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Partial Discharge Pulse Propagation in Coaxial Cable
(2022-01-01)
Juntasorn, T.
;
Chancharoensook, P.
;
Pattanadech, N.
In the past, Coaxial cable was the signal cable used to transfer computer data. However, coaxial cables are now being modified for use in the high voltage coaxial cables to increase the security of power transmission in various areas. In addition to increased security, there is also an issue of stability maintenance and many perspectives as well. Because the cable that used to be utilized is still insulated. Therefore, Partial Discharge (PD) can still happen in the electrical system. This paper presents the PD propagation within the coaxial cable simulated via PSCAD/EMTDC program and carried out with RG-58 coaxial cable in a laboratory by testing the propagation of the PD pulse according to the conditions of different cable distances. From the experiment, the calculations will be reversed by considering on the differences of the time manner that PD pulse flows on the cable. The time reference point that the research studied has 2 points which are Peak to peak and Time of arrival(TOA). The comparison between simulation and experiment indicated the similar results with slight discrepancies caused by factors that can be accepted. TOA has smaller errors comparing with the peak to peak point showing that PD pulse flowing on the cable is attenuation and dispersion to the tailing wave part. That's the reason using Peak to Peak is a time reference point that has more errors. A thorough study of PD propagation is useful for in-depth analysis to locate the PD source accurately. As a result, the defect will be resolved on the spot.
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Insulation Diagnosis of Distribution Class Metal Oxide Surge Arrester Using Polarization and Depolarization Techniques
(2022-01-01)
Turatham, S.
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Pannil, P.
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Maneeroj, S.
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Methavithit, W.
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Zinck, M.
Imperfection of metal oxide surge arrester (MOSA) becomes a factor that affects the power supply quality on medium and high voltage networks. Understanding the coordination of MOSA insulation systems helps describe their failure. This paper presents the analysis of the dielectric response of imperfect MOSA from the factory using polarization and depolarization techniques. The experiments were taken on 21 kV and 24 kV MOSA samples which were validated by testing topics, i.e., the reference voltage, voltage-current characteristic curves, and partial discharge (PD). Polarization and Depolarization Current (PDC) was measured after 21 kV MOSA samples had taken PD testing and 24 kV MOSA samples had taken reference voltage testing. Resistivity, capacitance, and polarization index were interpreted for insulation diagnosis. The importance of non-destructive electrical diagnostics based on polarization methods is validated by PDC test results and is highlighted in detail in this paper. Finally, the results of different PDC were compared and discussed.
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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 Application of Polarization and Depolarization Current on the Large Turbo-generators
(2022-01-01)
Jeenmuang, S.
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Pannil, P.
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Mongkolsatitpong, S.
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Trakuldit, S.
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Wuti, V.
This paper represents the application of the polarization and depolarization current (PDC) measurement of the stator winding insulation of two large turbo-generators, which have the same rate of 50.8 MVA, and 11.5 kV. The PDC measurements were conducted on the stator winding insulation of both generators by using two different test circuits i.e., (individual) phase-to-ground insulation and interphase insulation circuits. Then, the PDC results of the two investigated generators were compared. To evaluate the phase-to-ground insulation condition of the stator winding insulation of both generators, the conventional dielectric parameters in the time domain, such as polarization index and insulation resistance, were also studied. Moreover, the PDC results in the time domain were converted into the dielectric dissipation factor in the frequency domain to allow the analyzing the phase-to-ground insulation of the stator winding of the generators. The PDC results of the phase-to-ground insulation circuits of both investigated generators illustrate the bent shape of PDC results which were affected by the influence of the stress control coating resulting in a high value of the Polarization index. Besides, the PDC results of the interphase insulation circuits of the first investigated generator illustrate the polarity reversal (or Anomalous current) of both PDC, while the second investigated generator illustrates the non-polarity reversal of both PDC. The polarity reversal of the PDC results of the interphase insulation was due to the dielectric loss of the interphase insulation is a lower influence when compared with that of phase-to-ground insulation.
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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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The Effects of Coupling and Grounding on the Partial Discharge Pulse Propagation in the Underground Cable
(2022-01-01)
Rojanasunan, W.
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Chancharoensook, P.
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Jeenmuang, S.
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Mongkolsatitpong, S.
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Pattanadech, N.
When a Partial Discharge (PD) pulse propagates through a cross-bonded (CB) power cable system, such pulse undergoes attenuation and dispersion along a cable. Moreover, the coupling effect occurs when a PD pulse propagates in HV cable joints and CB link lines. This paper aims to study the effects of coupling phenomena and groundings on the PD pulse propagation. The experiments were divided into 3 parts: the experiment for attenuation in the conductor and ground wire, the experiment for coupling effect, and the experiment for different grounding configuration. The experimental setups used a 30 m length of new 33 kV XLPE insulated cable. PD pulses was obtained from a PD calibrator, and the pulses are detected by Radio Frequency Current Transformer at various positions. The knowledge gained from this research should be useful for a deep understanding of pulse propagation and PD source localization in CB power cable systems.
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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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Design of a Multi-channel PD Detector for Improving Common-mode Noise Reduction Performance in Measuring and Monitoring System
(2022-01-01)
Tongchim, N.
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Phansiri, N.
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Jeenmuang, S.
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Pattanadech, N.
This paper deals with the design and implementation of a multi-channel partial discharge (PD) detector to improve noise reduction performance in the designed PD measuring and monitoring systems. Basically, the noise may be generated by the unexpected ground loop of the PD measuring system due to several coupling devices (CDs) being connected to the PD measuring instrument. In this paper, the signal-to-noise ratio (S/N ratio) was enhanced by using a bandpass filter and a programmable gain amplifier to filter the undesired noises and amplify the PD signal acquired in the CD. Besides, the category 7 cable (CAT7 cable) was utilized as a transmission line to transmit signals into the PD measuring instrument. This CAT7 cable with the grounded shield is comprised of 4 pairs of cables, i.e., the DC power supply cable, the PD signal cable, the test voltage signal cable, and the control signal cable used to connect between the coupling devices and the measuring instrument. Furthermore, at the input side of the measuring instrument, the Differential Receiver Amplifier was utilized to reduce the common-mode noise generated from the coupling device. Application of the proposed technique, the battery power supply, and the sophisticated isolation technique, e.g., fiber optic cable system of the active coupling device, are not needed. Furthermore, the designed PD detector was a simple and cheap price, including significant noise reduction.
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A locating diagnosis of partial discharge on cross-bonding ground system
(2021-05-19)
Inwanna, W.
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Mongkolsatitpong, S.
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Chancharoensook, P.
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Pattanadech, N.
At the present, Thailand has turned the attention to Underground Cable (UC) systems and trends to use it more to safety, stability and reliability of electrical system. However, one problem that can affect to this electrical system is the Partial Discharge (PD) problem. Most of PD problems are caused by incomplete installation, maintenance reason and insulation degradation on the weakest part, especially cable joint. This paper proposes a method of analysis to locate the PD source in UC systems with Cross Bonding (CB) focus on cable joints. This work has carried out in laboratory on CB system model using 50ohm R58 coaxial cable instead of underground cable. The PD detection technique according to IEEE 400.3 standard with a RFCT sensor to refer the appropriate signal. This work uses a PD diagnostic device that can filter noise from the PD groups and separate groups of PD for greater analysis accuracy. To determine which cable joint is PD source and to be able to fix it on the spot. The PD signal analysis are performed by using time of arrival method considered together with the characteristics and the polarity of the PD pulse.
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Application of Polarization and Depolarization Current Measurement for Rotating Machine Insulation Analysis
(2021-01-01)
Pattanadech, N.
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Nimsanong, P.
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Worthong, T.
Rotating machine is a vital asset of the power plants. For the motors and generators in service, the stator winding insulation is generally operated under thermal, electrical, ambient, and mechanical stresses. The combination of these stresses causes insulation degradation that can lead to early aging or severe damage and, finally, the failure of such machines. The failure of rotating machines may result in immense financial loss and other aspects. Polarization and depolarization current (PDC) measurement has been introduced as one of the time-domain dielectric spectroscopy test techniques applied for insulation condition testing. This paper represents the application of PDC measurement to evaluate the insulation for the stator bars/coil insulation experienced with various kinds of stresses. Moreover, the PDC field test of generators and high voltage motors used in the power plants is introduced. From the experiments, the dielectric parameters obtained from PDC measurements are clearly useful parameters to evaluate the electrical insulation of such rotating machines.

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