Power transformers lifetime
Power transformer lifetime is determined by lifetime of it’s cellulose insulation.
Once cellulose is degradet to unacceptable level it is considered that power transformer
should be replaced. Costs of such operation could be enormously high, depending on
the size of power transformer- hundreds thousands and millions of dollars. The majority
(aproximately 85%) of transformers beakdowns are attributed to the failure of the
insulating system. Therefore, it is very important to keep power transformer in reliable
operational condition as long as possible.
Best indicator of cellulose condition is Degree of Polimierization.
Cellulose consists of glycose molecules polymerized into chains of molecules. Under
the influence of high temperature and aging promoters, ie. water and acids, links
connecting polymers broke irretrievably, reducing mechanical and dielectric properties.
Degree of Polimerization is defined as value of the average chain length of a cellulose
molecule.
Here are some values which indicate condition of cellulose:
» New insulation material before oil impregnation
» After drying and impregnation of transformer
» Relatively high aging of insulation material
» Already mechanical unstable
Typical lifetime of power transformer is cca. 40-50 years. In nowadays industry average
age of power transformer is over 30 years.
Being an organic materia cellulose natural degradation is irrreversible process.
It is of the utmost imoprtance to prevent accelerated cellulose degradation, slow
it done as much as possible and remove all harmfull substances from oil and cellulose
insulation. You can read more about oil and cellulose degradation process here.
Only oil-cellulose revitalisation if implemented in right moment can give such results
that will significantly affect power transformer lifetime.
Following diagrams shows aging curves of revitalised (red) and not revitalised (green)
power transformers insulation system. Althogh both diagrams are based on experiance
and dispaly a somewhat different curves, one thing is in common- power transformer
lifetime prolongation after total insulation revitalisation.
Depending on insulation condition and when is revitalisation implemented power transformer
lifetime could be significantly incerased- from 10 to 25 years and more.
