Property of Laborelec
Technical seminar
SESSION 1 “Mineral insulating oil and its application in a transformer”
“Ageing and failure of insulating materials”
“Importance of selecting good quality transformer oil”
“Inhibited versus uninhibited insulating oils”
Santiago, Chile, 14/06/2018
steve.eeckhoudt@engie.com
steve.eeckhoudt@laborelec.com
1
Property of Laborelec
Some questions to be answered…
What is inside a power transformer ?
Why is there oil inside and why do we analyse it ?
How does this transformer and its oil ages/fails (and how to stop it) ?
Why should I use good quality transformer oil ?
How should I do that ?
What to choose: inhibited or uninhibited oils ?
2
Property of Laborelec
Some basics & transformer ageing factors
Large tank (‘chemical reactor’) containing …
Copper windings
Magnetic core material
Insulating (mineral) oil
Insulating paper
Water
Gases (air but also gases from degraded oil)
Some other parts:
Cooling radiators and fans
Bushings
Separate oil-filled compartment for OLTC / CB
Conservator tank (with/without rubber bag)
Silicagel
Buchholz relay
Oil sampling valve(s)
Online monitoring devices
…
3
Property of Laborelec
Some basics & transformer ageing factors
Functions of insulating oil are electrical insulation, cooling
… but also information carrier of this vital equipment (!)
By sampling and analysing insulating oil you can assess
- ageing status of oil
- ageing status of winding paper
- presence of internal transformer faults, caused
by design or construction abnormalities, ageing
phenomenon, material incompatibility, inadequate
maintenance of operation
4
Property of Laborelec
Similar to blood analysis
Functions of BLOOD is to transport oxygen, …
… but also information carrier of HUMAN BODY (!)
By sampling and analysing BLOOD, a doctor can assess
- ageing status of HUMAN BODY
- presence of DESEASES, …, caused by design
* bad nutrition
* insufficient movement
* excessive smoking/alcohol
* infections
* family genetics
* normal ageing
*…
- if more detailed and other specific tests are needed
5
Property of Laborelec
Similar to blood analysis
BLOOD ANALYSIS
OIL CONDITION MONITORING
Nurse
Sampling technician
Doctor
Transformer/oil expert
Regular check of sugar, iron, cholesterol, …
Regular check of DGA, water, corrosive sulfur, …
Trending is more important than absolute values
Generic items (family related)
Trending is more important than absolute values
Generic items (transformer family related)
If increase/decrease, extra actions
* Confirmation sample/analysis
* Specific blood analysis or X-rays/specialist doctor
* Medication, more sports, healthy foods, …
* Hospital and surgery
If increase/decrease, extra actions
* Confirmation sample/analysis
* Specific oil analysis or electrical measurements
* Re-passivation, dewatering, online monitoring, …
* Outage and internal inspection/reparation
One important difference: we can choose our oil type/quality, not our blood …
6
Property of Laborelec
What is mineral transformer/insulating oil ?
Source:
Petroleum
Natural gas (GTL-oil)
Recycled mineral transformer oil
Production:
Vacuum distillation
Solvent extraction and/or hydrogenation to remove impurities
Blending with additives to improve some functional properties
(pour point, oxidation stability, gassing tendency, …)
Transformer oil quality has improved a lot over the last
decades
7
Property of Laborelec
What is mineral transformer/insulating oil composed of ?
Mainly hydrocarbons:
Typical composition of a transformer oil
transformer oils
8
Property of Laborelec
What is a hydrocarbon ?
An organic molecule (mainly) composed of carbon and hydrogen atoms.
carbon atom
hydrogen atom
9
Property of Laborelec
Inhibited and uninhibited oil: what does it mean ?
10
Property of Laborelec
What is DBPC ?
DBPC
= 2,6 DiButylParaCresol
= BHT (Butylated HydroxyToluene)
Other additives (DBDS, passivator IRG39) – see further
11
Property of Laborelec
Some basics & transformer ageing factors
How does insulating oil ages ?
Ageing factors:
Temperature
Catalyst (esp. Cu)
Oxygen
Light
Oil quality
12
Property of Laborelec
Some basics & transformer ageing factors
How does insulating paper ages ?
13
Property of LaborelecRemember that >99% of the water
is inside the paper insulation and
only very few water is dissolved in
oil.
Water equilibrium is largely
depending on temperature !
Some basics & transformer ageing factors
How does insulating paper ages ?
Ageing factors:
Temperature
Water
Oil degradation products
(LMW acids)
Paper quality
(Kraft, TUP, NOMEX)
14
Property of Laborelec
“The perfect transformer oil still has to be invented”
Low cost
High electrical insulation
Good cooling capacity (low viscosity, low VI, high thermal conductivity, …)
Stable (resistant to oxidation & thermal degradation)
Highly biodegradable
High capacity to dissolve oil degradation products
Low viscosity at low temperatures
Compatible with transformer materials
High flash point
Low maintenance
Easy disposal
…
15
Property of Laborelec
Standards & specifications / minimum requirements
(since beginning of 20th century / BS of 1923)
A transformer oil must fulfill its tasks as long as the transformer lives.
1 - Electrical insulation
2 - Cooling medium
3 - Data provider on transformer
Also
- compatible with other transformer materials
- stable product
- respecting HSE-regulations
Most important international standards (unused insulating oil specification) are the IEC 60296 (2012)
and ASTM D3487 (2016) which indicate minimum requirements.
(CIGRE-survey, 2013: 10/23 use IEC 60296, others mostly local ‘IEC-based’ standards)
16
Property of Laborelec
Laborelec Purchase Specifications (LPS) for unused mineral
transformer oils
Last update:
August 2016
17
Property of Laborelec
Laborelec Purchase Specifications (LPS) for unused mineral
transformer oils
Last update:
August 2016
IEC 60296-based with
extra requirements
18
Property of Laborelec
When to perform oil analyses according unused oil standard
or purchase specification ?
When purchasing a new transformer:
Request to your transformer OEM an insulating oil according to a specific standard
(edition or year of publication should be mentioned !!) or a specific purchase specification.
Transformer OEM should supply a recent oil acceptance report which was provided by an
independent organism.
Request to your transformer OEM specific brands/types of insulating oil which were
recently approved by an independent organism according to a specific standard (edition or
year of publication should be mentioned !!) or a specific purchase specification.
Some recommendations by LABORELEC:
- Choose for inhibited oils
- Make use of LABORELEC PURCHASE SPECIFICATIONS as they already take into
account some new developments not covered by current IEC 60296 (Ed.4/2012)
19
Property of Laborelec
When to perform oil analyses according unused oil standard
or purchase specification ?
Upon oil delivery on-site:
Check N° of delivered batches (drum, IBC, tank) as to check conformity of delivery by oil
supplier.
Some recommendations by LABORELEC:
- Not all tests of standard / purchase specification are needed
- Basic program normally includes the following tests
* viscosity and density
* S-content, structural analysis
* tan delta, IFT
* oxidation stability (or RPVOT when inhibited oil)
* PCB-content
* in some cases: additives and/or corrosive sulfur
20
Property of Laborelec
Which standards or purchase specifications (not) to use for
unused transformer oil ?
IEC 60296 Ed.3 (2003)
BS 148 (1998)
:
:
NOT TO BE USED
NOT TO BE USED
ASTM D3478 (2006/2009/2016)
:
NOT RECOMMENDED
IEC 60296 Ed.4 (2012)
LABORELEC PURCHASE SPECIFICATIONS
:
RECOMMENDED
IEC 60296 Ed.5 (2018/2019 ??)
:
??
21
Property of Laborelec
Which unused oil
analyses are performed ?
22
Property of Laborelec
Which unused oil
analyses are performed ?
GROUP 1 Functional properties:
cooling and electrical
insulation
23
Property of Laborelec
Which unused oil
analyses are performed ?
GROUP 2 Chemical composition, purity
& stability:
24
Property of Laborelec
Which unused oil
analyses are performed ?
GROUP 3 Health, Safety & Environment:
25
Property of Laborelec
Most important ones
in IEC 60296 Ed.4 ?
Refining quality
26
Property of Laborelec
Most important ones
in IEC 60296 Ed.4 ?
Inhibited or uninhibited oil
Natural occuring sulfides / DBDS
Synthetic phenolic antioxidant
(for instance DBPC / BHT)
27
Property of Laborelec
Most important ones
in IEC 60296 Ed.4 ?
Lifetime of the oil
28
Property of Laborelec
Most important ones
in IEC 60296 Ed.4 ?
Presence of
potentially
corrosive sulfur
species
29
Property of Laborelec
Important ones
in IEC 60296 Ed.5 ?
Stray gassing
behaviour
Presence of PAH by
updated method
30
Property of Laborelec
How does ENGIE implements acceptance testing ?
* Laborelec experts participate actively to IEC standardisation Working Groups
(ongoing IEC TC10 MT38)
* Laborelec keeps its PURCHASE SPECIFICATION up-to-date and informs ENGIE plants and
other end-customers
* ENGIE plants use PURCHASE SPECIFICATION when buying transformers / oils
(Since 2007, most large power transformers were filled with inhibited oil type)
* Laborelec performs biannual acceptance testing program for oil suppliers to list approved
oils per last PURCHASE SPECIFICATIONS
* Reference samples of biannual acceptance testing programs are stored in OILS library
(samples since 1980-ies)
31
Property of Laborelec
Shift from uninhibited oils to inhibited oils
Shift is triggered by …
* ‘Corrosive sulfur story’ (especially during 2005-2008 period) (1)
* Refining techniques and quality of available oil sources
(hydrogenation versus solvent refining)
* Technical advantages of inhibited oils
* Better resistance to oxidation/degradation (2)
* Less paper ageing under some conditions (3)
* Lower stray gassing behaviour (4)
* Easier condition monitoring practices (7)
* Quicker oxidation stability check (5)
* Lower potentially corrosive sulfur species (6)
32
Property of Laborelec
Shift from uninhibited oils to inhibited oils
Shift is slowed down by …
* Perception that ‘Inhibited’ (with an additive) is less in quality
than ‘uninhibited’ (with no additives) and the conservative energy sector
* Miscibility issues when mixing both types (8)
* The need to monitor the decrease of antioxidant
(9)
33
Property of Laborelec
(1) Corrosive
sulfur story
Since 2008 called IEC 62535
Conc DBDS
mg/kg
Corrosiveness
according CIGRE A232-TF1 method
INHIBITED OIL
oil 1
oil 2
oil 3
<10
<10
<10
non-corrosive
non-corrosive
non-corrosive
<10
50
77
84
113
124
187
188
non-corrosive
corrosive
corrosive
non-corrosive
corrosive
non-corrosive
corrosive
non-corrosive
NON-INHIBITED OIL
oil 1
oil 1
oil 2
oil 2
oil 3
oil 3
oil 4
oil 4
(before 1989)
(after 1989)
+ passivator
+ passivator
+ passivator
Laborelec data, 2006.
34
Property of Laborelec
(2) Better
resistance to oxidation/degradation
35
Property of Laborelec
(2) Better
resistance to oxidation/degradation
(6) Lower amount of potentially corrosive sulfur species
36
Property of Laborelec
(2) Better
resistance to oxidation/degradation
37
Property of Laborelec
(3) Argument
in favour of highly refined inhibited oils: slower paper ageing
(preliminary results – detailed study ongoing: first results 12/2017)
38
Property of Laborelec
(3) Argument
in favour of highly refined inhibited oils: slower paper ageing
(preliminary results – Master thesis ongoing: first results 05/2018)
39
Property of Laborelec
(4) Lower
stray gassing behaviour
Calculated 50% and 90% typical values for the
relevant stray gases from stray gassing tests
performed per ASTM D7150. These values
were calculated on a population of 10 inhibited
and 14 uninhibited unused oil samples of
different brands, commercially available on the
Asian and European market during 2012-2016
period.
Key gases are H2, but especially CH4 and C2H6.
Laborelec data, presented at CIGRE A2/D1 JWG 47 (Zurich, 2016) and CIGRE D1.70 (Nurnberg, 2017).
40
Property of Laborelec
(5) Quicker
(and better) oxidation stability check method available
41
Property of Laborelec
(5) Quicker
(and better) oxidation stability check method available
Left: Inhibited mineral transformer oil sample takes
306 minutes to reach pressure drop of O2 of 172 kPa.
Right: 809 minutes to reach pressure
drop of O2 of 172 kPa.
42
Property of Laborelec
(5) Quicker
(and better) oxidation stability check method available
Inhibited oils range between 300 and
700 minutes by ASTM D2112, while all
have total acidity of 0.07-0.12 mg/kg oil
per IEC 61125C 500h
43
Property of Laborelec
(5) Quicker
(and better) oxidation stability check method available
Data above is already updated – now RPVOT-values upto 650-700
44
Property of Laborelec
(8) Miscibility
issues when mixing both types
CASE 1
45
Property of Laborelec
(8) Miscibility
issues when mixing both types
46
Property of Laborelec
(8) Miscibility
CASE 2
issues when mixing both types
Oil mixtures (aged uninhibited + unused inhibited)
* 100% aged uninhibited oil
:
* 100% aged uninhibited oil
(after IEC 61125C 164h)
:
TAN = 0,30 mg KOH/g oil
total acids = 1,24 mg KOH/g oil
sludge = 0,48 %
* 75% aged uninhibited oil + 25% unused inhibited
(after IEC 61125C 164h)
:
total acids = 1,28 mg KOH/g oil
sludge = 0,40 %
* 25% aged uninhibited oil + 75% unused inhibited
(after IEC 61125C 164h)
:
total acids = 0,14 mg KOH/g oil
sludge = 0,01 %
47
Property of Laborelec
(8) Miscibility
issues when mixing both types
100% aged uninhibited oil
75% aged uninhibited oil
+ 25% unused inhibited
25% aged uninhibited oil
+ 75% unused inhibited
48
Property of Laborelec
(7) Easier
(9) The
condition monitoring practices (see ‘oils in-service’)
need to monitor the decrease of antioxidant
Only every 2-5 years a simple analysis by FTIR or HPLC of content of DBPC is
needed.
DBPC-decrease is not comparable and much slower compared to decrease of
Irgamet 39 ® under some conditions.
49
Property of Laborelec
Some conclusions
Mineral transformer oil and insulating paper will age and can lead to failure.
Ageing can be slowed down by selecting good quality transformer oil.
Request to oil supplier or transformer OEM (and check afterwards) oil conformity to standard.
Be aware of the differences between inhibited and uninhibited oils.
50
Property of Laborelec
51
Property of Laborelec
Technical seminar
SESSION 2 “Basics on DGA: formation of gases, sampling, analysis & interpretation”
“Type of internal faults”
“Interpretation of DGA-results using standards”
“Different levels of DGA-implementation”
Santiago, Chile, 14/06/2018
steve.eeckhoudt@engie.com
steve.eeckhoudt@laborelec.com
52
52
Property of Laborelec
Some questions to be answered…
Why is DGA so important for condition monitoring/assessment ?
How should I implement an adequate DGA-program for my transformer
fleet ?
How should I interpret a result or a routine report ?
53
Property of Laborelec
Some basics & transformer ageing factors
Functions of insulating oil are electrical insulation, cooling
… but also information carrier of this vital equipment (!)
By sampling and analysing insulating oil you can assess
- ageing status of oil
- ageing status of winding paper
- presence of internal transformer faults, caused
by design or construction abnormalities, ageing
phenomenon, material incompatibility, inadequate
maintenance of operation
54
Property of Laborelec
Some basics & transformer ageing factors
Functions of insulating oil are electrical insulation, cooling
… but also information carrier of this vital equipment (!)
By sampling and analysing insulating oil you can assess
- ageing status of oil
- ageing status of winding paper
- presence of internal transformer faults, caused
by design or construction abnormalities, ageing
phenomenon, material incompatibility, inadequate
maintenance of operation
by performing DGA
55
Property of Laborelec
Best practices for recurrent insulation oil testing program
Analysis package
DGA + %RS water-in-oil
- dissolved gases analysis by IEC 60567
- %RS water-in-oil by IEC 60814 and top-oil temperature
Analysis package
OIL AGEING
- breakdown voltage by IEC 60156
- acidity by IEC 62021-1
- tangent delta by IEC 60247
Analysis package
PAPER AGEING
- temperature corrected 2FAL-content by IEC 61198
- temperature corrected content of methanol by IEC PT 63025
Analysis package
CORROSIVE SULFUR
- potentially corrosive sulfur by IEC 62535
- content of Irgamet 39 ® by IEC 60666
14/06/2018
56
Property of Laborelec
Best practices for sampling frequency
During start-up: after 1 day, 1 week and 1 month (DGA)
During normal operational life:
DGA + %RS water-in-oil
OIL AGEING
PAPER AGEING
CORROSIVE SULFUR
14/06/2018
Specific program for HV-grid, BAT-, BBT-, … transformer
depends on insurance requirements, previous experiences,
ageing status, presence of online monitoring, …
:
:
:
:
every 3 to 24 months
every 12 to 48 months
every 12 to 48 months
initial screening / specific
57
Property of Laborelec
How are these dissolved gases created inside your transformer ?
Different gas sources
1 – By degradation of insulating oil
2 – By degradation of insulating paper
3 – By stray gassing
4 – Other sources of gases
58
Property of Laborelec
1 – By degradation of insulating oil
By the presence of thermal or electrical ‘faults/abnormalities’, the insulating oil and
paper is broken down into gases which dissolve inside bulk oil of main tank.
59
Property of Laborelec
1 – By degradation of insulating oil
C-H chemical bonds in the insulating oil are broken in the case of low-energy
electrical discharges
C-C chemical bonds in the insulating oil are broken in the case of higher
temperatures and high-energy electrical discharges
Gas molecules are formed from these unstable cut-off fragments:
hydrogen
:
H2
methane
:
CH4
ethane
:
C2H6
ethylene
:
C2H4
acetylene
:
C2H2
These gas molecules are dissolved in the oil (dissolved gas analysis or “DGA”) or occur as free gases.
60
Property of Laborelec
1 – By degradation of insulating oil
Which dissolved gases that are formed
depends on temperature.
61
Property of Laborelec
1 – By degradation of insulating oil
Which dissolved gases that are formed depends on temperature.
62
Property of Laborelec
2 – By degradation of insulating paper
C-O chemical bonds in the insulating paper are broken in the case relatively low
temperatures starting at ca. 100°C, at 300°C a complete carbonisation of paper
can be expected.
Gas molecules are formed from these unstable cut-off fragments:
carbon monoxide
:
CO
carbon dioxide
:
CO2
These gas molecules are also dissolved in the oil (dissolved gas analysis or “DGA”) or occur as free gases.
Besides CO and CO2, also water, furanic compounds and other paper degradation products are formed and dissolved
(partially) in the bulk oil.
63
Property of Laborelec
3 – By stray gassing
Through (early stage) oil oxidation and/or the presence of metal passivators,
dissolved gasses can be formed at lower temperatures not indicating a real
internal transformer fault.
Typical stray gasses at low temperatures are:
hydrogen
:
H2
methane
:
CH4
ethane
:
C2H6
Temperatures as low as 60°C can in some cases already cause the presence of
stray gasses. More stray gassing when using uninhibited oils.
See Technical Session 4.
64
Property of Laborelec
4 – Other sources of gases
Gases not caused as result of internal fault but for instance because of rusting or
other catalytic reactions with steel or other transformer materials (specific paints,
protective coatings, …).
Also exposing insulating oil to sunlight will create gases (H2, CO).
Typical gasses caused by catalytic reactions
hydrogen
:
H2
65
Property of Laborelec
How to perform oil sampling for good DGA-sample ?
Per IEC 60475 (Ed. 2011, chapter 4.2. in particular)
In VALIDATED Alu-cans or syringes (completely filled)
No plastic bottles to be used.
66
Property of Laborelec
Some data on different
sampling kits
How to perform oil sampling for good DGA-sample ?
A / Loss of gases if not completely filled sampling recipient:
B / Loss of gases when using completely filled sampling recipient:
Loss of H2
Loss of CO
Loss for CH4
ALU-can
-11%
ca. -5%
ca. -5%
Syringe
-10%
ca. -5%
ca. -5%
Dark glass bottle
-30%
ca. -5%
ca. -5%
67
Property of Laborelec
How to perform oil sampling for good DGA-sample ?
68
Property of Laborelec
How is DGA performed in the lab ?
Per IEC 60567 (Ed. 2011) (eq. ASTM D3612)
69
Property of Laborelec
Interpretation of DGA-results using international standards:
Most relevant standards
IEC 60599 (1999)
IEC 60599 (2007)
IEC 60599 (2015)
IEEE C57.104 (1991)
IEEE C57.104 (2006) = IEEE C57.104 (1991) with some minor changes
IEEE C57.104 (will – most probably – be published 2019)
Property of Laborelec
Interpretation at different levels:
• LEVEL 1 – Comparison with values from standards
Property of Laborelec
Interpretation at different levels:
• LEVEL 1 – Comparison with values from standards
• LEVEL 2 – Trending and ratio determination
Property of Laborelec
Interpretation at different levels:
• LEVEL 1 – Comparison with values from standards
• LEVEL 2 – Trending and ratio determination
• LEVEL 3 – Using specific typical values per transformer family
Property of Laborelec
Interpretation at different levels:
•
•
•
•
LEVEL 1 – Comparison with values from standards
LEVEL 2 – Trending and ratio determination
LEVEL 3 – Using specific typical values per transformer family
LEVEL 4 – Performing specific stray gassing tests (not always needed)
Property of Laborelec
•
LEVEL 1 – Comparison with limit or typical values from standards
IEC 60599 (2015)
Property of Laborelec
•
LEVEL 1 – Comparison with limit or typical values from standards
IEEE C57.104 (1991/2006)
Typical values do not depend on
• MVA
• Atmospheric protection
• Age
Property of Laborelec
•
LEVEL 1 – Comparison with limit or typical values from standards
Typical values will most probably depend on
• MVA
IEEE C57.104 (2017 DRAFT)
•
•
Atmospheric protection
Age
Property of Laborelec
•
Some comments on LEVEL 1 approach:
- better than no DGA follow-up
- these values are very general and no strict limits
- remark in IEC 60599
Property of Laborelec
HIGHLY RECOMMENDED !!!
•
LEVEL 2 –Trending and ratio determination
- Graphical plot of DGA-trend
Property of Laborelec
HIGHLY RECOMMENDED !!!
•
LEVEL 2 –Trending and ratio determination
- Use of ratios → “fault type determination”
Property of Laborelec
HIGHLY RECOMMENDED !!!
•
LEVEL 2 –Trending and ratio determination
- Use of Duval Triangles “fault type determination and fault trending”
Property of Laborelec
HIGHLY RECOMMENDED !!!
•
LEVEL 2 –Trending and ratio determination
- 2 important attention points using Duval Triangles !
1/ Most Duval Triangles simulations indicate fault at all gas
concentrations. Only use when one of the 3 gases is higher than
typical value.
Property of Laborelec
HIGHLY RECOMMENDED !!!
•
LEVEL 2 –Trending and ratio determination
- 2 important attention points using Duval Triangles !
2/ Duval Triangles are not the absolute truth ! Very useful for
trending of faults, but in some cases wrong diagnosis
(cf. CH4/C2H6 stray gassing)
Property of Laborelec
INFORMATIVE ONLY
•
LEVEL 2 –Trending and ratio determination
- Use of Duval Pentagons
Property of Laborelec
HIGHLY RECOMMENDED WHEN
SUFFICIENTLY LARGE OR SPECIFIC
TRANSFORMER FLEET
•
LEVEL 3 – Using specific typical values per transformer family
Example from LABORELEC data base … (status mid 2016, monitored by regular DGA)
4524 transformers
(excluding CB- or OLTC-samples)
494 transformers in M-E plants
(excluding European plants, HV-grids, industry)
131 BAT-transformers
(excluding BBT, MKC, …)
58 BAT-transformers of Hyundai
8 BAT-transformers of ABB
15 BAT-transformers of CG Pauwels
9 BAT-transformers of Hyosung
…
Property of Laborelec
HIGHLY RECOMMENDED WHEN
SUFFICIENTLY LARGE OR SPECIFIC
TRANSFORMER FLEET
•
LEVEL 3 – Using specific typical values per transformer family
Example from LABORELEC data base …
4524 transformers
(excluding CB- or OLTC-samples)
494 transformers in M-E plants
(excluding European plants, HV-grids, industry)
131 BAT-transformers
(excluding BBT, MKC, …)
58 BAT-transformers of Hyundai
8 BAT-transformers of ABB
15 BAT-transformers of CG Pauwels
9 BAT-transformers of Hyosung
…
Determine typical values
for group of ‘comparable’
transformers (age, oil,
conservation system, …)
Property of Laborelec
HIGHLY RECOMMENDED WHEN
SUFFICIENTLY LARGE OR SPECIFIC
TRANSFORMER FLEET
•
LEVEL 3 – Using specific typical values per transformer family
Example from LABORELEC data base …
494 tfos in M-E plants
131 BAT-tfos
58 tfos
8 tfos
15 tfos
79 BBT-tfos
…
Property of Laborelec
HIGHLY RECOMMENDED WHEN
SUFFICIENTLY LARGE OR SPECIFIC
TRANSFORMER FLEET
•
LEVEL 3 – Using specific typical values per transformer family
Example from LABORELEC data base … DETERMINATION OF ATYPICAL VALUES or OUTLIERS
Property of Laborelec
HIGHLY RECOMMENDED WHEN
SUFFICIENTLY LARGE OR SPECIFIC
TRANSFORMER FLEET
•
LEVEL 3 – Using specific typical values per transformer family
Example from LABORELEC data base … DETERMINATION OF ATYPICAL VALUES or OUTLIERS
Property of Laborelec
Interpretation at different levels:
• LEVEL 1 – Comparison with values from standards
• LEVEL 2 – Trending and ratio determination
• LEVEL 3 – Using specific typical values per transformer family
LEVEL 4 – Performing stray gassing tests in specific cases
(see Technical Sessions 4)
routine condition
monitoring
Property of Laborelec
Some conclusions
DGA is the most powerfull condition monitoring tool to estimate internal condition of a
power transformer.
The implementation of a specific program for your fleet is crucial as to keep your
transformer fleet in good condition for the longest time possible and avoid unnecessary
costs and shut-downs.
Interpretation is not just comparing with ‘limit values’ from standards. Trending and ratio
determination is (much) more important !
Build your own action values (if you have large fleet of identical units).
High-level of expertise & experience is needed to perform adequate interpretation of
analysis results.
91
Property of Laborelec
92
Property of Laborelec
Technical seminar
SESSION 3 “Oil ageing (part 1): relevant analyses & interpretation”
“Typical values & relevant standards”
“Case-studies related to water”
Santiago, Chile, 14/06/2018
steve.eeckhoudt@engie.com
steve.eeckhoudt@laborelec.com
senja.leivo@vaisala.com
93
Property of Laborelec
Some questions to be answered…
Which analyses to perform: enough, but not too much …
How should I implement an adequate program for my transformer fleet as
to estimate efficiently oil degradation or contamination ?
How should I interpret my analysis results and which maintenance actions
to take ?
Focus on water (%RS) and breakdown voltage !!
Water dynamics inside a power transformer
94
Property of Laborelec
Best practices for recurrent insulation oil testing program
Analysis package
DGA + %RS water-in-oil
- dissolved gases analysis by IEC 60567
- %RS water-in-oil by IEC 60814 and top-oil temperature
Analysis package
OIL AGEING
- breakdown voltage by IEC 60156
- acidity by IEC 62021-1
- tangent delta by IEC 60247
Analysis package
PAPER AGEING
- temperature corrected 2FAL-content by IEC 61198
(- temperature corrected content of methanol by IEC PT 63025)
Analysis package
CORROSIVE SULFUR
- potentially corrosive sulfur by IEC 62535
- content of Irgamet 39 ® by IEC 60666
95
Property of Laborelec
Best practices for recurrent insulation oil testing program
Analysis package
DGA + %RS water-in-oil
- dissolved gases analysis by IEC 60567
- %RS water-in-oil by IEC 60814 and top-oil temperature
Analysis package
OIL AGEING
- breakdown voltage by IEC 60156
- acidity by IEC 62021-1
- tangent delta by IEC 60247
Analysis package
PAPER AGEING
- temperature corrected 2FAL-content by IEC 61198
(- temperature corrected content of methanol by IEC PT 63025)
Analysis package
CORROSIVE SULFUR
- potentially corrosive sulfur by IEC 62535
- content of Irgamet 39 ® by IEC 60666
96
Property of Laborelec
Oil ageing (degradation and contamination): mechanisms
97
Property of Laborelec
Oil ageing (degradation and contamination): how to monitor ?
colour will increase
acidity will increase
water content will increase
tangent delta will increase
antioxidants will decrease
resistivity will decrease
interfacial tension (IFT) will decrease
sludge formation
…
98
Property of Laborelec
Oil ageing (degradation and contamination): how to monitor specifically ?
Which test methods for which transformers and with which sampling frequency ?
Specific oil ageing monitoring program (and interpretation of analysis results) should be
based on:
Comparison with values from standards
Trending
Determine your own typical values if larger transformer fleet
99
Property of Laborelec
Relevant international standards/documents for condition monitoring of oils-inservice
IEC 60422 Ed.4 of 2013 : Mineral insulating oils in electrical equipment – supervision and
maintenance guidance.
IEEE C57.106 of 2015 : Guide of acceptance and maintenance of insulating oil in equipment.
CIGRE/IEEE technical brochures or guidelines:
Oxidation stability (2013)
Copper sulphide (2009 / 2015)
Transformer maintenance (2011)
Water in transformers (2008 / 2018??)
Oil regeneration (2010)
Oil reclaiming (2015)
…
100
Property of Laborelec
Relevant international standards/documents for condition monitoring of oils-inservice
IEC 60422 Ed.4 of 2013
+
101
Property of Laborelec
Relevant international standards/documents for condition monitoring of oils-inservice
IEEE C57.106 of 2015
Class I:
Class II:
Class III:
Satisfactory condition for continued use.
Outside specification for water content and/or BDV
and reconditioning is needed.
Oil in poor condition not meeting limits in table 3;
oil should be reclaimed or replaced.
102
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Analysis method ?
IEC 60814
ASTM D1533
(result expressed in mg/kg or ppm)
Frequency of sampling ?
Zero-point
Basic recurrent analysis (together with DGA): every 3 to 24 months
Interpretation ?
IEC 60422 / IEEE C57.106
Trending of %RS (‘% relative saturation of water-in-oil’, taking into account temperature, acidity (and
aromatics), recently also described in IEEE C57.106 (2015-version).
Important !
Always register the temperature of top oil during sampling to allow calculation of %RS.
Most important water sources: paper degradation and atmospheric water (over Si-breather).
More than 99% of water is inside the paper not the oil and equilibrium is in function of temperature.
103
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Calculation of %RS !
Example:
At 40°C, saturation in new oil is 120 mg/kg
Measurement in oil: 30 mg/kg
What is %RS ?
104
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Calculation of %RS !
Example:
120
At 40°C, saturation in new oil is 120 mg/kg
Measurement in oil: 30 ppm/kg
30
→ % RS = ( 120 / 30 ) x 100%
= 25%
25%
105
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Calculation of %RS !
Example of impact of acidity on water
saturation in inhibited oil sample
106
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Water partitioning between oil and paper !
Limit of solubility (mg/kg)
Temperature
water goes from paper to oil
% dampness of paper
Temperature
water goes from oil to paper
Water content of the oil (mg/kg)
107
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Water partitioning between oil and paper !
Limit of solubility (mg/kg)
% dampness of paper
Question :
What do you prefer ?
(A) a transformer at 70°C with 23 mg/kg water-in-oil
(B) a transformer at 50°C with 18 mg/kg water-in-oil
Water content of the oil (mg/kg)
108
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Water partitioning between oil and paper !
Limit of solubility (mg/kg)
% dampness of paper
Question :
What do you prefer ?
(A) a transformer at 70°C with 23 mg/kg water-in-oil
2.4%
→ means ca. 1.7% of water inside paper under equilibrium conditions
1.7%
(B) a transformer at 50°C with 18 mg/kg water-in-oil
→ means ca. 2.4% of water inside paper under equilibrium conditions
18
23
Water content of the oil (mg/kg)
109
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Limit values ?
Per IEC 60422 (2013): in mg/kg
transformer >72.5 kV (after filling, before energization)
transformer <72.5 kV (after filling, before energization)
transformer >170 kV (in-service)
transformer 72.5-170 kV (in-service)
transformer <72.5 kV (in-service)
:
:
:
:
:
Per IEEE C57.106 (2015): in mg/kg
transformer >69 kV (after filling, before energization)
transformer <69 kV (after filling, before energization)
transformer >230 kV (in-service)
transformer 69-230 kV (in-service)
transformer <69 kV (in-service)
:
:
:
:
:
Laborelec general recommendation:
% RS <15
% RS 15-30
% RS >30
:
:
:
<10
<20
<15: GOOD
<20: GOOD
<30: GOOD
>20: POOR
>30: POOR
>40: POOR
<10
<20
<20
<25
<35
GOOD
SPECIFIC FOLLOW-UP
POOR
110
Property of Laborelec
Overview oil ageing analysis: 1/ WATER CONTENT / %RS
Possible actions ?
Resampling (with extra care sampling conditions)
Trending
Some other tests (BDV, …)
Relationship with online monitoring readings
Checking source of water (ageing related or not)
Reconditioning
Be aware: Reconditioning treatment can/will have impact on DGA, antioxidants, furans and/or metal
Passivators like Irgamet 39®.
111
Property of Laborelec
Moisture dynamics in a
loaded transformer
Moisture
load
Propertydynamics:
of Laborelec
• Water is released from surface
of insulation paper and
absorbed to oil as temperature
increases due to loading.
• There is continuous moisture
exchange between oil and
paper during temperature/load
fluctuation.
10 MVA, ONAN transformer
Moisture Property
dynamics:
desorption vs
of Laborelec
absorption rate
10 MVA, ONAN cooled transformer
Moisture
dynamics:
Property
of Laborelechysteresis
•
Hysteresis in moisture exchange between
oil and paper during temperature
transients.
– At cooling phase higher ppm value at
same temperature.
– Previous temperature cycles affect
ppm level.
•
Interpretation of instantaneous ppm
values challenging.
Equilibrium between the and oil rarely
exists
•
– due to load and temperature variations
→ constant moisture exchange
→ difficult to define correct moment to
take an oil sample.
Oil sample
loaded
Property of from
Laborelec
transformer
Oil sample
loaded
Property of from
Laborelec
transformer
3.3 %
2.2 %
Moisture
dynamics:
Property
of Laborelec%RS of oil
Moisture
%RS
Propertydynamics:
of Laborelec
1. Quick temperature decrease → %RS of oil increases
– Temperature may decrease due to lower load,
heavy raining and/or ambient temperature drop during
night.
2. Re-loading of cold wet transformer after service break.
– Moisture released from paper to cold oil
→ sudden increase of %RS.
• There is risk of very high %RS or even water saturation in
oil of wet transformers
▪ formation of liquid water i.e. "raining in oil"
▪ dramatic decrease of dielectric strength
→In worst case, arching and catastrophic failure!
Property of Laborelec
Online moisture
monitoring
Benefits of
%RSof online
Property
Laborelec monitoring
• Can be measured online.
– Only real time moisture
monitoring gives true picture
of moisture in transformer oil
24/7/365
• Indicates if dielectric strength of
oil is compromized due to
moisture.
• Indicates whether there is risk of
free water formation e.g. when
monitoring in the return pipe
after radiator.
Benefits
of %RS
Property of Laborelec
•
•
Gives better indication of moisture in solid insulation regardless of the oil type or age.
Averaging %RS allows elimination of moisture fluctuation.
avg top oil T ~ 40°C
ref. Cigre Brochure 349, WG A2.30
Ranking Property
transformer
of Laborelecfleet (ppm)
10...60 MVA primary distribution transformers
Rankin transformer
fleet (%RS)
Property of Laborelec
Property of Laborelec
Sensor installation
Installation
examples
Property of Laborelec
•
•
•
•
The sensor should be installed in a location
where oil flows freely around it.
Most beneficial locations are along oil
cooling circulation
→ representative oil.
Avoid "dead-ends" and bottom of pipe
bending.
If the sensor is not in oil flow the full
variation in temperature and moisture may
not be seen, but the most extreme peaks
may be ”filtered” off.
Effect of Property
sensor/sample
location
of Laborelec
WCO3
Radiator
WCO4
WCO2
WCO5
Ref. Valery Davydov
Property of Laborelec
Overview oil ageing analysis: 2/ BREAKDOWN VOLTAGE
Analysis method ?
IEC 60156 (result expressed in kV/2.5mm – spherical/mushroom electrodes)
ASTM D1816 (results expressed in kV/2mm, or in kV/mm – spherical/mushroom electrodes)
ASTM D877 (results expressed in kV/2.54mm – flat electrodes)
Frequency of sampling ?
Zero-point
Basic recurrent analysis (sometimes together with DGA): every 6 to 48 months
Interpretation ?
IEC 60422 / IEEE C57.106
Trending (combined with %RS)
Important !
In most cases, low BDV is related with too high water content.
If low BDV, is not related with water/%RS, check particle counting or dissolved metals.
128
Property of Laborelec
Overview oil ageing analysis: 2/ BREAKDOWN VOLTAGE
Limit values (for transformers)?
Per IEC 60422 (2013): in kV/2.5mm
transformer >72.5 kV (after filling, before energization)
transformer <72.5 kV (after filling, before energization)
transformer >170 kV (in-service)
transformer 72.5-170 kV (in-service)
transformer <72.5 kV (in-service)
:
:
:
:
:
Per IEEE C57.106 (2015): in kV/2mm
transformer >230 kV (after filling, before energization)
transformer 69-230 kV (after filling, before energization)
transformer <69 kV (after filling, before energization)
transformer >230 kV (in-service)
transformer 69-230 kV (in-service)
transformer <69 kV (in-service)
:
:
:
:
:
:
>60
>55
>60: GOOD
>50: GOOD
>40: GOOD
<50: POOR
<40: POOR
<30: POOR
>60
>55
>45
>50
>47
>40
129
Property of Laborelec
Overview oil ageing analysis: 2/ BREAKDOWN VOLTAGE
Possible actions ?
Resampling (with extra care sampling conditions)
Trending
Some other tests (%RS, particles, dissolved metals, …)
Relationship with online monitoring readings
Reconditioning
Be aware: Reconditioning treatment can/will have impact on DGA, antioxidants, furans and/or metal
Passivators like Irgamet 39®.
130
Property of Laborelec
Overview oil ageing analysis: 2/ BREAKDOWN VOLTAGE
Relationship between %RS and BDV
Source: VAISALA and IEEE data.
131
Property of Laborelec
Case 1
132
Property of Laborelec
Case 1
133
Property of Laborelec
Case 2
134
Property of Laborelec
Case 2
135
Property of Laborelec
Case 3
What do you observe ?
136
Property of Laborelec
Case 3
What would you recommend ?
137
Property of Laborelec
Case 3
92 ppm is still under IEC
or IEEE typical values
138
Property of Laborelec
CASE study 4:
A wet transformer
10 MVA
primary
distribution
Property
of Laborelec
transformer
Risk of breakdown! 30% dielectric strength left
Property of Laborelec
CASE study 5:
Online drying
Online
drying
Property
of Laborelec
• Online dryers can be used in connection to a
loaded transformer. Oil is circulated through
the drying unit removing water and then
returned back to the transformer.
• As only water on the surface of solid
insulation is involved in moisture exchange,
only that is available for drying at time.
• One main benefit with online drying is that
with wet transformers the oil can be kept dry
and thus dielectric strength of oil
maintained.
Transec CL3AM
Drykeep
MR MMS 1000
During
dryout
(top oil)
Property
of Laborelec
During
dryout
(bottom oil)
Property
of Laborelec
Oil moisture
before
Property of
Laborelecand after
dryout
Moisture in oil
recovers slowly
from paper
after drying
finished
During drying,
moisture of oil
and very
surface of
paper is
removed
Property of Laborelec
Summary & some recommendations on oil ageing assessment:
•
A lot of tests exist; choose specific program (which analyses and which sampling frequency) in function of
transformer, type of oil and its degradation/contamination status.
•
Water and breakdown voltage are very important oil analyses and can be related to DGA.
•
Oil temperature during sampling is important/necessary as to estimate risk of water presence.
•
Oil treatment/filtration also has disadvantages, but sometimes necessary to ensure sufficient electrical
insulation oil properties.
146
Property of Laborelec
147
Property of Laborelec
Technical seminar
SESSION 4 “DGA: Case studies”
Santiago, Chile, 14/06/2018
steve.eeckhoudt@engie.com
steve.eeckhoudt@laborelec.com
148
Property of Laborelec
Some questions to be answered…
How will water impact DGA-data and breakdown voltage ?
How should I interpret a result or a routine report ?
Specific case-studies: what can we observe through DGA and how
to act upon these results ?
149
Property of Laborelec
Case 1
Case 2
DGA, water and BDV
Case 3
Case 4
Case 5
Hot spot & partial discharges
150
Property of Laborelec
How to read a routine report ?
151
Property of Laborelec
How to read a routine report ?
MAIN GAS for ‘PD’
Type: partial discharges, but also catalytic effects or
stray gassing
152
Property of Laborelec
How to read a routine report ?
MAIN GASES for ELECTRICAL FAULTS
(called ‘D1’ or ‘D2’ -faults)
Type: discharges, OLTC-gases, ...)
153
Property of Laborelec
How to read a routine report ?
MAIN GASES for PAPER AGEING
(CO2/CO-ratio change should trigger a furan or methanol
analysis)
154
Property of Laborelec
How to read a routine report ?
MAIN GAS for HIGH-TEMPERATURE THERMAL FAULT
(called ‘T2’ or ‘T3’ -faults)
Type: local hot spot, bad connection, ...
155
Property of Laborelec
How to read a routine report ?
MAIN GASES for LOW-TEMPERATURE THERMAL FAULT
(called ‘T1’ -faults)
Type: bad cooling, overloading, stray gassing, ...
156
Property of Laborelec
Case 1
157
Property of Laborelec
Case 1
free water !!
Arcing and fatale damage to windings
because of cooling water entrance.
Specs of cooling water conditioning were
not respected.
Transformers GR2.1 and GR2.2 could be
saved just in time.
158
Property of Laborelec
Case 2
159
Property of Laborelec
Case 2
Original oil drained and
refilled with NYNAS 10 GBN
Passivation after oil filtering
Several months
out-of-service
Recommendation Laborelec:
Take transformer out-of-service
because of paper ageing, high water
content and highly corrosive oil with
a T1-fault
In meantime: install online DGA
transformer failure
160
Property of Laborelec
Case 2
It is recommended to
graphically plot you
historical DGA
161
Property of Laborelec
Case 2
Reason of failure:
Start-up after long period of shut-down during (very) cold period and without oil circulation.
162
Property of Laborelec
Case 3
163
Property of Laborelec
Case 3
Key gases here are:
H2, C2H4, C2H2 and CO
Diagnosis made by Laborelec:
Local hot spot, outside winding
paper.
164
Property of Laborelec
Case 3
Detanking & repair of Cu-strip
problem (not) solved ??
165
Property of Laborelec
Case 3
Problem solved: 6 - 9 % of
dissolved gases in paper
migrates slowly to bulk oil.
Fast forward to 2013 …
166
Property of Laborelec
Case 4
167
Property of Laborelec
Case 4
Oil drain &
installation of
more cooling
What can cause H2-increase ?
168
Property of Laborelec
What can cause H2-increase ?
•
•
•
•
High water content → partial discharges (fault type PD)
Air bubbles → partial discharges
Stray gassing
Catalytic effects with transformer materials
Not possible as low/stable water content
Possible (also CH4/H2-ratio)
Not possible as no new oil used nor additive addition
Highly unlikely
PD-measurements confirmed most likely hypothesis of partial discharges by air bubbles
Bad filling practices identified as cause of PD / H2-increase.
169
Property of Laborelec
Oil drain &
installation of
more cooling
Oil drain & degassing
and proper filling
Fast forward to 2008 …
170
Property of Laborelec
Case 5
Transformer:
HV-GRID single phase transformer
Rating: 166 MVA
Start-up: 01/1981
OEM: ACEC
Oil: Fina Diekan / uninhibited
Voltage: 380/36 kV
Cooling: OFAF
171
Property of Laborelec
Case 5
Transformer:
HV-GRID single phase transformer
Rating: 166 MVA
Start-up: 01/1981
OEM: ACEC
Oil: Fina Diekan / uninhibited
Voltage: 380/36 kV
Cooling: OFAF
‘new fault’
gases over
‘old fault’
gases
172
Property of Laborelec
Case 5
Transformer:
HV-GRID single phase transformer
Rating: 166 MVA
Start-up: 01/1981
OEM: ACEC
Oil: Fina Diekan / uninhibited
Voltage: 380/36 kV
Cooling: OFAF
‘new fault’
gases over
‘old fault’
gases
173
Property of Laborelec
Case 5
Transformer:
HV-GRID single phase transformer
Rating: 166 MVA
Start-up: 01/1981
OEM: ACEC
Oil: Fina Diekan / uninhibited
Voltage: 380/36 kV
Cooling: OFAF
Recommendation of Laborelec on 16/09:
Action to track down fault is needed on very short-term
(electrical measurements, internal inspection, …)
Keep at least a weekly frequency for DGA-sampling and
detailed analysis
Reply HV-grid operator experts (10/2014):
“Electrical measurements revealed a very clear hot spot
on LV-bushing connection. Oil of transformer will be
drained and internal inspection is foreseen to localise
and repair damage”.
174
Property of Laborelec
Some conclusions
DGA is the most powerfull condition monitoring tool to estimate internal condition of a power
transformer.
The implementation of a specific program for your fleet is crucial as to keep your transformer fleet in good
condition for the longest time possible and avoid unnecessary costs and shut-downs.
Interpretation is not just comparing with ‘limit values’ from standards. Build your own action values if
possible.
High-level of expertise/experience is needed to perform adequate interpretation of results.
175
Property of Laborelec
176
Property of Laborelec
Technical seminar
SESSION 5 “DGA: on-line versus off-line monitoring”
“Stray gassing”
Santiago, Chile, 15/06/2018
steve.eeckhoudt@engie.com
steve.eeckhoudt@laborelec.com
senja.leivo@vaisala.com
177
Property of Laborelec
Some questions to be answered…
When to use online DGA ?
What is available on the market ?
Different measuring principles of online DGA ?
Some case studies
What is ‘stray gassing’ and what to know on this new ‘hot topic’ ?
178
Property of Laborelec
Basics on online DGA-monitoring
For very critical or ‘sick’ transformers where high DGA-sampling frequency is needed, online DGAdevices are available and can be installed.
179
Property of Laborelec
Basics on online DGA-monitoring
These devices measure with very short time interval all/some gases and/or water content / %RS.
180
Property of Laborelec
Basics on online DGA-monitoring
Data trends are available for experts / maintenance staff for detailed interpretation.
181
Property of Laborelec
Basics on online DGA-monitoring
Data trends are available for experts / maintenance staff for detailed interpretation.
182
Property of Laborelec
Which type of online DGA-monitoring devices are available ?
First review of equipment in CIGRE D1.01 (2010, will be updated 2018/2019).
Status 2016, a lot of options …
ABB (CoreSense)
Camlin (Totus)
Gatron (TGM)
GE (Hydran M2, Hydran 201Ti, Minitrans,Transfix)
Lumasense (SmartDGA Gauge, Guard, Guide)
Morgan Schaffer (Calisto, Calisto 2, Calisto 5, Calisto 9)
Messko (M Sense)
MTE (Hydrocal 1001, 1003, 1005, 1008, 1009)
Qualitrol Serveron (TM1, TM3, TM8, TM8-F)
Siemens (Sitram H2 Guard)
Vaisala (OPT100, MHT410)
…
183
Property of Laborelec
How to check accuracy ?
First review of equipment in CIGRE D1.01 (2010).
11 devices were checked for accuracy by 19 different oil labs. Accuracy of tested devices ranged
between 8% and 34% (average of 18%).
ENGIE Laborelec approach:
184
Property of Laborelec
Recommendations when considering online DGA-monitoring
•
‘Early warning’ system (mono/combined gas value) versus ‘Online diagnostic’ tool (all DGA gases)
•
Overall cost should be considered, not only purchase of device.
•
Check accuracy of device during regular offline DGA analysis. Repeatability is even more important
than accuracy.
•
Choose a good supplier with good after-sales servicing
•
Set adequately the alarm levels
•
Implement a strict procedure when alarm is exceeded (Who does what when ?)
•
Online monitoring data can help with interpretation of the offline DGA
(not only the online DGA & water, but also top oil temperature, loading, ...)
185
Property of Laborelec
Online DGA
monitoring
Senja Leivo
Senior Industry Expert at Vaisala Finland
Member of CIGRE A2/D1.47 and D1.52 working groups
March 2018
Property
of Laborelec
Why online DGA
monitoring?
1. Online monitoring detects faults at their early phase
→ Enables corrective actions before severe transformer failure.
→ Cost reduction in maintenance and repair
→ Avoid consequential costs of catastrophic failures.
2. Enables safe use of a transformer at its end-of-life phase
3. In new transformers, reveals faults originated from manufacturing,
transportation or installation
4. Majority internal faults can be detected with online DGA
▪ DGA is only online method that can detect various fault types.
5. Following rate of change of gases with online monitoring is more reliable
than with laboratory samples. (ref. CIGRE TB409, D1.01 TF 15)
Leivo
6. DetectsSenja
faults
which might otherwise go unnoticed between regular oil
sampling intervals.
Cost
of online
monitor
Property
of Laborelec
In the overall cost of a monitor, it’s not only the cost of
the instrument to be considered, but also the costs
associated with its installation and operation in service
over the whole lifetime.
→ Total cost of ownership to be considered when
selecting a monitor
Fault gasesProperty
in different
transformer faults
of Laborelec
Single/dual gas
monitors can be
used as early
warning devices.
Indication / Fault gas
Cellulose aging
CO
CO2
X
X
Miner. oil
decomposition
Thermal faults, paper
C2H6 C2H4 C2H2
H2
X
X
X
X
X
X
X
H2 O
X
X
Leaks
H2 monitor most
common.
CH4
X
X
X
Thermal faults,
oil @ 150-300°C
X
X
-
Thermal faults,
oil @ 300-700°C
X
X
X
-
X
Thermal faults,
oil >700°C
X
X
X
X
Partial discharges
X
-
X
Arching
X
X
X
X
X
Why
multigas
monitoring?
Property
of Laborelec
▪ It enables fault analysis based on
concentration of different gases.
▪ Not all faults produce significant
amount of hydrogen.
▪ Few gases only do not indicate
fault type
▪ Fault types:
PD partial discharge
S stray gassing
T1 thermal fault <300°C
O over heating (oil)
C carbonization (paper)
T2 thermal fault 300-700°C
T3 thermal fault >700°C
D1 Low energy discharge (sparking)
D2 High energy discharge (arching)
Temperature at fault location
Ref. Dr. Michel Duval
When
multigas
monitoring?
Property
of Laborelec
•
Continuous monitoring of key fault gases gives
early and immediate notification of developing
faults that may lead to transformer failure.
– Many failures can be prevented through real-time
correlation of DGA data to e.g. load and oil/winding
temperature.
•
Only comprehensive online DGA monitoring can
provide
information that enables automatic condition
assessment.
– Enables use of diagnostics tools for rapid warning
and diagnosis of developing faults.
•
Comprehensive online DGA monitoring
recommended by CIGRE for
– critical and/or heavily loaded
power transformers
– transformers having gassing pattern.
Gas
extraction
methods
Property
of Laborelec
• Gases can be extracted from oil by
– Vacuum with mercury piston (~100% extraction
rate*),
only in laboratory.
– Partial vacuum (~90%*), Vaisala’s online DGAmonitor uses vacuum extraction.
– Head space <30%* (depends on temperature, gas
composition and pressure)
• Gas concentrations in oil must be calculated
based on gas solubility values (majority of
*New Techniques for Dissolved Gas-in-Oil Analysis
gases remains in oil).
IEEE Electrical Insulation Magazine, March/April
2003 — Vol. 19, No. 2
Property of Laborelec
Online DGA
technologies
GasProperty
chromatography,
of Laborelec online
• Separation & identification of gases is
based on their retention times through a
long thin column.
• Column inner surface changes over time
due to e.g. contamination with heavier
hydrocarbons / material ageing
→ retention times change
→ requires frequent calibration.
– GC is not a fundamental method,
relies on references of pure gases.
• HS as gas extraction → gas in oil
analysis relies on predefined or generic
gas solubility values.
GC: pros
and cons
Property
of Laborelec
• Technology advantages
– Accuracy and repeatability
– No cross-sensitivity
• Technology challenges:
– Gas cylinder changes: cost and safety issue.
– Chromatography quality carrier gas, expensive.
– Requires calibration gases.
– Gas leaks → more frequent change of gas cylinders.
– Column ageing & contamination due to heavier hydrocarbons
→ poor gas separation → need to be replaced.
➢ Maintenance needed.
– Life time costs → Higher total cost of ownership.
Infrared technology,
(NDIR non-dispersive IR)
Property of Laborelec
• Infrared is a fundamental method, where light is
absorbed by type and number of gas molecules
present in known gas volume.
– Gases have a unique absorption fingerprint.
• The absorption wavelength of a given gas does not
change, this means no recalibration for gas
identification is needed (assuming other drift
mechanisms eliminated).
• IR cannot be used to measure H2, N2 and O2
→ Another technology needed for those.
Infrared ’fault
gas’ of
absorption
Property
Laborelec wave lengths
Property
of
Laborelec
Infrared technologies, IR
▪ NDIR = Non-dispersive infrared
▪ IR light wavelengths are selected with band-pass filters
▪ Photoacoustic spectroscopy NDIR
–Sound generated by absorption is measured
▪ Transmission NDIR
–Transmitted IR light intensity is measured
PAS (photo
acoustic
spectroscopy)
Property
of Laborelec
• Based on IR absorption
• Main technology advantages:
– No carrier / calibration gas
needed
– Good
zero accuracy
▪ Main
technology
challenges:
▪ Possible cross-sensitivity and contamination
▪ Sensor (microphone) gain drift
→ at higher concentrations accuracy issue
▪ Sensor detector sensitive to
– Vibration, pressure, temperature, mechanical stresses
▪ Durability of moving/wearing components.
▪ Lifetime issues and maintenance needs → total cost of ownership.
Transmission
NDIR
Technologies
Property of
Laborelec
• Detection based on change in light intensity at
selected wave lengths.
• For long term stability requires signal reference.
→ Vaisala measures also signal under vacuum
(=reference signal)
PropertyTransmission
of Laborelec vs PAS
NDIR technologies:
Property of Laborelec
Things to consider
when selecting an
online monitor
DGA monitorsProperty
- what of
isLaborelec
relevant for the user?
No monitoring
of monitors!
No false alarms.
Maintenance
needs.
No leaks.
Robust design.
Stable long-term
measurement for
gas trending.
Easy to install.
Tolerates all
climate conditions.
Lifetime costsProperty of Laborelec
▪ Concerning the overall costs of a
monitor, it’s not only the price of
the instrument to be considered,
but also the costs associated with
the installation and operation in
service over its whole lifetime.
→ Total cost of ownership
to be considered when selecting a
monitor.
+20%
Property of Laborelec
Case study 1,
400 MVA transformer
Property
of Laborelec
Faulty 110 kV
2a/b/c
bushing and winding
outlet main-contacts
PAINT
▪ Repairs took place 2013 and 2014.
Source: Fingrid Oyj, Finland
▪ As fault gas levels remained high, degassing was scheduled 11/2015
Property of Laborelec
Property
of Laborelec
Gas trends after
degassing
9% of initial C2H4
level
Property
of
Laborelec
Ethylene vs top oil temperature
20 ppm increase in one day!
Property of Laborelec
Case 2
Added value of
basic online DGAdevice in nuclear
power plant: avoid
failure
07/2005
01/2006
210
Property of Laborelec
Case 3
Detanking & repair of Cu-strip
211
Property of Laborelec
Case 3
Added value of multigas
online DGA-device:
detailed follow-up of DGA
after transformer repair
Detanking & repair of Cu-strip
Trend ??
212
Property of Laborelec
Stray gassing: some context
Recently lots of discussions within
CIGRE JWG A2/D1.47
CIGRE WG D1.70
IEC TC10 MT38
IEC TC14
Especially important for
uninhibited or passivated oils
and during first years of oil use
Questions from utilities/industry to OEM/oil suppliers
Specific stray gassing requirements of utilities to oil suppliers
On what exactly ??
213
Property of Laborelec
What is stray gassing ?
More precisely: formation of especially H2, CH4 and C2H6 in transformer oil when this
oil is in-service at acceptable transformer conditions (for instance formed at
temperatures between as low a 60-90°C).
214
Property of Laborelec
Experiences within ENGIE
Detailed stray gassing research within ENGIE / Laborelec started in 2005-2006.
Very worried O&M staff of nuclear power plant when
checking start-up readings of online monitoring
devices !
____ : H2-trend GSU P4
____ : H2-trend GSU P8
____ : H2-trend GSU P12
215
Property of Laborelec
Experiences within ENGIE
Detailed stray gassing research within ENGIE / Laborelec started in 2005-2006.
____ : H2-trend GSU P4
____ : H2-trend GSU P8
____ : H2-trend GSU P12
216
Property of Laborelec
Experiences within ENGIE
Detailed stray gassing research within ENGIE / Laborelec started in 2005-2006.
Specific stray gassing tests
performed per ASTM D7510
and CIGRE TB296:
____ : H2-trend GSU P4
____ : H2-trend GSU P8
____ : H2-trend GSU P12
Lesson 1: Different oil types,
even different oil batches of
same type, can produce gases
during start-up phase under
acceptable transformer
temperatures. But why ?
217
Property of Laborelec
Experiences within ENGIE
Status 2017 & lots of testing – most important messages:
• SG can start with temperatures as low as 60°C
• Uninhibited oils yield more SG than inhibited oils
• The following factors influence the SG-behaviour:
- Temperature
- Presence of transformer materials
- Presence of oxygen
- Presence of phenolic antioxidant (DBPC / BHT)
• SG is related to the presence of metal passivators or the resistance of
the oil to oxidation
• SG of oil can make condition monitoring of transformer in-service much
more difficult
218
Property of Laborelec
Main causes of stray gassing
• Presence of metal passivators: especially H2
• By presence of IRGAMET 39 (in unused oils or after passivation)
• By presence of IRGAMET 30 (in unused oils)
• Uninhibited oils with lower oxidation stability: especially CH4 and C2H6
• Uncertainty: is it T1-fault (overheating) or acceptable stray gassing ??
219
Property of Laborelec
Main causes of stray gassing
• Presence of metal passivators: especially H2
Addition of 100 ppm of Irgamet 39® → 150-200 ppm of H2 is produced at 80°C
Addition of 500 ppm of Irgamet 39® → 300-350 ppm of H2 is produced at 80°C
(lab research 2010)
→ (Minor) drawback of most applied corrosive sulphur mitigation action.
220
Property of Laborelec
Impact of metal passivators and antioxidant on stray gassing
221
Property of Laborelec
Impact of metal passivators and antioxidant on stray gassing
222
Property of Laborelec
Impact of metal passivators and antioxidant on stray gassing
223
Property of Laborelec
Importance when buying new/unused insulation oils
Laborelec Purchase Specifications (LPS) for unused mineral
transformer oils
Last update:
August 2016
224
Property of Laborelec
Importance when buying new/unused insulation oils
Recommendations by LABORELEC:
Choose for inhibited oils
Make use of LABORELEC PURCHASE PECIFICATIONS
as they already take into account some new developments
not covered by current IEC 60296 (Ed.4/2012)
225
Property of Laborelec
Typical values
Stray gassing
Unused oils
Calculated 50% and 90% typical values
for the relevant stray gases from stray
gassing tests performed per ASTM
D7150. These values were calculated
on a population of 10 inhibited and 14
uninhibited unused oil samples of
different brands, commercially available
on the Asian and European market
during 2012-2016 period.
226
Property of Laborelec
Typical values
Stray gassing
Unused oils
Calculated 50% and 90% typical values
for the relevant stray gases from stray
gassing tests performed per ASTM
D7150. These values were calculated
on a population of 10 inhibited and 14
uninhibited unused oil samples of
different brands, commercially available
on the Asian and European market
during 2012-2016 period.
227
Property of Laborelec
Importance when performing condition monitoring by DGA
CH4- and C2H6-increase in DGA does not
mean by definition T1-overheating fault as
per IEC 60599 or Duval Triangle 1 or 4 but
can be only unharmful stray gassing,
especially when it concerns uninhibited oils.
Methods are available as to prove that gassing
behavior is T1-fault or acceptable stray gassing.
228
Property of Laborelec
Importance when performing condition monitoring by DGA
229
Property of Laborelec
Importance when performing condition monitoring by DGA
Possibility to perform specific stray gassing tests at multiple temperatures
230
Property of Laborelec
Some recommendations when having doubtful DGA-results
• When increase of H2, CH4 and C2H6 is observed, perform expert
interpretation of trend as to distinguish stray gassing from partial
discharges, catalytic effect gassing or T1 overheating fault.
• Inhibition (addition of ca. 0.3% of DBPC) of uninhibited oil can be
‘low cost’ solution as to prove stray gassing is gassing cause and to
further increase lifetime of insulation oil.
231
Property of Laborelec
Inhibition as to decrease stray gassing
Some recent data on impact of inhibition on uninhibited transformer oil:
232
Property of Laborelec
What about international standards on this topic ?
Changing standards takes time …
IEC TC10 MT38 (started 2017…)
IEC 60599 (2015)
CIGRE TB (2006)
CIGRE A2.D1 JWG47 (update TB in 2018 ?)
CIGRE D1.70 (started 2017…)
233
Property of Laborelec
What about international standards on this topic ?
Changing standards takes time …
ASTM D7150 method (2013)
Publications in IEEE DEIS
Revised IEEE C57.104 (to be published in 2018 ?)
234
Property of Laborelec
Some conclusions
Online DGA is complementary to offline DGA and can be very usefull (GSU’s, sick and
very critical transformers) but is not necessary for all transformers in-service.
If it should be used or what system to use, should be determined case-by-case.
Stray gassing is not fully covered in standards nor Duval triangles at this moment.
Be aware of this phenomenon especailly when using uninhibited oils or passivated oils.
Standards are modified at this stage as to improve stray gassing testing methods and
interpretation of results.
Typical/limit values for stray gassing already exist (also in LABORELEC PURCHASE
SPECIFICATIONS).
In some cases, inhibition can be a usefull actions to decrease stray gassing.
235
Property of Laborelec
236
Property of Laborelec
Technical seminar
SESSION 6 “Oil ageing (part 2): relevant analyses & interpretation”
“Typical values & relevant standards”
“PCB-analysis”
Santiago, Chile, 15/06/2018
steve.eeckhoudt@engie.com
steve.eeckhoudt@laborelec.com
237
Property of Laborelec
Some questions to be answered…
Which analyses to perform: enough, but not too much …
How should I implement an adequate program for my transformer fleet as
to estimate oil ageing ?
How should I interpret results and which maintenance actions to take ?
PCB’s: context, analysis methods and interpretation
238
Property of Laborelec
Overview oil ageing analysis: 3/ ACIDITY
Analysis method ?
IEC 62021-1 / ASTM D664 (potentiometric titration)
IEC 62021-2 / ASTM D974 (colorimetric titration)
(result expressed in mg KOH/g oil)
Frequency of sampling ?
Zero-point
Basic recurrent analysis: every 12 to 48 months
Interpretation ?
IEC 60422 / IEEE C57.106
Trending (if increase, look at trends or tan delta and/or IFT)
Important !
Acidity will increase rate of paper degradation, and, in advanced state,
also lead to sludge formation.
239
Property of Laborelec
Overview oil ageing analysis: 3/ ACIDITY
Some important data
Acidity trend is strongly related to unused oil quality.
- Uninhibited oil (with natural inhibitors)
=…
- ‘White’ oil (without inhibitors)
=…
- ‘Old-school’ inhibited oil
(with DBPC and natural inhibitors)
=…
- Highly refined inhibited oil (with DBPC)
=…
240
Property of Laborelec
Overview oil ageing analysis: 3/ ACIDITY
Some important data
Acidity trend is strongly related to unused oil quality.
- Uninhibited oil (with natural inhibitors)
=B
- ‘White’ oil (without inhibitors)
=A
- ‘Old-school’ inhibited oil
(with DBPC and natural inhibitors)
=D
- Highly refined inhibited oil (with DBPC)
=C
241
Property of Laborelec
Overview oil ageing analysis: 3/ ACIDITY
Limit/action values ?
Per IEC 60422 (2013): in mg KOH/g oil
transformer after filling, before energization
transformer >170 kV (in-service)
transformer 72.5-170 kV (in-service)
transformer <72.5 kV (in-service)
:
:
:
:
Per IEEE C57.106 (2015): in mg KOH/g oil
transformer after filling, before energization
transformer >230 kV (in-service)
transformer 69-230 kV (in-service)
transformer <69 kV (in-service)
:
:
:
:
Laborelec general recommendation:
unused transformer oil
transformer (after filling, before energization)
transformer in-service
transformer in-service
:
:
:
:
<0.03
<0.10: GOOD
<0.10: GOOD
<0.15: GOOD
>0.15: POOR
>0.20: POOR
>0.30: POOR
<0.03 (<0.015 in 2006-version !!)
<0.10
<0.15
<0.20
max. 0.01 (typical values: <0.01)
<0.01
<0.08 → ACCEPTABLE
>0.08 → SPECIFIC FOLLOW-UP
(action in function of oil type, other parameters)
242
Property of Laborelec
Overview oil ageing analysis: 3/ ACIDITY
Possible maintenance actions ?
More frequent sampling
Addition of DBPC-inhibitor
Reclaiming (with addition of DBPC-inhibitor)
Oil change
Do nothing
When to reclaim or when to change oil ?
Basic guidance in IEEE C57.637 (2015), but transformer characteristics
also are important in decision.
243
Property of Laborelec
Overview oil ageing analysis: 3/ ACIDITY
Most commonly implemented types of oil filtration ?
Vacuum dehydration (‘reconditioning’)
Adsorption of oil-soluble contaminants (‘reclaiming’)
(adsorbents used can be Fuller’s earth / attapulgite clay,
activated bauxite/aluminia, alumina-silicates (zeolites), …)
244
Property of Laborelec
Overview oil ageing analysis: 3/ ACIDITY
Most commonly implemented types of oil filtration ?
Adsorbents to be used (Fuller’s earth / attapulgite clay,
activated bauxite/aluminia, alumina-silicates (zeolites), …)
depend on oil ageing status (acidity but also water content),
oil type (inhibited or uninhibited), oil volume, …
0.90
Example: Assume that a spent oil has and acidity of
0.35 mg KOH/g oil. To reduce the acidity to 0.05 mg
KOH/g oil, approximately 0.90 lb of attapulgite clay
will be required for each gallon of oil treated.
245
Property of Laborelec
Overview oil ageing analysis: 4/ INTERFACIAL TENSION (IFT)
Analysis method ?
ASTM D971 / EN 14210
IEC 62961 (draft method)
(result expressed in mN/m)
Frequency of sampling ?
Zero-point
Second-line analyses when considering oil reclaiming or when
‘strange values’ of acidity and/or tan delta
Interpretation ?
IEC 60422 / IEEE C57.106
Important !
Most sensitive analysis to detect ageing/contamination.
Not recommended as recurrent/routine test by IEC,
only as complementary test.
Inhibited and uninhibited oils have typically other trend.
246
Property of Laborelec
Overview oil ageing analysis: 4/ INTERFACIAL TENSION (IFT)
Limit/action values ?
Per IEC 60422 (2013): in mN/m
unused transformer oil
transformer after filling, before energization
transformer (in-service): UNINHIBITED OIL
transformer (in-service): INHIBITED OIL
:
:
:
:
Per IEEE C57.106 (2015): in mN/m
unused transformer oil
transformer after filling, before energization
transformer >230 kV (in-service)
transformer 69-230 kV (in-service)
transformer <69 kV (in-service)
:
:
:
:
:
>40
>38
>32
>30
>25
Laborelec general recommendation:
unused transformer oil
transformer (after filling, before energization)
transformer in-service
:
:
:
>40 (typical values: 43-47 mN/m)
>38
-
>40
>35
>25: GOOD
>28: GOOD
<20: POOR
<22: POOR
247
Property of Laborelec
Overview oil ageing analysis: 4/ INTERFACIAL TENSION (IFT)
Inhibited oil versus uninhibited oil ?
248
Property of Laborelec
Overview oil ageing analysis: 4/ INTERFACIAL TENSION (IFT)
oil
water
249
Property of Laborelec
Overview oil ageing analysis: 5/ TAN DELTA
Analysis method ?
IEC 60247 (no unit)
ASTM D924 (expressed in %)
Also known as ‘dielectric dissipation factor’ or ‘power factor’
Frequency of sampling ?
Zero-point
Basic recurrent analysis: every 12 to 48 months
Interpretation ?
IEC 60422 / IEEE C57.106
Important !
Very sensitive analysis to detect ageing/contamination.
Inhibited and uninhibited oils have typically other trend.
250
Property of Laborelec
Overview oil ageing analysis: 5/ TAN DELTA
Inhibited oil versus uninhibited oil ?
251
Property of Laborelec
Overview oil ageing analysis: 5/ TAN DELTA
Limit/action values ?
Per IEC 60422 (2013): in - (measurement at 90°C)
unused transformer oil
transformer >170 kV (after filling, before energization)
transformer <170 kV (after filling, before energization)
transformer >170 kV (in-service)
transformer <170 kV (in-service)
:
:
:
:
:
Per IEEE C57.106 (2015): in unused transformer oil
transformer >230 kV (after filling, before energization)
transformer <230 kV (after filling, before energization)
transformer in-service
:
:
:
:
Laborelec general recommendation: (measurement at 90°C)
unused transformer oil
transformer (after filling, before energization)
transformer in-service
transformer in-service
:
:
:
:
:
<0.005
<0.01
<0.015
<0.10: GOOD
<0.10: GOOD
at 25°C
<0.0005
<0.0005
<0.0005
<0.005
>0.20: POOR
>0.50: POOR
at 100°C
<0.003
<0.003
<0.004
<0.05
<0.005 (typical values: <0.001)
<0.01
<0.10 → ACCEPTABLE
>0.10 → SPECIFIC FOLLOW-UP
(action in function of oil type, other parameters)
252
Property of Laborelec
Overview oil ageing analysis: 6/ DBPC-content
Analysis method ?
IEC 60666 (can be FTIR or HPLC)
ASTM D2668
(result expressed in %)
Frequency of sampling ?
Zero-point analysis
Only for inhibited oil, sampling frequency every 12 to 48 months.
Interpretation ?
IEC 60422 / IEEE C57.106
Important !
Also known as BHT (butylated hydroxyl toluene).
Good quality inhibited oil can last for >30 years under normal
transformer utilization conditions.
Require to your oil lab a LoQ of 0.005% as to identify ‘traces’ of DBPC’ !!!
253
Property of Laborelec
Overview oil ageing analysis: 6/ DBPC-content
Limit/action values ?
Per IEC 60422 (2013):
transformer in-service with inhibited oil
:
Per IEEE C57.106 (2015): in %
transformer in-service with inhibited oil
:
>60% of original amount: GOOD
<40% of original amount: POOR
>0.08
Laborelec general recommendation: in %
unused inhibited transformer oil
:
0.2 - 0.4
transformer in-service
:
>50% of original amount: ACCEPTABLE
transformer in-service
:
<50% of original amount:
Assessment to do nothing, perform re-inhibition,
re-inhibition together with oil reclaiming or oil change in
function of acidity, IFT, … and other transformer
characteristics.
254
Property of Laborelec
Overview oil ageing analysis: 6/ DBPC-content
Impact of DBPC on acidity trend
uninhibited
inhibited
255
Property of Laborelec
Overview of the other oil ageing analysis:
Particle counting
Dissolved metals
Resistivity
Oxidation stability
RPVOT
Colour and appearance
Foaming
Flash point
Sediment and sludge
Density
Viscosity
…
IEC 60970
ASTM D7151
IEC 60247
IEC 61125C
ASTM D2112
IEC 60422 / ASTM D1500
ASTM D892
ASTM D92 / ASTM D93
IEC 60422 Annex C
ASTM D4052
ASTM D7042
Second-line tests:
perform when abnormal
routine test results (or as
zero-point analysis)
256
Property of Laborelec
Important oil analysis not to forget:
PCB’s
Not condition monitoring, but related to environment & human health protection !!
257
Property of Laborelec
Some basics on PCB’s
Man-made organic molecules, which have excellent properties inside power transformers (stable, electrical
insulation, cooling, fire-safety, …).
Usage of PCB’s has decreased significantly since the 70’ties as it became clear that these persistent
molecules were carcinogenic to humans and environment (IRAC/EPA).
… but still (very much) present in transformer/energy/electricity industry
Molecular structure:
PCB = poly chlorinated biphenyl
12 C (carbon) atoms
4 up to 10 Cl (chlorine) atoms
258
Property of Laborelec
Some basics on PCB’s
There are 209 ‘PBC-congeners’.
PCB fluids are known a lot under their commercial name and are mixtures
of different congeners. The more Cl present, the more toxic in general and
the more persistent (slower biodegradable).
Some examples
Aroclor (Monsanto)
Santotherm (Mitsubitshi)
Inerteen (Westinghouse)
Pyralène (Prodolec)
Clophen (Bayer)
…
Aroclor 1242 (’12’ meaning 12 C-atoms, ’42’ meaning ca. 42% of molecular weight is Cl)
Aroclor 1254 (’12’ meaning 12 C-atoms, ’54’ meaning ca. 54% of molecular weight is Cl)
Aroclor 1260 (’12’ meaning 12 C-atoms, ’60’ meaning ca. 60% of molecular weight is Cl)
259
Property of Laborelec
PCB-determination
Different analytical methods exist in order to make PCB risk assessment.
Most used international standards:
ASTM D4059 / EPA 8082A (determination of 3 Aroclor molecules)
IEC 61619 / EN 12766-2A (determination of sum 109 individual congeners)
EN 12766-2B (determination of 6 specific congeners: C28, C52, C101, …)
What methods to use ?
- Depends on local regulations !!
260
Property of Laborelec
PCB-determination
Europe/Asia, analysis per IEC 61619 or ASTM D4059 and based on analysis result:
For LATAM, country/region specific:
PCB-equipment
PCB-contaminated equipment
Non-PCB equipment
PCB-free equipment
> 500 ppm
50 to 500 ppm
2-50 ppm
< 2 ppm
PCB-oil
PCB-contaminated oil
PCB-free oil
> 500 ppm
2 to 500 ppm
< 2 ppm
(example classification in Philippines)
261
Property of Laborelec
PCB-method comparison
Some recent data:
IEC 61619 and ASTM D4059 give very
similar results.
EN 12766-2B can give overestimation of
PCB-content.
Source: IIS-RRT of February 2016.
Confirmed by LABORELEC experience.
Source: IIS-RRT of January 2017.
262
Property of Laborelec
PCB-method: QA-check through RRT
263
Property of Laborelec
PCB-analysis
1 value is reported, but its quite a complex analysis…
264
Property of Laborelec
Summary & some recommendations on oil ageing assessment
•
A lot of tests exist; choose specific program (which analyses and which sampling frequency) in function of
transformer, type of oil and its ageing status.
•
Water, breakdown voltage and acidity are necessary basic test.
•
Oil temperature during sampling is important.
•
Do not perform too much oil treatments
•
If large fleet, determine your own typical values
(cf. DGA)
•
PCB-test: making inventory and/or risk
assessment/management is needed
265
Property of Laborelec
266
Property of Laborelec
Technical seminar
SESSION 7 “Insulating paper ageing: why important and influencing parameters”
“Oil analyses & interpretation of paper ageing”
“Typical values & relevant standards”
Santiago, Chile, 15/06/2018
steve.eeckhoudt@engie.com
steve.eeckhoudt@laborelec.com
267
Property of Laborelec
Some questions to be answered…
How should I keep insulating paper ageing to a minimum ?
How should I implement an adequate program for my transformer fleet as
to estimate paper ageing status ?
How should I interpret oil analysis results and which actions to take ?
268
Property of Laborelec
Functions of insulating oil are electrical insulation, cooling
… but also information carrier of this vital equipment (!)
By sampling and analysing insulating oil you can assess
- ageing status of oil
- ageing status of winding paper
- presence of internal transformer faults, caused
by design or construction abnormalities, ageing
phenomenon, material incompatibility, inadequate
maintenance of operation
269
Property of Laborelec
Functions of insulating oil are electrical insulation, cooling
… but also information carrier of this vital equipment (!)
By sampling and analysing insulating oil you can assess
- ageing status of winding paper
Even with transformer out-of-service,
winding paper cannot be accessed.
270
Property of Laborelec
Why is assessing insulating paper ageing important ?
Wood:
40-60%
20-40%
20-40%
cellulose
hemi-cellulose
lignin
Insulation Kraft paper:
>90%
cellulose
<5%
hemi-cellulose
<5%
lignin
A power transformer contains a very high amount of paper (Kraft paper, thermally
upgraded paper, NOMEX ®, …) as insulation material.
If winding paper is end-of-life, the transformer is considered end-of-life as there
will be an increased risk of failure because of insufficient (mechanical) paper
quality/properties.
But how can insulating paper quality be expressed ?
271
Property of Laborelec
How to express ‘paper quality’ ?
Insulating paper quality is characterized by its Degree of Polymerization (or
“DP” = average n° glucose monomers in cellulose chain or average length of
cellulose).
CH2OH
H
OH
CH2OH
O
H
HO
O
H
OH
H
H
OH
OH
H
O
H
OH
H
H
H
H
H
O
O
H
OH
H
H
H
H
O
H
OH
H
OH
O
H
CH 2OH
OH
CH 2OH
n
New paper (before drying process)
New paper (after drying process)
End-of-life paper
•
•
•
: DP of 1300-1100
: DP of 1000-900
: DP of 250-150
272
Property of Laborelec
How to express ‘paper quality’ ?
Insulating paper quality is characterized by its Degree of Polymerization (or
“DP” = average n° glucose monomers in cellulose chain or average length of
cellulose).
273
Property of Laborelec
How to express ‘paper quality’ ?
Insulating paper quality is also characterized
by its tensile strength.
274
Property of Laborelec
Which transformer parameters will impact paper ageing ?
Ageing of insulating paper is
(in)direct influenced by:
•
•
•
•
Temperature
Oil quality / acidity
Water content
Oxygen
Ageing of insulating paper is
irreversible.
275
Property of Laborelec
Which transformer parameters will impact paper ageing ?
Importance of temperature and water content:
276
Property of Laborelec
What can be done to slow down paper ageing ?
Decrease the impact of influencing parameters !!
Influencing parameter
Water
Oil quality / acidity
Temperature
Oxygen
Some comments
New transformer (water content <0.5%): keep it
dry as long as possible !
(check silica gel, membrane sealing, adequate OCM, …)
Choose a good unused oil type (see IEC 60296 / Laborelec Purchase Spec 08/2016)
Sufficient cooling / do not overstress
- rate of paper degradation x2 if temperature + 6°C at 100-110°C oil temperature
- rate of paper degradation x2 if temperature + 8°C at > 120°C oil temperature
(CIGRE TB 494, 2012)
Membrane sealing & adequate OCM
277
Property of Laborelec
How to detect paper ageing through oil analysis ?
Different methodologies
By determination of CO and CO2 (per IEC 60567)
By determination of furans (per IEC 61198)
By determination of methanol (per IEC PT 63025 (draft))
How to interpret the results to estimate DP-value ?
278
Property of Laborelec
Determination of CO and CO2
Some background:
- These 2 dissolved gases are formed during paper degradation, but are also
formed during oil degradation (thus not paper-specific ageing markers).
- Formation of CO and CO2 are also determined by presence of oxygen, water
and oil type.
- No general applicable model exists as to determine DP-value for CO and CO2values at this moment.
Some typical values: IEC 60599, 2015 version
279
Property of Laborelec
Determination of CO and CO2
Recommendations:
- Do not (only) use strict values of IEC 60599 and IEEE C57.104.
- Trend CO and CO2 and perform furans or methanol if ratio CO2/CO is having
sudden change (can be increase or decrease) together with the appearance
of other dissolved gases.
280
Property of Laborelec
Determination of furans
Some background:
- 5 molecules used since end 1980’ies which are paper specific paper ageing
markers, which also partially dissolved in the oil.
…
281
Property of Laborelec
Determination of furans
Some background:
- 5 molecules used since end 1980’ies which are paper specific paper ageing
markers, which also partially dissolved in the oil.
…
water
282
Property of Laborelec
Determination of furans
Some background:
- 5 molecules used since end 1980’ies which are paper specific paper ageing
markers, which also partially dissolved in the oil.
Focus on 2FAL, although other 4 are
still analysed/reported.
According Stebbins (2003):
5-HMF → related to oxidation
2-FOL → related to high moisture
2-FAL → related to normal ageing or general overheating
5-MEF → related to high temperatures
2-ACF → unknown, very rarely observed
Lots of studies tried to establish ratios for interpretation (cf. DGA
diagnosis) but today, all results indicate that this approach is not
applicable to real case transformers.
283
Property of Laborelec
Determination of furans
Correlation 2FAL (furans) with DP-values:
- Easy under laboratory conditions
(but not easy at all in real life !)
!!
- 2FAL-concentration in oil depends on lots of factors (paper/oil ratio, oil type,
paper type, presence/absence of oxygen, water content, performed oil filtrations,
temperature of oil as impact in paper/oil equilibrium, …)
- Use the literature models (2FAL versus DP) very carefully !
- DP of paper inside a transformer is not homogenously
spread but depends on location of paper inside
the transformer.
284
Property of Laborelec
Determination of furans
Correlation 2FAL (furans) with DP-values:
- 2FAL-concentration in oil depends on lots of factors (paper/oil ratio, oil type,
paper type, presence/absence of oxygen, water content, performed oil filtrations,
temperature of oil as impact in paper/oil equilibrium, …)
2FAL-content
DP
Incubation time
Incubation time
285
Property of Laborelec
Determination of furans
Literature models (2FAL versus DP):
Take into account:
1/ Models exist for ageing of Kraft paper but also some
models exist specifically for TU paper.
2/ Some models are made based on sealed-tube
laboratory research and some models are based on
dismantling experiences of a transformer fleet.
Typically furan values (for instance 90% typical values)
from US databases are much lower than European
databases (type of paper, oil used, …)
286
Property of Laborelec
Determination of furans
DP of paper inside a transformer is not homogenously spread:
287
Property of Laborelec
Determination of furans
DP of paper inside a transformer is not homogenously spread:
Based on transformer dismantlings, ageing model can be made up per ‘specific transformer family’.
Highly recommended by Laborelec and CIGRE working groups.
Ageing model of a family of similar power
transformer within ENGIE power plants.
Example:
At 1 ppm of 2FAL, DP-values ranges between 300
and 600 (real dismantlings).
As per Chendong (1991): average DP = 430
As per De Pablo (1999): average DP = 900
As per Vuarchex (2002): average DP = 530
288
Property of Laborelec
Determination of furans
Some typical values:
- Determine your own typical values (if your transformer fleet is sufficiently large).
- 90, 95 & 99% typical values for absolute 2FAL-content:
Kraft paper
free breathing
(in ppb 2FAL)
AVERAGE
90% TV
95% TV
99%
298
609
1150
3733
TU paper
sealed
85
144
362
1402
free breathing
122
80
413
2910
sealed
39
44
102
480
Shkolnik, 2012.
289
Property of Laborelec
Determination of furans
Some typical values:
- 90, 95 & 99% typical values for 2FAL increase rate:
Kraft paper
(in ppb/year 2FAL)
AVERAGE
90% TV
95% TV
99%
TU paper
free breathing
sealed
free breathing
121
130
294
1842
6
13
37
212
80
14
44
995
sealed
59
6
13
85
Shkolnik, 2012.
290
Property of Laborelec
Determination of furans
Recommendations:
- Only 2FAL is used to correlate with DP / paper ageing status.
- Determine your own typical values for 2FAL.
- Make use of dismantling experiences (if similar transformers still in-service).
- Use the literature ageing models (2FAL versus DP graph) very carefully.
- Furans have disadvantages and in some cases methanol analysis can be a
better option to estimate paper ageing.
291
Property of Laborelec
Determination of methanol
2000: Furans → some disadvantages observed by Laborelec
• Very little (or even no) furans when using some thermally upgraded
papers (TUP)
• Under some conditions, practically no furans but significant paper
ageing
• 2FAL only formed when DP-value < 750/800
• Impact of temperature (and acidity) on the partitioning/equilibrium of
this ageing marker between oil and paper (temperature-correction
model needed!)
292
Property of Laborelec
Determination of methanol
2007: Methanol (literature & own research) showed some advantages
• Only formed by paper ageing, (practically) not from oil
• Also formed when using thermally upgraded papers
• Under sealed conditions, more CH3OH than furans (membrane
sealed transformers)
• Linear production of CH3OH and from beginning of paper ageing
(when DPv < 1200)
293
Property of Laborelec
Determination of methanol
2007-2014: Methanol applicability research
294
Property of Laborelec
Determination of methanol
2007-2014: Methanol applicability research – some results
CH3OH also formed when using TUP.
295
Property of Laborelec
Determination of methanol
2007-2014: Methanol applicability research – some results
CH3OH also early-stage ageing marker.
296
Property of Laborelec
Determination of methanol
2014: Implementation of methanol in ENGIE transformer fleet
Since 2010:
Validation of applicability of methanol by regular testing on specific transformer fleet
(for instance: all step-up transformers of NUC-fleet in Belgium since 2010)
Since 2014:
Integration in OCM-programs of temperature-correction model of ageing markers.
(Validation of model to correct methanol and 2FAL at temperature of 20°C)
Presence of methanol, water and 2FAL in oil is temperature-dependent. Fluctuating temperature &
loading of transformer creates migration of these 3 ageing markers between paper and oil.
Similar to “corrected water / %RH” parameter.
297
Property of Laborelec
Determination of methanol
2014: Temperature-correction model
MeOH (mg/kg)
2,50
2,00
1,50
60
50
40
30
1,00
0,50
0,00
T(°C)
MeOH
MeOH 20°C
20
T(°C)
10
0
298
Property of Laborelec
Determination of methanol
2014: Integrated in OCM programs for ENGIE-transformer fleet
1/ DGA + %RS
(every 3-12 months)
2/ OIL AGEING
(every 12-48 months)
3/ PAPER AGEING (only furans)
(every 12-48 months)
3/ PAPER AGEING (new package)
(every 12-48 months)
MeOH, EtOH, 2FAL (absolute and Tcorrected values)
4/ CORR
(specific)
299
Property of Laborelec
Case 1:
3 same transformers, age (2006), loading,
DGA, oil properties, top-oil emperature,…
PAPER AGEING
300
Property of Laborelec
Case 2:
3 same transformers, age (2008), loading,
DGA, oil properties, top-oil emperature,…
PAPER AGEING
301
Property of Laborelec
Case 3:
Temperature-correction effect on 1
transformer during 2014 period on 3
polar paper ageing markers
302
Property of Laborelec
Determination of methanol
How to perform interpretation ?
→ Typical values per fleet of similar transformers
→ Dismantling experiences
303
Property of Laborelec
Determination of methanol
How to perform CH3OH-analysis ?
304
Property of Laborelec
Summary & some recommendations on paper ageing assessment
• Insulating winding paper will age and can cause failure.
• CO and CO2 can be used as to trigger furan or methanol analysis, but not separately to evaluate DP.
• Only 2FAL is used to correlate with DP / paper ageing status.
• Determine your own typical values for 2FAL and 2FAL-increase rate.
• Make use of dismantling experiences (if similar transformers still in-service) !!
• Use the literature ageing models (2FAL versus DP graph) very carefully.
• Furans have some disadvantages and in some cases (for instance: young membrane-sealed transformers
with TUP), methanol analysis can be a better option to estimate paper ageing.
• Keep paper ageing influencing factors (water, temperature, …) under control from the beginning.
305
Property of Laborelec
306
Property of Laborelec
Technical seminar
SESSION 8 “Corrosive sulphur: what to know on this ‘hot topic’ ?”
“Relevant oil analyses & interpretation”
“Discussion on possible actions when testing corrosive”
Santiago, Chile, 15/06/2018
steve.eeckhoudt@engie.com
steve.eeckhoudt@laborelec.com
307
Property of Laborelec
Some questions to be answered…
When should I be concerned ?
Which analyses to perform ?
Which actions can be taken when my oil tests (potentially) corrosive ?
Advantages and drawbacks of the 5 risk mitigation actions
ENGIE Laborelec approach
308
Property of Laborelec
Some history
Beginning 21st century, several failures related to deposits which were
caused by ‘corrosive sulphur’.
2004: lots of research started within CIGRE / IEC / IEEE / Laborelec … .
2006: discovery of DBDS-molecule in transformer oil.
2006: method to determine corrosive sulphur (ASTM D1275B)
2008: method to determine potentially corrosive sulphur (IEC 62535).
2010: method to determine metal passivator (IEC 60666)
2012: method to determine DBDS (IEC 62697-1)
2012: revision of IEC 60296, as to avoid corrosive unused oils.
2013: revision of IEC 60422, as to determine corrosive in-service oils and mitigate risk.
2009…2015: CIGRE technical brochures on detection methods, risk assessment
and long term mitigation.
309
Property of Laborelec
What is copper sulphide ?
Copper sulphide (Cu2S) deposits can be formed on Cu-windings or inside insulating paper when reactive
sulphur species in the oil (in lots of cases DBDS, but also other reactive sulphur species) react with Cu, even
under normal operating temperatures (starting at ca. 80°C).
How can a transformer fail because of copper sulphide ?
Copper sulphide deposits form inside the winding
(surface Cu-paper) and the deposits ‘grow’ to the
outside through different layers of paper, eventually
‘bridging’ between 2 conductors.
Copper sulphide deposits can also be formed on bare Cu-parts,
and after some time release conductive Cu2S-particles which can
lead to dielectric breakdown.
310
Property of Laborelec
What is DBDS ?
DBDS or dibenzyl disulphide is a molecule which can be used as additive and which will increase the
oxidation stability of oils, but under certain conditions corrode Cu.
A large part of the corrosive sulphur related transformer failures reported over last 2 decades had insulating
oil who did contain significant concentrations of DBDS.
Addition of metal passivator to oil can protect bare Cu against corrosion of DBDS or other corrosive sulphur
species.
Can be found mostly in uninhibited transformers oils (produced 1989-2006) from different suppliers in
concentrations of 50-350 ppm.
Detection method: IEC 62697-1
DBDS = dibenzyl disulphide
311
Property of Laborelec
What is a metal passivator ?
These additives form thin films on copper, preventing the catalytic effect of copper in oil and the formation of harmful
copper sulphide deposits in paper by reaction with corrosive sulphur compounds contained in the oil. They can protect the
oil from the catalytic action of metals and slow down the rate of oxidation of oil. Passivators therefore slow down the
oxidation process in IEC 61125 as they passivate the surface of the catalyzing copper-wire, thus leading to an ‘optimistic’
result of the oxidation stability test. Some of them are also used to reduce the electrostatic charging tendency of oils.
Products commonly found :
* TTAA (Irgamet 39®, N-bis(2-Ethylhexyl)-aminomethyl-tolutriazole)
* BTA (benzotriazole)
* TTA (5-methyl-1H-benzotriazole)
* TAA (Irgamet 30®, N,N-bis(2-ethylhexyl)-1H-1,2,4-triazole-1 methanamine)
Detection method
IEC 60666
IEC 60666
IEC 60666
UPLC-MSMS-method
BTA = benzotriazole
312
Property of Laborelec
When is my transformer fleet concerned ?
You have transformers commissioned between 1989 and 2007, and its mineral oil was not tested yet on
presence of (potentially) corrosive sulphur.
You used oils produced between 1989 and 2007 to top-up.
Oil types (can be inhibited/uninhibited) which are most
probably potentially corrosive:
NYNAS NYTRO
SHELL
TOTAL
MOBIL
…
10BN, 10GB, 10GBN, 3000, 10X(T)
DIALA AX, B, M, S, some DX
ISOVOLTINE II (…-2008)
Most oils which are potentially corrosive contain DBDS.
data: Laborelec oil library analysis of 1 supplier (2007)
313
Property of Laborelec
Also inhibited oils
When is my transformer fleet concerned ?
You have transformers commissioned between 1989 and 2007, and its mineral oil was not tested yet on
presence of (potentially) corrosive sulphur.
You used oils produced between 1989 and 2007 to top-up.
Oil types (can be inhibited/uninhibited) which are most
probably potentially corrosive:
NYNAS NYTRO
SHELL
TOTAL
MOBIL
…
10BN, 10GB, 10GBN, 3000, 10X(T)
DIALA AX, B, M, S, some DX
ISOVOLTINE II (…-2008)
Most oils which are potentially corrosive contain DBDS.
DBDS-containing oils with metal passivator
were sold during 2006-2007 period.
This supplier had potentially corrosive oils on
market between 1989 and end 2006 with DBDSconcentrations between 50 and 350 ppm.
data: Laborelec oil library analysis of 1 supplier (2007)
314
Property of Laborelec
Which oil analyses to perform ?
Some more detail on the numerous corrosive sulphur analyses
ISO 5662 (1997): Cu-strip method (140°C during 19h)
DIN 51353 (1985): Ag-strip method (100°C during 18h)
ASTM D1275 (2003): Cu-strip method (140°C during 19h)
ASTM D1275B (2006): Cu-strip method (150°C during 48h)
ASTM D1275 (2015): Cu- and Ag-strip method (150°C during 48h)
IEC 62535 (2008): paper wrapped Cu-strip method (150°C during 72h)
In-house methods …
315
Property of Laborelec
Which oil analyses to perform ?
Some more detail on the numerous corrosive sulphur analyses
Incubation set-up of Cu-strip as per ASTM D1275
ISO 5662 (1997): Cu-strip method (140°C during 19h)
DIN 51353 (1985): Ag-strip method (100°C during 18h)
ASTM D1275 (2003): Cu-strip method (140°C during 19h)
ASTM D1275B (2006): Cu-strip method (150°C during 48h)
ASTM D1275 (2015): Cu- and Ag-strip method (150°C during 48h)
IEC 62535 (2008): paper wrapped Cu-strip method (150°C during 72h)
In-house methods …
Incubation set-up of Cu-strip
wrapped with paper as per IEC
62535
316
Property of Laborelec
Which oil analyses to perform ?
Some more detail on the numerous corrosive sulphur analyses
Interpretation by inspection of Cu-strip
ISO 5662 (1997): Cu-strip method (140°C during 19h)
DIN 51353 (1985): Ag-strip method (100°C during 18h)
ASTM D1275 (2003): Cu-strip method (140°C during 19h)
ASTM D1275B (2006): Cu-strip method (150°C during 48h)
ASTM D1275 (2015): Cu- and Ag-strip method (150°C during 48h)
IEC 62535 (2008): paper wrapped Cu-strip method (150°C during 72h)
In-house methods …
Interpretation by inspection of Cu-strip and paper
317
Property of Laborelec
Which oil analyses to perform ?
On unused oils, request conformity to IEC 60296 Ed.4 or LABORELEC PURCHASE SPECIFICATION Ed. 2016
Unused should
* test clearly non-corrosive per IEC 62535 and DIN 51353
* have no metal passivators per IEC 60666 (< 5 ppm)
* have no DBDS per IEC 62697-1 (< 5ppm).
318
Property of Laborelec
Which oil analyses to perform ?
On ‘doubtful’ transformer oil in-service the following analyses are recommended as to decide if corrosive
sulphur risk assessment is needed.
In some cases, also
DIN 51353 and/or IEC
62697-1 are
recommended
319
Property of Laborelec
Risk assessment and possible actions for oils in-service ?
If oil tests ‘non corrosive’ per IEC 62535 and contains no metal passivator per IEC 60666, no further actions
are needed. Except retesting if contamination is expected (cf. PCB-analysis).
If oil tests ‘potentially corrosive’ per IEC 62535, risk assessment to determine best mitigation action is
required.
Items to be taken into account when performing risk assessment:
•
•
•
•
•
•
•
•
•
•
•
•
•
Are Cu-windings enamelled ?
Is transformer highly loaded ?
Is transformer having a thermal issue ?
Is OLTC present ?
Is oil passivated ?
When was oil passivated ?
Is oil having a low O2-content ?
Are other corrosive sulphur oil analyses needed ?
(DBDS, DIN 51353, …)
What about historical oil analyses ?
(DGA, acidity, inhibitor, furans, …)
How critical is unit ?
Risk acceptance by owner ?
Requirements by insurance company ?
…
Example of most appropriate mitigation action:
-
DO NOTHING
OIL FILTRATION
OIL CHANGE
OIL PASSIVATION
REPLACE TRANSFORMER
320
Property of Laborelec
Risk assessment and possible actions for oils in-service ?
Impact of oil composition on corrosive sulphur deposits during IEC 62535 testing:
Inhibited corrosive
oils have the
tendency to depose
Cu2S on/in paper
Mineral oil 1
DBPC:
DBDS:
Irgamet 39:
0.25 %
85 ppm
ND
Mineral oil 2
DBPC:
DBDS:
Irgamet 39:
0.24 %
ND
ND
Mineral oil 3
DBPC:
ND
DBDS:
95 ppm
Irgamet 39: ND
321
Property of Laborelec
Risk assessment and possible actions for oils in-service ?
Impact of metal passivator on corrosive sulphur deposits during IEC 62535 testing:
Mineral oil 1
DBPC:
0.25 %
DBDS:
85 ppm
Irgamet 39: ND
Mineral oil 1 + metal passivator
DBPC:
0.25 %
DBDS:
85 ppm
Irgamet 39:
207 ppm
Mineral oil 3
DBPC:
ND
DBDS:
95 ppm
Irgamet 39: ND
Mineral oil 3 + metal passivator
DBPC:
ND
DBDS:
95 ppm
Irgamet 39:
127 ppm
322
Property of Laborelec
Possible actions for oils in-service ?
Most appropriate mitigation action:
- DO NOTHING
very low cost
corrosive molecules remain in contact with Cu-windings
- OIL PASSIVATION
low cost
corrosive molecules are not removed but Cu-windings protected
disadvantages: passivator depletion and H2 stray gassing
- OIL FILTRATION
intermediate cost
corrosive molecules are removed
- OIL CHANGE
intermediate cost
corrosive molecules are removed
- REPLACE TRANSFORMER
very high cost
problem solved
Choice will be influenced
by cost of intervention
and this price will be
determined partly by size
of transformer and level
or corrosiveness
323
Property of Laborelec
Possible actions for oils in-service ?
Most appropriate mitigation action:
Mitigation actions after risk assessment
within ENGIE Laborelec transformer fleet
(> 400 transformers concerned).
- DO NOTHING
- OIL PASSIVATION
>50%
30-40%
- OIL FILTRATION
<2%
- OIL CHANGE
<2%
- REPLACE TRANSFORMER
<2%
Passivation:
Reclaiming:
Oil change:
Mix:
>80%
ca. 5%
ca. 5%
ca. 5%
Mitigation actions chosen based on CIGRE A2.42 TF03 survey
(CIGRE TB 625, 2015)
324
Property of Laborelec
Attention points when implementing passivation
•
Passivation will not remove the already formed Cu2S-deposits before the addition of metal passivator.
•
Passivator depletion will occur in most cases.
325
Property of Laborelec
Attention points when implementing passivation
•
High temperatures, acidic oil and oxygen presence can deplete passivator content quite rapidly. As per
CIGRE TB 625, only the case in ca. 15% of passivated units.
ENGIE GSU-transformer of 1972, retrofilled with NN 10GBN in 2001 and passivated in 2007.
Transformer had T1 thermal fault and was also breathing type.
•
Addition of metal passivator can create stray gassing.
This stray gassing (mostly H2, CO, CO2, CH4) is not harmful but can make routine condition monitoring
by DGA (much) more difficult.
New standards like IEC 60599 already give (limited) guidance on how to differentiate passivator stray
gassing from real DGA internal faults.
326
Property of Laborelec
Attention points when implementing passivation
•
Addition of metal passivator can create stray gassing.
3 similar GSU-transformers commissioned in 2006, filled with NN 3000P.
327
Property of Laborelec
Attention points when implementing passivation
•
Passivators will be removed when performing reclaiming. They can also be partially removed when
performing reconditioning, depending on temperature and vacuum applied.
•
Passivation has been found to be not efficient as to protect silver (Ag) selector contacts from corrosive
sulphur. Especially elemental sulphur is highly reactive with Ag-contacts. DIN 51353 is more sensitive to
detect elemental sulphur than the IEC 62535 method.
328
Property of Laborelec
Attention points when implementing oil filtration
•
Oil filtration techniques (specific reclamation with adsorbents) used onsite/online can remove (potentially)
corrosive species, but after filtration process special analysis program is needed to check oil properties:
•
Does the oil test non-corrosive to DIN 51353 after oil filtration ?
(several cases in UK & Sweden, where reclaimed oil turned corrosive to silver)
Inadequate
reclaiming
329
Property of Laborelec
Attention points when implementing oil filtration
•
Oil filtration techniques (specific reclamation with adsorbents) used onsite/online can remove (potentially)
corrosive species, but after filtration process special analysis program is needed to check oil properties:
•
Does the oil test non-corrosive to DIN 51353 after oil filtration ?
(recent case in Belgian HV-grid; 80 kV transformer, uninhibited Fina Diekan 1640 produced in
1975, S = 1900 ppm)
Inadequate
reclaiming
330
Property of Laborelec
Attention points when implementing oil filtration
•
Oil filtration techniques (specific reclamation with adsorbents) used onsite/online can remove (potentially)
corrosive species, but after filtration process special analysis program is needed to check oil properties:
•
What about impact of removal of sulphur compounds on oxidation stability ?
Removal of DBDS will decrease oxidation stability of insulating oil.
331
Property of Laborelec
Attention points when implementing oil change
•
Efficiency will depend on concentration of corrosive sulphur species as residual oil volume is ca. 5-10%.
So typically concentration of corrosive sulphur will be diluted by factor 10 up to 25.
•
Relatively few references, more related with cost than effectiveness of technical solution or difficulty of
this quite simple maintenance action.
332
Property of Laborelec
Summary & some recommendations on corrosive sulphur risk mitigation
• Insulating oils made between 1989 and 2007 can produce Cu2S (or Ag2S) deposits under some conditions.
• DBDS is involved in majority of the corrosive sulphur related failures.
• Other important risk determining factors are temperature (high load, inefficient cooling, …) and oxygen
content.
• Adequate oil analyses are available; choose the right ones.
• Electrical measurements can not predict the presence of Cu2S-deposits. Although resistance
measurements can be useful for Ag2S deposit determination of selector contacts.
• By performing detailed risk assessment, the best mitigation action can be determined. Passivation has
been proven to be very successful, but also oil filtration or oil change can be performed. Also doing
nothing, transformer replacement or improving cooling/reducing load can be adequate countermeasures.
333
Property of Laborelec
Summary & some recommendations on corrosive sulphur risk mitigation
• When buying new/unused oil, refer to IEC 60296 Ed.4 to avoid all corrosive sulphur issues.
• Passivation has some inconveniences like stray gassing or passivator depletion. This is however not
always the case and are in most cases only minor problems.
• When implementing oil filtration (reclaiming/regeneration), check oxidation stability and corrosive sulfur
against Ag-strip (by DIN 51353).
• Practically no (potentially) corrosive oils are available on the market, although be prudent as recycled oils
will gain in importance.
• Corrosive sulphur issue and corrosive oils are still around in lots of transformers in-service. But do not
panic or overreact; not all transformers will form Cu2S-deposits and not all transformers with Cu2S-deposits
will fail.
334
Property of Laborelec
335