Abstract
For a practical Frequency Response Analysis (FRA) interpretation applicable to power transformers, frequency dependent electrical parameters of the core and windings in broad frequency range should be identified through non-destructive measurements. Since the core parameters are determined in Part I, electrical parameters of windings (resistances, capacitances) and leakage paths surrounding windings (leakage/zero-sequence impedances) of a distribution transformer will be discussed in this paper. Due to the fact that most parameters associated with the windings currently can only be measured at or around power frequency through diagnostic testing methods, the practical parameter-based FRA interpretation is not possible. To deal with this problem, the paper proposes a new approach based on the combination of different measured driving-point impedances and relevant analysis of the duality-based equivalent circuit in determining frequency dependent parameters associated with transformer windings. Results show that the physical FRA interpretation can be reasonable obtained for the test transformer in low and medium frequency range.
Highlights
Electrical parameters associated with transformer windings consist of resistances, Manuscript Received on March 15th, 2017, Manuscript Revised on November 01st, 2017
Since the electrical parameters are not fully determined and can only be measured in a very low frequency range, it is stated that the determination of all electrical parameters in broad frequency range for a reasonable FRA interpretation in low and medium frequency range is valuable and meaningful
To be able to solve the problem, this paper introduces a case study in determining frequency dependent electrical parameters associated with transformer windings for FRA purpose on a 200 kVA 10.4/0.46 kV YNyn6 opened transformer
Summary
Electrical parameters associated with transformer windings consist of resistances, Manuscript Received on March 15th, 2017, Manuscript Revised on November 01st, 2017. Apart from conventional methods that measure transformers at power frequency, several advanced methods are developed and performed by means of specialized testing devices such as the CPC100 device in a very low frequency range from 15 Hz to 400 Hz to determine leakage and zero-sequence inductance, stray losses, ground and inter-winding capacitances [5] These parameters are not fully beneficial for a physical FRA interpretation since the frequency range for FRA measurements is normally from 20 Hz to 2 MHz. To be able to solve the problem, this paper introduces a case study in determining frequency dependent electrical parameters associated with transformer windings for FRA purpose on a 200 kVA 10.4/0.46 kV YNyn opened transformer. Measurements of frequency responses of driving-point impedances performed at transformer terminals by means of a scattering-parameter vector-network analyzer (VNA) of Omicron are found suitably with selected settings: low applied field (1 Vrms opencircuited) and broad frequency range
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