Novel Condition Monitoring techniques for Large Oil/Paper insulated Transformers : Reconstruction of the Transformer FRA Response Performed via Bushing Taps.

  • Novel Condition Monitoring techniques for Large Oil/Paper insulated Transformers : Reconstruction of the Transformer FRA Response Performed via Bushing Taps.

Overview

There is a need to be able to perform FRA on a transformer on-line in order to detect winding deformation. This will eliminate the need to take the transformer of-line to perform the test, and reduce the down-time necessary to preform the test. This needs to us a signal injection and extraction topology that can be connected to an energised unit permanently or when needed. Bushing taps available on capacitively graded bushings provides such a convenient signal injection and extraction points. It is therefore necessary to know what the addition of the signal injection and extraction paths via the bushing taps will do to the measured FRA signature. We thus produced a mathematical model of an online FRA measurement chain using transmission matrices. The model can be used to mathematically reconstruct the transformer winding spectrum.

Background

Frequency Response Analyses (FRA) is widely used as a non-destructive method to determine if there have been geometric changes in the physical configuration of large power transformers. Geometric changes will show up as changes in the electric frequency respond in both the magnitude and phase of the response.

Outcomes

(a) Mathematical model of an on-line FRA measurement chain using transmission matrices. (b) Comparison of the measured winding spectra and the reconstructed winding spectra from online measurements.

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