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Analysis and Comparison of Characteristics for Offline PD Measurements in Turbo-Generators at Different Test Time Intervals
(2022-01-01)
Dorkmai, K.
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Pannil, P.
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Tattiwong, K.
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Maneerot, S.
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Suksawat, D.
Partial discharge (PD) measurement is widely used for the condition assessment of high voltage equipments. It is a tool to detect the localized discharges occurring in the weakness point sites, which causes deterioration that can lead to failure. Hence, it is essential to diagnose the PD behavior to prevent the consequent failure which maybe takes place. This paper presents an analysis of the offline PD measurements performed on the stator winding insulation system of three turbo-generators which consist of a hydrogen-cooled generator rate of 211.75 MVA, 15.75 kV, and two air-to-water heat-cooled generators which the same rate of 50.8 MVA, 11.5 kV, which were located in the power plant. Firstly, the offline PD measurements of these generators have been energized to the star point side and the high voltage coupling capacitor is installed on the high voltage terminal side, according to IEC 60034-27-1. Additionally, the test voltages were applied to the test object with a step voltage profile. To analyze the PD behaviors of the stator winding insulation, the PD characteristics such as the PD pulses, PD magnitude, and phase-resolved PD (PRPD) patterns were monitored and recorded. Besides, the effect of applied test voltage-time, i.e., 1, 3, and 5 minutes, on such characteristics were reported and compared. Finally, the PD behavior of the stator winding insulation of these generators showed clearly different results for PD measured at different recording times. The highly fluctuating PD magnitude and PD pulse shape at the initial duration of the measurement, and then gradually decreases to convergence to a stable charge magnitude as the test-time increases.
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The Study of Polarization and Depolarization Current Measurements on Service-Aged 22 kV XLPE Underground Cables with Presence of Water Trees
(2022-01-01)
Udomluksananon, P.
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Kunakorn, A.
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Maneerot, S.
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Bunlaksananusorn, C.
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Pannil, P.
This paper represents the condition assessment of service-aged 22 kV XLPE insulated underground cables. From the investigation, the water trees were detected in the insulation layer. The visual inspection of underground cables reveals the presence of copper carbonate contaminated on the copper tape layer. Some underground cables have the discontinuity of the copper tape layer. To evaluate the insulation condition of the underground cables, the polarization and depolarization current (PDC) measurements were performed on both the service-aged and the new (or unused) cables. The underground cables to experiment with the length of insulation screen equal to 1 m were prepared. In this research, the PDC measurements were performed on different aspects, i.e., the testing voltages (600 V, 800 V, and 1000 V), the testing positions, the effect of the discontinuity of the copper tape layer which occurred during service, the influence of the presence of copper carbonate, and the influence of water trees in XLPE cables. The dielectric response of the underground cables by using polarization and depolarization current measurements can diagnose the problems in service-aged underground cables, but this paper needs more test data for accurate interpretation.
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Frequency Domain Spectroscopy of Pressboard Impregnated with Natural Ester under Thermal Stress
(2022-01-01)
Chumpiboon, K.
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Vittayakorn, W.
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Kittikhuntharadol, Y.
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Maneerot, S.
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Pattanadech, N.
One of the most popular insulating liquids is mineral oil, which is used in many high-voltage apparatuses, especially in transformers. For a few decades, the concept of the use of alternative insulating liquids has been presented. Natural ester is a vegetable-based insulating liquid. Pressboard is a type of electrical insulation paper made of cellulose. Frequency Domain Spectroscopy (FDS) has been used to assess the insulation characteristics such as oil-impregnated paper. In this paper, the FDS of pressboard impregnated with natural ester under thermal stress and pressboard impregnated with natural ester were studied. In the experiment, the pressboard test specimens were heated at 100 degrees Celsius in a vacuum oven for 48 hours to reduce the moisture. Then, the test specimens were impregnated with natural ester for 0, 8, 16, and 24 hours. After that, they were simulated with thermal stress by heating at 150 degrees Celsius in a vacuum oven for 0, 30, and 90 days. To analyze their dielectric integrity, FDS was performed by DIRANA. The test cell for solid insulation testing, according to JIS C2111 was prepared and used for the FDS experiment. The result shows that the characteristics of the natural ester-impregnated pressboard that had been subjected to thermal stress were slightly different when compared with the same impregnation time of the pressboard.
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Estimating conductivity and interfacial polarization loss factors of oil-paper insulation for power transformers
(2020-07-01)
Nimsanong, P.
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Maneerot, S.
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Pattanadech, N.
This paper proposes the method for categorizing the estimating conductivity and interfacial polarization loss factors of the oil-paper insulation. The simulated dielectric responses in the time domain of oil-paper insulation with various conditions were studied. Lumped equivalent circuit, so-celled extended Debye model, for modeling the oil-paper insulation obtained from simulated results, were estimated by using ohm's law for conduction current, and a curve fitting technique with exponential functions applied to the depolarization current idep(t). The complex capacitance, conductivity loss factor, and interfacial polarization loss factor of the insulation system in the frequency domain from 0.01 mHz to 1 Hz can be calculated.
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Evaluation of loss factor of mineral oil and alternative fluids with temperature normalization
(2020-07-01)
Maneerot, S.
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Nimsanong, P.
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Pattanadech, N.
This paper proposes the evaluation of loss factor of mineral oil and alternative fluids the natural ester (FR3) with temperature normalization. The oil samples (i.e., mineral oil, natural ester, and palm oil) were prepared for experiments. The oil samples were dried at 70 °C under 200 mbar in the controlled temperature oven and then cooled down to ambient temperature. The moisture contents of the oil samples were measured according to ASTM D1533. The test cell, according to IEC61620, was employed in these measurements. The polarization currents, ipol(t), of such oil samples under electric field stress of 0.2 kV/mm with a temperature range from 30 to 70 °C were measured, The test results are summarized in this paper. The step response measurement results were analyzed for conductivities, permittivity, and loss factor value. It was found that increasing temperature causes increasing conductivities but decreasing permittivity of oil samples.
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A fast and accurate dielectric response measurement for transformer moisture assessment and remaining life estimation
(2020-07-01)
Nimsanong, P.
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Maneerot, S.
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Pattanadech, N.
This paper proposes a fast dielectric response measurement for transformer moisture assessment and remaining life estimation. The dielectric response measurements in the time domain for in-service transformers with various insulation conditions categorized into four levels, i.e., excellent, good, fair, and poor conditions, were investigated. The dielectric response measurements were investigated by polarization and depolarization time for 100, 500, 1000, and 3000 seconds. For the dielectric response of oil-paper insulation of such a transformer, the conductivity of oil in ducts and moisture content in paper can be estimated by using the curve fitting technique in advanced evaluation tool in PDC-Analyzer-1MOD. Besides, significant parameters, i.e., dc resistance, insulation resistance, polarization index, tan δ of oil, complex capacitance, conductivity and interfacial polarization loss factors in the low-frequency range, the paper remaining life time, and bubbling inception temperature were evaluated with a single dielectric response measurement result. To confirm the PDC measurement test results, other insulation test techniques were performed. The dielectric response results obtained from PDC measurement were compared with the results from the other mentioned techniques. It was found that the polarization time for 3000 seconds and depolarization time for 500 seconds is suitable for assessing the moisture content in paper and other dielectric parameters comparatively.
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Studies of Electrical and Thermal Characteristics of Natural Ester Immersed Transformer Compared with Mineral Oil Immersed and Palm Oil Immersed Transformer
(2018-11-14)
Maneerot, S.
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Jariyanurat, K.
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Nimsanong, P.
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Bunlaksananusor, C.
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Kunakorn, A.
This paper represents studies of electrical and thermal characteristics of natural ester immersed transformer compared with mineral oil immersed and palm oil immersed transformer by designing and constructing three single-phase transformers with rated 400/1000V 10kVA, the first transformer used mineral oil, the second transformer used natural ester, and the last one used palm oil, for studying about electrical properties, thermal properties and chemical properties under different types of liquid insulation in each transformer. First of all, three types of liquid insulation were tested with many item such as dielectric breakdown strength according to IEC 60156, dielectric dissipation factor following to ASTM D924-99. Besides, dielectric breakdown strength of impregnated pressboard were also investigated following to IEC 60243-1. Moreover, the chemical properties of the insulations were tested for some properties such as moisture content in accordance with ASTM D1533-00, interfacial tension according to ASTM D0971-99, acidity according to ASTM D974-02. After that, transformers were operated at 100 % of designed rated with inductor load for four months by which the temperature, current, and voltage were recorded every hour. Every two months, the liquid insulation was sampling from each transformer to be investigated. From the test results, they can concluded that natural ester are the alternative liquid insulation for using instead of mineral oil. In part of palm oil, it has good properties but it has the weak points about dielectric dissipation factor and acidity which are higher than the others.
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Different Moisture Contents of Pressboard Effect on Electrical and Chemical Characteristics of Liquid Insulation
(2018-11-14)
Jongvilaikasen, K.
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Pumyoy, S.
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Jariyanurat, K.
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Maneerot, S.
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Pattanadech, N.
This paper represents electrical and chemical characteristics of mineral oil samples obtained from the test cell containing the pressboards with different moisture contents immersed in the mineral oil. The pressboards with the dimension of 100×l00 mm and the thickness of 12.8 mm were used in the experiment. The pressboards were divided into two groups. The first group contained the moisture content of 3 % while the second group contained the moisture content of 7%. Then, four pressboards of each group were inserted between plane to plane electrodes contained in the test cell by which one electrode was energized by 12 kV AC; another electrode was grounded. Three identical mineral oil samples were taken from the test cells after the pressboards and mineral oil had experienced by electric field stress for 5, 10, and 15 days respectively to investigate on the changing of electrical and chemical properties of the mineral oil. The tests were performed with each oil sample on the topics of breakdown voltage, power factor, moisture content, acid number, interfacial tension and dissolved gas analysis. From the experiments, the electrical and chemical characteristics of the mineral oil with the pressboards containing different moisture contents were clearly different.
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Effect of Contaminant on Breakdown Characteristics of Mineral Oil and Palm Oil
(2018-11-14)
Maneerot, S.
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Pattanadech, N.
This paper details an investigation of the effect of contaminant particles at several different temperatures on the 50 Hz AC breakdown voltage of two dielectric liquids - mineral oil and palm oil. The liquids in the test cell used were comprised of various combinations of the following: a) three particle types (cellulose, spherical iron and copper) of approximately 20 μm diameter, b) three contaminant concentrations i.e.0.001% m/V, 0.003% m/V and 0.005% m/V, and c) four liquid temperatures i.e. 25°C, 50°C, 70°C, and 90°C. were investigated with mushroom shaped electrodes in accordance with IEC 60156. The results obtained in this test process showed that the presence of the added particles in the tested dielectric liquids consistently provided a reduction in breakdown voltage, and that the reduction factor varied according to particle type, particle concentration, liquid type, and liquid temperature, and on whether they consisted of cellulose insulation material or copper and iron conducting material summarizing the test results, it was shown that higher contaminant concentration produced lower breakdown voltages, that the addition of copper particles had the most significant effect on reducing breakdown strength, and that the greatest reduction of breakdown strength was measured in the contaminated mineral oil test samples at a test temperature of 70°C.
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Effect of contaminant on breakdown characteristics of mineral oil and commercial natural ester
(2018-07-02)
Maneerot, S.
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Pattanadech, N.
This research paper presents the results of an investigation into the effect produced by the addition of various contaminant particles at various temperatures on the 50 Hz AC breakdown voltage of mineral oil and natural ester. The test cell apparatus employed mush room-shaped electrodes according to IEC 60156 and the various liquid samples which were prepared for the tests contained various combinations of the following: a) three different contaminant particles (cellulose, spherical iron and copper) of approximately 20 µm diameter, b) three different concentrations of contaminant particles (0.001% m/V, 0.003% m/V and 0.005% m/V) and c) four different temperatures for the test cell liquids (25°C, 50°C, 70°C, and 90°C). The test results show that the presence of the added particles in the tested dielectric liquids resulted in a reduction of breakdown voltage, with the 4 major determinants of the reduction being a) change in particle type, b) change in particle concentration, c) change in liquid type, and d) change in liquid temperature. The most important findings from the testing and analysis conducted are as follows: 1) higher contaminant concentrations resulted in lower breakdown voltages, 2) the addition of copper particles had the most significant effect on reducing breakdown strength, and 3) that the largest decrease in breakdown strength was recorded during testing of the contaminated mineral oil test samples and the FR 3mineral oil test samples at 70°C.

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