Abstract
A transformation algorithm of dielectric response from time domain to frequency domain is presented. In order to shorten measuring time of low or ultralow frequency dielectric response characteristics, the transformation algorithm is used in this paper to transform the time domain relaxation current to frequency domain current for calculating the low frequency dielectric dissipation factor. In addition, it is shown from comparing the calculation results with actual test data that there is a coincidence for both results over a wide range of low frequencies. Meanwhile, the time domain test data of depolarization currents in dry and moist pressboards are converted into frequency domain results on the basis of the transformation. The frequency domain curves of complex capacitance and dielectric dissipation factor at the low frequency range are obtained. Test results of polarization and depolarization current (PDC) in pressboards are also given at the different voltage and polarization time. It is demonstrated from the experimental results that polarization and depolarization current are affected significantly by moisture contents of the test pressboards, and the transformation algorithm is effective in ultralow frequency of 10−3 Hz. Data analysis and interpretation of the test results conclude that analysis of time-frequency domain dielectric response can be used for assessing insulation system in power transformer.
Highlights
Most of dangerous breakdowns in high voltage (HV) apparatus are caused by the aging effects of HV insulation system
The change of dielectric conductivity cannot be shown in RVM. Many researchers focus their attention on the analysis of time domain and frequency domain dielectric responses which has been used for diagnosing insulation aging of high voltage apparatus [4, 5]
Based on theoretical analysis in this paper, the test results of polarization and depolarization current in pressboards are given at different voltage and polarization times
Summary
Most of dangerous breakdowns in high voltage (HV) apparatus are caused by the aging effects of HV insulation system. Insulation diagnosis methods for large oilimpregnated power transformer include frequency domain method (frequency domain spectroscopy, FDS) [1], time domain voltage method (return voltage meter, RVM) [2], and current method (polarization and depolarization current, PDC) [3]. The change of dielectric conductivity cannot be shown in RVM Many researchers focus their attention on the analysis of time domain and frequency domain dielectric responses which has been used for diagnosing insulation aging of high voltage apparatus [4, 5]. In. Mathematical Problems in Engineering this paper, the principles of dielectric response are analyzed theoretically on the basis of the analysis of polarization and depolarization current, and frequency domain properties of dielectric dissipation factor will be obtained according to transform algorithm of depolarization current data, which provide a convenient and fast measurement for the low frequency characteristics of dielectric dissipation factor
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