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    The Experiment of Partial Discharge for Cast Resin Transformer
    (2024-01-01)
    Aiamrungruang, Phitthaya
    ;
    Pannil, Pittaya
    ;
    Dorkmai, Kritsada
    ;
    Maneerot, Sakda
    ;
    Jeenmuang, Siwakorn
    Dry-type cast resin transformers, utilizing epoxy resin insulation instead of traditional liquid insulation like mineral oil, are designed to prioritize safety, avoid fire hazards, be environmentally compatible, and endure short circuits well. Limitations of dry-type transformers are the installation area by which it should be dry, free from dust, excessive moisture, fertilizers, chemicals, and other corrosive fumes or fumes. This paper investigates the Partial Discharge (PD) phenomena occurring on a 12 kV dry-type transformer surface using HighFrequency Current Transformers (HFCT) with 100 kHz -20 MHz bandwidth as a PD detection device. The simulated PD sources were made from the conductive wire. Moreover, the scheme of winding connections in the dry-type transformer related to cross-talk phenomena between transformer coils is also reported. The recorded Phase-resolved PD (PRPD) and the PD Inception Voltage (PDIV) have been summarized and compared, as described in this paper.
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    Partial Discharge Testing on MV Motor - Case Study
    (2023-01-01)
    Jeenmuang, Siwakorn
    ;
    Rojanasunan, Warisanan
    ;
    Dorkmai, Kritsada
    ;
    Chumpiboon, Komin
    ;
    Udomluksananon, Patt
    A failure of a medium voltage (MV) motor during its operation could force an outage of the power plant and also lead to a loss of cost. Hence, the method to ensure the insulation quality of such a motor is needed. Partial discharge (PD) testing is one of the effective methods used to determine the defect and evaluate the integrity of the machine insulation. This paper presents the application of off-line PD testing on MV motors. In the experiment, the PD test instrument conforming to standard IEC 60270 was used as a charge-based measurement. Moreover, during the PD testing, an acoustic imaging camera was employed as an alternative technique for locating the PD sources in the stator winding part. Once PD takes place, it can generate the pressure acoustic wave that propagates surrounding the PD source. Thus, the PD source in the area of endwinding can be located by this technique. From the charge-based PD test results, the phase-resolved PD (PRPD) pattern was considered to identify the type of PD source. It was found that almost MV motors tested have delamination in the bulk insulation. In some cases, the PRPD pattern exhibits the discharge in the area of the overlap region between the semiconductive and stress grading coating in the slot exit, which confirms by using the acoustic technique.
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    The Dielectric Properties in Frequency Domain of the 22 kV Underground Cables with Defective Joint
    (2023-01-01)
    Udomluksananon, Patt
    ;
    Jeenmuang, Siwakorn
    ;
    Chumpiboon, Komin
    ;
    Dorkmai, Kritsada
    ;
    Rojanasunan, Warisanan
    The failure that occurs in the underground cable systems leads to losses in many aspects, not only in the power system but also in the commercial and business. The most failure location in medium voltage underground cable systems is cable joint and cable termination, where the defects occur from poor workmanship. This paper represents the mean to investigate the dielectric properties of the 22 kV XLPE underground cable system to assess the insulation's integrity of the underground cable system. In the experiments, the underground cable system specimens were prepared by simulating the defects in cable joints, i.e., the iron powder on the XLPE surface and the incision on the XLPE surface; moreover, the underground cable system with the healthy condition joint was prepared to represent the new (or unused) underground cable system. To compare the dielectric properties in the frequency domain of the 22 kV underground cable systems with defective joints and the healthy condition joint, the frequency domain spectroscopy (FDS), the off-line non-destructive test, was performed in this research. From the test results, the dielectric dissipation factor shows a significantly different value in the case of iron powder when compared with the healthy condition joint. It reveals the loss peak on the curve at a frequency of 1 Hz. However, the case of incision on the XLPE surface is almost similar to the healthy condition case. The real part of the complex capacitance of all three cases has a constant value in the measured frequency ranges using the log-log scale. However, the imaginary part capacitance shows the distinct value of all three cases, of which the trends are the same as the dielectric dissipation factor curve.
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    THE DIELECTRIC CHARACTERISTICS OF 22 KV XLPE UNDERGROUND CABLES WITH DEGRADED ARTIFICIAL JOINT
    (2023-01-01)
    Udomluksananon, Patt
    ;
    Boonsaner, Nutthaphan
    ;
    Wiangtong, Theerayod
    ;
    Jeenmuang, Siwakorn
    ;
    Chumpiboon, Komin
    This paper represents the dielectric characteristics of the 22 kV underground cable test specimen. Two 3 m XLPE underground cables were connected with the heat-shrinkable joint that has been simulated with some artificial defects. The healthy heat-shrinkable terminations are at both ends of the cable test specimen. For this research, the underground cables with the healthy joint, the joint with a copper powder contaminant on the XLPE surface, and the joint with an incision on the XLPE surface were prepared to perform the experiment. To compare the dielectric characteristics of the underground cables with the healthy joint and degraded artificial joints, the polarization and depolarization currents (PDC) measurements and the very low frequency-tangent delta (VLF-TD) testing, according to IEEE standard 400.2-2013, were conducted. From the PDC measurements, the test results are not clearly different for the underground cables with the defective joint when compared to the healthy joint case, except for the electrical conductivity and insulation resistance that show the difference between them. The VLF tangent delta parameters and mean tangent delta comparison curve show differences in each case, which can contribute to assessing the condition of the underground cable systems.
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    INVESTIGATION OF STATOR WINDING INSULATION CONDITION OF MV MOTORS BASED ON DIELECTRIC RESPONSE MEASUREMENT
    (2023-01-01)
    Pattanadech, Norasage
    ;
    Jeenmuang, Siwakorn
    ;
    Dorkmai, Kritsada
    ;
    Chumpiboon, Komin
    ;
    Udomluksananon, Patt
    This paper presents an investigation of the stator winding insulation condition of medium voltage (MV) motors operated in a power plant. The investigated motors have the same voltage rate of 6.6 kV. Such motors continuously encounter various stresses during service which alter the dielectric properties of the insulation system. Thus, the dielectric response measurement (DRM) was utilized in this research to evaluate the integrity of insulation of stator winding insulation, whether the bulk insulation e.g., moisture absorption, or the surface insulation e.g., existing conductive contamination over- or even moisture adsorption along the endwiding surface. In addition, polarization and depolarization current (PDC) and frequency domain spectroscopy (FDS), as techniques based on DRM, were employed to allow the analysis in both time and frequency domains. Such techniques were performed on the whole MV motors during the shutdown for time-based maintenance, both before and after cleaning and drying for comparison purposes. The visual inspection of such motors evidences that there has considerable dust over the endwinding surface. Such motors were thus thoroughly cleaned to remove such visible dust over the surface of the endwinding. Then, the DRM test results before and after cleaning, were comparably analyzed to characterize the dielectric properties due to such contaminant. Therefore, the effect of the contaminants on the dielectric properties of the stator winding insulation system is introduced and discussed.