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Dielectric Frequency Response Analysis of 230 kV Service Aged OIP and RIP Bushings: Case Studies
(2025-01-01)
Pattanadech, Norasage
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Jeenmuang, Siwakorn
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Ostria, Elmer
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Suksagoolpanya, Suthat
Transformer bushings are critical components that enable current to pass through the transformer enclosure while providing insulation between the high-voltage conductor and the grounded housing. A failure in the bushing could potentially result in transformer failure. This paper presents case studies on the evaluation of 230 kV Oil-Impregnated Paper (OIP) and 230 kV Resin-Impregnated Paper (RIP) bushings using Dielectric Frequency Response (DFR) analysis. The bushings investigated in this study were service-aged units removed from the field. For the 230 kV OIP bushing, the paper insulation was peeled off starting from the outermost layer. This allowed for DFR testing on individual insulation sections. The results indicated moisture absorption and provided information on the moisture distribution within the paper insulation. Furthermore, a 230 kV RIP bushing suspected of having poor contact between the outermost foil layer and the test tap connection was also investigated. The DFR results from this case revealed the observable impact of such connection issues on the DFR test. In summary, DFR analysis has proved that it is a very useful technique for testing and diagnosing various common bushing degradation mechanisms that can lead to severe failure of the bushings and the transformers.
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Study of Problem and Effect Mitigation Technique of Unbalance Capacitance in 500 kV Single Phase Transformers
(2024-01-01)
Suksagoolpanya, Suthat
;
Pattanadech, Norasage
This article presents the study of the effect of unbalanced stray capacitance in single-phase 500 kV power transformers and establishes the mitigation technique. The power transformers were operated in Wang Noi Substation for transmitting the electrical power. There are 3 units of single-phase power transformer. Previously, a transformer of phase B failed after being serviced for several years. Thus, the new power transformer was ordered instead of the failed one. However, once the new system had been operated, the hotspots at the surge arrester of tertiary winding (22 kV) were found and the unbalance of phase voltages was observed, resulting in overvoltage as a root cause of the problem. Once a thorough investigation was done, it was found that there was an effect of unbalanced stray capacitance between tertiary winding and ground core since the new power transformer has some different designs compared with the remaining. Hence, the mitigation technique was performed by adding the capacitor parallel to the tertiary winding until the voltage balance was achieved. Simulation with the PSCAD program was performed to determine the optimum value for additional capacitors, i.e., voltage balance, using an iterative method. In this article, the capacitors used for additional were capacitor voltage transformers, which have been installed. As a result of the troubleshooting, the voltage at the 22 kV bus was more balanced as well as not causing overvoltage, and the hotspots at the surge arrester of tertiary winding were not detected resulting in gaining the stability and reliability of using these transformers.
1
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Dielectric Response Analysis on Artificial ZnO Surge Arrester Degradation Using Polarization and Depolarization Current Based Method
(2024-01-01)
Chuayin, Chaitawat
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Pattanadech, Norasage
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Zinck, Matthieu
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Methavithit, Winai
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Suksagoolpanya, Suthat
This paper presents an alternative method to investigate the problems of surge arrester based on dielectric response analysis. The study is made using a 21-kV, 25-kA station class surge arrester to be test specimens, the former Zinc Oxide (ZnO) varistors inside were removed and replaced with artificial degraded ZnO varistors (impulse ageing, tracking problems, moisture ageing under wet and dry condition and cracking ZnO varistors). The experiments are carried out by Polarization and Depolarization Current (PDC) measurement. The test result analyses were proposed in terms of both the time domain and frequency domain. The measurement results show significant differences in dielectric response characteristics between healthy surge arresters and aged surge arresters. In addition, the dielectric response analysis tends to characterise the problems of surge arrester i.e., conduction problems and polarization problems which will be further discussed in this paper.
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Investigation of Leakage Current Behavior Based on Current Symmetry Due to Multiple Positive and Negative Impulses
(2024-01-01)
Chuayin, Chaitawat
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Pattanadech, Norasage
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Zinck, Matthieu
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Suksagoolpanya, Suthat
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Sontayananon, Nattawittayawud
The failure of Metal Oxide Surge Arrester becomes a major issue of the utilities. A strategy which is commonly utilized to diagnosis the problems is leakage current measurement in any terms of current e.g., total leakage current, resistive leakage current, capacitive leakage current. This paper aims to study the symmetrical behavior of the leakage current caused by positive and negative multiple lightning currents. The asymmetrical leakage currents were observed with 24 kV, 10kA commercial surge arrester which divided in to 2 groups. The experiment was conducted by measuring the leakage current at rated voltage and 1-mA reference voltage before applying a prepare of 5 shots of 10-kA positive and negative standard impulse current (8/20 μs) to groups I and II individually. After that, more 5 shots were applied to the specimens once more. The resistive leakage current at rated voltage and 1-mA reference voltage measurement were then performed after each impulse current application. Hence, groups I and II were applied with 15-shots multiple negative and positive impulse current respectively. The resistive leakage current at rated voltage and 1-mA reference voltage were performed after each 5 shots of impulse current. The experiment results show that (1) applying multiple impulse currents will make the asymmetrical leakage current. (2) positive polarity multiple impulse current creates asymmetry more than negative polarity. (3) negative polarity will increase the positive peak of leakage current and vice versa for positive polarity.
1
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Application of Dielectric Spectroscopy Analysis to Identify Unhealthy Surge Arrester by Using PDC Measurement Technique
(2024-01-01)
Chuayin, Chaitawat
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Pattanadech, Norasage
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Zinck, Matthieu
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Suksagoolpanya, Suthat
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Methavithit, Winai
At present, power grid asset management is becoming a topic of greater interest, as is the condition-based diagnosis of surge arresters to ensure power supply reliability on medium and high voltage networks. Extensive studies on failure mode and arrester forensics have been conducted and are continuing, investigating with various techniques, to predict and investigate their failures. This paper presents the investigation of dielectric spectroscopy of 21-kV MV surge arresters to identify unhealthy problems using Polarization and Depolarization current (known as PDC) measurement techniques, four artificial problems (which consist of lightning, cracking, moisture ingressive, and tracking problems) were simulated on surge arresters. With the PDC measurement, it is allowed to be interpreted in both the time domain and frequency domain. The dielectric parameters will be further presented and compared. The significant relationship of dielectric response characteristics is validated by test results and is highlighted in detail in this paper. Finally, an alternative invasive offline measurement technique is proposed for surge arrester failure detection.
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Dissolved Gas Analysis of Palm Oil Compared with Mineral Oil from Different Types of Breakdown Voltage
(2020-10-25)
Suksagoolpanya, Suthat
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Jongvilaikasem, Korraya
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Jariyanurat, Kitipod
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Banthoengjai, Thanpilin
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Jeenmuang, Siwakorn
Natural products are required instead of chemical materials for saving the environment. Nowadays, the palm oil is a new alternative liquid insulation that may be used in a transformer. Normally, the characteristics of liquid insulation can be investigated and analyzed by various methods. One of the diagnosis methods widely used is a dissolved gas analysis technique (DGA). The propose of this paper is to study the interpretation of dissolved gases in the palm oil compared with that of in the mineral oil which is caused by different kinds of breakdown phenomena, i.e. AC breakdown, positive lightning impulse breakdown, and negative lightning impulse breakdown. An AC breakdown voltage test according to IEC 60156 was performed by using 3 difference gap spacing which were 1.0, 1.5, and 2.0 mm. For lightning impulse tests, the test cell was contained needle-sphere electrodes with 10, 15, and 20 mm gap different spacing. The lightning impulse tests were performed in accordance with IEC 60897. Each experiment was performed for 5, 10, and 15 times. For a material preparation, the mineral oil and the palm oil was heated at 80oC for 12 hours. Then, it was naturally cooled before filling into the test cell to perform AC and lightning impulse breakdown tests. After that, the mineral oil and the palm oil was sampled out of the test cell to perform the DGA experiment. The dissolved gases from the mineral oil and the palm oil were interpreted by applying IEC and IEEE gas interpretation techniques. It was found that the breakdown voltages of the palm oil were less than the mineral oil but the palm oil generates more dissolved gases than the mineral oil. Moreover, Duval pentagon for natural ester fluid seemed to be the most suitable method to interpret dissolved gases in the palm oil compared with the IEC ratio, Doernenburg ratio, Roger ratio, and Duval triangle.

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