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Investigation of polarization and depolarization current measurements for the assessment of oil-paper insulation of aged transformers

Investigation of polarization and depolarization current measurements for the assessment of oil-paper insulation of aged transformers,10.1109/TDEI.200

Investigation of polarization and depolarization current measurements for the assessment of oil-paper insulation of aged transformers   (Citations: 30)
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Moisture and ageing strongly influence the dielectric properties of oil/paper insulation system of power transformer. Moisture measurement in oil sample generally gives inconclusive information since oil/paper moisture equilibrium is temperature dependent and takes a long time to be in equilibrium. Direct moisture measurement of paper sample is not practicable for in-service transformers. The measurement and evaluation of the "dielectric response" and conductivity is one possible way of diagnosing a transformer insulation condition. In a recent research project, polarization and depolarization current measurement has been used for assessing the condition of oil/paper insulation. The polarization and depolarization current (PDC) analysis is a nondestructive dielectric testing method for determining the conductivity and moisture content of insulation materials in a transformer. On the basis of this analysis it is possible to take further actions like oil-refurbishment, drying or replacement of the winding of the transformer. This paper presents a description of the PDC technique with the physical and mathematical background and some results of PDC measurements on several transformers. Analyses and interpretation of the field test data are also presented in this paper.
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    • ...[18]. These impurities will alter the PD characteristics of particles in oil...

    Junhao Liet al. Partial-Discharge Characteristics of Free Spherical Conducting Particl...

    • ...Among these methods, the most important are those based on time domain (reverse voltage and absorption/resorption currents measurements) and frequency domain dielectric response analysis (complex relative permittivity and loss factor measurement in a wide range of frequencies) [10-14]...

    Laurentiu Badicuet al. Oil impregnated paper condition assessment using time spectroscopy met...

    • ...The classical diagnostic techniques are based on the measurement of insulation resistance (IR), capacitance, dielectric loss factor (DLF), partial discharges (PD), interfacial polarization (IP), dissolved gas analysis (DGA), viscometric degree of polymerization (DP), dielectric strength of paper and pressboard, and moisture content [4]...
    • ...There has been a significant amount of research performed on the application of PDC measurement to the large power transformers [4-6]...
    • ...The conduction current is due to the movement of free charges across the dielectric length and has a constant value as long as the dielectric is energized [4]...
    • ...The polarization current readings after the transients (ip(+0)) are considered to evaluate the conductivity of the oil, which can be written as shown [4]...
    • ...Assuming σoil >> σpaper, the paper conductivity can be approximated as [4]...
    • ...Figure 4. Experimental Setup used for the PDC Measurement [4]...

    Anuradha Kumaret al. Time domain spectroscopy measurements for the insulation diagnosis of ...

    • ...Commercially available as well as locally manufactured PDC measuring systems have been used in different studies [10, 11]...
    • ...CONFIGURATIONS A. PDC measurements [11] The PDC measurements were carried out by equipment designed and developed by the researchers at the University of Queensland...

    C. Ekanayakeet al. Application of polarization based measurement techniques for diagnosis...

    • ...Their lifetime is predominantly determined by the condition of its insulation system, which is continuously subjected to thermal, electrical, mechanical, and chemical stresses, during their operation [1, 2]. In most power transformers, the insulation system consists of oil-impregnated paper or pressboard for insulating and supporting, and transformer oil acting as insulation and coolant...
    • ...Where �0 ’(�& ) is the real part of the complex dielectric permittivity and �0 ’’(�& ) is the imaginary part, while �1 0 the dc conductivity [2, 8, 16]...
    • ...For a linear dielectric, when the charging time is sufficiently long, the difference between polarization and depolarization currents equals to the conduction current [2, 20]...

    Shi-Qiang Wanget al. Investigation on dielectric response characteristics of thermally aged...

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