCHANGER

2 AND CONCENTRATION OF C2H2

30 PPM



2. KEY GAS CONCENTRATIONS

KEY GAS KEY GAS CONCEN- SUSPECTTRATION (PPM) INDICATION

C2H2 > 20 POWER DISCHARGEH2 >100 PARTIAL DISCHARGEΣCXHY >1000 THERMAL FAULT

UPTO ΣC1, C2, C3 HYDROCARBON >500UPTOΣC1, C2, HYDROCARBONS

COξ >10000 CELLULOSEX = 1,2 DEGRADATION



3. PROCEDURE

DENOTE R1 IF ALL RATIOS ARE BELOW THE LIMITSR2 IF ANY RATIO IS LARGER THAN THE LIMIT K1 IF KEY CONCENTRATION OF ALL GASES BELOW THE LIMITSK2 IF KEY CONCENTRATION OF ATLEAST ONE GASIS HIGHER THAN THE LIMIT



RESULTS

K1 & R1 NO ACTION, TRANSFORMER IS NOT PROBABLY HEALTHY

K2 & R2 TRANSFORMER MOST PROBABLY FAULTY, ADDITIONAL ANALYSES NEEDED

K1 &R2 POSSIBLE INCIPIENT FAULT, ADDITIONAL ANALYSES NEEDED

K2 & R1 POSSIBILITY OF MORE THAN ONE FAULT, FURTHER INVESTIGATION NEEDED


(B) IEC 60599 :1. 3 BASIC GAS RATIOS

C2H2 CH4 C2H4C2H4 H2 C2H6

1.1CASE CHARACTERISTICS C2H2 CH4 C2H4

FAULT C2H4 H2 C2H6

PD PARTIAL DISCHARGES <0.01 BUT NS <0.1 <0.2

D1 DISCHARGES OF LOW ENERGY >1 0.1-0.5 >1D2 DISCHARGES OF HIGH ENERGY 0.6-2.5 0.1-1.0 >2T1 THERMAL FAULT-T<300ºC <0.01 >1 <1 T2 THERMAL FAULT <0.1 >1 1- 4

300 ºC<T<700 ºC T3 THERMAL FAULT <0.2 >1 4

T > 700 ºC


1.2 SIMPLIFIED SCHEME OF INTERPRETATION

CASE C2H2 / CH4 / C2H4 /C2H4 H2 C2H6

PD < 0.2

D > 0.2

T < 0.2


2. 90% TYPICAL CONCENTRATION VALUES

Values in microlitres per litre

Tr.sub-type H2 CO CO2 CH4 C2H6 C2H4 C2H2

NO OLTC 60-150 540-900 5 100-13 000 40-110 50-90 60-280 3-50

COMMUNI- 75-150 400-850 5 300-12 000 35-130 50-70 110-250 80-270 CATINGOLTC


3. RATES OF GAS INCREASE :

HYDROGEN <5METHANE <2ETHANE <2ETHYLENE <2ACETYLENE <0.1CARBON MONOXIDE <50CARBONDIOXIDE <200


1.3 CO2 / CO RATIO :IF INCREMENTED RATIO < 3

- PAPER DEGRADATION SUSPECTED- ASK FOR FURANIC COMPOUND ANALYSIS OR DP

1.4 O2 / N2 RATIO :

- REFLECTS AIR IF RATIO CLOSE TO 0.5- IF RATIO LESS THAN 0.3 EXCESSIVE CONSUMPTION OF OXYGEN DUE TO OIL OXIDATION AND/OR PAPER AGEING

1.5 C2H2 / H2 RATIO :

- HIGHER THAN 2 TO 3 INDICATES OLTC CONTAMINATION


RECOMMENDED METHOD OF DGA INTERPRETATION :

• REJECT OR CORRECT INCONSISTENT DGA VALUES

• CALCULATE RATE OF GAS INCREASE SINCELAST ANALYSIS

• IF ALL GASES ARE BELOW TYPICAL VALUES OF GAS CONCENTRATIONS AND RATES OFGAS INCREASE, REPORT AS “NORMAL DGA / HEALTHY EQUIPMENT”


• IF AT LEAST ONE GAS IS ABOVE TYPICAL VALUES OF GAS CONCENTRATIONS AND RATES OF GAS INCREASE CALCULATE GASRATIOS AND IDENTIFY FAULT USING TABLE.CHECK FOR EVENTUAL ERRONEOUS DIAGNOSIS.

• IF NECESSARY SUBTRACT LAST VALUES FROMPRESENT ONES BEFORE CALCULATING RATIOS,PARTICULARLY IN THE CASE OF CO, CO2.


• IF DGA VALUES ARE ABOVE TYPICAL VALUESBUT BELOW 10XS (S = DETECTION LIMIT)CAUTION SHOULD BE EXERCISED WHEN CALCULATING GAS RATIOS AT LOW LEVELS.KEEPING IN MIND THE POSSIBLE VARIATIONSRESULTING FROM THE REDUCED PRECISION

• DETERMINE IF GAS CONCENTRATIONS AND RATES OF GAS INCREASE ARE ABOVE ALARMVALUES. VERIFY IF FAULT IS EVOLVING TOWARDS FINAL STAGE. DETERMINE IF PAPERIS INVOLVED.


• TAKE PROPER ACTION ACCORDING TO BESTENGINEERING JUDGEMENT.

• IT IS RECOMMENDED TO :

1) INCREASE SAMPLING FREQUENCY(QUARTERLY, MONTHLY OR OTHER) WHEN THE GAS CONCENTRATIONS AND THEIRRATES OF INCREASE EXCEED TYPICAL VALUES

2) CONSIDER IMMEDIATE ACTION WHEN GASCONCENTRATIONS AND RATES OF GASINCREASE EXCEED ALARM VALUES.


MINIMUM DETECTION CAPABILITIES

GAS CONCENTRATION : ppm(v/v)

H2 2

CO 5

CO2 10

CH4 0.1

C2H6 0.1

C2H4 0.1

C2H2 0.1


(C) IEEE STD. C57.104-1991

1. KEY GAS METHOD

1.1 THERMAL - OIL

- PRINCIPAL GAS - ETHYLENE

- DECOMPOSITION PRODUCTS INCLUDEETHYLENE & METHANE TOGETHER WITHSMALL QUANTITIES OF HYDROGEN ANDETHANE. TRACES OF ACETYLENE MAYBE FORMED, IF THE FAULT IS SEVEREOR INVOLVES ELECTRICAL CONTACTS


1.2 THERMAL - CELLULOSE

- PRINCIPAL GAS CO

- LARGE QUANTITIES OF CO2 & CO AREEVOLVED FROM OVERHEATED CELLULOSEHYDROCARBON GASES, SUCH AS METHANE AND ETHYLENE WILL BE FORMED IF THEFAULT INVOLVES AN OIL IMPREGNATEDSTRUCTURE


1.3 ELECTRICAL - CORONA

- PRINCIPAL GAS - HYDROGEN

- LOW ENERGY ELECTRICAL DISCHARGES PRODUCE H2 AND CH4 AND SMALL QUANTITIESOF C2H6 AND C2H4.

- COMPARABLE AMOUNTS OF CO & CO2 MAYRESULT FROM DISCHARGES IN CELLULOSE


1.4 ELECTRICAL - ARCING

- PRINCIPAL GAS - ACETYLENE

- LARGE QUANTITIES OF H2 & C2H2 AREPRODUCED WITH MINOR QUANTITIES OFCH4 & C2H4.

- CO2 & CO MAY ALSO BE FORMED IF THEFAULT INVOLVES CELLULOSE

- OIL MAY BE CARBONISED


2. USE OF GAS RATIOS

- ATTRIBUTED TO DOERNENBURG ANDROGERS

- ARRAY OF 5 RATIOSR1 = CH4 / H2 R2 = C2H2 / C2H4R3 = C2H2 / CH4R4 = C2H6/C2H2R5 = C2H4 / C2H6

- RATIOS 1, 2, 3 & 4 - DOERNENBURG

- RATIOS 1,2,5 - ROGERS


DOERNENBURG RATIO METHOD

1. VALUES OF KEY GASES COMPARED WITH FOLLOWING ASCONCENTRATIONS (L1 IN PPM) AND IF AT LEAST ONE OF THE GAS CONCENTRATIONS EXCEEDS THE LIMITING VALUES, THE UNIT IS CONSIDERED FAULTY


KEY GAS CONCENTRATION, L1 PPM

H2 100

CH4 120

CO 350

C2H2 35

C2H4 50

C2H6 65


3. DETERMINE RATIOS OF KEY GASES ASFOLLOWS :

THE RATIO PROCEDURE IS VALID IF AT LEAST ONE OF THE GASES IN EACHRATIO R1, R2, R3 & R4 EXCEEDS LIMIT L1,OTHERWISE UNIT SHOULD BE RESAMPLED.


3.1 RATIOS FOR KEY GASES - DOERNENBURG

SUGGESTED FAULT RATIO 1(R1) RATIO 2(R2) RATIO 3(R3) RATIO 4 (R4)DIAGNOSIS CH4/H2 C2H2/C2H4 C2H2/CH4 C2H6/C2H2

EXTRACTED EXTRACTED EXTRACTED EXTRACTED

1. THERMAL >1,0 <0.75 <0.3 >0.4DECOMPOSITION

2. CORONA (LOW <0.1 Not signi- <0.3 >0.4INTENSITY PD) ficant

3. ARCING (HIGH >0.1 <0.75 >0.3 <0.4INTENSITY PD) <1.0


3.2 ROGERS RATIOS FOR KEY GASES :

CASE R2 R1 R5 SUGGESTED FAULTC2H2/ CH4/ C2H4/ DIAGNOSIS C2H4 H2 C2/H6

0 <0.1 >0.1 <1.0 UNIT NORMAL<1.0

1 <0.1 <1.0 <1.0 LOW ENERGY DENSITYARCING-PD

2 0.1- 0.1- >3.0 ARCING-HIGH ENERGY3.0 1.0 DISCHARGE

3 <0.1 >1.0 1.0-3.0 LOW TEMP. THERMAL

4 <0.1 >1.0 1.0-3.0 THERMAL < 700 ºC

5 <0.1 >1.0 >3.0 THERMAL > 700 ºC


FAULTS DETECTABLE BY DGA : LEGEND

PD PARTIAL DISCHARGES

D1 DISCHARGES OF LOW ENERGY

D2 DISCHARGES OF HIGH ENERGY

T1 THERMAL FAULTS t < 300°C

T2 THERMAL FAULTS 300 °C < T < 700 °C

T3 THERMAL FAULTS > 700 °C


SYSTEM OR COMPONENT DEFECTS OR FAULTS DETECTABLE BY DGA

SYSTEM DEFECT FAULT AND FAULTSCOMPONENTS (REVERSIBLE) FAILURE-MODE DETECTABLE BY

(NOT REVERSIBLE) DGA (EXAMPLES)

DIELECTRIC

MAJOR INSULATION - EXCESSIVE WATER - DESTRUCTIVE PD - DISCHARGES (D1)MINOR INSULATION - OIL CONTAMINATION - LOCALISED TRACKING - DISCHARGES (D1)LEADS INSULATION - SURFACE CONTAMINATION - CREEPING DISCHARGE - DISCHARGES (D1,D2)ELECTROSTATIC - ABNORMAL AGED OIL - EXCESSIVE AGING/ / - THERMAL FAULT(T1,T2)SHIELDS - ABNORMAL CELLULOSE AGING OVERHEATED

- PD OF LOW ENERGY CELLULOSE

- LOOSE CONNECTIONS CAUSING - DISCHARGES (D1)SPARKING





ELECTROMAGNETICCIRCUIT

- LOOSENING CORE CLAMPING - EXCESSIVE VIBRATION CORE - OVERHEATING DUE TO HIGH AND SOUNDWINDINGS STRUCTURE STRAY FLUX - GENERAL OVERHEATING THERMAL FAULT (T1)INSULATION - SHORT CIRCUIT (OPEN-CIRCUIT) - LOCALIZED HOT SPOT THERMAL FAULT (T2,T3)CLAMPING STRUCTURE IN GROUNDING CIRCUIT - SPARKING/DISCHARGE DISCHARGES (D1)MAGNETIC SHIELDS - ABNORMAL CIRCULATING - ONE OR MORE TURNS DISCHARGES (D2)GROUNDING CIRCUIT CURRENT ARE SHORT CIRCUITED

- FLOATING POTENTIAL COMPLETELY- AGING LAMINATION - STRANDS WITHIN THE

SAME TURN ARE SHORTCIRCUITED





MECHANICAL

- LOOSENING CLAMPING - LEADS SUPPORT FAILURE

WINDINGS - WINDING DISTORTIONCLAMPING - RADIALLEADS SUPPORT - AXIAL

- TWISTING

- FAILURE OF INSULATION DISCHARGES (D1,D2)

CURRENT CARRYING CIRCUIT

LEADS - POOR JOINT - LOCALIZED HOT SPOT THERMAL FAULT (T2,T3)

WINDING - POOR CONTACTSOPEN-CIRCUIT DISCHARGES (D1,D2)

- CONTACT DETERIORATION SHORT-CIRCUIT


TYPICAL DEFECTS OR FAULTS IN SELECTOR SWITCH & DRIVE MOTOR OF OLTC DETECTABLE BY DGA

COMPONENTS DEFECT FAILURE MODE FAULTSOR FAULT DETECTABLE BY

DGA (EXAMPLES)

SELECTOR SWITCH

DIELECTRIC

SOLID INSULATION : - EXCESSIVE WATER DESTRUCTIVE PD DISCHARGES (D1)- BETWEEN TAPS, - OIL CONTAMINATION LOCALIZED TRACKING DISCHARGES (D1)- TO GROUND, - SURFACE CONTAMINATION CREEPING DISCHARGE DISCHARGES (D1,D2)- BETWEEN PHASES - PD OF LOW ENERGY EXCESSIVELY AGED /

- BARRIER BOARD & - ABNORMALLY AGED OIL OVERHEATED CELLULOSE THERMAL FAULT (T1,T2)- BUSHINGS

LIQUID INSULATION :- ACROSS CONTACTS

ADJACENT STUDS IN FLASHOVER DISCHARGES (D1)COMBINED SELECTORDIVERTER TAPCHANGER



COMPONENTS DEFECT OR FAILURE MODE FAULTSFAULT DETECTABLE BY

DGA (EXAMPLES)

ELECTRICAL

CONNECTIONS - POOR CONNECTIONS - OVERHEATING THERMAL FAULT (T1) CONTACTS - MIS-ALIGNED CONTACTS - SPARKING / ARCING DISCHARGES (D1) - SELECTOR CONTACTS - SILVER COATING - OVERHEATING - THERMAL FAULT (T1)- CHANGEOVER SWITCH DISTURBED / WORN - CARBON BUILD UP THERMAL FAULT (T2,T3)- COURSE FINE - POOR CONTACT PRESSURE BETWEEN CONTACTS

THROUGH BUSHINGS




DGA (EXAMPLES)

MECHANICAL

DRIVE SHAFT - DAMAGED OR BROKEN OUT OF SYNCH OPERATIONSELECTOR CONTACTS - INCORRECT ALIGNMENT OF SELECTOR & DIVERTER

WITH DIVERTER SWITCH SWITCHES ARCING DISCHARGES (D1, D2)

OPERATION- TRAVEL BEYOND THE

END STOP




DGA (EXAMPLES)

DRIVE MECHANISM

DRIVE SHAFT - INCORRECT TIMING INCORRECT OPERATION OFMECHANICAL END STOPS - OPERATION BEYOND THE SELECTOR SWITCHMOTOR AND GEAR DRIVE END STOP IN RELATION TO DIVERTERCONTROL EQUIPMENT - BROKEN GEARSAUXILLARY SWTICHES - MISALIGNED COUPLING TAPCHANGER JAMMED

- WORN,DAMAGED OR ON A TAP - WILL NOTBROEKN AUXILLARY OPERATESWITCHES


TYPICAL DEFECTS FOR BUSHINGS DETECTABLE BY DGA


DGA (EXAMPLES)

CONDENSER LOCAL NATURECORE RESIDUAL MOISTURE PARTIAL

POOR IMPREGNATION IONIZATION PARTIAL DISCHARGES(PD)WRINKLES IN PAPER GASSINGDELAMINATED PAPER THERMAL RUN AWAY THERMAL FAULT (T2,T3)

OVER-STRESSINGSHORT-CIRCUIT LAYER DISCHARGES(D1,D2)

INGRESS OF MOISTUREINGRESS OF AIR PUNCTURE DISCHARGES(D1)GRAPHITE INK MIGRATION EXPLOSION THERMAL FAULT(T2,T3)DIELECTRIC OVERHEATING DISCHARGES(D2)X-WAX DEPOSIT PARTIAL DISCHARGES (PD)

BULK NATUREAGING OF OIL-PAPER BODYTHERMAL UNSTABLE OIL FLASHOVERGAS UNSTABLE OIL EXPLOSIONS DISCHARGES(D1)OVER-SATURATION DISCHARGES(D2)


TYPICAL DEFECTS FOR BUSHINGS DETECTABLE BY DGA


DGA (EXAMPLES)

CORE SURFACE CONTAMINATION PD DISCHARGES (D1)

OIL MOISTURE CONTAMINATION SURFACE DISCHARGES (D1)INTERNAL PORCELAIN AGING DISCHARGESURFACE GASSING

TAPS UNGROUNDINGS PD DISCHARGES (D1)SHORTED ELECTRODES

CONDUCTOR OVERHEATING OVERHEATING THERMAL FAULT (T1,T2)- TOP CONTACT GASSING- FOOT CONTACT SPARKING DISCHARGES (D1)- DRAW RODCIRCULATING CURRENT IN THERMAL FAULT(T2,T3)THE HEAD

EXTERNAL CRACKS FLASHOVER DISCHARGES (D1)PORCELAIN CONTAMINATION

SURFACE DISCHARGE


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Transformer Life Management Condition Assessment and Dissolved Gas Analysis

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