Abstract
Although the standard Frequency Response Analysis (FRA) test has been approved as an efficient tool to diagnose mechanical failures in power transformers, the demand to interpret FRA traces in practical and physical way is still requested. That means physical electrical parameters of transformers should be determined reasonably based on real measurements and afterwards are applicable for the interpretation. For purpose of FRA interpretation in practical manner, electrical parameters of power transformers in a physical equivalent circuit should be determined. As a first step, the paper introduces a new approach in determining frequency dependent core impedances of a distribution transformer based on the combination of circuit analysis of a duality-based model, measurements of driving-point impedances and experimental formulas. From that, two important contributions can be drawn. Firstly, frequency dependent core impedances are ready as available components in the circuit for FRA interpretation in broad frequency range. Secondly, the core parameters could be useful indicators for detecting relevant failures in cases there is no more failure on transformer windings.
Highlights
The core is an important component of power transformers, which provides magnetic links between the windings
The dual electrical equivalence of the core is still not widely approved for FRA investigations since it has been understood that the core does not play any key role in analysis of frequency responses of power transformers in medium and high frequency range
In order to introduce a practical approach in analysis of the transformer core for purpose of FRA interpretation in low and medium frequency range, this paper introduces a new approach in determining frequency dependent core parameters
Summary
The core is an important component of power transformers, which provides magnetic links between the windings. In order to introduce a practical approach in analysis of the transformer core for purpose of FRA interpretation in low and medium frequency range, this paper introduces a new approach in determining frequency dependent core parameters. Two important contributions of the paper can be drawn: the applicability of the approach for any transformer, and the availableness of frequency dependent core impedances in broad frequency range for the feasibility of FRA interpretation via circuit simulation. Core section impedances of the transformer are analyzed based on measurements of frequency responses of open-circuit driving-point impedances at the high-voltage (HV) side at low frequencies. The measurements are performed by Science and Technology Development Journal, vol 20, no.K3- 2017 mean of a commercial scattering-parameter vector-network analyzer (VNA) with chosen settings appropriate for FRA purpose: open-circuit voltage of 1 Vrms, broad frequency range from 20 Hz to 2 MHz with 801 points, receiver bandwidth of 30 Hz
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