Introduction

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.

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.