A critical review of the definition of FRA resonance frequency of transformers as per IEEE Std C57.149-2012

Pramanik, S and Satish, L (2015) A critical review of the definition of FRA resonance frequency of transformers as per IEEE Std C57.149-2012. In: ELECTRIC POWER SYSTEMS RESEARCH, 121 . pp. 52-57.

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Abstract

The explanation of resonance given in IEEE Std C57.149-2012 to define resonance during frequency response analysis (FRA) measurements on transformers implicitly uses the conditions prevalent during resonance in a series R-L-C circuit. This dependence is evident from the two assertions made in the definition, viz., resulting in zero net reactive impedance, and, accompanied by a zero value appearing in the phase angle of the frequency response function. These two conditions are satisfied (at resonance) only in a series R-L-C circuit and certainly not in a transformer, as has been assumed in the Standard. This can be proved by considering a ladder-network model. Circuit analysis of this ladder network reveals the origin of this fallacy and proves that, at resonance, neither is the ladder network purely resistive and nor is the phase angle (between input voltage and input current) always zero. Also, during FRA measurements, it is often seen that phase angle does not traverse the conventional cyclic path from +90 degrees to -90 degrees (or vice versa) at all resonant frequencies. This peculiar feature can also be explained using pole-zero maps. Simple derivations, simulations and experimental results on an actual winding are presented. In summary, authors believe that this study dispels existing misconceptions about definition of FRA resonance and provides material for its correction in IEEE Std C57.149-2012. (C) 2014 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Publication:	ELECTRIC POWER SYSTEMS RESEARCH
Publisher:	ELSEVIER SCIENCE SA
Additional Information:	Copy right for this article belongs to the ELSEVIER SCIENCE SA, PO BOX 564, 1001 LAUSANNE, SWITZERLAND
Keywords:	IEEE C57.149-2012; Transformer winding; Frequency response; Resonance; Impedance; Admittance
Department/Centre:	Division of Electrical Sciences > Electrical Engineering
Date Deposited:	20 Apr 2015 06:42
Last Modified:	20 Apr 2015 06:42
URI:	http://eprints.iisc.ac.in/id/eprint/51212

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