Signs (visual inspection)
The direct visual signs of this criticality are only highlighted by internal inspection of the transformer. In case of failure (or end-of-life) of twin machines, for example, it is good practice to perform a total sludge diagnostic (through sampling, analysis and interpretation) in order to declare the criticality and classify comparative references. In the presence of “insoluble deposits (sludge)”, the following are observed:
– Insoluble deposits (e. g. sludge or copper sulfide) on insulating papers and at the bottom of the casing
– Obstructions of oil circulation ducts used for cooling windings and papers.
Representative sampling
During external inspection of the transformer it is necessary to take representative samples of insulating oil in accordance with the reference standard and the operating instructions attached to the sampling kits (read more).