Maintenance & Reliability Week South Africa. 24th of November 2010, Johan Grövik

Transcription

1 Maintenance & Reliability Week South Africa 24th of November 2010, Johan Grövik

2 Development from a different perspective Source: NASA picture Satellite photo of earth at night 2

3 Outline Trends and directions Transformer oil specifications Transformer oil requirements and environment Maintenance Antioxidant concentration Maintenance Good to know Questions and answers 3

4 The energy sector is being transformed Mega - drivers Population growth Increasing urbanization Global warming Scarcity of fossil fuels Rising energy cost Ageing power infrastructure Industrial growth Rising living standard The solution for sustainable energy supplies is to increase electricity consumption The global power generation will increase by 60 % by

5 Projection Electricity growth in the world World installation of electricity generation will increase with 87% over the period of

6 Power transformers Play an important key role Power transformation and power transformers will serve an important key role in the future Examples HVDC transformers (>800 kv) Bulk power transportation over long distances Shunt reactors - For better power quality High current transformer -More efficient industrial usages Phase shifting transformers - For large grid inter connections Future demands More up time Longer life time Energy & material efficiency More demanding conditions 6

7 Supply vs. demand - Transformers XX Under capacity Over capacity Over capacity Transformer capacity outlook 2011 Power transformers + 25 to 30 % Distribution transformers + 30 % 7

8 Transformer market demand Installed Transformer capacity per year 1, 950, 640 MVA 2, 011, 131 MVA Conversion factors Insulating Oil demand is estimated to 1,250,000 Mt India & China oil demand China; Mt India; Mt 8

9 KEY FACTS Insulating oil specifications Insulating oil requirements Classification according to inhibitor content ASTM 3487;2000 Type I Type II Max 0.08 wt% inhibitor Max 0.30 wt% inhibitor International standards National standards Utility requirements Independent bodies IEC 60296;2003 Uninhibited Trace inhibited Inhibited Natural inhibitors Max 0.08 wt% inhibitor Max 0.4 wt% inhibitor 9

10 Utility requirements - transformers Reliable transformers Available transformers Low maintenance cost Cost effective (losses) Safe operation (people and environment) Long lifetime (Return of investment) 10

11 What is the lifetime of a transformer dependent on? Design / Manufacturing / Material Operating conditions Ambient temperature Design and materials Manufacturing and installation Follow up and maintenance Operations e.g. load Maintenance 11

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 12

13 A tough environment for the insulating oil Moisture MVA/t oil Oxygen Acids 10 Power transformers 8 Age OIL / CELLULOSE Temp./ Load 6 4 Metals Upgraded Cellulose Sludge formation 2 0 Distribution transformers Higher and higher stress on the insulating oils 13

14 Product grades versus specifications Specifications ASTM D3487 IEC Local specifications Product differentiation Standard grade High grade Super grade Special products 14

15 Rigorous quality control 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. Distillation Refining Formulation CRUDE DISTILLATE BASE OIL INSULATING OIL Careful crude oil selection All vessels & trucks have strict cleaning procedures Dedicated cisterns & pipes Quality assurance throughout the process Independent bodies verifying quality 15

16 Values and benefits daily operations Low pour point Good flow properties at very low temperatures Transformer can be energized in low temperatures Excellent insulator Can withstand very high electrical stress Excellent compatibility with cellulose Very strong and stable insulation system enable compact design and high voltages Information carrier Record & store fault gases Allow to detect electrical & thermal faults Diagnostic tool to prevent failures and avoid outages 16

17 Values and benefits - life cycle Low viscosity oils Good oxidation stability High solvency Lower operating temperatures Low acid values and low sludge production Keep sludge dissolved in oil Better circulation properties Less maintenance over time Slow degradation of oil and paper Longer transformer life 17

18 Main type of oil degradation reactions Thermal degradation Hydrolysis Oxidation 18

19 Antioxidant molecule Antioxidant DBPC Di-tert-butyl-para-cresol 19

20 Acidity level and Inhibitor content oil immersed transformers Acidity / Inhibitor 0,4 Inhibitor (%) 0,3 0,2 0,1 Acidity (mg KOH/g) No of samples (increased inhibitor content to the right) 20

21 Mixability of transformer oils General rule for new oils New oils complying to the same specification and class (type) are considered to be mixable in all proportions Examples; Nynas Nytro Libra and Shell Diala B; Nynas Nytro 11GBX-US For oils in service Within warranty period top up with the same oil After 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 oil To mix new oil with very aged in service oil, condition poor, should be avoided 21

22 Remedial actions on oil Degassing/filtration To correct poor breakdown voltage/high water content/high particle content If 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 reclamation To remove ageing products + water/particles For larger units mainly, for smaller units oil change is likely a cheaper alternative Can be made on line, while the unit is in service of off line The oil has to be inhibited after to restore ageing characteristics Do 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 22

23 Follow up of transformer oils in service The two most common guidelines are: For IEC grades IEC For ASTM grades IEEE C 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 factor Ageing characteristics, e g acidity, inhibitor content IEC documents can be bought via and IEEE via 23