Transformer Life Management Condition Assessment and Dissolved Gas Analysis
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Transcript of 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
19/09/2006 Prepared by : VKL 2
OUTLOOK
• MECHANISMS OF LIFE DEGRADATION PHENOMENA
• KEY DETERIORATION PROCESSES
• LIFE ASSESSMENT AND CONDITION MONITORING TECHNIQUES & RECOMMENDATIONS
• DISSOLVED GAS ANALYSIS
19/09/2006 Prepared by : VKL 3
TRANSFORMER LIFE INVOLVES SEVERAL MECHANISMS OF
DEGRADATION
19/09/2006 Prepared by : VKL 4
COMPONENTS OF TECHNICAL LIFE OF A TRANSFORMER
1) THERMAL LIFE
2) DIELECTRIC LIFE
3) MECHANICAL LIFE
4) LIFE OF ACCESSORIES
19/09/2006 Prepared by : VKL 5
Thermal LifeTime to critical decomposition DP<200
Is the Life of Transformermechanical life of Aged paper?
AGED
19/09/2006 Prepared by : VKL 6
Dielectric LifeTime span to critical reduction of dielectric margin
19/09/2006 Prepared by : VKL 7
Mechanical weakness and Deformation under cumulative stresses
of through faults
19/09/2006 Prepared by : VKL 8
Impairment of electromagnetic circuit
19/09/2006 Prepared by : VKL 9
Life of OLTC
19/09/2006 Prepared by : VKL 10
Limited life of bushings
19/09/2006 Prepared by : VKL 11
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”
19/09/2006 Prepared by : VKL 12
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.
19/09/2006 Prepared by : VKL 13
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
19/09/2006 Prepared by : VKL 14
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
19/09/2006 Prepared by : VKL 15
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
19/09/2006 Prepared by : VKL 16
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
19/09/2006 Prepared by : VKL 17
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
19/09/2006 Prepared by : VKL 18
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
19/09/2006 Prepared by : VKL 19
The life cycleSAFETYMARGIN
CRITICALLEVEL
FAILED
NORMAL DEFECTIVE FAULTY
19/09/2006 Prepared by : VKL 20
Review of key deterioration processes
19/09/2006 Prepared by : VKL 21
Deterioration processes
Moisture contaminationParticles in oil Oil oxidationPaper agingSurface contaminationImpact of oil by-products
19/09/2006 Prepared by : VKL 22
Moisture contamination
19/09/2006 Prepared by : VKL 23
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.
19/09/2006 Prepared by : VKL 24
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.
19/09/2006 Prepared by : VKL 25
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.
19/09/2006 Prepared by : VKL 26
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
19/09/2006 Prepared by : VKL 27
The main insulation components of a core-type transformer
Angle ring
Clamping plate
Spacer block
Paper wrap around copper wireCylinder
19/09/2006 Prepared by : VKL 28
Insulation components. Thin structure
Turn coil, conductors (paper)Barriers (pressboard)Angle ring
Diffusion time constant – a few days-month
19/09/2006 Prepared by : VKL 29
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
19/09/2006 Prepared by : VKL 30
Thick components absorb miserable amount of moisture
φ= 55%
Thin
Thick
50 days
19/09/2006 Prepared by : VKL 31
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
19/09/2006 Prepared by : VKL 32
Moisture profile
19/09/2006 Prepared by : VKL 33
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
19/09/2006 Prepared by : VKL 34
Free water through poor sealing is repeatable worldwide case
19/09/2006 Prepared by : VKL 35
19/09/2006 Prepared by : VKL 36
Accumulation of free water on the bottom core yoke
19/09/2006 Prepared by : VKL 37
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.
19/09/2006 Prepared by : VKL 38
Particles in oil
19/09/2006 Prepared by : VKL 39
Particles origin
ForeignDebris
Oil
ManufacturingDebris
Componentdelivered particles
Oil deliveredparticles
19/09/2006 Prepared by : VKL 40
Particles mode
Cellulose fibers, iron,aluminum,copper
Manufacturing
Cellulose fibers, iron,aluminum,copper
ForeignManufacturingInstallation, Repair
Cellulose fibers, iron,aluminum,copper
Component wear out:Pumps, coolers, OLTC, contacts, cellulose
Polymers, carbonOil : oxidation pyrolysis by-products/
19/09/2006 Prepared by : VKL 41
Type of particles
Floating in oil In solution in oilOn surface depositionMigration through paper layers
19/09/2006 Prepared by : VKL 42
Particles microscopic analysis
Quartz
Coke
InsectFragment Paper fiber
Copper
19/09/2006 Prepared by : VKL 43
Insulation contamination
19/09/2006 Prepared by : VKL 44
Surface contamination
19/09/2006 Prepared by : VKL 45
Attraction by field and Deposit conductive sediments
Oil sludge deposit
Carbon depositConductive particles deposit
19/09/2006 Prepared by : VKL 46
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
19/09/2006 Prepared by : VKL 47
Corrosive Deposits on Coils
19/09/2006 Prepared by : VKL 48
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
19/09/2006 Prepared by : VKL 49
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.
19/09/2006 Prepared by : VKL 50
Oil oxidation
19/09/2006 Prepared by : VKL 51
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
19/09/2006 Prepared by : VKL 52
Paper aging
19/09/2006 Prepared by : VKL 53
Thermal Life is a function oftemperature, water and by-products
][36524
11
_ 27313350
yearseA
DPDPLifeExpected TStartEnd +⋅
∗•
−=
Hot spot temperature
Water & acids
19/09/2006 Prepared by : VKL 54
Aging profile
19/09/2006 Prepared by : VKL 55
End of life can come under 20Aging profile of 700 MVA, 420 kV, 14 years
Hot spot area
19/09/2006 Prepared by : VKL 56
Impact of oil by-product on degradation of insulation
properties
19/09/2006 Prepared by : VKL 57
Predominant deterioration of surface layers from oil side
Oil side
Copper side
Destruction of surfacelayers
19/09/2006 Prepared by : VKL 58
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
19/09/2006 Prepared by : VKL 59
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
19/09/2006 Prepared by : VKL 60
Condition Assessment and Maintenance
19/09/2006 Prepared by : VKL 61
Main maintenance modes
Reactive – reacting to problems as theyarise due to emergencies
Proactive – work programme basedon monitored data
19/09/2006 Prepared by : VKL 62
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
19/09/2006 Prepared by : VKL 63
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
19/09/2006 Prepared by : VKL 64
Aims of transformer surveillance
• Predictive maintenance• Life extension• Refurbishment• Replacement strategy
19/09/2006 Prepared by : VKL 65
Drivers to install surveillance equipment
• Need to reduce maintenance costs
• Increased use of power electronics
• Maintenance equipment inefficient for
modern electronics-based schemes
19/09/2006 Prepared by : VKL 66
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
19/09/2006 Prepared by : VKL 67
Transformer surveillance – off-line measurements
• Recovery voltage method (RVM)• Leakage inductance• Low frequency impulse• Fourier analysis• Frequency response analysis (FRA)• Dielectric loss angle
19/09/2006 Prepared by : VKL 68
Transformer surveillance – intrusive measurements
• Degree of polymerisation (DP index)• Winding clamping pressure• OLTC contact wear• Gel permeation chromatography• X-ray photoelectron spectroscopy
19/09/2006 Prepared by : VKL 69
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
19/09/2006 Prepared by : VKL 70
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
19/09/2006 Prepared by : VKL 71
Maintenance strategies
• CM - corrective maintenance
• TBM - time based maintenance
• CBM - condition based maintenance
• RCM - reliability centred maintenance
19/09/2006 Prepared by : VKL 72
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
19/09/2006 Prepared by : VKL 73
DISSOLVED GAS ANALYSIS (DGA)OF MINERAL OIL INSULATING
FLUIDS IN TRANSFORMERS -INTERPRETATIONS
19/09/2006 Prepared by : VKL 74
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
19/09/2006 Prepared by : VKL 75
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
19/09/2006 Prepared by : VKL 76
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
19/09/2006 Prepared by : VKL 77
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)
19/09/2006 Prepared by : VKL 78
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
19/09/2006 Prepared by : VKL 79
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
19/09/2006 Prepared by : VKL 80
FAILURE ANALYSIS AND DGA (CONTD)
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
19/09/2006 Prepared by : VKL 81
FAILURE ANALYSIS AND DGA (CONTD)
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
19/09/2006 Prepared by : VKL 82
FAILURE ANALYSIS AND DGA (CONTD)
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
19/09/2006 Prepared by : VKL 83
FAILURE ANALYSIS AND DGA (CONTD)
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
19/09/2006 Prepared by : VKL 84
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
19/09/2006 Prepared by : VKL 85
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
19/09/2006 Prepared by : VKL 86
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
19/09/2006 Prepared by : VKL 87
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
19/09/2006 Prepared by : VKL 88
PFGC VALUES CALCULATED ON DIFFERENT NETWORKS, in ppm
13005001800480270240LCIE-shell12006001050830340900LCIE-core15003101000700460550LCIE-hydro
9844088509934241318Labelec
9844088509934241318HQ
3000350750900400600PFGC
COC2H2C2H6C2H4CH4H2
19/09/2006 Prepared by : VKL 89
AGC VALUES CALCULATED ON DIFFERENT NETWORKS, in ppm
10001001700340200110LCIE-shell
110070800120150240LCIE-core
1300120670240230290LCIE-hydro
956295805421194665Labelec
1700170400350120250HQ
AGC
COC2H2C2H6C2H4CH4H2
19/09/2006 Prepared by : VKL 90
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
19/09/2006 Prepared by : VKL 91
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
19/09/2006 Prepared by : VKL 92
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
19/09/2006 Prepared by : VKL 93
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
19/09/2006 Prepared by : VKL 94
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.
19/09/2006 Prepared by : VKL 95
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.
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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.
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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.
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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.
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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
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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.
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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.
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DGA INTERPRETATION METHODS (CONTD.)
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”
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DGA INTERPRETATION METHODS (CONTD.)
III) KEY GAS METHOD (CONTD.)
• THIS TECHNIQUE PROVIDES GRAPHS FOR 4 GENERAL FAULT TYPES
• THERMAL (OIL DECOMPOSITION)• THERMAL (CELLULOSE
DECOMPOSITION)• ELECTRICAL (CORONA)• ELECTRICAL (ARCING)
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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.
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DGA INTERPRETATION METHODS (CONTD.)
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
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DGA INTERPRETATION METHODS (CONTD.)
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.
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DGA INTERPRETATION METHODS (CONTD.)
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.
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DGA INTERPRETATION METHODS (CONTD.)
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.
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DGA INTERPRETATION METHODS (CONTD.)
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.
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DGA INTERPRETATION METHODS (CONTD.)
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
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DGA INTERPRETATION METHODS (CONTD.)
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
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DGA INTERPRETATION METHODS (CONTD.)
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.
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DGA INTERPRETATION METHODS (CONTD.)
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
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DGA INTERPRETATION METHODS (CONTD.)
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.
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DGA INTERPRETATION METHODS (CONTD.)
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.
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DGA INTERPRETATION METHODS (CONTD.)
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
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DGA INTERPRETATION METHODS (CONTD.)
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.
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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.
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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.
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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
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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.
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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
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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
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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
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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)
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DGA INTERPRETATION (CONTD.)
KEY RATIO NO.5 C2H2 / H2 (ACETYLENE/HYDROGEN)
INDICATION : INTANK TAPCHANGER
2 AND CONCENTRATION OF C2H2
30 PPM
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DGA INTERPRETATION (CONTD.)
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
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DGA INTERPRETATION (CONTD.)
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
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DGA INTERPRETATION (CONTD.)
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
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(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
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1.2 SIMPLIFIED SCHEME OF INTERPRETATION
CASE C2H2 / CH4 / C2H4 /C2H4 H2 C2H6
PD < 0.2
D > 0.2
T < 0.2
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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
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3. RATES OF GAS INCREASE :
HYDROGEN <5METHANE <2ETHANE <2ETHYLENE <2ACETYLENE <0.1CARBON MONOXIDE <50CARBONDIOXIDE <200
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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
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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”
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• 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.
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• 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.
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• 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.
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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
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(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
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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
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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
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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
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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
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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
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KEY GAS CONCENTRATION, L1 PPM
H2 100
CH4 120
CO 350
C2H2 35
C2H4 50
C2H6 65
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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.
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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
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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
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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
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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
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SYSTEM OR COMPONENT DEFECTS OR FAULTS DETECTABLE BY DGA
SYSTEM DEFECT FAULT AND FAULTSCOMPONENTS (REVERSIBLE) FAILURE-MODE DETECTABLE BY
(NOT REVERSIBLE) DGA (EXAMPLES)
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
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SYSTEM OR COMPONENT DEFECTS OR FAULTS DETECTABLE BY DGA
SYSTEM DEFECT FAULT AND FAULTSCOMPONENTS (REVERSIBLE) FAILURE-MODE DETECTABLE BY
(NOT REVERSIBLE) DGA (EXAMPLES)
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
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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
19/09/2006 Prepared by : VKL 155
TYPICAL DEFECTS OR FAULTS IN SELECTOR SWITCH & DRIVE MOTOR OF OLTC DETECTABLE BY DGA
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
19/09/2006 Prepared by : VKL 156
TYPICAL DEFECTS OR FAULTS IN SELECTOR SWITCH & DRIVE MOTOR OF OLTC DETECTABLE BY DGA
COMPONENTS DEFECT FAILURE MODE FAULTSOR FAULT DETECTABLE BY
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
19/09/2006 Prepared by : VKL 157
TYPICAL DEFECTS OR FAULTS IN SELECTOR SWITCH & DRIVE MOTOR OF OLTC DETECTABLE BY DGA
COMPONENTS DEFECT FAILURE MODE FAULTSOR FAULT DETECTABLE BY
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
19/09/2006 Prepared by : VKL 158
TYPICAL DEFECTS FOR BUSHINGS DETECTABLE BY DGA
COMPONENTS DEFECT FAILURE MODE FAULTSOR FAULT DETECTABLE BY
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)
19/09/2006 Prepared by : VKL 159
TYPICAL DEFECTS FOR BUSHINGS DETECTABLE BY DGA
COMPONENTS DEFECT FAILURE MODE FAULTSOR FAULT DETECTABLE BY
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
19/09/2006 Prepared by : VKL 160
Thank You