Morgan Schaffer Calistos DGA - Naturgy Besós

Early detection of an emerging failure in a step-up transformer of the Besós Naturgy CC plant.


Armoured type primary transformer with a 500MVA - 21KV/229KV output.

The problem

A Calisto 2 DGA monitor installed on the transformer suddenly alerts of an increase of 100 ppm of H2 and 50 ppm of CO. The situation worsens two days later, reaching 500 ppm of H2 and 280 ppm of CO.

The solution

Urgent analyses in the laboratory corroborates the data advanced in real time by the Calisto monitor, confirming the presence of fault gases in the oil. An analysis of the types of gas found and their concentration, allowed diagnosing a thermal fault with signs of carbonisation. To prevent catastrophic failure of the transformer, a decision was made to place the transformer out of service and carry out thorough checks of its components.

The results

An inspection of the low voltage coil revealed that a bushing was not properly connected, which was causing it to overheat, reaching a temperature above 700ºC, and severely degrade the insulation. The Morgan Schaffer Calisto 2 monitor that is installed in the transformer allowed detecting this fault early and prevented an irreparable failure of this asset. Finally, the breakdown was repaired and the transformer resumed its operation but this time incorporating a multigas monitor to monitor the absence of new system faults.

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