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Maintenance & Reliability Week South Africa 2
Development from a different perspective
Source: NASA picture “ Satellite photo of earth at night”
Maintenance & Reliability Week South Africa 3
Outline
Trends and directions
Transformer oil specifications
Transformer oil requirements and environment
Maintenance – Antioxidant concentration
Maintenance – Good to know…
Questions and answers
Maintenance & Reliability Week South Africa 4
The energy sector is being transformed
Population growth
Increasing urbanization
Global warming
Scarcity of fossil fuels
Rising energy cost
Ageing power infrastructure
Industrial growth
Rising living standard
Mega - drivers
The solution for sustainable
energy supplies is to increase
electricity consumption
The global power generation will
increase by 60 % by 2030
Maintenance & Reliability Week South Africa 5
Projection Electricity growth in the world
World installation of electricity generation will increase with 87% over the period of 2007-2035
Maintenance & Reliability Week South Africa 6
Power transformers – Play an important key role
Power transformation and power transformerswill serve an important key role in the future
ExamplesHVDC transformers (>800 kV)– Bulk power transportation over long distancesShunt reactors- For better power quality High current transformer-More efficient industrial usagesPhase shifting transformers- For large grid inter connections
More up time
Longer life time
Energy & material efficiency
More demanding conditions
Future demands
Maintenance & Reliability Week South Africa 7
Supply vs. demand - Transformers
2002 2005 2009 20XX
Over capacity
Under capacity
Over capacity
Transformer capacity outlook 2011
Power transformers + 25 to 30 %
Distribution transformers + 30 %
Maintenance & Reliability Week South Africa 8
Transformer market demand
Installed Transformer capacity per year1, 950, 640 MVA 2, 011, 131 MVA
Conversion factors
Insulating Oil demand is estimated to1,250,000 Mt
India & China oil demand
China; 350 - 450 000 Mt
India; 200 - 250 000 Mt
Maintenance & Reliability Week South Africa 9
KEY FACTS
Insulating oil specifications
International standards
National standards
Utility requirements
Independent bodies
Insulating oil requirements Classification according to inhibitor content
ASTM 3487;2000
Type I Max 0.08 wt% inhibitor
Type II Max 0.30 wt% inhibitor
IEC 60296;2003
Uninhibited Natural inhibitors
Trace inhibited Max 0.08 wt% inhibitor
Inhibited Max 0.4 wt% inhibitor
Maintenance & Reliability Week South Africa 10
Utility requirements - transformers
Reliable transformers
Available transformers
Low maintenance cost
Cost effective (losses)
Safe operation (people and environment)
Long lifetime (Return of investment)
Maintenance & Reliability Week South Africa 11
What is the lifetime of a transformer dependent on?
Operating conditions
Ambient temperature
Design and materials
Manufacturing and installation
Follow up and maintenance
Design / Manufacturing / Material
MaintenanceOperationse.g. load
Maintenance & Reliability Week South Africa 12
What are the requirements of an insulating oil?
Provide good cooling
Act as an electrical insulator
Have an excellent cold start property
Last the lifetime of transformer
Act as an information carrier
Maintenance & Reliability Week South Africa 13
A tough environment for the insulating oil
Moisture
Acids
Temp./Load
Sludge formation
Upgraded Cellulose
Metals
Age
Oxygen
OIL /CELLULOSE
0
2
4
6
8
10
MVA/t oil
1965 1970 1975 1980 1985 1990
Power transformers
Distribution transformers
Higher and higher stress on the insulating oils
Maintenance & Reliability Week South Africa 14
Product grades versus specifications
SpecificationsASTM D3487IEC 60296Local specifications
Product differentiationStandard gradeHigh gradeSuper gradeSpecial products
Maintenance & Reliability Week South Africa 15
DISTILLATE BASE OIL
Rigorous quality control
Careful crude oil selection
Production and delivery of a premium quality insulation oil is not an easy task. Insulating oil is very sensitive product, where both raw materials and contaminations can destroy it all.
Quality assurance throughout the process
All vessels & trucks have strict cleaning
procedures
Dedicated cisterns & pipes
Independent bodies verifying quality
Distillation Refining Formulation
CRUDE INSULATING OIL
Maintenance & Reliability Week South Africa 16
Values and benefits – daily operations
Low pour point
Excellent insulator Can withstand very high electrical stress
Transformer can be energized in low temperatures
Very strong and stable insulation system enable compact design and high voltages
Diagnostic tool to prevent failures and avoid outages
Information carrier
Record & store fault gases
Allow to detect electrical & thermal faults
Good flow properties at very low temperatures
Excellent compatibility with cellulose
Maintenance & Reliability Week South Africa 17
Values and benefits - life cycle
Low viscosity oils
Lower operating temperatures
Good oxidation stability
Low acid valuesand low sludge production
Less maintenance over time
Slow degradation of oil and paper
Longer transformer lifeHigh solvency Keep sludge
dissolved in oilBetter circulation properties
Maintenance & Reliability Week South Africa 18
Main type of oil degradation reactions
Thermal degradation
Oxidation
Hydrolysis
Maintenance & Reliability Week South Africa 19
DBPC
Antioxidant
Di-tert-butyl-para-cresol
Antioxidant molecule
Maintenance & Reliability Week South Africa 20
0
0,1
0,2
0,3
0,41 24 47 70 93 116
139
162
185
208
231
254
277
300
323
346
369
Acidity / Inhibitor Inhibitor (%)
No of samples (increased inhibitor content to the right)
Acidity (mg KOH/g)
Acidity level and Inhibitor content- 400 oil immersed transformers
Maintenance & Reliability Week South Africa 21
Mixability of transformer oilsGeneral rule for new oils
New oils complying to the same specification and class (type) are considered to be mixable in all proportionsExamples; Nynas Nytro Libra and Shell Diala B; Nynas Nytro 11GBX-US
For oils in serviceWithin warranty period top up with the same oilAfter warranty period the general rule above apply, but
If oil according to that rule is not available inhibited oils can be used for all other oils in proportions up to 5 %In other cases a mixability study is recommended for the proportions to be used. The mix should not be considerably worse than the in service oilTo mix new oil with very aged in service oil, condition poor, should be avoided
Maintenance & Reliability Week South Africa 22
Remedial actions on oilDegassing/filtration
To correct poor breakdown voltage/high water content/high particle contentIf the water content is high in a transformer oil the major amount of water is sitting in the cellulose. To remove this water via the oil is not feasible due to the slow equilibrium process
Oil reclamationTo remove ageing products + water/particlesFor larger units mainly, for smaller units oil change is likely a cheaper alternativeCan be made on line, while the unit is in service of off lineThe oil has to be inhibited after to restore ageing characteristicsDo not expect to have a “new oil” after the reclamation. There will always be ageing products trapped in the cellulose contributing to oil properties and ageing by time
Maintenance & Reliability Week South Africa 23
Follow up of transformer oils in serviceThe two most common guidelines are:
For IEC grades IEC 60422For ASTM grades IEEE C 57.106
The follow up frequency, after warranty period, is linked to voltage class, importance of equipment and age/condition of oil and equipment.
Most important oil characteristics to follow up:Dielectric properties;e g breakdown voltage, water content, loss factorAgeing characteristics, e g acidity, inhibitor content
IEC documents can be bought via www.iec.ch and IEEE via www.ieee.org