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Hybrid Posi cast - based PID - PDA Control Using System Identification for Continuous Tunnel Kilns
(2026-06-30)
Pannil, Pittaya
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Sungsorn, Teenapong
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Trisuwannawat, Thanit
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Julsereewong, Amphawan
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Thepmanee, Teerawat
This paper proposes a hybrid Posicast-based proportional-integral-derivative with proportional-derivative-acceleration (PID-PDA) controller for temperature regulation in delay-dominant continuous tunnel kilns. The controller is developed based on a system-identified second-order-plus-dead-time (SOPDT) model derived from industrial data and implemented in discrete time for programmable logic controllers (PLCs). A unified framework enables comparison with a standard PLC-based proportional-integral (PI) controller, an internal model control (IMC)-tuned PI controller, and a Smith Predictor-PI controller under identical conditions. Simulation results demonstrate faster response, negligible overshoot, and reduced tracking error, with improved settling time and lower, integral of absolute error (IAE), integral of squared error (ISE), and integral of time-weighted absolute error (ITAE), while maintaining comparable control effort. Robustness analysis confirms stable performance under plant perturbations, with IAE variations within approximately ± 10 (servo) and ± 1 (disturbance). The controller is validated on an Allen-Bradley PLC in a silicon controlled rectifier (SCR)-based heating system. Experimental results show improved steady-state performance, including reduced bias, lower mean absolute error (MAE) and root mean squared error (RMSE), reduced oscillation amplitude, and compliance within the ± 1 temperature band. The proposed approach provides a practical, robust, and high-performance solution for upgrading existing PLC-based systems without hardware modifications.
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Polarity-Dependent DC Dielectric Behavior of Virgin XLPO, XLPE, and PVC Cable Insulations
(2025-10-01)
Ruangwong, Khomsan
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Pattanadech, Norasage
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Pannil, Pittaya
Reliable DC cable insulation is crucial for photovoltaic (PV) systems and high-voltage DC (HVDC) networks. However, conventional materials such as cross-linked polyethylene (XLPE) and polyvinyl chloride (PVC) face challenges under prolonged DC stress—notably space charge buildup, dielectric losses, and thermal aging. Cross-linked polyolefin (XLPO) has emerged as a halogen-free, thermally stable alternative, but its comparative DC performance remains underreported. Methods: We evaluated the insulations of virgin XLPO, XLPE, and PVC PV cables under ±1 kV DC using time-domain indices (IR, DAR, PI, Loss Index), supported by MATLAB and FTIR. Multi-layer cable geometries were modeled in MATLAB to simulate radial electric field distribution, and Fourier-transform infrared (FTIR) spectroscopy was employed to reveal polymer chemistry and functional groups. Results: XLPO exhibited an IR on the order of 108–109 Ω, and XLPE (IR ~ 108 Ω) and PVC (IR ~ 107 Ω, LI ≥ 1) at 60 s, with favorable polarization indices under both polarities. Notably, they showed high insulation resistance and low-to-moderate loss indices (≈1.3–1.5) under both polarities, indicating controlled relaxation with limited conduction contribution. XLPE showed good initial insulation resistance but revealed polarity-dependent relaxation and higher loss (especially under positive bias) due to trap-forming cross-linking byproducts. PVC had the lowest resistance (GΩ-range) and near-unit DAR/PI, dominated by leakage conduction and dielectric losses. Simulations confirmed a uniform electric field in XLPO insulation with no polarity asymmetry, while FTIR spectra linked XLPO’s low polarity and PVC’s chlorine content to their electrical behavior. Conclusions: XLPO outperforms XLPE and PVC in resisting DC leakage, charge trapping, and thermal stress, underscoring its suitability for long-term PV and HVDC applications. This study provides a comprehensive structure–property understanding to guide the selection of advanced, polarity-resilient cable insulation materials.
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Experiment of Dielectric Frequency Response for Aged ZnO Surge Arrester
(2025-01-01)
Aiamrungruang, Phitthaya
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Methavithit, Winai
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Pannil, Pittaya
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Chuayin, Chaitawat
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Zinck, Matthieu
Condition-based monitoring of surge arresters has gained increasing attention in modern power system asset management, especially for medium-voltage equipment. This paper presents an investigation into the dielectric frequency response (DFR) analysis technique as a diagnostic method to evaluate aging and unhealthy conditions in 21-kV metal oxide surge arresters (MOSA). Four types of simulated defects, excessive number of lightning current stress, cracking, moisture ingress, and tracking, were introduced to represent common field failures. The DFR technique enables frequencydomain interpretation of dielectric properties, providing insight into insulation behavior over a wide frequency range. The test results show a significant variation in capacitance and dissipation factor corresponding to different defect types. Among these, moisture ingress exhibited the most severe deterioration. The findings suggest that DFR is a viable offline diagnostic method that can support preventive maintenance strategies for high-voltage surge arresters.
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Overload Duration Analysis of Mineral Oil and Natural Ester in Retrofilled Distribution Transformers
(2025-01-01)
Pongpitak, Siriwut
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Pannil, Pittaya
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Pattanadech, Norasage
Natural ester fluids such as FR3 provide higher fire safety, better biodegradability, and extended insulation life compared with mineral oil. Retrofilling existing transformers with FR3 offers a practical means to enhance safety and environmental performance without redesigning the unit. This study evaluates the thermal performance and overload endurance capability of a 160 kVA distribution transformer before and after retrofilling from mineral oil to FR3. Results show that steady-state temperature rises increased modestly after retrofilling (+1.3-4 K for top oil and windings) but remained within IEC limits. Under 1.5 p.u. normal cyclic loading, the mineral-oil unit reached its 120 °C hot-spot limit after 5 hours and 20 minutes, whereas the FR3 unit stabilized near 126 °C and did not reach its 140 °C limit within 10 hours. Under 1.8 p.u. long-time emergency loading, FR3 extended the time-to-limit to 5 hours and 20 minutes, compared with 4 hours and 30 minutes for mineral oil (18.5% increase). Overall, FR3 trades slightly higher temperature rises for a wider operational safety envelope and longer overload endurance, supporting safer peak-shaving and contingency operations in retrofilled assets. These findings provide actionable insights for utilities considering FR3 retrofilling as a cost-effective transformer upgrade strategy.
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Polarity-Dependent Dielectric Behavior of XLPO-Insulated PV Cables Under High-Voltage AC and DC Stress: Leakage Current and PRPD Analysis
(2025-01-01)
Ruangwong, Khomsan
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Pattanadech, Norasage
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Pannil, Pittaya
This study investigates the dielectric behavior of cross-linked halogen-free polyolefin (XLPO) insulation in H1Z2Z2-K photovoltaic cables under a direct current (DC) stress of ± 999.6 V. The results indicate significant polarity-dependent responses, with insulation resistance (IR) rising from 1.61 T Ω under negative DC to 2.30 T Ω under positive DC. Furthermore, the polarization index (PI) and dielectric absorption ratio (DAR) improve from 6.73 and 2.14 to 12.78 and 2.43, respectively. The Loss Index, obtained from polarization-depolarization current (PDC) analysis, increases from 0.935 to 0.991, suggesting enhanced dielectric stability with positive bias. Additionally, the partial discharge inception and extinction voltages (PDIV and PDEV) are recorded at 8.3 kV for DC and 1.93 kV for AC, exhibiting symmetrical behavior that indicates corona and surface discharge dominance and minimal space charge retention. These findings highlight the importance of considering space charge dynamics and polarity-aware diagnostics in evaluating non-certified XLPO-insulated cables in photovoltaic applications.
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The Experiment of Dielectric Frequency Response of Serviced Aged Distribution Transformer
(2024-01-01)
Posrimahapoch, Purichaya
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Maneerat, Noppadol
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Daengdee, Danaiwat
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Jeenmuang, Siwakorn
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Pannil, Pittaya
Outdoor Distribution Transformers typically encounter random environments and affect moisture in any ingress ways, e.g., defective breathing, oil leakage, or human error during internal inspection, etc. Such moisture is a very important enemy of the insulation integrity of the transformer. It may cause the failure of the transformer eventually. Therefore, the condition of the transformer insulation needs to be monitored. Dielectric Frequency Response (DFR), also known as Frequency Domain Spectroscopy (FDS), and Polarization and Depolarization Current (PDC) are nondestructive tests providing efficient diagnostic for transformer insulation. The test results can be used to estimate moisture content and oil conductivity. In this paper, the dielectric investigation of a 315 kVA, 22 kV serviced aged distribution transformers, which have been retired for 6 months after being utilized for more than 20 years, was conducted. The experiment results of the DFR and the PDC tests including the investigated mineral oil characteristics (i.e., oil breakdown voltage, moisture content, and tan delta) are reported and analyzed. They should be useful to understand the condition of the transformers.
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Partial Discharge Investigation of 22kV Distribution Transformer
(2024-01-01)
Dechothamsathit, Vorawut
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Pannil, Pittaya
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Yamsiri, Thummanoon
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Chumpiboon, Komin
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Jeenmuang, Siwakorn
This paper presents an off-line partial discharge (PD) experiment conducted on a 22 kV/400 V distribution transformer, which was decommissioned after 20 years of service. The study investigates the impact of reduced oil levels within the transformer on PD characteristics that are expected to facilitate PD activity within the transformer. The experiments were performed with reduced oil levels below the top clamp and using both single-phase and three-phase voltage excitations, with PD measurements recorded for each case. The PD signals were measured using High-Frequency Current Transformers (HFCTs) and capturing current pulses of PD in the frequency range of 100 kHz to 20 MHz. Additionally, transformer oil tests were performed, including moisture content, oil breakdown voltage, and oil conductivity. The results of the PD measurements and oil tests are introduced and discussed in this paper.
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The Effect of Insulating Oil Conditions in Transformer Bushing on Dielectric Response Analysis
(2024-01-01)
Srisub, Chanatip
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Maneerat, Noppadol
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Rojanasunan, Warisanan
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Buranaaudsawakul, Techatat
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Pannil, Pittaya
The bushing is one of the important parts of a transformer. Once the transformer is operated; each transformer part including its bushing starts the degradation mechanism. In some cases, the dielectric strength degradation of the bushing can lead to severe consequences. Thus, the study and diagnosis of the bushing conditions are important. This study aims to investigate the characteristics of the oil-impregnated pressboard bushing under various oil conditions by filling the new mineral oil with a controlled moisture content and letting it reach an equilibrium state to examine the dielectric response of such bushing. To determine the dielectric characteristics of the investigated bushing, A Frequency Domain Spectroscopy (FDS) device was utilized. In the experiment, the dissipation factor, capacitance, and current measurement of the bushing with different water content level were measured. The bushing test object was tested with the frequency range of 1 mHz -1 kHz. The effect of moisture clearly influenced the low-frequency ranges of the FDS. The result will be discussed in the paper.
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The Experiment of Partial Discharge for Cast Resin Transformer
(2024-01-01)
Aiamrungruang, Phitthaya
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Pannil, Pittaya
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Dorkmai, Kritsada
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Maneerot, Sakda
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Jeenmuang, Siwakorn
Dry-type cast resin transformers, utilizing epoxy resin insulation instead of traditional liquid insulation like mineral oil, are designed to prioritize safety, avoid fire hazards, be environmentally compatible, and endure short circuits well. Limitations of dry-type transformers are the installation area by which it should be dry, free from dust, excessive moisture, fertilizers, chemicals, and other corrosive fumes or fumes. This paper investigates the Partial Discharge (PD) phenomena occurring on a 12 kV dry-type transformer surface using HighFrequency Current Transformers (HFCT) with 100 kHz -20 MHz bandwidth as a PD detection device. The simulated PD sources were made from the conductive wire. Moreover, the scheme of winding connections in the dry-type transformer related to cross-talk phenomena between transformer coils is also reported. The recorded Phase-resolved PD (PRPD) and the PD Inception Voltage (PDIV) have been summarized and compared, as described in this paper.
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Experience in Partial Discharge Investigation of a 155 MVA Air-Cooled Generator
(2024-01-01)
Pathanrat, Khomsan
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Chumpiboon, Komin
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Jeenmuang, Siwakorn
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Worthong, Tehneht
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Pannil, Pittaya
This paper presents the Partial Discharge (PD) and Polarization and Depolarization Current (PDC) investigation for a 155 MVA air-cooled generator. The visual inspection of the stator winding insulation was carried out during the annual preventive maintenance. Several defects in the area of the end winding stator were evidenced. Thereafter, the refurbishment of these problems was performed to improve the stator winding insulation condition, and the offline PD & PDC test was conducted accordingly. Besides, the online PD was continuously monitored, through capacitive PD sensors which have been installed on the terminal of the generator two units per phase. The operating conditions during online PD measurement were also recorded. In this paper, the results from both offline and online PD measurements were presented.

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