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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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Study of asymmetrical leakage currents of metal oxide surge arrester due to multiple current impulses
(2020-09-13)
Chuayin, C.
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Zinck, M.
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Kunakorn, A.
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Pattanadech, N.
This paper presents the study of asymmetrical leakage current of metal oxide surge arrester (SA) after being tested with multiple current impulses. The study is made using 2 SAs specimens of 21 kV rated voltage, 5 kA nominal discharge current. The experiment is divided into 4 steps; 10 shots of positive discharge current impulses, reference voltage measurement, 5 shots of negative discharge current impulses and reference voltage measurement. Initial conditions of the SAs are assessed prior to the testing: temperature measurement, 1 mA reference voltage and resistive leakage current at rated voltage. Then, both specimens are applied current lightning impulses at 200% of rated discharge current (10 kA) and the temperature is measured after. The lightning current impulse is 8/20 µs waveform and the duration between each impulse is 10s. Prior to the application of multiple current impulses, the difference of resistive current peak amplitude of specimen 1 and 2 were 3% and 0.95% respectively. Following positive current lightning impulses, the value changed to be 71.245% and 72.75% respectively. The specimens were then left to cool down in the room temperature for 1 day. After application of negative current lighting impulses, difference of resistive leakage current of specimen 2 changed to be 1.99%, and specimen 1 broke down after 2 impulses. Asymmetrical leakage current phenomena caused by the impulse current may negatively affect the breakdown characteristic of the SA which should be relevant with the collected charge inside the SA material, however, the opposite polarity of the applied impulse currents may eliminate such problem.
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Polarization and depolarization current characteristics of thermally stressed stator bars
(2019-07-01)
Pattanadech, N.
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Srichuen, N.
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Wang, C.
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Kaewdee, N.
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Poungpat, T.
Polarization and depolarization current (PDC) measurement was used in this research to investigate the insulation integrity of stator bars. This method is non-destructive testing. This paper presents the PDC analysis of thermally stressed stator bars divided into two main groups. The first group was heated at 100^{\circ}C and the second group was heated at 130 ^{\circ}C for 36 hours. After 12, 24 and 36 hours of heating process, PDC measurement of each test specimen was performed. PDC test results including capacitance ratio and dielectric dissipation factor were analyzed and reported.
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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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Dielectric Properties of Mineral Oil-based Nanofluids using Zinc Oxide Nano-composites for Power Transformer Application
(2018-11-14)
Muangpratoom, P.
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Kunakorn, A.
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Pattanadech, N.
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Vittayakorn, W.
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Thungsook, K.
This research paper describes and analyzes various experiments designed to investigate the dielectric properties (at a series of pre-determined test temperatures and % moisture content) of mineral oil-based nanofluids produced by the incorporation of zinc oxide (ZnO) powder (of mean diameter less than 100nm) into a standard mineral oil, with the surfactant sorbitan mono-oleate (Span 80) added to modify the surface of the nanoparticles in all but the control sample. Five different nanofluid test samples (one control sample and four modified samples) based on the standard mineral oil were produced for testing: 1) a control sample containing no Span 80 and no ZnO, 2) a modified sample with Span 80, and ZnO volume fraction of 0.01 %, 3) a modified sample without Span 80, and ZnO volume fraction of 0.01 %, 4) a modified sample with Span 80, and ZnO volume fraction of 0.03%, and 5) a modified sample without Span 80, and ZnO volume fraction of 0.03 %. In addition, the five liquid samples above were tested to determine AC breakdown voltage at seven different temperatures in the range of 35°C to 90°C. The test circuit was set up in accordance with IEC 60156 using a sphere-sphere electrode configuration with gap spacing of 2.5 mm. Several significant results were obtained from the investigation. Firstly, ZnO nanoparticles had a positive effect on all the test solutions in which they were used. Second, a positive relationship was confirmed between breakdown voltages, temperature rise. Third, a negative correlation was established between higher concentration of ZnO nanoparticles and breakdown voltage. Fourth, the use of surfactant proved to have both positive and negative effects on breakdown voltages.
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Effect of different temperatures on AC breakdown voltage of mineral oil based nanofluids
(2018-07-02)
Muangpratoom, P.
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Kunakorn, A.
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Pattanadech, N.
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Vittayakorn, W.
This study seeks to make improvements in the dielectric properties of transformer oil through the application of nanotechnology. In particular, two nanoparticles are examined experimentally: titanium dioxide (TiO<inf>2</inf>), and barium titanate (BaTiO<inf>3</inf>). Each has a mean diameter not exceeding 100 nm. The nanofluid samples comprised the nanoparticles mixed into the mineral oil through differing procedures. In the first case, the transformer oil was combined with 0.01% volume fraction of the nanoparticle; the second sample used 0.03% volume fraction of the nanoparticle volume fraction. A magnetic stirrer was then used for sample dispersal before an ultrasonic dispersant method was used on the prepared nanofluids so that sample homogeneity could be assured. The experimental process then recorded the AC breakdown voltage characteristics for the liquids through a range of temperatures from 35°C up to 90°C. The findings indicate that the AC breakdown voltages for mineral oils containing nanoparticles exceed those for unmodified mineral oils.
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Frequency dependence parameter analysis of underground cables with and without joint
(2018-06-29)
Nimsanong, P.
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Kunakorn, A.
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Pattanadech, N.
This paper represents the dielectric investigation of XLPE power cables with and without cable joint (premolded joint) by using polarization and depolarization current (PDC) measurement. To investigate the polarization phenomena of the underground cable (case 1) and the underground cable with the premolded joint (case 2), the XLPE cables with the cross-section area of 240 mm<sup>2</sup> and 5 m long with rate voltage of 12/20(24) kV with and without premolded joint were used in the experiment. In this research work, the DC voltage of 1,000V was applied to insulation system for measuring polarization current, i<inf>pol</inf>(t). Then, suddenly disconnected the DC applied voltage source to short circuit the tested cable to measure depolarization current, i<inf>dep</inf>(t), In case 1, the PDC measurement was only for 100 seconds due to its homogeneous insulation of XLPE cable; only conduction current and interfacial polarization current with short relaxation time existed. In case 2, the PDC measurement was done for 2,000 seconds. In this case the polarization current was from XLPE cable mentioned and the interfacial polarization current from the barrier between XLPE cable and cable joint. From the experiment, the frequency dependence of the complex capacitance and dielectric dissipation factor of the underground cable and the underground cable with the premolded joint were analyzed. It is found that the trend of real part of the complex capacitance and the conduction loss of both case studies is not much different. However, the trend of imaginary part of the complex capacitance and polarization loss of both case studies is clearly different. Two peaks of imaginary parts of complex capacitance and polarization loss of the underground cable with joint is from XLPE and the junction of XLPE and joint.
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Analyses of rogowski coils for partial discharge measurement
(2017-10-27)
Chonpathomphikunloed, W.
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Paophan, B.
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Kunakorn, A.
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Yutthagowith, P.
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Leelachindakrairerk, M.
This paper presents analyses of toroidal air core Rogowski coils (RCs) with self-integrator for partial discharge (PD) measurement. The RC is the electromagnetic transfer device for measuring fast current pulse. The RC has linear characteristic and no saturation due to the air core. There are four configurations of the RCs in the consideration in this paper. From each designed RC, inductance and turn of each RC was determined almost the same values but different configurations. To analyses of the developed RCs, those RCs were employed to measure partial discharge current with various artificial charge levels from 10 pC to 50 pC. Also, comparison of the PD signals measured by the developed RCs and low inductive shunt resistor was carried out. From the experimental results, the best developed RC has the highest sensitivity or lowest background noise. It composes of two copper winding wound in the different directions. The first winding is wound around the toroidal air core and the other winding is wound with the opposite direction of the first winding. The both winding are crossed at the inner of the toroidal core. This RC also has wind frequency bandwidth for PD detection. The developed RC is an attractive sensor in partial discharge measurement.
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Implementation of a Rogowski's coil for partial discharge detection
(2017-01-30)
Paophan, B.
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Kunakorn, A.
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Yutthagowith, P.
This paper presents the implementation of a Rogowski's coil for a special purpose on partial discharge detection. A numerical integrator and a filter are used with the Rogowski's coil to calculate partial discharge current and apparent charge. Implementation of the Rogowski's coil in a laboratory, such as a unit step response, linearity of the measurement, and partial discharge detection, is performed. It is found that the partial discharge current and the apparent charge which are detected by the Rogowski's coil are agreed well with the measurement from the conventional method.
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Fast, simple, accurate fundamental frequency estimation
(2016-01-01)
Yutthagowith, P.
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Kunakorn, A.
This paper presents a simple, fast, accurate fundamental frequency estimation method with good resistance to harmonics and noise. In the proposed method named the accumulated sum method (ASM), a new data sample of a measured signal is constructed using the summation of the samples in the original sampling data. The effects of harmonics and noise are mitigated by the proposed algorithm. Performance comparison of the proposed method, the method based on the discrete Fourier, and the accurate method named shifting window average method (SWAM) is demonstrated by using simulated signals with varied fundamental frequency from 45 Hz to 65 Hz and with additive harmonics and noise. In the simulation, the sampling frequency and the number of samples is fixed to 5000 samples/s and 100, respectively. From the simulation results, the proposed method exhibits good immunity to harmonics and noise. Due to its low required processing effort and high precision, this method is a good candidate for online frequency estimation in the presence of harmonics and noise signals.

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