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Detection and Classification of Partial Discharges in High Voltage DC

Rahimi, Mohammad Reza | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46763 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Vakilian, Mehdi
  7. Abstract:
  8. In past decades, the measurement of partial discharges (PDs) in high voltage equipments, was appreciated as one of the most efficient methods for evaluation of the equipment insulation condition. Generators, transformers, cables and transmission lines are especially checked to detect the presence of any partial discharge.
    In AC high voltage systems, the measurement method is well established and known. The Phase resolved method is used to determine the partial discharge signals. These methods have been used for many years and their success in differentiating the various sources of partial discharge have proven. Although phase resolved method works on AC; due to lack of frequency concept in a DC system, this method cannot be used for DC. Although the standard methods for partial discharge measurement is well established in AC voltage systems, in DC voltage systems a standard method for partial discharge measurement is not agreed on. Different theories are developed to interpret partial discharge phenomenon under DC voltage, however these theories are not well established as in the case of AC partial discharge.
    In this thesis, to differentiate among the partial discharge pulses related to different insulation defects, experimental models of some of these defects are developed and the related partial discharge signals are measured and verified against the proposed method. For evaluation of the partial discharge activities under DC voltage, the following fundamental quantities are employed:
    Magnitude of electric charge transferred during a partial discharge (q)
    Instant of partial discharge occurence (ti) or the time interval between to successive partial discharge (Δt)
    Based on these measured fundamental parameters, the density function of discharge magnitude H(q), the density function of the time interval between discharges H(Δt) and the density function of pulse width (versus pulse height) have been extracted. Employing the first two density function of H(q) and H(Δt) some of the statistical features such as: skewness, kurtosis and the equivalent weibull distribution parameters are determined. These information are employed to differentiate among different partial discharge sources
  9. Keywords:
  10. Partial Discharge ; High Voltage Equipment ; Insulation Defect Models ; Direct Current Voltage

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