Abstract
To facilitate better interpretation of dielectric response measurements—thereby directing numerical evidence for condition assessments of oil-paper-insulated equipment in high-voltage alternating current (HVAC) transmission systems—a novel approach is presented to estimate the parameters in the extended Debye model (EDM) using wideband frequency domain spectroscopy (FDS). A syncretic algorithm that integrates a genetic algorithm (GA) and the Levenberg-Marquardt (L-M) algorithm is introduced in the present study to parameterize EDM using the FDS measurements of a real-life 126 kV oil-impregnated paper (OIP) bushing under different controlled temperatures. As for the uncertainty of the EDM structure due to variable branch quantity, Akaike’s information criterion (AIC) is employed to determine the model orders. For verification, comparative analysis of FDS reconstruction and results of FDS transformation to polarization–depolarization current (PDC)/return voltage measurement (RVM) are presented. The comparison demonstrates good agreement between the measured and reconstructed spectroscopies of complex capacitance and tan δ over the full tested frequency band (10−4 Hz–103 Hz) with goodness of fit over 0.99. Deviations between the tested and modelled PDC/RVM from FDS are then discussed. Compared with the previous studies to parameterize the model using time domain dielectric responses, the proposed method solves the problematic matching between EDM and FDS especially in a wide frequency band, and therefore assures a basis for quantitative insulation condition assessment of OIP-insulated apparatus in energy systems.
Highlights
The overall reliability of a power grid depends to a great extent on the sound operation of the grid-connected power apparatus
The extended Debye model was employed in this paper to characterize the dielectric response of insulation bodies in oil-impregnated paper (OIP) bushings
In order to obtain the parameters in the equivalent circuit of extended Debye model (EDM), a syncretic algorithm that integrates a genetic algorithm (GA) and the Levenberg–Marquardt (L-M) algorithm was applied to solve the optimization using the recorded frequency domain spectroscopy (FDS) of an OIP bushing at 30 ◦ C, 70 ◦ C, and 80 ◦ C
Summary
The overall reliability of a power grid depends to a great extent on the sound operation of the grid-connected power apparatus. Power transformers, potential or current transformers, oil-filled power cables, and other oil-immersed high-voltage equipment substantially represent the critical assets thereof. The apparatus are subjected to intricate operational and loading conditions and encounter multifactor threats. A transformer may suffer from conditions like magnetizing inrush [1], overloading [2], and internal insulation faults like moistened or ageing insulation [3]. The composite media of oil-impregnated paper (OIP) constitutes the main internal insulation body of most equipment applied for high-voltage alternating current (HVAC) transmission. Faults in internal insulation are recognized as the main cause of failures in power equipment
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