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    Dielectric Response Analysis of Mineral Oil Immersed Transformer Insulation during Manufacturing Process
    (2019-06-01)
    Nganpitak, Tritod
    ;
    Nimsanong, Phethai
    ;
    Maneerot, Sakda
    ;
    Pattanadech, Norasage
    Polarization and Depolarization current (PDC) method is one of non-destructive insulation testing methods that can be used for diagnosis the insulation conditions of high voltage equipment. This paper presents the PDC analysis of an oil immersed distribution transformer measured during the manufacturing process. A 22 kV, 30 kVA single phase transformer was designed and constructed. During manufacturing process, the polarization current and depolarization current of the transformer insulation were measured for 6 case studies as follows: 1) paper insulation between iron core and low voltage (LV) windings before dry and vacuum in the oven, 2) paper insulation between LV and high voltage (HV) windings before dry and vacuum in the oven, 3) paper insulation between iron core and LV windings after dry and vacuum in the oven, 4) paper insulation between LV and HV windings after dry and vacuum in the oven, 5) oilpaper insulation between iron core and LV windings after dry and impregnation process and 6) oil-paper insulation between LV and HV windings after dry and impregnation process. Then, PDC test results were analyzed. It was found that the moisture content in the paper insulation clearly affected the capacitance at power frequency, and PDC shapes. Besides, the impregnation process had a good effect on the capacitance ratio and dielectric dissipation factor. Moreover, the current difference of dry paper insulation between HV and LV windings presented the nonlinear characteristic both before and after impregnation process.
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    Dielectric response analysis of mineral oil immersed transformer, Natural Ester(FR3) immersed transformer, and palm oil immersed transformer
    (2019-06-01)
    Maneerot, Sakda
    ;
    Nimsanong, Phethai
    ;
    Siriworachanyadee, Jompatara
    ;
    Leelajindakrairerk, Monthon
    ;
    Jariyanurat, Kittipod
    Currently alternative liquid insulation such as natural ester (FR3) is widely used as distribution transformer insulation because it provides outstandingly dielectric characteristics and natural friendly including highly affordable fire safety. Besides, palm oil is interesting liquid insulation for such transformers because of its distinguish dielectric properties. To analyze the dielectric properties of insulating material, polarization and depolarization current (PDC) measurement is one of the widely accepted non-destructive test technique. This paper presents the dielectric response analysis for the insulation system of a mineral oil immersed transformer, a natural ester (FR3) immersed transformer, and a palm oil immersed transformer by analyzing PDC test results. Three identical single phase transformers with 22kV/460V 30 kVA rated were designed and constructed. The first transformer was fully filled with mineral oil. The second and the third transformer was fully filled with natural ester (FR3) and palm oil respectively. After finishing the construction process, PDC measurement technique was applied for these transformers. The PDC measurement were performed for three case studies as follows: 1) dielectric response for the insulation between high voltage winding and low voltage winding, 2) dielectric response of high voltage winding insulation and low voltage connected to ground 3) dielectric response of high voltage and low voltage winding insulation by which the high voltage lead was connected to the low voltage lead. From the test results, it can be concluded that the dielectric response of the insulation system of the mineral oil immersed transformer was obviously different compared with that of the natural oil (FR3) immersed transformer and the palm oil immersed transformer. Moreover, the PDCs obtained from the tests were also analyzed and reported in this paper.
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    Dielectric Properties of Resin Rich Stator Coil of High Voltage Motor during Processing
    (2018-11-14)
    Boonsathitthavorn, S.
    ;
    Phumipunepon, N.
    ;
    Kitcharoen, P.
    ;
    Pattanadech, N.
    One of the non-destructive test methods commonly used to characterize the electrical properties of power equipment is polarization and depolarization current testing. The objective of this paper is to study of the change of dielectric properties during the manufacturing stages of a stator coil used in 6.6 kV 260 kW motor. There were five steps to manufacture the resin rich stator coil. The first step, the copper coil was wound around by NOMEX paper. Then the slot portion of the stator coil was wound by KREMICAL tape as the second process and by the conductive tape as the third process. Then, the insulation and conductive layer of the stator coil were pressed and cured at 160°C for one and a half hour as the fourth process. The pressing and curing will combine the multi insulation to be homogeneous insulation of the stator coil. The final step, the end winding portion was wounded by Filosam tape and polyester tape. The polarization and depolarization currents were measured and recorded after finishing each manufacturing process. From the test results, the polarization currents and depolarization currents obtained from each step were clearly different. Then the polarization and depolarization currents, conduction current and capacitance of the test results were analyzed and reported in this paper.