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TRANSFORMER OIL Analysis
M.G.Morshad / ACM ( Elect)
Transformer Maintenance Division / TPS II
Transformer Insulating system
Oil Paper
1. Acts as a Coolant
2. Act as an insulation
3. Protects the Paper from chemical
a...
Transformer oil classifications
NAPTHANIC OIL
 Naphtha oil is more easily oxidized than Paraffin oil.
 But oxidation pro...
Oxidation Inhibitor in mineral oil
Mineral insulating oil undergo oxidative degradation process in the presence of oxygen ...
5
Heat transferring
capacity of transformer
oil
Approximate Oil
requirement for
transformer
Capacity Oil Requirement
Up to 1...
TRANSFORMER OIL SPECIFICATIONS
IEC -60296 – General Specification
• Functional Properties:
Viscosity, Pour point, Water co...
TRANSFORMER OIL SPECIFICATIONS
NEW OIL:
An unused mineral insulating oils intended to use in transformers for
insulation a...
TRANSFORMER OIL SPECIFICATIONS
Unused Mineral Insulating oils filled in New
transformers
• IS – 1866/2000 – Code of Practi...
TRANSFORMER OIL SPECIFICATIONS
IS-335/1993 ( New Oil)
• Appearance ------------
• Density at 29.5˚C (Max)
• Kinematic Visc...
TRANSFORMER OIL SPECIFICATIONS
IS-335/1993 (Ageing characteristics)
• Ageing characteristics
a) Resistivity (Min)
1) at 27...
TRANSFORMER OIL SPECIFICATIONS
IS-1866/2000-Recommended Limits of Unused Mineral Oil filled in New Transformer
Property Hi...
TRANSFORMER OIL SPECIFICATIONS
IS-1866/2000-Violation Limits for in service oils
Property Highest voltage of Equipment (KV...
TRANSFORMER OIL SPECIFICATIONS
IS-1866/2000-Frequency of testing
Property Frequency of testing
Appearance In conjunction w...
TRANSFORMER OIL SPECIFICATIONS
IS-1866/2000-Recommended Actions
Property Recommended Actions
Appearance As dictated by oth...
TRANSFORMER OIL SPECIFICATIONS
IS-1866/2000-Classification of oils in service.
• Group 1: This group contains oils that ar...
17
In order to take account of different user of mineral oil requirements, equipment
has been placed in various categories...
PHYSICAL PROPERTIES OF OIL
Physical
Properties
Definition Purpose Effects
Appearance
The oils should be clear,
transparent...
PHYSICAL PROPERTIES OF OIL
Physical
Properties
Definition Purpose Effects
Flash point
It is the lowest temperature at
whic...
CHEMICAL PROPERTIES OF OIL
Chemical
Properties
Definition Causes Effects
Neutralization
Number
or Acidity
It is the number...
ELECTRICAL PROPERTIES OF OIL
Electrical
Properties
Definition Causes Effects
Dielectric
Strength
It is the minimum voltage...
TRANSFORMER OIL TEST PACKAGE
(As per IS: 1866)
22
Inference of the oil test result
1. Determination of moisture in the solid insulation
( on the basis of Ooman graph)
2. De...
24
Moisture
(Dielectric Status)
1. Decomposes solid insulation
2. Reduces BDV
3. Increases oil heating
Slug & Sediments
(A...
Pale
yellow
Good
oil
Yellow
Proposition
‘A’ oil
Bright
yellow
Marginal
oil
Amber
Bad
oil
Brown
Very bad
oil
Dark
brown
Ext...
ACIDITY OR NEUTRALISATION NUMBER(NN)
 Acids in the oil originate from decomposition/oxidation of oil.
 These organic aci...
Determination of oil quality based on
IFT & NN
IFT NN MIN = IFT/NN Colour Oil Quality & Observations
30 - 45 0.00 – 0.10 3...
Interfacial Tension, Acid Number, Years
in Service
Condition of paper with increase of acid
content in oil
Moisture in transformer oil
1.Moisture may be present in four possible forms
1.Free water – That is water that has settled...
Moisture in transformer oil – Relative saturation
Water content in oil sample taken at 60 Deg C
(as per lab analysis)
45 p...
Moisture in transformer oil
3. Moisture Distribution
The internal moisture distributed not
uniformly.
When the transform...
Moisture in transformer oil
4. Damages caused by moisture
 Moisture in oil reduces the insulating ability (BDV) of the oi...
Determination of moisture accumulation in
solid insulation through water ppm in oil
35
36
Calculation of moisture accumulation in solid
insulation through water ppm in oil
Parameters Formula Value
Oil capacity...
Effects of moisture accumulation in
the solid insulation
38
Limit value : Water ppm in transformer oil
New oil
(72 – 170 KV Transformer)
(>170 KV Transformer)
(< 72 Transformer)No...
+
+
+
+
+
+
-
-
-
-
-
-
-
+
+
+
-
+
+
-
+
+
+
- +
-
-
+
+
+
+
+
-
Leakage current
Charging
current
Charging
current
High A...
Limit value : Break Down Voltage in KV
< 72.5 KV Transformer
72.5 -170 KV Transformer
> 170KV Transformer
BDV value of tr...
As transformer oil is act as pure insulator, its resistance ( R ) should be is
always as high possible.
Resistance R = ρ x...
Limit value (at 90 Deg C) : Resistivity
(Very Good)
(Good)
(Min)
Resistivity is measured by
applying 500 V DC voltage
acro...
DDF / Tan Delta
O
Φ = (90-∂)
∂
B
C
A
OA = Applied voltage,
OC = Charging current,
OB = Total current ( Charging current + ...
Charging current
Leakage current
Total
current
O
BA
C
δ3
δ2
Limit value ( At 90 Deg C) : Tan Delta
Angle value % Value
Ide...
Resistivity & tan delta
(indicates deteriorating status of the dielectric
due to oxidation & contaminations of oil)
Presen...
46
Transformer oil processing
Removal of
Free & dissolved water,
Dissolved combustible gas
Solid particulate matter
RECLAIMIN...
Off line reconditioning through filter machine
Magnetic
Filter
Automatic
Heater
Fine
Filter
Gear
Pump
Vacuum
Pump
Vacuum
C...
49
Molecular sieve material
When transformer is in service, moisture available in the paper insulation is absorbed by oil
...
Oil Reclaiming / Regeneration process as per IEC
60422
Oil reclamation remove oxidation inhibitors. Additives
shall be rep...
51
Dissolved Gas Analysis (DGA)
 Due to normal aging or internal faults different types of gases
are generated which subsequ...
Generation of gases
1. Hydrocarbons
& Hydrogen
Methane CH4
Ethane C2H6
Ethylene C2H4
Acetylene C2H2
Hydrogen H2
2. Carbon ...
Types of Faults & generation of gases
1. Corona
OIL CELLULOSE
H2 H2,CO,CO2
1. Low temperature heating
OIL CELLULOSE
CH4,C2...
NormalOperation&aging
Thermal Fault
Overloading
Over heating of oil and paper
FailureofPumps,Fans
Misdirectionflowofcoolin...
Dissolved Gases
CIGRE
(1976)
ELECTRA
(1978)
ALSTHOM
(1980)
ERDA
H2 ( Hydrogen) 235 28.6 200 100
CH4 ( Methane) 100 42.2 20...
Acceptance limits (2)
Gases
CIGRE CPRI CBIP
0 - 5
Yrs
6 - 10
Yrs
11-15
Yrs
0 - 4
Yrs
4 – 10
Yrs
> 10
Yrs
< 4
Yrs
4-10
Yrs
...
Acceptance limits (3)
as per IS: 9434 / 1992 , IS: 10593 / 1983 & IEC 599 –1978
GAS
LESS THAN FOUR YEARS
IN SERVICE (PPM)
...
Fault identification (1) - by Key gas
methods
Type of faults Dissolved Gasses
Over heating of solid insulating materials
(...
Fault identification (2) - by gas ratio
methods
61
Significance of acetylene (C2H2) in oil
 Generation of acetylene (C2H2) of any amount above a few ppm
indicates high-ener...
Significance of CO/CO2 ratio in oil
 If there is a sudden increase in H2 with only carbon monoxide (CO) and carbon dioxid...
Significance of atmospheric gases (O2 & N2)
in oil
 Oxygen may be present inside the transformer due to ingression of air...
Fault Analysis ( 1) - by Roger methods
CH4
H2
C2H6
CH4
C2H4
C2H6
C2H2
C2H4 Faults
0.1 0 0 0 Partial discharge
0 0 0 0 Norm...
Fault Analysis (2) - by IEC 599 and CBIP
methods
C2H2
C2H4
CH4
H2
C2H4
C2H6 Ratio of the dissolved gases
0 1 0 Ratio less ...
fault analysis (3) – by IEEE (Std). C57-104™
Condition 1: Transformer is operating satisfactorily.
Condition 2: A fault ma...
68
Recommendations – IEEE (Std). C57-104™
Fault analysis (4) - by DUVAL triangle
 In order to display a DGA result in the Triangle, one must start with the
concent...
Duval Triangle
70
Classification of faults- Duval method
Faults
Thermal Type Electrical Type
T1
Thermal Fault
t<300 Deg C
T2
Thermal Fault
3...
Duval Table for interpretation
72
73
74
solid insulation
 Paper and cloth used in transformer is known as solid insulation.
 The main constituent of paper and c...
Reasons for degradation of solid
insulation
1. Thermal degradation ( Heat) :
Heat produced during the operation of transfo...
Aging process of transformer’s solid
insulation
Moisture
Oil impregnated solid insulation
Heat
Chemical degradation of sol...
78
DP values and aging of transformer
Years
DP Values
Age (Yrs) DP Values
0 >1000
1 975
12 700
22 450
25 390
35 125
79
Interpretation of DP values
80
Furan analysis
 The mechanical properties of insulating paper can be established by direct
measurement of its tensile str...
Inference of the chemical compounds obtained
during furan analysis of transformer oil
82
Aging & Furfural in oil – BHEL study
Age (Years) Furfural (mg/Ltr)
2 0.01
5 0.02
6 0.03
7 0.04
8 0.05
9 0.06
10 0.08
11 0....
Relation between furan content in oil and DP
values of solid insulation
84
Limiting values for furan analysis
85
8686
conversion table I
1% = 10,000ppm
Percent (%) ppm
0.0000% 0 ppm
0.0001% 1 ppm
0.0010% 10 ppm
0.0100% 100 ppm
0.1000% ...
87
Torr mm Hg Atm. PSI kg/sq.cm kPa mBar
760 760 1.00 14.69 1.03 101.31 1013.3
600 600 0.79 11.66 0.82 79.98 800.0
500 500...
88
Water Boiling
point (Deg C)
Vacuum Gauge
Reading
(mmHg)
0 755.42
10 750.79
20 742.47
30 728.18
40 704.68
50 667.50
60 6...
TR Oil
Temp
Water solubility
level in TR oil
0 Deg C 22 ppm
10 Deg C 36 ppm
20 Deg C 55 ppm
30 Deg C 83 ppm
40 Deg C 121 p...
Transformer oil-specifications new
Transformer oil-specifications new
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Transformer oil-specifications new

  1. 1. TRANSFORMER OIL Analysis M.G.Morshad / ACM ( Elect) Transformer Maintenance Division / TPS II
  2. 2. Transformer Insulating system Oil Paper 1. Acts as a Coolant 2. Act as an insulation 3. Protects the Paper from chemical attack 4. Prevention of sludge buildup 5. Used as Diagnostic Tool 1. Mechanical Strength 2. Dielectric Strength 3. Dielectric Spacing
  3. 3. Transformer oil classifications NAPTHANIC OIL  Naphtha oil is more easily oxidized than Paraffin oil.  But oxidation product i.e. sludge in the naphtha oil is more soluble than Paraffin oil.  Thus sludge of naphtha based oil is not precipitated in bottom of the transformer.  Hence it does not obstruct convection circulation of the oil, means it does not disturb the transformer cooling system PARAFFINIC OIL  Oxidation rate of Paraffin oil is lower than that of Naphtha oil  But the oxidation product or sludge is insoluble and precipitated at bottom of the tank and obstruct the transformer cooling system.  It has high pour point due to the wax content  In India it is generally used because of its cheaper and easy availability. SILICON OIL Fire retardant, hence it is used only for fire prone area.  Lower heat dissipation capacity and high moisture absorbing capacity  Costlier than mineral oil Transformer Oil Mineral Oil (petroleum product ) Synthetic Oil (Chemical Product)
  4. 4. Oxidation Inhibitor in mineral oil Mineral insulating oil undergo oxidative degradation process in the presence of oxygen to form acid & sludge. To prevent these process , oxidation inhibitor is used for interrupting process of oxidation and thereby minimize oil deterioration and extend the operating life of the transformer the oil. Depending on the presence of oxidation inhibitor, mineral insulating is categorized as – 1. Uninhibited oil 2. Inhibited oil 1. Uninhibited oil New insulating oil as normally refined contains small amounts of certain chemical compounds that act as oxidation inhibitors. These naturally occurring materials retard oil oxidation until such time as they are expended. The rate at which the inhibitors in the oil are used up is dependent upon the amount of oxygen available, soluble contaminants in the oil, catalytic agents in the oil, and the temperature of the oil 2. Inhibited oil, To increase the oxygen inhibitor beyond its natural limit, oxygen inhibitor is added in the oil for reducing the rate of oxidation process in a view to increase the life expectancy of the transformer . Phenolic materials are quite good for this purpose and the two most commonly used inhibitors are 2,6-ditertiary- butylphenol (DBP) and 2,6-di-tertiary-butyl-4- methylphenol or 2,6-di-tertiary-butyl-paracresol (DBPC).
  5. 5. 5
  6. 6. Heat transferring capacity of transformer oil Approximate Oil requirement for transformer Capacity Oil Requirement Up to 1.5 MVA 0.85 KL / MVA 1.6 to 16 MVA 0.50 KL / MVA > 16 to 250 MVA 0.28 KL / MVA Approximate solid insulation requirement for transformer 6 Solid insulation Requirement Thick Press board ( Barrier ) 5% of total oil weight Thin press board (Barrier) 3% of total oil weight Paper insulation ( Winding insulation ) 2% of total oil weight
  7. 7. TRANSFORMER OIL SPECIFICATIONS IEC -60296 – General Specification • Functional Properties: Viscosity, Pour point, Water content, BDV, Density, Tanδ. • Stability Properties: Appearance, Acidity, IFT, corrosive Sulfur, Antioxidant additive • Performance Properties: Oxidation Stability, Sludge • HSE Properties: Flash Point, PCB content, PCA content 7
  8. 8. TRANSFORMER OIL SPECIFICATIONS NEW OIL: An unused mineral insulating oils intended to use in transformers for insulation and cooling purpose. • IS-335/1993 – Specification for uninhibited new insulating oils. • IS-12463/1988 – Specification for inhibited mineral insulating oils. • IEC -60296/2003 – Specification for unused mineral insulating oils for transformers and switchgear. This standard cover both uninhibited and inhibited oils. • ASTM – D3487/2000- Standard Specification for Mineral Insulating Oil used in Electrical apparatus. This standard also covers both uninhibited and inhibited oils. 8
  9. 9. TRANSFORMER OIL SPECIFICATIONS Unused Mineral Insulating oils filled in New transformers • IS – 1866/2000 – Code of Practice for Electrical Maintenance and supervision of Mineral Insulating oil in Equipment. (Refer Table.1 for limiting values of various parameters) • IEC – 60422/1998 – Supervision and maintenance guide for mineral insulating oils in electrical equipment. In service Mineral Insulating oils • IS – 1866/2000 – Code of Practice for Electrical Maintenance and supervision of Mineral Insulating oil in Equipment. 9
  10. 10. TRANSFORMER OIL SPECIFICATIONS IS-335/1993 ( New Oil) • Appearance ------------ • Density at 29.5˚C (Max) • Kinematic Viscosity (Max) 1) at 27˚C ------------------ 2) at 40˚C ------------------ • IFT at 27˚C (Min) --------- • Flash Point (Min) --------- • Pour Point (Max) --------- • Neutralization Value 1) total Acidity (Max) ---- 2) Inorganic acidity ------ • Corrosive Sulphur ------- • Clear and transparent • 0.89 g/cm2 • 27 cSt • Under consideration • 0.04 N/m • 140˚C • -6˚C • 0.03 mg KOH/gm • Nil • Non-corrosive • Electric Strength (BDV) 1) New unfiltered Oil(Min) 2) After filtration (Min) • Dielectric dissipation factor (tan δ)at 90˚C(max) • Specific resistance (Resistivity) 1) at 90˚C (Min) 2) at 27˚C (Min) • Oxidation Stability 1) Acidity (max) 2) total sludge (max) • 30 KV (rms) • If the above value is not attained, the oil shall be filtered to 60 KV (rms) • 0.002 • 35 x 1012 ohm-cm • 1500 x 1012 ohm-cm • 0.4 mg KOH/gm • 0.1 % by weight 10
  11. 11. TRANSFORMER OIL SPECIFICATIONS IS-335/1993 (Ageing characteristics) • Ageing characteristics a) Resistivity (Min) 1) at 27˚C 2) at 90˚C b) Tanδ at 90˚C (Max) c) Total acidity (Max) d) Total sludge (Max) • Presence of Oxidation inhibitor • Water content • SK value • 2.5 x 1012 ohm-cm • 0.2 x 1012 ohm-cm • 0.20 • 0.05 mg KOH/gm • 0.05 % by weight • The oil shall contain natural anti oxidant additives. • 50 ppm • Under consideration 11
  12. 12. TRANSFORMER OIL SPECIFICATIONS IS-1866/2000-Recommended Limits of Unused Mineral Oil filled in New Transformer Property Highest voltage of Equipment (KV) <72.5 72.5-170 >170 Appearance Clear, Free from sediment and suspended matter Density at 29.5˚C (g/cm2),Max 0.89 0.89 0.89 Viscosity at 27˚C (cSt),Max 27 27 27 Flash Point (˚C),Min 140 140 140 Pour Point (˚C),Max -6 -6 -6 Total acidity(mgKOH/gm),Max 0.03 0.03 0.03 Water content (ppm), Max 20 15 10 IFT at 27˚C (mN/m),Min 35 35 35 Tanδ at 90˚C, Max 0.015 0.015 0.010 Resistivity at 90˚C(x10e12ohm-cm),Min 6 6 6 BDV (KV),Min 40 50 60
  13. 13. TRANSFORMER OIL SPECIFICATIONS IS-1866/2000-Violation Limits for in service oils Property Highest voltage of Equipment (KV) <72.5 72.5-170 >170 Appearance Clear and without visual contaminations Water content (ppm), Max No Free water 40 20 BDV (KV),Min 30 40 50 Total acidity(mgKOH/gm),Max 0. 3 0. 3 0. 3 IFT at 27˚C (mN/m),Min 15 15 15 Resistivity at 27˚C(x10e12ohm-cm),Min 1 1 1 Resistivity at 90˚C(x10e12ohm-cm),Min 0.1 0.1 0.1 Tanδ at 90˚C, Max 1.0 1.0 0.2 Flash Point (˚C),Min Maximum decrease of 15˚C from initial value Sediment and sludge No sediment or perceptible sludge should be detected. Results below 0.02% by mass may be neglected.
  14. 14. TRANSFORMER OIL SPECIFICATIONS IS-1866/2000-Frequency of testing Property Frequency of testing Appearance In conjunction with other Quantitative tests Water content After filling or refilling prior to energizing, then after three and 12 months, subsequently along with DGA BDV After filling or refilling prior to energizing, then yearly Total acidity Yearly IFT After filling or refilling prior to energizing, then yearly Resistivity After filling or refilling prior to energizing, then yearly Tanδ After filling or refilling prior to energizing, then yearly Flash Point Yearly Sediment and sludge Yearly
  15. 15. TRANSFORMER OIL SPECIFICATIONS IS-1866/2000-Recommended Actions Property Recommended Actions Appearance As dictated by other tests Water content Check Source of water and consider reconditioning BDV Recondition the oil or alternatively, if more economical or other tests dictate replace oil Total acidity Replace or reclaim oil IFT Replace or reclaim oil Resistivity Replace or reclaim oil Tanδ Replace or reclaim oil Flash Point Replace the oil, equipment may require inspection Sediment and sludge Where sediment is detected recondition the oil 15
  16. 16. TRANSFORMER OIL SPECIFICATIONS IS-1866/2000-Classification of oils in service. • Group 1: This group contains oils that are in satisfactory condition for continued use. The frequency can be followed as described earlier. • Group 2: This group contains oils that requires reconditioning for further service. (Low BDV and High water content). The frequency can be followed as described earlier after reconditioning. • Group 3: This group contains oils in poor condition that it can restore satisfactory properties only after reclaiming. Insulating oils this group should be reclaimed or replaced depending on economic considerations. • Group 4: This group contains oils, in such poor state that it is technically advisable to dispose of them. 16
  17. 17. 17 In order to take account of different user of mineral oil requirements, equipment has been placed in various categories as O, A, B, C, D, E, F, G O : 400 KV and above A : 170 to 400 KV B : 72.5 to 170 KV C : transformers <72.5 KV. OCB, switchgear D : Instrument transformers >170 KV E : Instrument transformers <170 KV F : Diverter tanks of on-load tap-changers G : Circuit breakers <72.5 KKV Categories of equipment
  18. 18. PHYSICAL PROPERTIES OF OIL Physical Properties Definition Purpose Effects Appearance The oils should be clear, transparent, and free from suspended matter. To determine the presence of moisture, sediments, carbon, fibers, dirt in the oil which changes the appearance of the oil, Decreases the Electrical strength, IFT value etc., Density It measures the weight of oil with respect to the mass of an equal volume of pure water at the same temperature To ensure that the free water always remains at the bottom and oil can circulate easily due to lighter weight. (Lower the density better the heat transferring capacity ) Since density is inversely proportional to temperature , heat dissipation capacity of the oil decreases with the decrease of temperature Kinematic Viscosity It measures the resistance of the oil to continuous flow without the effect of external force To ensure the mobility of oil at low temperature since presence of sediments, moisture and aging of the oil increases the viscosity value. (Lower the viscosity better the oil quality & heat transferring capacity) Heat removal capacity from windings increases with Low viscosity at low temperature and prevent localized overheating. Interfacial Tension It measures the molecular attractive force between water and oil molecule. To determine the presence of polar contaminates such as of sludge and other degrading products as a result of oxidation (Higher the IFT better the oil quality heat transferring capacity ) Oil with lower IFT reduces the cooling effect due to presence of sludge & oil decay product
  19. 19. PHYSICAL PROPERTIES OF OIL Physical Properties Definition Purpose Effects Flash point It is the lowest temperature at which oil vapour gets ignited. To determine the self ignition temperature of oil for safe operation and storing . (Higher the flush point safer the operation & storing hazards) Low value to the specified value – Risk of fire in transformer Pour point It is the lowest temperature at which oil stops to flow due to solidification. To determine the lowest temperature at which oil stop flowing due to solidification. (Lower the flush point safer the operation & storing hazards) Low value to the specified value – transformer oil stop flowing. Sludge & Sediments Solid matter comprises insoluble in solvent. It can be determined by Centrifuge method Oxidation or degradation products of insulating materials, fibers of various origins, carbon, and metallic oxides etc., arise from the conditions of service of the equipment. (Good oil must be free form sludge & sediments ) Reduces the electric strength and hinder heat transfer. 19
  20. 20. CHEMICAL PROPERTIES OF OIL Chemical Properties Definition Causes Effects Neutralization Number or Acidity It is the number of milligram of Potassium hydroxide required to neutralize completely the acids present in 1 gm of the transformer oil. Oxidation of insulating oil due to aging Corrosion of various parts of transformer, Lower the electric strength and causes Insulation degradation Oxidation Stability It the evolution of acid and sludge formation tendency of new mineral oil due to oxidation Moisture Metal corrosion which minimizes the life of the transformer Moisture It measures in ppm the presence of moisture in the oil By breathing action, Chemical reaction Decreases electric strength (BDV) Electric dissipation factor (Tan Delta) Resistivity Dissolved Gases It measures of dissolved Gases produced in the oil due to decomposition of oil Thermal degradation Arcing, Partial discharge H2 = Partial discharge H2,CH4 = Low energy discharge CH4 = Low temp hot spot H2, C2H2 = Arcing C2H4 = High temp
  21. 21. ELECTRICAL PROPERTIES OF OIL Electrical Properties Definition Causes Effects Dielectric Strength It is the minimum voltage that oil can withstand due to its dielectric strength Solid impurities Water content , Fiber Conductive particles Higher the value, Higher the purity Resistivi ty The resistivity of a liquid is a measure of its electrical insulating properties under prescribed conditions. High resistively reflects low content of free ions and ion- forming particles and normally indicates a low count ratio of conductive contaminants. Moisture , Acidity Solid contamination Higher the value , better the condition of the oil Dielectric Dissipation Factor / Tan Delta PF = Cos φ = Cos ((90-∂) = Sin ∂ = Tan ∂ Heat dissipation in the insulator due to leakage Current = OA x OB Tan ∂ (Watt) Since heat dissipation in the insulator increases With increase of PF / Cos φ / Tan ∂ - this factor is known as dielectric dissipation factor and should be as low as possible Soluble varnishes, resins , Moisture Increased value causes in increase in temperature, increase in corrosion(Applied voltage V)O Φ = (90-∂) ∂ A B C Capacitive current Actual current
  22. 22. TRANSFORMER OIL TEST PACKAGE (As per IS: 1866) 22
  23. 23. Inference of the oil test result 1. Determination of moisture in the solid insulation ( on the basis of Ooman graph) 2. Decision of hot oil circulation / drying out for improving dielectric properties by removing moisture from oil & solid insulation ( On the basis of Water PPM,, BDV) 3. Decision of providing air bellow at conservator, Silica jel breather leak arrester for preventing air ingression ( On the basis of presence of oxygen ) 4. Decision of discarding oil for loosing its dielectric or cooling properties ( On the basis of Resistivity, Tan delta ,BDV, IFT , Acidity , Colour) 5. Tracing of internal fault due to thermal and electrical stress (On the basis of DGA) 6. Aging status of the solid insulation ( On the basis of Furna Analysis ,CO2 / CO ratio)
  24. 24. 24 Moisture (Dielectric Status) 1. Decomposes solid insulation 2. Reduces BDV 3. Increases oil heating Slug & Sediments (Aging status) 1. Reduce cooling effects 2. Indicates decomposition of solid insulation DGA (Internal status) 1. Reduce life 2. Unforeseen failure 3. Sever damages Water ppm BDV Tan ∂ Resistivity Test results are within the limit Test for 1. Hot oil circulation 2. Drying out Replace Oil Transformer is healthy. No action is required. No No Yes Yes Test for Test results are within the limit IFT Acid Number Sludge content Oil Colour Test results are within the limit Yes (CO2/CO)<5 O2 >2000 Number (CH4, C2H4, C2H2) > Limit value Test for Conduct Furan Analysis No Test results are within the limit Yes Replace Oil 1. RLA Study & DP test 2. Refurbishing of solid insulation 3. Disposal of transformer Duval Triangle Analysis (H2, CH4, C2H4, C2H6, C2H2) > Limit value Roger Ratio Analysis 1. Internal Inspection 2. Tightness checking 3. Spare parts changing No
  25. 25. Pale yellow Good oil Yellow Proposition ‘A’ oil Bright yellow Marginal oil Amber Bad oil Brown Very bad oil Dark brown Extremely bad oil Black Oils in disastrous condition Discarded oil OIL QUALITY WITH COLOUR
  26. 26. ACIDITY OR NEUTRALISATION NUMBER(NN)  Acids in the oil originate from decomposition/oxidation of oil.  These organic acids are detrimental to the insulation system and can induce corrosion inside the transformer when water is present.  An increase in the acidity is an indication of the rate of deterioration of the oil with SLUDGE . The acidity of oil in a transformer should never be allowed to exceed 0.25mg KOH/g oil. INTERFACIAL TENSION(IFT)  The Interfacial Tension (IFT) measures the tension at the interface between two liquid (oil and water) which do not mix and is expressed in dyne/cm.  The test is sensitive to the presence of oil decay products and soluble polar contaminants from solid insulating materials. Good oil will have an interfacial tension of between 40 and 50 dynes/cm. Oil oxidation products lower the interfacial tension and have an affinity for both water (hydrophilic) and oil.  This affinity for both substances lowers the IFT. The greater the concentration of contaminants, the lower the IFT, with a badly deteriorated oil having an IFT of 18 dynes/cm or less.
  27. 27. Determination of oil quality based on IFT & NN IFT NN MIN = IFT/NN Colour Oil Quality & Observations 30 - 45 0.00 – 0.10 300 - 1500 Pale Yellow Very Good (provides all the required function) 27.1 – 29.9 0.05 – 0.10 271 - 600 Yellow Good(provides all the required function , a drop in IFT to 27.0 may signal the beginning of sludge & sediment) 24 – 27 0.11 – 0.15 160 - 318 Bright Yellow Acceptable (not providing proper cooling and winding protection. Organic acids are beginning to coat winding insulation; sludge in insulation voids is highly probable.) 18.0 - 23.9 0.16 - 0.40 45 - 159 Amber Bad (sludge has already been deposited in and on transformer parts in almost 100 percent of these units. Insulation damage and reduced cooling efficiency with higher operating temperatures characterize the Very Bad and Extremely Bad categories. 14.0 - 17.9 0.41 - 0.65 22 - 44 Brown Very Bad 9.0 - 13.9 0.66 - 1.50 6 - 21 Dark Brown Extremely Bad oil 1500300 600271 318160456 22 Very Good Good Acceptable / Bad / Very Bad / Extremely bad
  28. 28. Interfacial Tension, Acid Number, Years in Service
  29. 29. Condition of paper with increase of acid content in oil
  30. 30. Moisture in transformer oil 1.Moisture may be present in four possible forms 1.Free water – That is water that has settled out of the oil in a separate layer. It is this water which is indicated by a lower IR value of the transformer. 2.Emulsified water – Water that is suspended in the oil and has not yet settled out into free water . It is indicated by “caramel” colour oil. A high Tan Delta value indicates the possible presence of this suspended water trapped in oil decay products. 3.Water in solution – It remain dissolved in the oil. 4.Chemically bound water – It remains chemically attached to the insulating paper and it is released when oxidized. Water dissolved in oil (High Temp) Water dissolved in oil (Low temp) Water available in the paper insulation Temp Water solubility level in TR oil 0 Deg C 22 ppm 10 Deg C 36 ppm 20 Deg C 55 ppm 30 Deg C 83 ppm 40 Deg C 121 ppm 50 Deg C 173 ppm 60 Deg C 242 ppm 70 Deg C 331 ppm 80 Deg C 446 ppm 90 Deg C 592 ppm 100 Deg C 772 ppm With the increase of temperature ,water saturation level of oil increases and transformer oil absorbs moisture from the paper insulation till its gets saturated . Moisture movement Moisture movement With the decrease of temperature ,water saturation level of oil decreases and transformer oil exudes moisture which is absorbed by paper and subsequently deposited as free water at the insulation layers and bottom of the transformer . 2. Movement of Moisture between oil and paper insulation
  31. 31. Moisture in transformer oil – Relative saturation Water content in oil sample taken at 60 Deg C (as per lab analysis) 45 ppm Water solubility level in oil at 60 Deg C (as per graph) 242 ppm Relative saturation (RS) at 60 Dec C (45/242)x100 = 18.36% Percent saturation water in oil adjusted to 20°C Condition of cellulosic insulation 0 – 5 % Dry insulation 6 – 20 % Moderate wet, low numbers indicate fairly dry to moderate levels of water in the insulation. Values toward the upper limit indicate moderately wet insulation 21 – 30 % Wet insulation > 30 % Extremely wet insulation Condition of solid insulation based on relative saturation (RS) of oil as per IEEE 62:1995 (B6) Relative saturation (RS) indicates migration of moisture quantity between solid insulation and oil during operation
  32. 32. Moisture in transformer oil 3. Moisture Distribution The internal moisture distributed not uniformly. When the transformer is energized water is attracted to areas of strong electric fields, since water is a polar liquid having a high permittivity or dielectric constant.  It also begins to migrate to the coolest part of the transformer . This location is normally the insulation in the lower one-third of the winding  Paper insulation has a much greater affinity for water than does oil. Thus, insulation acts just like blotting paper or paper towels; it soaks up water superbly. The water will distribute itself unequally, with much more water being in the paper than in the oil. 33
  33. 33. Moisture in transformer oil 4. Damages caused by moisture  Moisture in oil reduces the insulating ability (BDV) of the oil . This may occur from the following events:  During periods of high load and high ambient temperatures, oil absorbs the moisture from the paper that may decrease BDV of the oil and causes dielectric breakdowns.  With sudden high loads, water can boil off conductor surfaces and the vapour bubbles can cause dielectric failures as they rise to the top.  During the cool-down period after high load, the relative saturation of oil will increase. At its extreme at 100% relative saturation, water will precipitate out and greatly reduce the dielectric strength of the oil.  Moisture in paper causes the following destructive effects :  Moisture and oxygen cause paper insulation to decay much faster and to form acids, metal soaps, sludge, and more moisture.  Sludge settles on windings and inside the structure, causing transformer cooling to be less efficient. Acids cause an increase in the rate of decay, which forms more acid, sludge, and moisture at a faster rate  Expansion of the paper insulation, altering the mechanical pressure of the transformer clamping system.  Loss of insulating ability (Dielectric Breakdown Voltage)  Increased corrosion of the core and tank Progressive consumption of oil additives 34
  34. 34. Determination of moisture accumulation in solid insulation through water ppm in oil 35
  35. 35. 36 Calculation of moisture accumulation in solid insulation through water ppm in oil Parameters Formula Value Oil capacity of Transformer V 80,000 Liters Density of oil D 0.86 Kg / Liters Mass of the oil M = V x D 68800 Kg Mass of the solid insulation SM = M x 0.1 6880 Kg Water ppm in oil at 60 Deg C ( Lab test ) WCO 20 ppm Corresponding water content in solid insulation ( as per the graph) WCP 2.2% Approximate weight of water in solid insulation SM X WCP /100 150 Kg
  36. 36. Effects of moisture accumulation in the solid insulation
  37. 37. 38 Limit value : Water ppm in transformer oil New oil (72 – 170 KV Transformer) (>170 KV Transformer) (< 72 Transformer)No free water Dry Oil 1. The presence of water molecule in the oil is measured by Karl Fisher Titration methods. 2. The limit value of water ppm ( part per million) need to be maintained as per the guideline of IS 335 shown in the above graph
  38. 38. + + + + + + - - - - - - - + + + - + + - + + + - + - - + + + + + - Leakage current Charging current Charging current High AC Voltage Effect on presence of polar particles in Transformer oil The insulating properties of transformer oil decreases with the increase of soluble polar particles such as water molecule, sludge & sediments, varnish, resin etc, in the oil. The polar particle present in the oil gets ionized under the influence of high AC voltage. These ionized particles gets attracted by the opposite polarity causing the flow of leakage current through the oil (insulator). The intensity of the leakage current increase with increase of concentration of polar particulates in the oil. Because of this reasons BDV, Resistivity & Tan delta value of the transformer oil gets affected due to presence of polar particles such as water molecule, sludge & sediments, varnish, resin etc in the oil.
  39. 39. Limit value : Break Down Voltage in KV < 72.5 KV Transformer 72.5 -170 KV Transformer > 170KV Transformer BDV value of transformer oil mainly depends on water ppm in the oil and it decreases with the increase of water ppm in oil .In such case BDV of oil is improved by reducing water ppm in oil through filtration .  BDV of oil may also decrease due to low resistivity of oil caused by degradation of oil or contamination of oil with soluble polar particles. In such case oil needs to be replaced after confirming low resistivity & IFT value and high tan delta & acidity value with colour of oil.  BDV of oil is determined by applying AC voltage across a gap of 2.5mm ,filled with transformer oil to be tested .  The voltage at which the spark is observed between the gap , is the BDV of the oil.  Average of six such BDV value is taken as the actual BDV of the oil.
  40. 40. As transformer oil is act as pure insulator, its resistance ( R ) should be is always as high possible. Resistance R = ρ x L/A where L = length & A = Area of the oil of the oil column and ρ = Resistivity i.e. Resistance of per unit length of oil. Hence to maintain high resistance ,resistivity of the oil should be as high as possible or conductivity should be as low as possible. With the increased concentration of polar particle in the oil, the conductivity gets increased proportionally due to flow of leakage current. Hence low Resistivity indicates : 1.Contamination of oil with polar particles produced by oxidation of oil due to overheating , moisture & oxygen or aging of oil. 2.In such case oil replacement is required after confirming low IFT value, high tan delta & acidity value with colour of oil. 3.Some time excess moisture contamination also can reduce resistivity. It is confirmed with low BDV. In such case oil filtration can improve the oil resistivity . 4.Because of covalent, oil also shows low resistivity at increased temperature. Resistivity
  41. 41. Limit value (at 90 Deg C) : Resistivity (Very Good) (Good) (Min) Resistivity is measured by applying 500 V DC voltage across the oil sample after heating up the sample at 90 Deg C which is the maximum allowable operating temperature of transformer
  42. 42. DDF / Tan Delta O Φ = (90-∂) ∂ B C A OA = Applied voltage, OC = Charging current, OB = Total current ( Charging current + Leakage current) Charging current = OB Sin φ , Leakage current = OB Cos φ , PF = Cos φ = Cos ((90-∂) = Sin ∂ = Tan ∂ ( since ∂ is very small) Dielectric leakage current = OB Cos φ = OB Tan ∂ Heat dissipation in the oil due to leakage current = V x I x PF = OA x OB Cos φ = OA x OB Tan ∂ (Watt) Applied Voltage Capacitor chargingcurrent Being a pure insulator, transformer oil behaves like dielectric of a capacitor under high AC voltage and it absorb charging current at 900 leading with respect to the applied voltage and maintain the PF angle of the insulator at 90 Deg. With the increase of concentration of soluble polar particle in the oil, PF angle (Φ) decrease and angle ∂ increases due to flow of leakage current. As result of this Tan delta value of the Transformer oil gets increased .  Since oil is a covalent compound, its resistivity decrease at increased temperature and conductivity increases. As a result of this Tan Delta value is also increased with temperature.  Since heat dissipation in the insulator increases with increase of PF / Cos φ / Tan ∂ - this factor is known as dielectric dissipation factor DDF and should be as low as possible. Inferences : 1.Increase in Tan delta value indicates the contamination of oil with soluble ionized particles such as water molecule, sludge & sediments, varnish, resin etc or due to loosing of insulating properties of oil as a result of accelerated aging.. 2. Oil heating increases with the increase of tan delta value.
  43. 43. Charging current Leakage current Total current O BA C δ3 δ2 Limit value ( At 90 Deg C) : Tan Delta Angle value % Value Ideal TAN δ 0.000 AB/OB 0.000 δ0 0.0 Deg OC 0.% of OB Normal TAN δ1 0.002 AB/OB 0.002 δ1 0.1 Deg OC 0.2 % OB Maximum ( > 72.5 KV Transformer) TAN δ2 0.200 AB/OB 0.200 δ2 11.3 Deg OC 20 % OB Maximum (< 72.5 KV Transformer) TAN δ3 1.000 AB/OB 1.000 δ3 45 Deg OC 100 % OB δ1 Normal Max > 72.5 KV Transformer Max < 72.5 KV Transformer Tan delta value is measured by applying 1000 V AC voltage across the oil sample after heating up the sample at 90 Deg C which is the maximum allowable operating temperature of transformer
  44. 44. Resistivity & tan delta (indicates deteriorating status of the dielectric due to oxidation & contaminations of oil) Presence of the Polar particles / Increase in temperature 200 C 900 C Presence of dissolved & free water / Increase in temperature 200 C 900 C Water ppm & bdv (indicates present status of the dielectric due to contaminations of oil with water ) Resistivity Ώ cm Tan Delta % BDV in KV Effect of temperature on oil parameters
  45. 45. 46
  46. 46. Transformer oil processing Removal of Free & dissolved water, Dissolved combustible gas Solid particulate matter RECLAIMING ( Chemical process) for oil having higher acid number and lower IFT RECONDITIONING ( Mechanical process) for oil having higher water ppm Removal of Free & dissolved water, Removal of - Sludge & sediments (Polar, Acidic & Colloidal materials) OFF Line process Circulating hot oil through filter & vacuum chamber in FILTER MACHINE ON Line process Circulating oil continuously through cartridge banks filled with molecular sieve Circulating oil continuously through fuller earth column OFF Line process
  47. 47. Off line reconditioning through filter machine Magnetic Filter Automatic Heater Fine Filter Gear Pump Vacuum Pump Vacuum Chamber Transformer Tank filled with oil Transformer oil is sucked from the bottom of the tank and passes through the magnetic filter where metallic particles are removed and then it is heated up to 60 Deg C with the help of automatic heaters. Heated oil is then pushed into a vacuum chamber where it is made to fall in droplets forms for increasing surface area and timing so that dissolved water in the oil gets evaporated ( under 760mm of vacuum, water gets evaporated at 40 Deg C) and extracted by vacuum pump along with other dissolved gases. Then the degassed oil is passed through fine filter where particles of size 3 to 5 micron is removed and pushed into the top of the tank through gear pump. This process is going on continuously till the oil parameters - water ppm, BDV, Resistivity & Tan Delta are achieved.
  48. 48. 49 Molecular sieve material When transformer is in service, moisture available in the paper insulation is absorbed by oil due to increase in water saturation level as result of oil temperature. In such condition if the oil is circulated through the water absorbing cartridge filled with molecular sieve material, moisture present in the oil gets absorbed by the sieve. As a result of this process, moisture available in the paper is extracted by sieve through the media of transformer oil. This process is applicable only when the transformer is in service . On line reconditioning through molecular sieve
  49. 49. Oil Reclaiming / Regeneration process as per IEC 60422 Oil reclamation remove oxidation inhibitors. Additives shall be replaced in the reclaimed oil after the reclaiming process and before the equipment is re-energized The most widely used additives are 2,6-di-tert-butyl- paracresol (DBPC) and 2,6-di-tert-butyl-phenol (DBP).
  50. 50. 51
  51. 51. Dissolved Gas Analysis (DGA)  Due to normal aging or internal faults different types of gases are generated which subsequently dissolve in oil.  Hence dissolved gas analysis of the transformer oil gives indication of the nature of fault inside the transformer.  A sudden increase in key gases and the rate of gas production is more important in evaluating a transformer than the accumulated amount of gas  The advantages of dissolved gas analysis are - 52
  52. 52. Generation of gases 1. Hydrocarbons & Hydrogen Methane CH4 Ethane C2H6 Ethylene C2H4 Acetylene C2H2 Hydrogen H2 2. Carbon oxides Carbon monoxide CO Carbon dioxide CO2 3. Non fault gases Nitrogen N2 Oxygen O2 At elevated temperature between 500K and 200K, following reaction takes place and gases are produced which remains dissolved in the oil. C (Solid) +2H2 (Gas) CH4 (Gas) 2CH4 (Gas) + 2H2 (Gas) C2H4 (Gas) + 2H2 (Gas) C2H4 (Gas) C2H2 (Gas) + H2 (Gas) C2H4 (Gas) + H2 (Gas) C2H6 (Gas) C2H2 (Gas) + 2H2 (Gas) C2H6 (Gas) Types of gases 53
  53. 53. Types of Faults & generation of gases 1. Corona OIL CELLULOSE H2 H2,CO,CO2 1. Low temperature heating OIL CELLULOSE CH4,C2H6 CO2,(CO) 2. High temperature heating OIL CELLULOSE C2H4,H2,(CH4,C2H6) CO,(CO2) 2. Arcing H2,C2H2,(CH4,C2H6,C2H4) TYPES OF FAULTS THERMAL FAULTS ELECTRICAL FAULTS 54
  54. 54. NormalOperation&aging Thermal Fault Overloading Over heating of oil and paper FailureofPumps,Fans Misdirectionflowofcoolingoil duetoloosenessofoildirecting baffle Hot spot - causing overheating of oil & paper Blockingofoilductbysludge presentintheoil Improper cooling Badleadsconnection/Poor contactinthetapchanger Electrical Fault Deteriorated /damaged insulation Dischargingofstaticelectrical chargesthatbuilduponshields orcoreandstructureswhich arenotproperlygrounded Electricalarcingbetween windingsandground,between windingsofdifferentpotential, orinareasofdifferent potentialonthesamewinding, Arcinginthetransformerdue toshortcircuit/groundfault Arcinginthetransformerdue tovoltagesurgesuchasa lightningstrikeorswitching surge Hummingduetoloosenessof windingsthatcauseswinding heatingasresultoffriction FormationofKey gasesintheoilas resultof decompositionof oilandburningof paperinsulation. External Conditions Exposureofoiltotheenvironmentduetooil leakandnotprovidingairbellows&silicajel breatherintheconservator Accumulationof environmental gases-O2,CO2, N2,H2Ointheoil Types of Faults & generation of gases
  55. 55. Dissolved Gases CIGRE (1976) ELECTRA (1978) ALSTHOM (1980) ERDA H2 ( Hydrogen) 235 28.6 200 100 CH4 ( Methane) 100 42.2 200 200 C2H2 ( Acetylene) 330 - 200 30 C2H4 (Ethylene) 145 74.6 200 300 C2H6 (Ethane) 270 85.6 200 200 CO (Carbon Monoxide) 670 289 1000 - CO2 (Carbon Dioxide) 4250 3771 10000 - Acceptance limits (1)
  56. 56. Acceptance limits (2) Gases CIGRE CPRI CBIP 0 - 5 Yrs 6 - 10 Yrs 11-15 Yrs 0 - 4 Yrs 4 – 10 Yrs > 10 Yrs < 4 Yrs 4-10 Yrs > 10 Yrs H2 100 200 300 150 300 500 100/150 200/300 300/400 CH4 60 200 200 30 80 130 50/70 100/150 200/300 C2H2 40 200 300 15 30 40 20/30 30/50 100/150 C2H4 80 300 300 30 50 150 100/150 150/200 200/400 C2H6 40 100 200 30 50 110 30/50 100/150 800/1000 CO 700 700 700 300 500 700 200/300 400/500 600/700 CO2 8000 9000 9000 4000 - 10000 3000/5000 4000/5000 9000/12000 58
  57. 57. Acceptance limits (3) as per IS: 9434 / 1992 , IS: 10593 / 1983 & IEC 599 –1978 GAS LESS THAN FOUR YEARS IN SERVICE (PPM) 4-10 YEARS IN SERVICE (PPM) MORE THAN 10 YEARS IN SERVICE (PPM) HYDROGEN 100-150 200-300 200-300 METHANE 50-70 100-150 200-300 ACETYLENE 20-30 30-50 100-150 ETHYLENE 100-150 150-200 200-300 ETHANE 30-50 100-150 800-1000 CARBON MONOXIDE 200-300 400-500 600-700 CARBON DIOXIDE 3000-3500 4000-5000 9000-12000 59
  58. 58. Fault identification (1) - by Key gas methods Type of faults Dissolved Gasses Over heating of solid insulating materials (Insulating papers, Cloths, Parma Wood , Press Board ) Key Gas - Carbon mono oxide (CO & CO2) Overheating of oil Key Gas – Ethylene (CH4 ,C2H4 & H2) Arcing in oil Key Gas – Acetylene (H2 ,C2H2) Overheating of Paper and Oil Key Gas - Carbon mono oxide (CO, CO2, CH4, C2H4 & H2) Arcing of Oil and Paper Key Gas – Acetylene (C2H2, H2, CO, CO2) Corona Discharge Key gas Hydrogen (H2) Partial Discharge Key gas Hydrogen (H2) 60
  59. 59. Fault identification (2) - by gas ratio methods 61
  60. 60. Significance of acetylene (C2H2) in oil  Generation of acetylene (C2H2) of any amount above a few ppm indicates high-energy arcing.  Trace amounts (a few ppm) can be generated by a very hot thermal fault (500 Deg C or higher).  One time arc, caused by a nearby lightning strike or a high voltage surge, can also generate a small amount of C2H2.  If C2H2 is found in the DGA, oil samples should be taken weekly or even daily to determine if additional C2H2 is being generated.  If no additional acetylene is found and the level is below the acceptable limits, the transformer may continue in service.  However, if acetylene continues to increase, the transformer has an active high-energy internal arc and should be taken out of service immediately.  Further operation is extremely hazardous and may result in explosive catastrophic failure of the tank, spreading flaming oil over a large area. 62
  61. 61. Significance of CO/CO2 ratio in oil  If there is a sudden increase in H2 with only carbon monoxide (CO) and carbon dioxide (CO2) and little or none of the hydrocarbon gases, CO2/CO ratio indicates the degradation of cellulose insulation due to overheating.  With normal loading and temperatures, the CO2 / CO ratio is found to be between 7 to 20 .  If H2, CH4, and C2H6 increase significantly with CO2/CO ratio less than 5 , it indicates the probability of problem.  If the ratio is 3 or under, severe and rapid deterioration of cellulose is certainly occurring  The ratio should be based on the gas generation of both CO2 and CO between successive DGAs and not on accumulated total CO2 and CO gas levels  Extreme overheating from loss of cooling or plugged oil passages will produce a CO2/CO ratio around 2 or 3 along with increasing Furans 63
  62. 62. Significance of atmospheric gases (O2 & N2) in oil  Oxygen may be present inside the transformer due to ingression of air through breather, leaks and air packets tapped in the winding.  The oxygen reacts on the cellulose of the insulating paper and leads to the formation of organic acids, which dissolved in oil and consequently form sludge.  This sludge blocks the free circulation of the oil and thus increases the operating temperature.  The presence of sludge in transformer oil reduces the resistively and increases the tan delta of the oil.  Many experts and organizations, including EPRI, believe that presence of oxygen above 2,000 ppm, in the oil greatly accelerates paper deterioration with moisture above safe levels.  It is recommended that if oxygen reaches 10,000 ppm in the DGA, the oil should be de-gassed and new oxygen inhibitor needs to be installed.  Nitrogen may be present inside the transformer due to leaking of N2 filled bellow provided in the conservator tank air and exposure of oil to atmosphere through leaks , breathers etc. Presence of nitrogen in the air indicates the leaking of conservator bellow or exposure of oil to the atmosphere. 64
  63. 63. Fault Analysis ( 1) - by Roger methods CH4 H2 C2H6 CH4 C2H4 C2H6 C2H2 C2H4 Faults 0.1 0 0 0 Partial discharge 0 0 0 0 Normal deterioration 1 0 0 0 Over heating >150 Deg C 1 1 0 0 Over heating 150 – 200 Deg C 0 1 0 0 Over heating 200 – 300 Deg C 0 1 1 0 General condition of overheating 1 0 1 0 Circulating current / Overheating of joints 0 0 0 1 Flash over without power flow 0 1 0 1 Current breaking through tap changer 0 0 1 1 Arc with power flow •Ratio less than 0.1 is designated as 0 •Ratio greater 1 is designated as 1 65
  64. 64. Fault Analysis (2) - by IEC 599 and CBIP methods C2H2 C2H4 CH4 H2 C2H4 C2H6 Ratio of the dissolved gases 0 1 0 Ratio less than 0.1 1 0 0 Ratio from 0.1 to 1.0 1 2 1 Ratio from 1.0 to 3.0 2 2 2 Ratio greater than 3 Fault detection chart C2H2 C2H4 CH4 H2 C2H4 C2H6 Faults & Causes 0 0 0 No fault Normal aging 0 1 0 Partial discharge of low intensity . Discharge in gas filled cavities, resulting from incomplete impregnation / super saturation / cavitations of high humidity 1 1 0 Partial discharge of high intensity As above but leading to tracking / perforation of solid insulation 1 to 2 0 1 to 2 Discharge of low energy Continuous sparking in oil, between bad connection of different potential or to floating potential. Break down of oil between solid material 1 0 2 Discharge of high energy Discharges with power follow through. Arcing / breakdown of oil between windings or coils or between coils & earth , tap changer breaking current 0 0 1 Thermal fault of low temp (150 Deg C) General overheating of insulated conductor 0 2 0 Thermal fault of low temp (150 to 300 Deg C) Local over heating of the core due to concentrations o f flux , increasing hot spot temperature, varying from small hot spots in core, shorting links in core 0 2 1 Thermal fault of medium temp (300 to 700 Deg C) Over heating of copper due to eddy current, bad contracts / joints, circulating current between core and tank 0 2 2 Thermal fault of high temp (more than 700 Deg C) Over heating of copper due to eddy current, bad contracts / joints, circulating current between core and tank 66
  65. 65. fault analysis (3) – by IEEE (Std). C57-104™ Condition 1: Transformer is operating satisfactorily. Condition 2: A fault may be present. Take DGA samples at least often enough to calculate the amount of gas generation per day for each gas. Condition 3: A fault or faults are probably present. Take DGA samples at least often enough to calculate the amount of gas generation per day for each gas. Condition 4: TDCG within this range indicates excessive decomposition of cellulose insulation and/or oil. Continued operation could result in failure of the transformer. 67
  66. 66. 68 Recommendations – IEEE (Std). C57-104™
  67. 67. Fault analysis (4) - by DUVAL triangle  In order to display a DGA result in the Triangle, one must start with the concentrations of the three gases, (CH4 ) = A, (C2 H4 ) = B and (C2 H2 ) = C, in ppm.  Calculate the sum of these three values: (CH4 + C2 H4 + C2 H2 ) = S, in ppm,  Calculate the relative proportion of the three gases, in %: X = % CH4 = 100 (A/S), Y = % C2 H4 = 100 (B/S), Z = % C2 H2 = 100 (C/S).  Plot X, Y and Z in the DUVAL Triangle  Point of intersection will be laying in a particular zone indicated in the triangle  Interpret the reason from the DUVAL table This special graph for Duval triangle can be obtained by sending email to duvalm@ireq.ca. 69
  68. 68. Duval Triangle 70
  69. 69. Classification of faults- Duval method Faults Thermal Type Electrical Type T1 Thermal Fault t<300 Deg C T2 Thermal Fault 300<t<700 Deg C T3 Thermal Fault t>700 Deg C PD Partial Discharge T2 Thermal Fault 300<t<700 Deg C T3 Thermal Fault t>700 Deg C 71
  70. 70. Duval Table for interpretation 72
  71. 71. 73
  72. 72. 74
  73. 73. solid insulation  Paper and cloth used in transformer is known as solid insulation.  The main constituent of paper and cloth is fibrous material known as Cellulose  Cellulose is an organic compound whose molecule is made up of a long chain of glucose monomers (rings), typically numbering between 1000 and 1400  With breaking down of cellulose chain, the number of glucose ring decreases in the cellulose molecule  Degree of polymerization (DP) is the average number of glucose rings in the cellulose molecule and DP values state the aging status of the insulating paper  DP value > 900 indicates good paper whereas DP value < 200 indicates bad papers. Glucose Glucose Glucose 75
  74. 74. Reasons for degradation of solid insulation 1. Thermal degradation ( Heat) : Heat produced during the operation of transformer breakdowns the glucose monomers in the cellulose molecule. Because of this, the chain length of cellulose gets reduced and free glucose molecules, moisture, CO, CO2 gases and organic acids are produced. Because of this reason overheating of transformer leads to reduction of its life Cellulose Glucose molecule +H2 O+CO+CO2 2. Hydrolytic degradation (Moisture): Water and acid separate the bonds between the glucose units in cellulose chain and produce free glucose. Because of this reason only after careful drying of insulating paper, transformers are put into service HEAT 76
  75. 75. Aging process of transformer’s solid insulation Moisture Oil impregnated solid insulation Heat Chemical degradation of solid insulation (Paper) And production of Acids, Peroxides, O2, H2O, Furan contents Lighting /Switching impulse Dielectric degradation Mechanical degradation Short circuit Conduction & Ionization (Partial Discharge) Glow discharge (Corona) Insulation Failure Oxygen 77
  76. 76. 78
  77. 77. DP values and aging of transformer Years DP Values Age (Yrs) DP Values 0 >1000 1 975 12 700 22 450 25 390 35 125 79
  78. 78. Interpretation of DP values 80
  79. 79. Furan analysis  The mechanical properties of insulating paper can be established by direct measurement of its tensile strength or degree of polymerization (DP).  Direct measurement of these properties is not practical for in-service transformers since it requires removal of a few strips of paper from suspect sites.  This procedure can conveniently be carried out during transformer repairs. The results of these tests will be a deciding factor in rebuilding or scrapping a transformer.  Since it is usually not practical (and often dangerous to the transformer) to obtain a paper sample from a de-energised, in-service transformer an alternative method has been found.  When a cellulose molecule de-polymerises (breaks into smaller lengths or ring structures), a chemical compound known as a furan is formed.  By measuring the quantity and types of furans present in a transformer oil sample, the paper insulation overall DP can be inferred with a high degree of confidence. The types and concentration of furans in an oil sample can also indicate abnormal stress in a transformer, whether intense, short duration overheating or prolonged, general overheating.  Furan analysis can be used to confirm Dissolved Gas Analysis where carbon monoxide present indicates problems with solid insulation 81
  80. 80. Inference of the chemical compounds obtained during furan analysis of transformer oil 82
  81. 81. Aging & Furfural in oil – BHEL study Age (Years) Furfural (mg/Ltr) 2 0.01 5 0.02 6 0.03 7 0.04 8 0.05 9 0.06 10 0.08 11 0.10 12 0.12 13 0.15 14 0.18 15 0.21 16 0.24 17 0.30 18 0.37 19 0.48 20 0.60 21 0.75 22 0.90 23 1.05 24 1.20 25 1.35 26 1.80 27 2.25 28 2.70 29 3.15 30 3.65 83
  82. 82. Relation between furan content in oil and DP values of solid insulation 84
  83. 83. Limiting values for furan analysis 85
  84. 84. 8686 conversion table I 1% = 10,000ppm Percent (%) ppm 0.0000% 0 ppm 0.0001% 1 ppm 0.0010% 10 ppm 0.0100% 100 ppm 0.1000% 1000 ppm 1.0000% 10000 ppm 2.0000% 20000 ppm 3.0000% 30000 ppm 4.0000% 40000 ppm 5.0000% 50000 ppm 6.0000% 60000 ppm 7.0000% 70000 ppm 8.0000% 80000 ppm 9.0000% 90000 ppm 10.0000% 100000 ppm 20.0000% 200000 ppm 30.0000% 300000 ppm 40.0000% 400000 ppm 50.0000% 500000 ppm 60.0000% 600000 ppm 70.0000% 700000 ppm 80.0000% 800000 ppm 90.0000% 900000 ppm 100.0000% 1000000 ppm 1ppm = 0.0001% ppm Percent (%) 0 ppm 0.0000% 1 ppm 0.0001% 2 ppm 0.0002% 3 ppm 0.0003% 4 ppm 0.0004% 5 ppm 0.0005% 6 ppm 0.0006% 7 ppm 0.0007% 8 ppm 0.0008% 9 ppm 0.0009% 10 ppm 0.0010% 20 ppm 0.0020% 30 ppm 0.0030% 40 ppm 0.0040% 50 ppm 0.0050% 60 ppm 0.0060% 70 ppm 0.0070% 80 ppm 0.0080% 90 ppm 0.0090% 100 ppm 0.0100% 200 ppm 0.0200% 300 ppm 0.0300% 400 ppm 0.0400% 500 ppm 0.0500% 600 ppm 0.0600% 700 ppm 0.0700% 800 ppm 0.0800% 900 ppm 0.0900% 1000 ppm 0.1000% 2000 ppm 0.2000% 3000 ppm 0.3000% 4000 ppm 0.4000% 5000 ppm 0.5000% 6000 ppm 0.6000% 7000 ppm 0.7000% 8000 ppm 0.8000% 9000 ppm 0.9000% 10000 ppm 1.0000% 100000 ppm 10.0000% 1000000 ppm 100.0000%
  85. 85. 87 Torr mm Hg Atm. PSI kg/sq.cm kPa mBar 760 760 1.00 14.69 1.03 101.31 1013.3 600 600 0.79 11.66 0.82 79.98 800.0 500 500 0.66 9.67 0.68 66.65 666.7 400 400 0.53 7.68 0.54 53.32 533.3 300 300 0.39 5.83 0.41 39.99 400.0 200 200 0.26 3.84 0.27 26.66 266.7 100 100 0.13 1.99 0.14 13.33 133.3 80 80 0.11 1.56 0.11 10.66 106.7 60 60 0.08 1.13 0.08 8.00 80.0 40 40 0.05 0.711 0.05 5.33 53.3 20 20 0.03 0.426 0.03 2.67 26.7 10 10 0.01 0.142 0.01 1.33 13.3 5 5 0.01 0.142 0.01 0.67 6.7 2.5 2.5 0.00 0.00 0.00 0.33 3.3 1 1 0.00 0.00 0.00 0.13 1.3 conversion table II
  86. 86. 88 Water Boiling point (Deg C) Vacuum Gauge Reading (mmHg) 0 755.42 10 750.79 20 742.47 30 728.18 40 704.68 50 667.50 60 610.62 70 526.30 80 404.24 90 234.24 92 193.01 94 149.10 96 102.38 98 52.73 100 0.00 conversion table III
  87. 87. TR Oil Temp Water solubility level in TR oil 0 Deg C 22 ppm 10 Deg C 36 ppm 20 Deg C 55 ppm 30 Deg C 83 ppm 40 Deg C 121 ppm 50 Deg C 173 ppm 60 Deg C 242 ppm 70 Deg C 331 ppm 80 Deg C 446 ppm 90 Deg C 592 ppm 100 Deg C 772 ppm conversion table III
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