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Author: search.filters.author.Nimsanong, P.Subject: search.filters.subject.Polarization and depolarization current

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    VLF dielectric response and HF localized dielectric discharge measurement for rotating machine insulation assessment
    (2020-08-14)
    Nimsanong, P.
    ;
    Pattanadech, N.
    This paper represents the very low frequency (VLF) dielectric response and high frequency (HF) localized dielectric discharge measurement for rotating machine insulation assessment. The integral conditions of stator winding insulation, the so-called aging condition, were investigated by the dielectric response measuring technique. The polarization and depolarization currents in the VLF range from 0.0001 to 1 Hz were measured under an external step electric field. The local conditions of stator winding insulation, the so-called weak spot condition, were examined by the partial discharge (PD) measuring technique. The PD pulse currents were detected by a capacitive sensor in a wide-band range, where the bandwidth of the measuring system was set between 30 kHz and 30 MHz. The medium voltage rotating machine rated 6.6 kV and 240 to 2,270 kW under different service conditions, i.e., new stator winding, moisture contamination, dirt contamination as well as thermally and severely aged insulation, was studied. Besides, four case studies on measuring the PD in service rotating machines rated 11–15 kV, 7100 to 211,000 kW as well as the attenuation of the PD pulses were conducted and demonstrated. With several case studies, this paper introduces new dielectric parameters, the so-called charge ratio (QR) and charge difference gradient (QDG), to identify the dielectric mechanism occurring in the stator winding insulation caused by the polarization and conduction processes. It can be concluded that the proposed parameters are a valuable tool for assessing the aging condition. In the case of the PD measurement, it was found that the PD pulse is strongly attenuated in the slot section. This paper also introduces the combination of both the dielectric response and PD measurement results, which can be very useful for assessing a complete insulation condition in the rotating machine. Moreover, the criteria for insulation conditions are suggested in this paper to evaluate the integral and local conditions for the rotating machine insulation. The local discharge in the machine causes electromagnetic waves, which may get released from the non-perfect characteristics of the enclosure. This signal may interfere with the functioning of other nearby electronic devices, especially the communication equipment. Therefore, maintaining the excellent condition of the insulation system by the proposed technique detailed in this paper will support the highly effective operational efficiency of the communication system as well.
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    Polarization and depolarization current measurement applied for investigation of underground cable system problems
    (2019-07-01)
    Pattanadech, N.
    ;
    Phongsirichairojna, T.
    ;
    Navapittayaratana, N.
    ;
    Nimsanong, P.
    ;
    Jirathipchaisakul, T.
    This research investigates the problems in XLPE cables system. The 12/20(24) kV underground cable with the cross section area of 240 mm<sup>2</sup> was used in the experiment. Two 3 meter long cables were connected by a cable joint where the defect was simulated on. The dielectric investigation of XLPE cable system by polarization and depolarization current (PDC) measurement was performed comparatively among four different cases: a healthy cable with healthy heat shrinkable joint (case1), a cable joint with an incision on XLPE surface (case2), a cable joint contaminated with 20 micron iron powder on XLPE surface (case3) and a cable joint contaminated with 20 micron copper powder on XLPE surface (case4). Diagnostic parameters, PDC shapes, dielectric dissipation factor (DDF) and conduction current, derived from PDC test results for analyzing the dielectric response are proposed in this paper.
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    Dielectric diagnosis of 24kV XLPE cable using polarization and depolarization current, conventional partial discharge measurements and high frequency current measurement
    (2016-01-01)
    Nimsanong, P.
    ;
    Pattanadech, N.
    ;
    Yutthagowith, P.
    Medium voltage power cables are an important element of electric power distribution. Most of cable failures occurring in XLPE insulation and cable accessories are due to insulation failure. This research work represents the dielectric investigation of 12/20(24) kV XLPE power cables including cable joints by using polarization and depolarization current (PDC) measurement, conventional partial discharge measurement according to IEC 60270, and high frequency current measurement measured by high frequency current transformer (HFCT). In this research work, six case studies, case 1: PE sheath damaged, case 2: semi-conducting layer damaged, case 3: void defect in extruded cable, case 4: void defect in extruded cable at cable joint, case 5: semiconductive contaminant at cable joint, and case 6: conductive contaminant at cable joint, were investigated. The test results showed that two basic properties, polarization and depolarization current, of cable insulation can be utilized for classification of cables with joint problems. The defects in extruded cable and cable joint can be identified by the PDC shapes. However, to clarify the problems occurring at the cables by conventional PD measurement and HFCT measurement was performed. Moreover, it was found that the sensitivity of HFCT was clearly lower than conventional tool.