Terminal Configuration and Sensitivity Analysis of Tank Current Measurement for FRA Diagnostics of Three-Phase Transformer Winding Model

Abstract

This paper presents an in-depth analysis of tank current measurement for fault detection in a three-phase transformer winding model. In the first part of analysis, a unique fault detection sensitivity of tank current is presented for a three-phase winding model followed by determining the best terminal configuration to improve the sensitivity further. As a consequence of fault in three-phase winding model, it is found that tank current measurement always exhibits new additional resonance peaks. This feature is very unique for tank current response compared to the features in conventional FRA measurements. Further, an attempt is also made to quantify the fault-detection sensitivity of tank current by defining two indices. One index (named as “S-index”) is defined by the number of new extra resonance peaks in tank current magnitude response as a consequence of fault. Another is the well-known “root mean square deviation” between the two responses before and after the fault. Higher the index values, more is the sensitivity for tank current to fault detection. Using these indices, this paper also determines that the fault detection sensitivity is more for tank current if the non-tested phase terminals are kept shorted and grounded. Simulation results and experimental measurements on a practical three-phase winding model demonstrate the facts too. For practical viability, authors would also like to extend the present work for actual transformers in near future.