The Power Transformer Winding Input Admittance and Frequency Response
Abstract
The frequency response analysis is increasingly more widely used to estimate the electrical and mechanical condition of power transformer windings. The frequency response measurement procedure has been prescribed in the existing international and national standards. However, the interpretation of measurement results still remains a subject of discussion. Various approaches have been used to interpret the results, including an analysis of transformer windings’ complex impedances and admittances obtained by calculations from frequency responses. To improve the frequency response interpretation, the article presents an analysis of power transformer winding input and output currents and admittances based on simplified equivalent circuits. Qualitative and quantitative results are presented, which show that the admittances obtained from measured frequency responses differ essentially from the true input admittances of the windings. The main factors causing the differences between these winding admittances are considered. It is shown that despite the existing differences, the current through the neutral and the winding admittance determined from the measured frequency response can also be used in practice to determine the power transformer winding natural oscillation frequencies.
References
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1. IEC 60076-18:2012. Power Transformers – Part 18: Measurement of Frequency Response. International Electrotechnical Commission. July, 2012.
2. GОSТ R 59239-2020 (IEC 60076-18:2012). Transformatory silovye i reaktory. Metod izmereniya chastotnyh harakteristik (Power transformers and reactors. Method for frequency response measurement). М.: Standartinform, 2021, 50 p.
3. C57.149-2012. IEEE Guide for the Application and Interpretation of Frequency Response Analysis for Oil-Immersed Transformers. IEEE PES, 2013, DOI: 10.1109/IEEESTD.2013.6475950.
4. DL/T 911–2004. Frequency Response Analysis on Winding Deformation of Power Transformers. The Electric Power Industry Standard of People's Republic of China. 2005 [Electron. resource], URL: https://www.chinesestandard.net/PDF.aspx/DLT911-2004 (Date of appeal 31.03.22).
5. CIGRE Brochure 342. Mechanical-Condition Assessment of Transformer Windings Using Frequency Response Analysis (FRA). Working Group A2.26, April, 2008.
6. CIGRE Brochure 812. Advances in the Interpretation of Trans-former Frequency Response Analysis (FRA). Working Group A2.53, September 2020.
7. Picher P., et al. Current State of Transformer FRA Interpretation. – Procedia Engineering, 2017, vol. 202, pp. 3–12, DOI:10.1016/j.proeng.2017.09.689.
8. Samimi M.H., Tenbohlen S. FRA Interpretation Using Numerical Indices: State-of-the-art. – International Journal of Electrical Power and Energy Systems, 2017, vol. 89, pp. 115–125, DOI:10.1016/j.ijepes.2017.01.014.
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