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Transient Analysis to Distinguish Mechanically Switched Capacitors Using Discrete Wavelet Transform and Artificial Intelligence
(2026-01-01)
Thongsuk, Surakit
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Bunjongjit, Sulee
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Yoomak, Suntiti
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Ananwattanaporn, Santipont
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Jettanasen, Chaiyan
Capacitor banks are widely used in modern power systems for reactive power compensation and voltage regulation. However, switching operations of mechanically switched capacitors (MSCs) can generate transient phenomena, such as inrush currents, which may resemble fault currents and lead to misoperation of protection systems. Therefore, accurate detection and classification of transient events are essential for reliable system operation. This study proposes a hybrid approach for transient signal analysis and classification by integrating the discrete wavelet transform (DWT) with artificial intelligence (AI) techniques, including probabilistic neural networks and fuzzy inference systems (FIS). The DWT performs time–frequency analysis to extract multi-scale wavelet features from three-phase current signals. The proposed method enables both discrimination between inrush and fault currents and multi-class classification of transient events among six capacitor switching conditions, namely base case, pre-insertion resistor, pre-insertion inductor, current limiting reactor, 6% reactor, and synchronous closing. The methodology is validated using PSCAD/EMTDC simulations under isolated and back-to-back capacitor switching scenarios. The results demonstrate that the proposed DWT–AI approach achieves high classification accuracy exceeding 95%, outperforming conventional methods based on DWT alone and DWT combined with FIS. Furthermore, the proposed method improves protection system performance by reducing false tripping caused by transient inrush currents, while maintaining reliable fault detection capability. The findings confirm that integrating time–frequency signal processing with AI-based classification provides an effective and practical solution for transient event discrimination in MSC capacitor bank systems.
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Application of Neutral Grounding Resistor in High Voltage Photovoltaic Solar Substation System
(2025-01-01)
Pothosarn, Chaichan
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Patcharoen, Theerasak
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Srisuksai, Panu
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Ngaopitakkul, Atthapol
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Kunakorn, Anantawat
Faults in a distribution system with additional renewable energy sources can lead to unnecessary operation of protection devices due to higher detected fault currents compared to conventional systems. In addition, the voltage at the point of interconnection may temporarily drop to a low level, causing inverter-based generators to disconnect from the system. This study, therefore, proposes an investigation into the use of neutral grounding resistors in a 115 kV high-voltage (HV) substation unit located within a solar power generation system. The approach aims to limit ground fault current and reduce temporary voltage sags to maintain the connection status of inverter and ensure compliance with low voltage fault ride-through (LVRT) capability. The case study is modeled after an actual grid network consisting of two feeders, with one feeder connected to a solar power plant. PowerFactory DIgSILENT software is used to simulate the system and analyze the impact of various neutral grounding resistance values. The results of this study can be applied to the selection of neutral grounding resistors for system, helping to reduce fault current, extend relay operating time within the allowable delay range, and minimize unnecessary tripping of overcurrent protection relays in the system.
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Comparative Fault Detection Between DWT and STFT in Overcurrent Relays
(2024-01-01)
Chiradeja, Pathomthat
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Ananwattanaporn, Santipont
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Lertwanitrot, Praikanok
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Ngaopitakkul, Atthapol
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Kunakorn, Anantawat
This study proposes a protection relay using a microcontroller to detect and classify faults in transmission lines based on the Wavelet transform. An experimental model was constructed from an actual 115 kV transmission system prototype. The current signal was observed based on the fault type, phase, and position. Clark's transform and the discrete Wavelet transform (DWT) were applied to transform signals for analysis. The positive and zero sequences obtained from Clark's transform were used for fault detection and fault classification, respectively. Moreover, the performances between the DWT and the short-time Fourier Transform (STFT) were compared in terms of accuracy and processing time. In addition, the double-detection technique was used to confirm the accuracy of fault detection. Results show that the proposed method is efficient for fault detection and classification. This finding allows the researcher to choose the appropriate analytical method. Moreover, it can also be used as the basis for overcurrent relay algorithm design in the effort to develop more advanced technologies.
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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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Effective design of a two-stage surge protective device for AC low voltage system protection
(2024-01-01)
Kunakorn, Anantawat
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Paophan, Busayapol
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Yutthagowith, Peerawut
This study describes a useful technique for the optimal design of a two-stage surge protective device in the mitigation of overvoltage in low-voltage AC power systems. Two metal oxide varistors (MOVs) and a single inductor are used to form the protection circuit. A genetic algorithm based on MATLAB software is applied for the determination of the proper inductance. The conditional optimization is set to minimize the overvoltage generated by a combination wave generator. Meanwhile, the proposed SPD does not affect the voltage drop in the power frequency voltage (50 Hz). In the simulation process, the current-voltage (I-V) characteristics of SPDs are collected from the manufacturer's datasheet. The simulation results with the proposed circuit are confirmed by those calculated by ATP/EMTP software. Experiments for validation of the proposed approach were also carried out in a high-voltage laboratory to check the performance of over-voltage mitigation. According to the experimental and computational results, the proposed circuit performs well in terms of over-voltage mitigation. It has been confirmed that the presented approach is attractive for overvoltage mitigation in low-voltage AC power systems.
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Accurate Assessment of Moisture Content and Degree of Polymerization in Power Transformers via Dielectric Response Sensing
(2023-10-01)
Kunakorn, Anantawat
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Pramualsingha, Sarawuth
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Yutthagowith, Peerawut
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Nimsanong, Phethai
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Kittiratsatcha, Supat
Power transformers are essential apparatuses used to transfer electrical energy from one voltage-level circuit to another. For reliable systems, preventive maintenance of the transformers is required to ensure good services of all mechanical, electrical, and insulation parts. Oil-immersed paper is most often used for transformer insulation. To ensure such good insulation performance and for assessing insulation conditions, advanced transformer sensing, monitoring, and effective assessment techniques are required. This paper introduces an effective technique for assessing the insulation conditions in power transformers, which are crucial for ensuring reliable energy transfer. The method utilizes advanced transformer sensing and monitoring, focusing on oil-immersed paper insulation commonly used in transformers. The technique employs dielectric response sensing, obtained from frequency-domain spectroscopy tests, to estimate degrees of polymerization (DP) and percentages of moisture content (PMCs) in the oil-immersed paper insulation. These parameters are well-known indicators of insulation performance. The approach is based on the weighted k-nearest neighbor regression, using a database of dielectric loss factors at low frequency and oil conductivities. To overcome limited data availability, linear interpolation and extrapolation techniques are applied to enlarge the database. Experimental verification and comparison with a previously developed method demonstrate the proposed technique’s superiority in accuracy and complexity. The maximum deviations of DP and PMC in the validation cases are 6.2% and 18.7%, respectively. In addition, to evaluate the validity of our proposed method in the case of a real power transformer, a comparative analysis of the DP and PMC values determined by the proposed method with those obtained through a previously developed and complicated approach was performed. The predicted results indicate that the DP and PMC values of the oil-immersed insulation fall within the ranges of 800 to 1000 and 1.5 to 2.0, respectively, which agree with the results determined by the complicated approach and closely align with real conditions. By offering a reliable and advanced means of assessing insulation conditions, this technique contributes to the preventive maintenance and overall efficiency of power transformers.
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Impact on Protective Device Sequence of Operation in Case Distributed Generation Integrated to Distribution System
(2023-07-01)
Ngamroo, Issarachai
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Kotesakha, Wikorn
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Yoomak, Suntiti
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Kunakorn, Anantawat
This study aims to evaluate the impact of the distributed generator (DG) connection to the grid. The simulated results present the parameters of the system required to install DG on the end of the main distribution feeder. Various parameters, such as voltage, current, and protective relay coordination are modelled after the actual provincial electricity authority (PEA) distribution system. Various case studies compared the coordination without and with DG connections to the grid by finding the difference of protective devices. The results indicate that the malfunction can be fixed in order of priority protective devices, which operate according to the parameter setting. Additionally, the coordinate functions between the recloser and fuse devices in both phase and ground configurations in the operating zone prevented the drop-out fuse melting or burning out. Based on the result, this problem is fixed by providing a directional recloser device and increasing the fuse-link rated with 40k installation for replacing the conventional sizing, which can improve the performance in case of fault occurrence to investigate the reliability and stability of the distribution system.
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A CASE STUDY ON DIELECTRIC RESPONSE MEASUREMENT OF HIGH VOLTAGE GENERATOR INSULATION SYSTEMS
(2023-01-01)
Kunakorn, Anantawat
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Jeenmuang, Siwakorn
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Pattanadech, Norasage
Dielectric response measurements (DRMs) are a non-destructive method that has long been widely employed to state the insulation condition of many power system components. Such methods can reflect the deterioration problems that occur in the insulation system of rotating machines, such as conductive contamination on the end winding surface, moisture absorption, and stress grading system deterioration. In this paper, the investigation of the DRM of the stator winding insulation of an indirect hydrogen-cooled generator rate of 211.75 MVA, 15.75 kV is presented. The DRMs are carried out using polarization and depolarization current (PDC) as well as frequency domain spectroscopy (FDS) on the stator winding insulation system. The experiments are performed on both phase-to-ground and interphase insulation. Various dielectric characteristics, which are polarization current, depolarization current and a dissipation factor are recorded and analysed. The phase-to-ground PDC results show the natural characteristic of the stress grading system as a hump occurring in the current trace. In addition, the measured PDC results are converted into a frequency window so that calculated parameters can be compared with the measured FDS test results.
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Systematic design and circuit analysis of lightning impulse voltage generation on low-inductance loads
(2021-12-01)
Yutthagowith, Peerawut
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Kitcharoen, Phattarin
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Kunakorn, Anantawat
The well-known circuit for the generation of lightning impulse voltage (LIV) on low-inductance loads was introduced by Glaninger in 1975, and the circuit component selection was proposed by Feser. However, the circuit and the approach for the component selection have some dif-ficulties for which further adjustment is required for obtaining the waveform parameters according to the standard requirement. In this paper, an extended Glaninger’s circuit with an additional series resistor is proposed. Furthermore, a systematic design and circuit analysis of LIV generation for low-inductance loads are developed. With the help of a circuit simulator, the circuit analysis for the component selection is described. The validity of the proposed circuit was confirmed by some experimental results in comparison with the simulated ones. The proposed circuit and component selection provide not only the generation waveform according to the standard requirement but also other promising performances in terms of the wide inductance load range from 400 µH to 4 mH, a voltage efficiency of over 80%, an overshoot voltage of below 5%, an undershoot voltage of below 40%, and a maximum charging capacitance of 10 µF. From the simulated and experimental results, the proposed circuit and component selection approach is very useful for the LIV tests on low-inductance loads instead of using the conventional approach based on trial and error.
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Fast and Effective Technique in Evaluation of Lightning Impulse Voltage Parameters
(2021-01-01)
Yutthagowith, Peerawut
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Kitwattana, Krit
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Kunakorn, Anantawat
This paper presents an approach for the waveform parameter evaluation of lightning impulse voltage in high voltage tests according to the IEC standards. Such waveform parameters are composed of peak voltage (U<inf>p</inf>), front time (T<inf>1</inf>), time to half (T<inf>2</inf>), and the overshoot rate (B<inf>e</inf>). An artificial neural network with a back-propagation learning algorithm was applied to determine a base curve and its parameters from 14 points along the recorded waveform between 20% of the peak voltage on the wave front part to 40% of the peak voltage on the wave tail part. The 29 waveforms recommended by the standard were used in the training process of the development of the network model, and some experimental cases were also utilized for verification of the proposed method. It is found that the waveform parameters evaluated by the proposed approach are in the tolerances of the standard requirements. Maximum absolute deviations of U<inf>p</inf>, T<inf>1</inf>, T<inf>2</inf>, and B<inf>e</inf> are 0.06%, 2.00%, 0.12%, and 0.79%, respectively. Due to that no iteration process in the proposed approach is required, the efficiency in calculation process is significantly faster than the standard recommended approach.

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