Maintenance & Reliability Week South Africa24th of November 2010, Johan Grövik

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Development from a different perspective

Source: NASA picture “ Satellite photo of earth at night”

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Outline

Trends and directions

Transformer oil specifications

Transformer oil requirements and environment

Maintenance – Antioxidant concentration

Maintenance – Good to know…

Questions and answers

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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

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Projection Electricity growth in the world

World installation of electricity generation will increase with 87% over the period of 2007-2035

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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

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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 %

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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

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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

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Utility requirements - transformers

Reliable transformers

Available transformers

Low maintenance cost

Cost effective (losses)

Safe operation (people and environment)

Long lifetime (Return of investment)

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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

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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

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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

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Product grades versus specifications

SpecificationsASTM D3487IEC 60296Local specifications

Product differentiationStandard gradeHigh gradeSuper gradeSpecial products

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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

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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

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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

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Main type of oil degradation reactions

Thermal degradation

Oxidation

Hydrolysis

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DBPC

Antioxidant

Di-tert-butyl-para-cresol

Antioxidant molecule

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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

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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

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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

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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