Comparison of FRA Data measured by Different Instruments with Different Frequency Resolution

摘要

In diagnoses of mechanical faults of power-transformer windings by frequency response analysis (FRA), repeatability of measurements is an important issue. Measuring instrument may influence the repeatability. For objective investigations of the repeatability, numerical indices are useful in comparing measured transfer functions (TFs). In calculating these numerical indices, the frequency resolutions in the measurements have to be identical. However, in the international standards, IEC60076-18:2012, the frequency resolution is not specified in detail, and in practice, they depend on instruments employed in the measurements. In this paper, a calculation method of the numerical indices in comparing TFs with different frequency resolution is proposed, and it is validated experimentally. Furthermore, the proposed method is applied to comparisons of TFs of three real power transformers measured simultaneously by three different measuring instruments. The comparison results show that the difference in the measuring instruments itself is negligible in the repeatability. However, the difference in grounding conditions originated in the measurement cables is not negligible. The acronyms of some phrases are shown in the appendix.