Download - Oil in Service
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Maintenance of in-service mineral
insulating oil
Dr B Pahlavanpour, Nynas UK
Subjectmatter,Name, Division2 2012-11-03
Functional Requirements for Oil
An insulant
A heat transfer and cooling medium
An arc quenching medium for tapchanger diverter switches and oil
filled switchgear
Must be compatible wi th the materials used in electrical
equipment
Subjectmatter,Name, Division3 2012-11-03
Oil Condition monitoring
Monitoring and maintaining oil quality is essential to ensure the reliable
operation of oil-filled electrical equipment.
Codes of practice for this purpose have been established by electrical
power authorities, power companies and industries in many countries.
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Subjectmatter,Name, Division4 2012-11-03
Transformer Failure
Before 1930
Lack of transformer oil maintenance
many kinds of oil in useLack of specification for manufacture of oil
Lack of standard for determining oil quality
Lack of understanding of what transpires inside
a transformer as it ages
Nynas-20125 2012-11-03
In Privatized Electricity Industr y
5 hours forced ou tage = 30 days loss of revenue
availability is more important than reliability
Subjectmatter,Name, Division6 2012-11-03
Why Oil Maintenance?
Insulating oil in-service is subjected to heat and air
Oil oxidation deterioration
If a certain amount of oil deterioration is exceeded, there is inevitably
some erosion of safety margins and the question of the risk of
premature failure has to be considered.
While the quantification of the risk can be very difficult, a first stepinvolves the identification of potential effects of increased deterioration.
Unused mineral oils are limited resources and should be handled with
this in mind.
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Subjectmatter,Name, Division7 2012-11-03
Maintenance standard
IEC60422 Mineral insulating oils in electrical equipment Supervisionand maintenance guidance.
IEEE C57, 106 IEEE Guide for acceptance and main tenance of i nsulatingoil in equipment.
Utility, organisation standards TGN158
Current situation of IEC6042
Subjectmatter,Name, Division8 2012-11-03
Subjectmatter,Name, Division9 2012-11-03
Aim
Prevent forced outage
Eliminate unnecessary maintenance
Provide the appropriate amount of maintenance at right time
Prevent premature ageing
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Subjectmatter,Name, Division10 2012-11-03
Basic oil characteristics required for reliable performance
High dielectric strength to withstand the electric stresses imposed in
service
Sufficiently low viscosity so that its ability to circulate and transfer heat
is not impaired
Adequate low-temperature properties down to the lowest temperature
expected at the installation site
Resistance to oxidation to maximise service life
Subjectmatter,Name, Division11 2012-11-03
IEC60422 recommendation
Three group of tests are recommended:
Routine tests (Group 1)
Complementary tests (Group 2)
Special Investigative tests (Group 3)
Subjectmatter,Name, Division12 2012-11-03
Routine tests (Group 1)
Minimum tests required to monitor the oil and to ensure that it is
suitable for continued service. If the results obtained from these tests
do not exceed recommended action limits usually no further tests are
considered necessary until the next regular period for inspection but,
under certain perceived conditions, complementary tests may be
deemed prudent.
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Subjectmatter,Name, Division13 2012-11-03
Complementary tests (Group 2)
These are additional tests, which may be used to obtain further
specific information about the quality of the oil, and may be used to
assist in the evaluation of the oil for continued use in service.
Subjectmatter,Name, Division14 2012-11-03
Special Investigative tests (Group 3)
These tests are used mainly to determine the suitability of the oil for
the type of equipment in use and to ensure compliance with
environmental and operational considerations.
Subjectmatter,Name, Division15 2012-11-03
Group one tests
Property Group Method
Colour and appearance 1 ISO 2049
Breakdown voltage 1 IEC 60156
Water content 1 IEC 60814
Acidity (neutralization value) 1 IEC 62021-1 or
IEC 62021-2
Dielectric dissipation factor (DDF)
and resistivity
1 IEC 60247
Inhibitor content 1 IEC 60666
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Subjectmatter,Name, Division16 2012-11-03
Group 2 tests
SedimentSludge
2 Annex C of IEC 60422
Interfacial tension (IFT) 2 ASTM D971
EN 14210
Particles (counting and sizing) 2 IEC 60970
Subjectmatter,Name, Division17 2012-11-03
Group 3 tests
Flash point 3 ISO 2719
Compatibility 3 IEC 61125
Pour point 3 ISO 3016
Density 3 ISO3675
Viscosity 3 ISO 3104
Polychlorinated biphenyls (PCBs) 3 IEC 61619
Corrosive sulphur 3 IEC 62535ASTM D1275B
DIN 51353
Dibenzyl disulfide (DBDS) content 3 IEC 62697-1
Passivator content 3 Annex B of IEC
60666
Oxidation stability 3 IEC 61125
Subjectmatter,Name, Division18 2012-11-03
Oil sampling
It is essential that every effort be made to ensure that samples are
representative of the insulating oil in equipment
Sampling should be performed by an experienced person, who has
received adequate training, in accordance with IEC 60475.
Where available, manufacturers instructions should be followed.
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Subjectmatter,Name, Division22 2012-11-03
Evaluation of mineral insulating oil in new equipment
Property Highest voltage for equipment (kV)
170
Appearance Clear, free from sediment and suspended matter
Colour (on scale given in ISO 2049) Max. 2,0 Max 2,0 Max. 2,0
Breakdown voltage (kV) >55 >60 >60
Water content (mg/kg) 20
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Subjectmatter,Name, Division25 2012-11-03
Frequency of examination of oils in service
It is impossible to lay down a general rule for the frequency of
examination of oils in service which will be applicable to all possible
situations that might be encountered.
Property Equipment category
O A B C D E F G
Group 1 (Routine
Tests) years
1 to 2 1 to 3 1 to 4 2 to 6 1 to 2 2 to 6 2 to 6 2 to 6
Group 3 (passivator content) 6 month or less, depending on the rate of
decrease and the absolute value.
Maintenance of in-service insulating oil26 2009
CMI = (P - F)/2
P= Time of detecting an upcoming failure
F= Moment of failure
Condition monitoring interval, CMI
Subjectmatter,Name, Division27 2012-11-03
Oil tests
Field tests
Only limited number of tests can be performed
Obtain a prompt estimation of oil condition
Establish the classification of service-aged oils
Eliminate any changes to the oil samples properties due to
transportation to a laboratory and/or storage of oil samples
Laboratory tests
More accurate
A complete examination scheme of recommended tests can be
performed
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Subjectmatter,Name, Division28 2012-11-03
Classification of the condition of oils in service
oils in service may be classified as:
Good
FairPoor
based on the evaluation of significant properties
Subjectmatter,Name, Division29 2012-11-03
Good
Oil in normal condition; continue normal sampling
No corrective action is require
Subjectmatter,Name, Division30 2012-11-03
Fair
Oil deterioration detectable;
more frequent sampling recommended
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Subjectmatter,Name, Division31 2012-11-03
Poor
Oil deterioration abnormal
schedule effective actions
Subjectmatter,Name, Division32 2012-11-03
Corrective action
Two types of contamination / deterioration of the oil can be considered
physical
chemical
Each one requires a different remedial action
Subjectmatter,Name, Division33 2012-11-03
Important point:
Where a test result is outside the limits recommended value
should be compared with previous results and
fresh sample obtained for confirmation before any other action is
taken.
If rapid deterioration or acceleration in the rate of deterioration is
observedmore frequent tests should be instituted promptly and/or
appropriate remedial action should be taken.
It may be desirable to consult the manufacturer of the equipment
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Subjectmatter,Name, Division34 2012-11-03
Colour and appearance
All
equipment
Clear and
without
visible
contamination
Dark and/or
turbid
As dictated by
other tests.
Dark colour is a symptom
of chemical contamination
or ageing.
Turbidity is a symptom of
high water content.
Subjectmatter,Name, Division35 2012-11-03
Breakdown voltage (kV)
O, A, D >60 50 to 60 50 40 to 50 40 30 to 40
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Subjectmatter,Name, Division37 2012-11-03
variation in saturation water content with oil
temperature and acidity
0
50
100
150
200
250
0 10 20 30 40 50 60
oil temperature during operation (C)
saturation
watercontentofoil(m
g/kg
)
saturation water content in unused oil (l og Ws =
7.0895 - 1567/T)
typical saturation water content in oxidised oil with
acidityof 0.3 mg KOH/g
Maintenance of in-service insulating oil38 2009
0,00
1,00
2,00
20 30 40 50 60 70 80 90 100
ts (C)
Correction
factor
st04,0e24,2f
Sampling oil temperature above 20 C
Maintenance of in-service insulating oil39 2009
Moisture correction factor
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Maintenance of in-service insulating oil40 2009
Sampling oil temperature below 20 C
T
15670895,7LogWs
% Saturation= (mg/kgof water/ Ws)x 100
Percent saturationwater in oil
Condition of cellulosic insulation
0 5 % Dry insulation
6 20 % Moderately wet, low numbers indicate fairly dry to
moderate levels of water in the insulation. Valuestoward the upper limit indicate moderately wet
insulation21 30 % Wet insulation
> 30 % Extremely wet insulation
Source : IEEE C57.106:2002 (B6)
Maintenance of in-service insulating oil41 2009
Effect of temperature
0
5
10
15
20
25
30
35
1 2 3 4 5 6 7 8 9 10 11 12
Time
Watercontent(ppm)
0
10
20
30
40
50
60
Temperature(C)
wa ter ppm wate r ppm 2 0 oi l te mp
Loaded Loaded Loaded
Loaded
Subjectmatter,Name, Division42 2012-11-03
Acidity (mgKOH/goil)
O, A, D 0,15
B, E 0,20
C 0,30
F, G Not a routine test.
Good: Continue normal sampling
Fair: More frequent sampling. Check the presence of
sediment and sludge.An inhibited oil that reached fair values
has possibly lost its oxidation protection.
Poor: Starting from a value of 0,15, Reclaim the oil or change
the oil
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Subjectmatter,Name, Division43 2012-11-03
Dielectric dissipation factor at 40 Hz to 60 Hz at 90 C
O, A 0,20
B, C 0,50
D 0,03
E 0,30
F, G Not a routine test.
Good: Continue normal sampling.
Fair: More frequent sampling. Check other parameters.
Poor: Reclaim oil, change the oil
Subjectmatter,Name, Division44 2012-11-03
Resistivity (Gm)
O, A >200 20 to 200 60 4 to 60 800 250 to 800 60 7 to 60 10 3 to 10 3 0,2 to 3 50 10 to 50 3 0,4 to 3
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Subjectmatter,Name, Division46 2012-11-03
Inhibitor content
Good Fair Poor
>60 % of
original value
40 % to 60 %
of originalvalue
70 and stable,
(rate of
decrease
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Subjectmatter,Name, Division49 2012-11-03
Interfacial tension (mN/m)
O, A,
B, C,
D
Inhibit
ed
Uninhi
bited
>28
>25
22 to 28
20 to 25
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Subjectmatter,Name, Division52 2012-11-03
Flash point
AllCategories
Maximum decrease 10
Equipment may requireinspection. Investigate.
Maintenance of in-service insulating oil53 2009
Do nothing
Risk of failure
Establish rate of deterioration
Establish type of contamination
Physical
Chemical
Take corrective action
Options for equipment owner
Subjectmatter,Name, Division54 2012-11-03
Summary of typical actions
Key factors Symptoms Corrective actions
Physical - High water content- Low breakdown voltage value
- High particles content
- Turbid (not clear)
- Reconditioning
Chemical - High colour value- Low IFT
- High acidity value- High dissipation factor value
- Presence of sediments or sludge, or both
- Low inhibitor content, for inhibited oil
- Low passivator content for passivator
containing oil
-Reclaiming
-- or change the oil
Restore original additive
concentration according to
recommendations
PCB PCB contamination detectable - Refer to local regulations
Corrosive
Sulphur
- Oil corrosiveness Perform risk assessment andcorrect as necessary
- Passivation
- Oil change
- Reclaiming
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Subjectmatter,Name, Division55 2012-11-03
Reconditioning
Reconditioning is a process that eliminates or reduces physical
contamination by means of physical processes (filtration, drying,
degassing etc.)
Reconditioning reduces the particle and water content of the oil
The process may also remove some dissolved gases and other
components such as Furanic compounds
it is recommended that the oil should not be vacuum treated at
temperatures over 85C.
If it is desirable to reduce particles or free water, cold treatment at
atmospheric pressure may be appropriate.
Subjectmatter,Name, Division56 2012-11-03
Conditions for processing inhibited and/or passivator containing
mineral insulating oils
Temperature (C) Minimum Pressure (Pa)
40 8
50 15
60 30
70 80
80 200
85 280
Subjectmatter,Name, Division57 2012-11-03
Vacuum Treatment of Insulating Oil
Pressure [Pa]
Working Temperature [C]
100000
10000
1000
100
10
1
0 40 50 65 100 150 200 250 300 350
Water Insulating Oil Working Point
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Subjectmatter,Name, Division58 2012-11-03
Removing water from liquid and solid insulation
On-line methods
Advantages:
Possible
fortransform
ers
that
cannotwithstand
vacuum
Transformer
remains inservice
Disadvantages:
Off-line methods
Advantages:
Efficiency
Speed
Disadvantages:
Transformer hasto be taken
out of
service for theduration
of the process
Cost
Subjectmatter,Name, Division59 2012-11-03
Reconditioning equipment
Filter
Filtering equipment usually forces oil under pressure through
absorbing material such as paper or other filter media.
Centrifuge
use for rough bulk cleaning where large amounts of contaminated
oil are to be handled.
Vacuum dehydrator
It is an efficient means of reducing the gas and water content of a
mineral insulating oil to very low values
Subjectmatter,Name, Division60 2012-11-03
Oil reconditioning application t o electrical
equipment
Direct reconditioning
The oil is passed through a purifier and then stored in suitable
clean containers
Reconditioning by circulation
The oil is circulated through the purifier, being taken from the
bottom of the tank of the electrical equipment and re -delivered tothe top
It is useful for removing suspended contaminants
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Subjectmatter,Name, Division61 2012-11-03
Oil Reclamation
This is a process that eliminates or reduces soluble and insoluble polar
contaminants from the oil by chemical and physical processing.
The resulting product should be evaluated on critical parameters
Reclamation of oils of moderate to high acidity will usually result in oils
with a lower oxidation resistance than the original new oil
IEC developed new standards for reclaimed oil IEC62701
Subjectmatter,Name, Division62 2012-11-03
Replacement of oil in electrical equipment
Lower than 72.5 KV
A small extra quantity of oil is needed to rinse the interior of the tank
and the immersed parts
It is essential that the tank and the surfaces of conductors and
insulators be cleaned effectively and subsequently be kept free from
fibres
Possibly up to 10% of the original oil m ight remain adsorbed in the
solid insulation and its contaminants may take some time to migrate
into the new oil
Subjectmatter,Name, Division63 2012-11-03
Replacement o f oil in tr ansformers rated 72,5 kV
and above
Use manufacturers recommendation
Removed used oil from main tank as much as possible
Rinse the winding with clean hot unused oil (hot flashing)
Apply vacuum with care (manufacturers recommendation)
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Subjectmatter,Name, Division64 2012-11-03
Passivation
Metal passivator is added as a stock solution, dissolved in insulating
oil
The stock solution can be added via an oil processing unit or other
suitable equipment.
This treatment is recommended for unused and in-service insulating oil
Subjectmatter,Name, Division65 2012-11-03
Renewal of additives
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).
Metal passivators will also be reduced or removed due to their polar
nature.
Subjectmatter,Name, Division66 2012-11-03
Decontamination of oils containing PCBs
Contaminated oil may change and replaced by unused oil
There are several processes and techniques available for either on-
site and off-site decontamination of PCB contaminated oils
All PCB dec ont aminati on m etho ds, ei ther off -sit e or o n-si te, have
to be applied by skilled companies complying fu lly with local
regulations.
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Subjectmatter,Name, Division67 2012-11-03
Dehalogenation process
Several process are available
Dehalogenation processes using sodium and lithium derivatives
Dehalogenation processes using polyethylene glycol and potassium
hydroxide (KPEG)
Dehalogenation in continuous mode by closed circuit process