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    Development of a partial discharge testing system for potential transformers
    (2018-04-27)
    Prombud, T.
    ;
    Kitcharoen, P.
    ;
    Yutthagowith, P.
    In this paper, the development of a partial discharge testing system for potential transformers (PTs) is presented. The system is composed of a low-voltage and 200-Hz power frequency converter connected with a low pass filter, a high-voltage transformer, and a conventional partial discharge detection system. The performances of the converter with three generated waveform, i.e. square wave, quasi-square wave, and unipolar pulse width modulation (PWM) are compared in terms of the DC charging voltage, the voltage difference (peak voltage/square root of 2 and rms voltage), total harmonic distortion of the output high voltage (THDv), and background noises in the partial discharge test. It is found that the unipolar PWM frequency converter provides the best performances in terms of the voltage difference, THDv, and background noise. The voltage difference and THDv are lower than 5%, and the background noise is less than 2.5 pC. In addition, the developed system has been used for the real partial test on a potential transformer in the distribution system successfully.
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    Dielectric properties of mineral oil compared with natural ester
    (2017-11-29)
    Jariyanurat, K.
    ;
    Nimsanong, P.
    ;
    Chaisiri, P.
    ;
    Maneerot, S.
    ;
    Kitcharoen, P.
    In this paper, dielectric properties of the mineral oil, ELECTROL A, and the natural ester, FR3, are comparatively investigated. AC breakdown voltages, dielectric dissipation factor, relative permittivity, partial discharge inception voltage and partial discharge of the mineral oil and of the natural ester are tested. In order to verify the capability in practical use of the mineral oil and the natural ester for transformer insulation systems, the impregnation of such liquids with pressboard insulation is performed. The impregnated pressboards are tested in the laboratory to measure the AC breakdown voltages. It is found that the natural ester shows superior dielectric properties to the mineral oil except the dielectric dissipation factor.