By Robert C. Breazeal
“NBDFR represents a quantum leap forward in regard to winding condition assessment.”
The NBDFR protocol consists of sequential insulation power factor measurements performed in a range of 1 - 400 hertz. The data derived from the series of CHL measurements constitutes the dielectric response for the winding. The subsequent evaluation consists of a geometric analysis of the plot where measured power factors and corresponding frequencies are graphed.
On the basis of specific characteristics observed within the plot, definite assertions may be made in regard to the condition of the cellulose and oil. In 2015, Southern California Edison (SCE) began utilizing NBDFR for CHL measurements in condition assessment of used distribution class transformers.
Beginning in 2016, SCE performed a series of controlled experiments where distribution transformers were subjected to prescribed overloads, while using NBDFR to document changes in the dielectric response as the oil and paper were thermally degraded.
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