APAR Industries Ltd , India
Emerging trends and challenges in
Quality and Performance standards
of Transformer Oil –
Critical Properties & Issues
By
D.V.Jagannathan
Contents
1 ) Emerging Trends & Challenges
2 ) Copper Sulphide Corrosion in Transformers
3 ) Changing Demands in Oil
4 ) New Standards for Corrosive Sulphur
5 ) New Standards for Oxidation Stability
6 ) Sulphur Vs Oxidation – The Balancing Act
7 ) Requirements of Transformer Oil
8 ) Critical Oil Properties and Significance
9 ) Sulphur in Transformer Oil
10 ) National Vs International Standards
11 ) Special Requirements and High Grade Options
12 ) Conclusions
Emerging Trends and Challenges
Transformer Industry has seen three dimensional effects of
Demand
-
Increased Power demands.
Higher Loads & Extra High Voltage requirements.
Design
-
Compactness driven by Material Cost considerations
leading to more severe Operating conditions.
Disasters
-
Major Transformer failures largely attributed to
Copper Sulphide formation.
-
Predominant in Power Transformers & Sealed Systems.
Transformer Failures
The Issues:
• Large Power Transformer and Reactor failures starting in 2000.
• Doble has recorded about 25 + units that have failed worldwide.
• Many of these are units only 5 to 7 years old.
• Sudden failures with no / hardly any advance warnings.
COPPER SULPHIDE CORRSION IN TRANSFORMERS
•
Transformer failures due to Copper Sulphide Corrosion problem being reported since
the turn of the century world wide - ( U S.A, Brazil, Sweden and also recently in India
•
PROBABLE CAUSES
1. Higher Corrosive & Mercaptan Sulphur levels in oils
2. Increased severity of working conditions - Higher Temperatures & Electrical Stress
3. Influence of Transformer Materials -Type & condition of paper insulation
4. Time Temperature Dependence
5. Change of Service Conditions
6. Impact of Transformer Design - Changing towards more compactness
•
Proper assessment based on Oil Properties & Performance, Operational Conditions,
Materials & Design Aspects of Transformer is essential
•
In most cases of such failures, sulphur content of oils were in the range of 0.3 to 0.5 % .
•
Modern Transformers demand non corrosive oils with lower sulphur contents made from
very low sulphur crudes and by deep hydro de sulphurization methods.
Changing Demands in Transformer Oil
• Compact Designs of higher operating temperatures require better Cooling.
• Longer trouble free Service Life requiring higher Oxidation Stability.
• Non Corrosive Oils to avoid Copper Sulphide Corrosion.
• Lower Gas evolution requirements in Transformers.
• Compliance to environmental / safety factors – PCB free / Low PCA.
• Revised standards with increased severity of Test conditions and
new Tests for :
- Oxidation Stability – IEC 61125 Method C and
- Corrosive Sulphur – ASTM D 1275 B & Cigre TF A2.32.01- CCD.
• For EHV Power / HVDC Transformers it is imperative to select the right
quality oil of upgraded specification for trouble free higher performance.
New Standards for Corrosive Sulphur
150 ASTM D 3487 – 2000 ( Reapproved 2006 )
Doble TOPS – 2006
(ASTM D 1275 B – Modified)
CIGRE TF.A2.32.01 *
Copper
Copper + Kraft Paper
140
ASTM D 3487
– 1988 / 2000
Temp 0 C.
Copper
(ASTM D 1275 A)
Copper
IEC 62535 Ed.1
(proposed)
100
IEC 296 - 1982
/ BS 148 -1984
Paper rating by
SEM - EDX
(ISO 5662 / BS 5680)
Copper
0
19
Hours
48
72
Other sensitive Test: DIN 51353 – IEC 60296 (2003) – Silver Strip, 100 0 C, 18 hrs.
* CIGRE TF.A2.32.01 (CCD) Test -- Produces results close to real case.
Oils that previously passed the less severe Tests are NOT able
to handle the higher Temperature & Duration of the new Tests
NTS
New Standards for Oxidation Stability
120
IEC 60296 – 2003
IEC 61125 C
(U)
(T)
(I)
Air
Air
Air
110
ASTM D 3487 – 00 ( 2006 ) - Type I & II
Doble TOPS – 2006 Uninhibited ,Type I
& Type II - Inhibited
Temp 0 C.
ASTM D 2440
Oxygen
100
IEC 296 -1982
IEC 74
Oxygen
0
72
Hours
164
332
500
NTS
Other Tests: PFVO & SFL in Doble TOPS – 2006 for all Types of Oils ( U , T (Type I) & I ( Type II)
ASTM D 2112 – RBOT in ASTM D 3487 – 00 ( 2006 ) for Type II Inhibited Oil &
in Doble TOPS – 2006 for Type I & Type II Inhibited oils
Also stringent Oxidation Stability limits for Special Applications in IEC 60296 – 2003
Sulphur Vs Oxidation – Balancing Act for Refiner
Requirement
Oxidation
Sulphur
Oxidation
Sulphur
Corrosive
High Stablility
Non Corrosive
Low Stablility
Sulphur
• Increased Oxidation Stability and Non Corrosive requirements in oils are
contradictory challenges for refiner.
• Sulphur removal also causes depletion of aromatics lowering oxidation stability.
• Thiophenes & Mono aromatics / lower size PCAs are natural inhibitors –
preferred in oil for control of oxidation stability and sulphur corrosion.
• Low aromatic oils have low corrosive sulphur but better BHT response.
• Optimized selective refining requires the right balancing act of
- Not just total sulphur removal but selective removal of the corrosive sulphurs
- Retaining the required aromatics for maintaining increased oxidation stability
Oxidation
Non Corrosive
High Stablility
Requirements of Transformer Oil
1.
Good Electrical Properties - For effective Insulation - High BDV & Resistivity
and Low Tan Delta ( Power Factor ).
2.
High Oxidation Stability
- For longer life and trouble free operation.
3.
Low Viscosity
- For good circulation and cooling – better heat transfer.
4.
Low Gassing Tendency
- For better Gas absorption and effective diagnostics
by DGA & Safe operation
5.
Low Sulphur and
Non corrosive
6.
High Solubility
- To avoid copper sulphide corrosion on conductors
and damage to winding under stressful conditions
- For less sludge and less oil deterioration
Consistent behavior with respect to time
-
Performance Durability
Constant availability of same quality base oils
-
Consistency
Transformer Oil Properties - Classification
FUNCTIONAL
-
HAVE IMPACT ON ITS FUNCTION AS INSULATING AND COOLING LIQUID
Viscosity, Density , Pour Point , Water Content ,Volume Resistivity ,
Breakdown voltage , Dielectric Dissipation Factor ( Tan Delta )
REFINING &
STABILITY
-
INFLUENCED BY QUALITY, TYPE AND DEGREE OF REFINING & ADDITIVES
Appearance , Interfacial Tension ( IFT) , Acidity, Carbon Type
Composition ( PNA ) , Aromatic Content , SK Value , Corrosive
Sulphur, Total Sulphur & Mercaptan Sulphur Content,
Oxidation Inhibitor Content
PERFORMANCE - RELATED TO LONG TERM BEHAVIOR OF OIL IN SERVICE AND ITS
REACTION TO HIGH ELECTRIC STRESS AND TEMPERATURE
Oxidation Stability , Gassing Tendency , Gas Content (DGA) ,
Impulse Breakdown Voltage, Electrostatic Charging Tendency,
Furan Content , Corrosivity
HEALTH,SAFET - RELATED TO SAFE HANDLING & ENVIRONMENT PROTECTION
& ENVIRONMENT
Flash Point , Density , PCA ( Polycyclic Aromatics ) ,
PCB / PCT ( Polychloro Biphenyls / Polychloro Terphenyls )
Oil Properties - Significance / Preference
Sr.No
PROPERTY
SIGNIFICANCE
PREFERENCE
1.
Density at 20 o C /
Specific Gravity
Mass Volume Calculations
Values Indicate Type of Oil
< 0.895
Values range from 0.81 to 0.895
Paraffinic Oils – 0.81 to 0.84
Naphthenic Oils – 0.85 to 0.895
2.
Kinematic Viscosity
In Heat transfer / Cooling
Lower Value
< 12 cSt at 40o C
3.
Flash Point
Safety & Fire Hazard
Higher Value
> 135 o C
4.
Pour Point
Minimum Operating Temp
Lower Value
< - 40 o C
5.
Interfacial Tension
Refining Quality
Higher Value > 40 x 10 -3 n / M
6.
Acidity / Neutralization No
Corrosion / Sludge build up /
affects electrical properties
Lower Value < 0.01 mg KOH / g
7.
Water Content
Affects electrical properties
Sludge / Paper deterioration
Lower Value < 30 ppm
8.
Sulphur Content
Decides corrosion chances
Lower Value < 0.15 %
9.
Corrosive Sulphur
Copper conductor corrosion
copper sulphide formation
To pass more severe test
ASTM D1275 B
10.
Oxidation Stabilitry
Service life / Deterioration of
electrical properties / Sludge
To pass more severe / stringent
tests IEC 61125 C
Oil Properties - Significance / Preference
Sr.No
PROPERTY
SIGNIFICANCE
PREFERENCE
11.
Ageing Characteristics
Service life / Deterioration of electrical
properties / Sludge
To pass specified test limits to
ensure ageing stability
12.
Breakdown Voltage
Electrical Strength – Lower values indicate
impurities like moisture / dirt / particles
Higher Values > 50 delivered
& > 70 after filtration
treatment
13.
Specific Resistance /
Resistivity, ohm - cm
Lower values indicate
conducting impurities
Higher Values > 2000 x 1012 at
27 o C & > 150 x 1012 at 90 o C
14.
Dielectric Dissipation Factor ,
Tan 
Higher values - presence of polars /
Decides refining quality
Lower Values < 0.005
15.
Power Factor , %
Percentage power loss - DDF x 100
Lower Values < 0.5
16.
Gassing Tendency
Decides extent of Gas evolution
/absorption,Important for DGA
Lower Values < + 5
In HVDC Transformers < 0
17.
Impulse Breakdown Voltage
Decides Insulation Life
Higher Values > 145
18.
PCA - Poly Cyclic Aromatics
Decides Gassing Tendency / Health hazards
while handling
Lower Values < 3 % but not
< 0.75 % due to higher gassing
19.
PCB / PCT
Highly Hazardous / Banned
Must be non detectable < 2
ppm
20.
2 FAL / Furans
Quality of refining / Higher values due to
used / rerefined oils
Very low level
In new oil < 0.1 ppm
VISCOSITY & VISCOSITY INDEX
• Viscosity
-
• Viscosity Index -
Influences Heat Transfer - Temperature rise
Lower the Viscosity better the circulation & cooling
Rate of change of Viscosity with respect to Temperature
Lower the VI better the circulation & cooling
Hydrocracked
Parrafinic Oil
( Higher VI )
• Viscosity @ 70oC,mm2/Sec
4.2
Hydrotreated
Naphthenic Oil
( Lower VI )
3.2
( 25 % Reduction )
WATER CONTENT & DIELECTRIC DISSIPATION FACTOR
•
Lower the Water Content higher the electric strength & lower the dissipation losses
•
Water solubility in oil depends on temperature & amount of polar / aromatic molecules
Higher aromatic content gives higher water saturation
•
Water ingress takes place due to breathing of drums when stored in areas of high
humidity and temperature . G - 4 filtration reduces water content to achieve higher
breakdown voltage but care to be taken to avoid over heating while filtration as water
solubility increases with temperature
-------------------------------------------------------------------------------------------------------------------------• DDF is measure of dielectric losses caused by the oil , depends on ionisable and
polar molecules in the oil
•
DDF increases with contamination by moisture , particles , soluble polar contaminants
and poor refining quality.
•
Very sensitive to contaminants like Engine Oils, Lubricants , Used Oils that can enter
from the filter machines due to their earlier use if proper care is not taken while filling
Transformers
CARBON TYPE COMPOSITION
PARAFFINIC
- SATURATED NORMAL (Straight Chain ) & ISOPARAFFINS ( Branched Chain)
Higher Pour Points, Higher Viscosities, Low Solubility for water and
oxidation products forming precipitated sludge, Lower Thermal stability
NAPHTHENIC - CYCLIC SATURATED HYDROCARBONS
CYCLOHEXANE TYPE & SIMILAR HIGHER RING COMPOUNDS
Excellent Low Temperature Properties, Better Solvency power than
Paraffins, Excellent Chemical & Oxidation Stability, Lower VIs help in
better Circulation and Cooling
AROMATIC
- CYCLIC UNSATURATED HYDROCARBONS
BENZENE TYPE & SIMILAR HIGHER RING COMPOUNDS
Different from Paraffinics & Naphthenics both chemically and physically,
Unstable and polar in nature
GENERAL GUIDE LINE
FOR CLASSIFICATION
OF OILS BY CP %
CP Below 50 %
CP 50 To 56 %
CP Above 56 %
-
Naphthenic Oils
Intermediate Oils
Paraffinic Oils
AROMATICS & PCA CONTENT
•
Aromatic Content in oil depends on Degree of Refining
Higher the degree of refining lower the aromatic content and vice versa
•
Mono aromatics & lower ring Poly Cyclic Aromatics up to certain levels act as
good natural radical destroying oxidation inhibitors - hence selectively retained
in the oil for better Oxidation Stability and better Gas Absorption with optimum
Electrical Properties
•
PCA content increases with increase in boiling range and aromatic content
•
Higher molecular size Poly Cyclic Aromatics are not preferred in the oil as they
have negative effect on the electrical properties like impulse breakdown voltage
and streaming charges
•
PCAs are also classified as carcinogens – need to be controlled up to acceptable
levels in the oil - Maximum limit of 3 % is specified in BS : 148 & IEC : 60296
standards and also as allowed by the severe environmental standard for labeling
in confirmation with the EU Regulation as per IP- 346
OXIDATION STABILITY
•
Improves with Degree of Refining thus with decrease in Aromatic Content
Oxidation Stability drops appreciably below 4 % CA and also above 12 % CA
•
Over refining causes depletion of preferable natural inhibitors like mono aromatics
and lower size poly cyclic aromatics
•
Oxidation stability is controlled by mono aromatics, poly cyclic aromatics and
the Nitrogen, Oxygen & Sulphur hetero cyclic polar compounds
•
IS 335 - 1993 Specifies Oxidation Stability at less severe conditions of 100 o C
•
To be measured in accordance with the more stringent, IEC 61125 - Method C
- Low air flow of 0.15 ltr / hr in oil with 90 cm copper coil at 120 0 c for test duration of
164 hrs for Uninhibited oil , 332 hrs for Trace Inhibited oil & 500 hrs for Inhibited oil
•
Inhibition of oil with DBPC helps to increase oxidation stability but requires careful monitoring
of inhibitor content and proper replenishment when it drops below the minimum required level
( half of original level ), otherwise the inhibited oil deterioration will be much faster.
Sulphur in Transformer Oil
Sulfur exists in varying Forms and Concentrations in transformer Oil after all Processes.
Some sulfur types are non Corrosive to Transformer Metals, where as certain types become very
Corrosive at higher operating temperatures.
Very corrosive in transformers:
ELEMENTAL SULFUR ( S )
- Most likely to be found residual after Solvent Extraction
- Not likely to survive Hydrotreating or Hydrocracking
HYDROGEN SULFIDE ( H2S ) - Exists as a stable Molecule and very Corrosive acid Gas
but rarely found in Purge Dried / Vacuum Dehydrated Oil
MERCAPTAN SULFUR ( RSH ) - Possibly found in the Oil after all Refining Processes
- Concentration will depend on the severity of process
Sulphur in Transformer Oil
THIOPHENES - Non Corrosive
• Found in the oil after all refining processes.
• Cyclic compounds with Sulfur embedded in the Ring are very Stable.
• They also Aid in the natural Inhibiting Process of Totally Uninhibited Oil.
Dibenzo Thiophene
Most simple Polyaromatic Thiophene
S
SULFIDES-THIO ETHERS ( RSR ) - Moderately Corrosive
• These compounds can be found after all refining processes.
• Concentrations found in the oil will be relative to the process severity.
Sulphur in Transformer Oil
DISULFIDES ( RSSR ) -
Can exist after all Refining Processes.
• Normally non Corrosive Stable compounds when ( R ) is straight chain paraffinic.
• When ( R ) is a ring structure - becomes susceptible to heat breakdown and forms
Mercaptan ( RSH ) & Hydrogen Sulfide (H2S) - very Corrosive to Transformer Metals.
• Some past studies rated Disulfides as Stable until this chemistry was better understood.
S
S
S
S
Dibutyl Disulfide ( R ) is Paraffinic
Dibenzyl Disulfide ( R ) is Aromatic or Ring
DBDS & Selective Refining
Problems due to DBDS
• Transformer failures were attributed to presence of DBDS in Oils.
• Earlier Sulphur Tests could not detect but the new Tests could detect.
• Should not remain in Hydrotreated Oil unless added to enhance Oxidation Stability.
• DBDS breaks up at higher Hot Spot Temperatures ( > 140 o C ) forming
Corrosive Elemental / Mercaptan Sulphurs.
• Essential that Oils are free of any DBDS.
Selective Refining
• Total Sulphur alone is not a sure indicator of whether an Oil is Corrosive.
• Corrosive character of Oil is the result of Sulphur type.
• Can be controlled by increasing Severity of treating Process to selectively
remove the unwanted Sulphurs.
Mitigation Methods
• Copper Sulphide formation is not reversible.
• Further Corrosion can be controlled by Mitigation methods.
• Commonly sugested Mitigation method is use of a Passivator.
• Depletion of Passivator while in service has been observed in some cases.
• Replenishment of Passivator on line - difficult to Monitor and Administer.
• Side effects of Passivator on Long Term usage – still not clear.
Solution does not lie in Mitigation by Passivation, but in
Replacement with Oils FREE of any Corrosive Sulphur
CORROSIVE AND MERCAPTAN SULPHUR
•
Type and levels of Sulphur compounds depend on origin of crude & degree and type of refining.
•
Have both characteristics - Negative - copper sulphide corrosion
Positive - as peroxide destroying inhibitors during oxidation process .
• Most of the standards specify only qualitative Corrosive Sulphur tests and not quantitative Corrosive &
Mercaptan Sulphur content tests.
• Type test provided in IS 335 and other standards are not adequate enough to assess the exact levels of
detrimental sulphur in oils as they are qualitative tests and at less severe test conditions .
• Only IEC 60296 specifies Total Sulphur Content limit as 0.15 %, max , by ISO 14596 ( WDXRF- Wave
length X - Ray Fluorescence Spectrometry ) / IP 373 ( Microcoulometry Oxidative) Methods & Corrosive
Sulphur by DIN 51353 ( Silver Strip , Temp 100 o C , Heating Time 18 Hrs ).
• Need to specify more stringent tests like :
A ) Modified ASTM D 1275 Method B for Corrosive Sulphur ( Temp 150 0c, Heating Time 48 hrs ,
N2 bubbling for15 mints. pre and 30 mints post start of test and keeping oxygen free subsequently )
B ) CIGRE TF. A2. 32. 01- CCD – Covered Conductor Deposition ( OIL + KRAFT PAPER,Temp 150 0 c,
Heating Time 72 hrs ) & IEC 62535 – CCD + SEM – EDX for detection of Copper Sulphide on Paper.
C ) Mercaptan Sulphur content by ASTM D 3227- 04 A / IP 342( Potentiometric Titration ) with very
low acceptance limits.
GASSING TENDENCY
•
Gassing Tendency / Gas Absorption under electrical stress is an important
performance property for safe functioning of High Voltage Transformers
•
It is a measure of rate of absorption or evolution of hydrogen in to oil in
prescribed laboratory conditions by method A of IEC 60628 or ASTM D 2300
•
Gassing Tendency limits are specified in BS 148 ( maximum + 5 ) and
ASTM D 3487 ( maximum + 30 ) standards for uninhibited oils.
IEC 60296 standard allows limits to be decided between oil manufacturer / user.
Doble TOPS specifies negative gassing. Not included in BIS - IS 335 standard
•
Mainly controlled by amount and type of Aromatics and PCA s in oil.
Gassing Tendency decreases with increase in Aromatic & PCA content
•
Also seen that it decreases with increase in Naphthenic content and
increases with increase in Paraffinic content even though these types
of hydrocarbons have no direct bearing on the Gassing Tendency
BREAKDOWN VOLTAGE UNDER IMPULSE CONDITION
•
Not commonly included in specifications except ASTM D 3487 / Doble TOPS
( minimum 145 k V ) of negative impulse breakdown voltage.
•
Breakdown behavior with DC impulse and heterogeneous gap is very different from
the AC breakdown strength. It is sensitive to both polarity and electrode geometry.
•
Measured by simulating lightning impulse striking a transformer during thunder strom
by the IEC 60897 or ASTM D 3300 Method.
•
It is the capacity of the oil for reducing short electric shocks such as arcing of wires
or the load on transformer while being connected and disconnected during switchovers.
•
Critical in electrical equipments as it indicates ability of the oil to resist electric
breakdown under transient voltage stresses ( lightning and switching surges ).
•
Impulse Breakdown Voltage decreases with increase in PCA content and vice versa.
Possible to achieve > 200 kV value in optimum refined oils with up to maximum 3 % PCA.
2- FAL , FURANS & PCB / PCT CONTENT
2- FAL
-
Caused from improper distillation in solvent extracted oils during refining
leaving residual furfural or from contamination with used oil.
- Preferable to have low level of 2 - FAL and related compounds in oils.
- IEC 60296 standard specifies maximum acceptable limit of 2- FAL in
new oil as 0.1 mg / kg as measured by IEC 61198 Method.
FURANS
-
-
PCB / PCT
-
Furanic compounds ( Furfuraldehyde ) are generated as byproducts during
degradation of cellulose materials such as paper, pressboard,wood , etc.
Serves as indicator of solid insulation degradation as they give more precise
and early warning of paper insulation deterioration in oil filled transformers.
Limit of Total Furans is specified in BS -148 Standard as1.0 mg / kg,max.
as measured by HPLC Method. Doble TOPS specifies Furanic Compounds
as optional test with limit of 25 µg / Litre,max. by ASTM D 5837 method.
Polychlorinated Biphenyls / Terphenyls - Not present in new insulation oils
produced from crude oils. Present only in synthetic / re-refined / used oils.
- To be measured in any mixture of old and new oils.
- Have negative environmental impact and hence banned by many countries.
Classified as hazardous waste and require special method of disposal.
- Unused mineral insulating oil should be free from PCB / PCT as tested by
IEC 61619 / BS EN 61619 / ASTM D 4059 Method.
Transformer Oil Standards - National Versus International
Sr.
No
CHARACTERISTICS
IS 335 /
IS12463
ASTM D 3487
TYPE I / II
DIN 57370
VDE 0370
AS 1767.1
CL I / II
IEC
60296
U/T/I
BS 148
CL I / II
Doble TOPS
Uninhibited /
Type I / Type II
1.
Aniline point , o C
--
63 Min
--
--
--
--
63 Min
2.
Colour , Max.
--
0.5
--
--
--
--
0.5
3.
Flash point ( PMCC ),
o C , Min
140
145 ( COC )
130
140 / 130
135
140 / 130
145 ( COC )
4.
I.F.T. @ 25 o C N/m,
Min
0.04
0.04
--
0 .04
--
--
0.04
5.
Pour Point o C Max
-6
- 40
--
- 30 / - 45
- 40
- 30 / - 45
- 40
6
Specific gravity
@ 20 o C Max
0.89 @
29.5 o C
@ 15 o C 0.91
0.895
0.895
0.895
0,895
0.91 @ 15 o C
7.
Kinematic Viscosity,
cSt ( SUS )
@100 o C Max
@40 o C , Max
@ 27 o C , Max
@ 0 o C , Max
@ -15 o C , Max
@ -30 o C , Max
--27
----
3 (36)
12 (66)
-76 (350)
---
--25(20O c)
-1800
-
-16.5 / 11
--800 / --- / 1800
-12
---1800
-16.5 / 11
--800 / --- / 1800
3
11
-76
---
Clear,Tpt,
free of
suspend
matter &
Sediment
Clear & bright
Clear &
bright
Clear &
bright
Clear
bright
Clear &
bright
--
8.
Visual examination
Transformer Oil Standards - National Versus International
S.No
CHARACTERISTICS
IS 335 /
IS12463
ASTM D
3487
TYPE I / II
DIN 57370
VDE 0370
AS 1767.1
CL I / II
IEC
60296
U/T/I
BS 148
CL I / II
Doble TOPS
Uninhibited /
Type I / Type II
9.
Dielectric breakdown
voltage, KV Min.
Delivered /
After treatment
30 / 60
30 / 50
30 / 50
30 / 50
30 / 70
30
30
10.
Dielectric breakdown
voltage Impulse
conditions, 25o C, KV Min.
Needle negative to
sphere grounded 1-in
( 25.4 mm ) gap , Min.
--
145
--
--
--
--
145
11.
Dissipation Factor
@ 60Hz, % , Max
@ 25 o C
@ 90 o C
0.002
0.05
@ 100oC
0.30
-0.005
-0.005
-0.005
-0.005
0.05
0.3 @ 100 o C
12.
Water Content,
ppm , Max
50
35
--
30 (B)
40 (D)
30 (B)
40 (D)
20 (B)
30 (D)
30
13.
Gassing Tendency F/G
µL / min , Max.
ASTM D 2300 Method B
--
+ 30
--
--
--
+5
Negative
Transformer Oil Standards - National Versus International
S.
No
CHARACTERISTICS
IS 335 /
IS12463
ASTM D
3487
TYPE I / II
DIN 57370
VDE 0370
AS
1767.1
CL I / II
IEC 60296
hrs. U / T / I
164 / 332 / 500
BS 148
CL I / II
Doble TOPS
Uninhibited /
Type I / Type II
14.
Oxidation stability
(Acid Sludge Test),Max .
72 hrs. Sludge % mass
TAN mg KOH/mg
100 o C
O2
---
110 o C
O2
0.15
0.50
100 o C
O2
---
120 o C
Air
---
120 o C
Air
110 o C
O2
0.15 / 0.15 / 0.1
0.5 / 0.5 / 0.3
164 hrs. Sludge % mass
TAN mg KOH/gm]
DDF at 90 o C
0.1
0.4
--
0.30
0.60
--
0.06
0.30
--
0.80
1.20
0.500
-Genl. Special
0.80 0.05
1. 20 0.30
0.500 0.05
120 oC
Air,
--0.80
1. 20
--
0.3 / 0.3 / 0.2
0.6 / 0.6 / 0.4
--
----
----
0.60
0.05
0.18
----
----
----
----
Oxidation Stability - RBOT
minutes, Min
-- / 195
195
--
--
--
--
NA / 195 / 220
Oxidation inhibitor
content % mass , MaxUninhibited
Trace inhibited ( Type I )
Inhibited oil (Type II )
0.05
-0.3
Nil
0.08
0.3
Nil
---
Nil
-0.15 - 0.4
NIL
0.08
0.08 - 0.4
Nil
---
NIL
0.08
0.3
15.
16.
17.
Ageing Resistance
according to Baader
(140 hrs / 110 o C)
Saponification No.,
mg KOH/gm
Sludge content, wt%, max
Dielectric Dissipation
Factor @90 o C, Max
Transformer Oil Standards - National Versus International
Sr.
No
CHARACTERISTICS
IS 335 /
IS12463
ASTM D
3487
Type I / II
DIN 57370
VDE 0370
AS 1767.1
CL I / II
IEC 60296
U/T/I
BS 148
CL I / II
Doble TOPS
Uninhibited /
Type I / Type II
18.
Corrosive Sulphur
Non
corrosive
Non
corrosive
Non
corrosive
Non
corrosive
Non
corrosive
Non
corrosive
Non corrosive
Test Method
IS 335
Annex - B
ASTM D
1275 A / B
DIN 51353
ASTM D
1275 A
DIN
51353
BS 5680
ASTM D 1275 B
Cu , 140 , 19
Cu , 140 , 19 /
Cu , 150 , 48
Ag, 100 ,18
Cu , 140 , 19
Ag, 100 ,18
Cu,100 ,19
Cu , 150 , 48
(Strip , Temp o C , Hrs )
19.
Total Sulphur
content, % Max.
--
--
--
--
0.15
Spl.Appln
--
--
20.
TAN, mg KOH/gm,
Max
0.03
0.03
0.03
0.01
0.01
0.03
0.015
21.
PCB Content, ppm
--
ND
ND
ND
ND
ND
ND
22.
PCA Content , %,
--
--
--
< 3.0
< 3.0
< 3.0
--
23.
Total Furans ,
mg / kg, Max
--
--
--
--
--
1
25 µg / L
24.
2 - Furfural Content
mg / kg , Max
--
--
--
--
0.1
--
--
25.
Power FactorValued
Oxidation ( PFVO )
--
--
--
--
--
--
To pass Doble
Limit Curve
26.
Sludge Free Life –
( SFL ) @ ± 8 Hrs
--
--
--
--
--
--
40 / 64 / 80
Hrs Min
Changes in new IEC 60296 : 2003 from the earlier IEC 296 : 1982 Standard
 Three Classes are replaced by only two namely Transformer Oil and Low Temperature
Switchgear oil.
 New concept of Lowest Cold Start Energizing Temperature ( LCSET ) for different ambient
temperature conditions have been included and new property like Electrostatic Charging
Tendency ( ECT ) has been added and values for the other properties have been revised.
 Class I , Class II , Class III for Uninhibited Oils & Class I A , Class II A & Class IIIA for
Inhibited Oils of IEC 296 are replaced with only three Types - (U) Uninhibited ,
(T) Trace Inhibited & (I) Inhibited in IEC 60296.
 Merging differences in the physical properties between the Classes and making it as one
general specification with lower Viscosity (< 12 cSt at 40 o C) & Pour point ( - 40 o C max)
 Increasing severity of Oxidation Stability Test conditions in IEC 61125 C (to 120 o C ) and
with Air instead of Oxygen to make it represent the real life Transformer operating condition.
 Differentiating the duration of Oxidation Stability test to 164 Hrs for ( U ), 332 Hrs for (T)
and 500 Hrs for ( I ) grades instead of only 164 Hrs as common for all types of grades.
 Including Special Application Requirements of higher oxidation stability for High Grade Oils
with more stringent limits for Total Acidity , Sludge, DDF @ 90 o C.and Sulphur Content.
Special Application Requirements
• Sealed Transformers / High Voltage applications including HVDC
need non corrosive oils with considerably higher oxidation stability.
• These special requirements are achieved with very low Sulphur and
low Aromatic Oils that have excellent BHT( Anti oxidant ) response.
• High Grade Oxidation Stability of special application requirements of
IEC 60296 Standard are generally met with Trace or fully Inhibited Oils.
• To meet this High Grade requirements very severely treated inhibited
Naphthenic or inhibited Iso Dewaxed Iso Paraffinic Oils are available.
• High performance Hydrotreated & Hydrocracked Oils can be designed
for effective Cooling, Low Gassing and essentially Sludge Free Life.
Conclusions
• Transformer Operating conditions have thrown new challenges for
refiners to produce high quality oils meeting latest standards and tests.
• Refiner needs to take a tight rope walk to satisfy the contradictory
requirements of both high oxidation stability and non corrosive oils.
•
Fingerprinting of oil by signature analysis and optimization of oil
properties by selective refining methods is essential to achieve this.
• Standard high oxidation stability and non corrosive requirements can be
met in Uninhibited Naphthenic oils by optimizing aromatics & sulphurs.
• For still higher special application oxidation stability and non corrosive
requirements new options of Inhibited Naphthenic and Isoparaffinc oils
are emerging.
Conclusions








Characterization of a good Transformer Oil is based on its :
Electro insulating properties
Cooling characteristics
Chemical and Oxidation stability
Behavior under severe electrical stresses
Compatibility with Transformer materials
Compliance to environmental factors
Satisfactory long service life
 Transformer Oil constitutes only 5 to 7 % of the cost of Transformer.
 Easy to compare the high cost incurred in Transformer failures
to the relatively negligible differential cost of High Grade Oils.
TRANSFORMER IS HEART OF POWER SYSTEM AND INSULATING OIL ITS BLOODLINE
Thank You