Application of digital filtering techniques to the determination of partial discharge location in transformers

The capacitative network representation of transformer windings has long been used for the study of pulse distribution along the windings. However, the author´s test results and those published in the literature show that theoretical analysis based on this equivalent network may not be applicable. It was found that the capacitive network approximations were valid only within certain ranges of frequency. The frequency ranges were determined through the analysis of terminal measurements. The capacitatively transferred components of the input pulse along the windings in the appropriate frequency range were then extracted by the aid of digital filtering techniques, and good agreement between measured and theoretical distributions was obtained. These techniques, in conjunction with a new straight-line interpolation method, were employed to locate simulated partial discharges in a 66 and 132 kV transformer winding. Measurement results showed that an accuracy of better than 5% of winding length was obtained