On-line diagnostics of oil-filled transformers

This paper deals with gas chromatographic diagnostics of power transformers which has been recognised in the world for some time-and in Slovenia for the past 15 years-as the most efficient physical-chemical on-line diagnostic method for determination of potential thermal or electrical faults in transformers. Today the method is increasingly complemented by sensor on-line monitoring of transformers. We have studied the correlations between signals of hydrogen sensor known as Hydran and the results of periodic DGA in the case of a power transformer with a built-in Hydran sensor in order to determine the applied value of sensor on-line monitoring. On the basis of the results of the investigation and the experience of Slovene and foreign researchers, we estimate that technologically and economically it is necessary to perform an annual DGA for optimal monitoring of power transformers. However, in the case of very important or problematic transformers, such an approach should be complemented by a Hydran sensor.