Punctured rubber bladders detected by UV-vis spectroscopy

For the design of power transformers, two mechanical solutions are used to hinder the contact of the oil with the outside atmosphere. One method favoured in the United States is to seal the transformer using a nitrogen cushion. The other method is to use an elastic rubber or plastic bag to separate the surface of the oil from the gas space in the conservator. Under service conditions, rubber bladder may be punctured due to aging or mechanical problems such as gasket wear, with potential oxygen inlet. Such problems need to be detected to avoid dramatic failures. In this contribution, three 500 kV generator step-up units belonging to Salto Grande were sealed and a periodic oil analysis procedure implemented to monitor the rubber bladers. Measuring the interfacial tension and the acidity of the oil, confirmed the lack of oxidation products while the analysis of the relative content of Dissolved Decay Products (DDP) in the oil by UV-vis spectrophotometry (ASTM D6802) showed a higher content of dissolved oxidation decay products in the units with punctured rubber by bladders.