The “Corrosion caused by dissolution of metals (C4) criticality was discovered by Sea Marconi through analysis of an extensive body of over 40 years of case histories in its database. These studies allowed us to experimentally correlate the concentration of dissolved metals (e.g. copper) with certain types of insulating fluids used in various electrical appliance families. High concentrations of copper dissolved in oil (up to 500 mg/kg) and degradation of the dielectric properties of the insulating oil (dielectric dissipation factor – DDF up to over 2) were observed. There was also a significant phenomenon of deposition of organo-metallic species on insulating papers which does not depend on the phenomenon of corrosive sulfur.

At the origins of criticality

Analysis of dissolved metals in insulating liquids was pioneered by Sea Marconi in 1984. Correlated with analysis of particles in oil, this investigation – which Sea Marconi was the first in the world to systematically perform in 1976 – allowed us to diagnose precisely specific criticalities of oils and transformers from the mid-1980s.

Il grafico qui sopra mostra un esempio di analisi statistica con correlazione tra anno di costruzione e concentrazione di rame per oli isolanti minerali su trasformatori di distribuzione

In 1995 Sea Marconi had the opportunity to study the phenomenon of metal dissolution in even greater depth.On that occasion, Sea Marconi was called on by a transformer construction company in South America to investigate the many cases of catastrophic failure. It concerned shunt reactors on a 500 KV network, all between 18 and 24 months. During the analytical investigation, Sea Marconi analysed the factors responsible for the failures but without establishing with certainty the cause of the catastrophic events. That expertise, however, surprisingly showed the trend of some types of copper-based oils in specific transformer families. This study was communicated to Cigré TF 15.01.05 and further detailed at the presentation to Cigre in Paris in August 2000.

Click here to access Sea Marconi's major publications on the topic:

Maina, V. Tumiatti, M. Pompili and R. Bartnikas, Dielectric Loss Characteristics of Copper Contaminated Transformer Oils, IEEE Trans. On Power Delivery, Vol. 25, NO. 3, 2010

Maina, V. Tumiatti, M.C. Bruzzoniti, R.M. De Carlo, J. Lukic, D. Naumovic-Vukovic, Copper Dissolution and Deposition Tendency of Insulating Mineral Oils Related to Dielectric Properties of Liquid and Solid Insulation, ICDL 2011, Trondheim, June 26-30 2011

M.C. Bruzzoniti, R.M. De Carlo, C. Sarzanini, R. Maina, V. Tumiatti, Determination of copper in liquid and solid insulation for large electrical equipment by ICP-OES. Application to copper contamination assessment in power transformers, Talanta, vol. 99, 2012, 703-711

M. De Carlo, M.C. Bruzzoniti; C. Sarzanini, R. Maina; V. Tumiatti, Copper Contaminated Insulating Oils-Testing and Investigations, IEEE Trans. On Dielectrics and Electrical Chim. Dott. Riccardo Maina Via Tiraboschi, 25 10149 Torino (TO) Insulation, vol. 20, No. 2, 2013, 557-563

R. M. De Carlo, C. Sarzanini, M.C. Bruzzoniti; R. Maina; V. Tumiatti; Copper-in-oil Dissolution and Copper-on-Paper Deposition Behavior of Mineral Insulating Oils, IEEE Trans. On Dielectrics and Electrical Insulation, vol. 21, No. 2, 2014, 666-673