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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.
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Development of a Capacitive Sensing Module to Detect the Concentration of Isopropyl Alcohol for Covid-19 Disinfection Using Small Capacitance to DC Converter
(2024-01-01)
Sriratana, Witsarut
;
Faijaree, Manasnit
;
Sriratana, Lerdlekha
;
Satthamsakul, Sutham
This paper presents the development of a sensing module for analyzing the concentration of disinfectant alcohol commercially available in Thailand during the Covid-19 epidemic situation to ensure the ingredients and percentage concentration by focusing on simplicity, low cost with reliable performance. Under the basic physical structure of the capacitance change [1]-[5], it consists of a New Sensor Module developed to fully interface with the small capacitance to DC converter for capacitive sensor [2] model. Inside the sensing structure, there were 2 modules of metal conductors. Each conductor was 3 mm. thick, placed in parallel with a fixed distance between the module of 1 mm. The cross-sectional areas of the plates of those two modules were different in order to compare the efficiency of the detector developed. The cross-sectional areas of the plates of Module A and B were 4 cm2 and 1 cm2, respectively. Experiments were performed with 3 concentrations of alcohol, 65%, 70% and 75%, to enhance the concentration detecting performance of the sensing module developed. The signal conditioning was generated from a small capacitance to DC converter for capacitive detection with a frequency of 100 kHz, which was the most suitable frequency for exciting the capacitance change which was the capacitive reactance of the alcohol used in this study. From experiments, it was found that the sensing module with a small cross-sectional conductive material would provide more accurate results in terms of linearity and repeatability. The errors were less than 2.72% compared to the module with a large cross-sectional conductor material which would have an error up to 4.73%.
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Non-destructive prediction of moisture content of lime (Citrus aurantifolia Swingle 'Paan') by multiple regression analysis of its electrical and physical properties
(2017-03-21)
Huong, H. T.
;
Teerachaichayut, S.
Large quantity of juice is an important index of lime quality that consumers seek for. Therefore, a non-destructive technique for prediction of lime juice quantity is needed. In this study, moisture content (MC) of lime which is an indicator of its juice quantity was predicted by multiple regression analysis of its electrical properties -capacitance (C), inductance (L) and impedance (Z) at various frequencies (0.012, 0.05, 0.1, 0.2, 5, 10, 20, 50, 100 and 200 kHz) - and physical parameters - weight and geometric mean diameter (GMD). Samples (n=82) were divided into a calibration set (n=55) and a prediction set (n=27). A calibration model for moisture content of lime was established and cross-validated by partial least squares regression (PLSR). Prediction results achieved a coefficient of determination (R2) of 0.934 and a root mean square error of prediction (RMSEP) of 1.822% wet basic, demonstrating that this technique has a real potential for development into a practical non-destructive lime screening method.
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Design of capacitive sensor for concentration measurement
(2006-12-01)
Thong-un, Natee
;
Sriratana, Witsarut
;
Tanachaikhan, Lerdlekha
This paper presents the analysis of ideal equivalent circuit of the developed concentration sensor probe for chemical solutions by regarding to reasonable costs and reliability of device. The designed sensor probe consists of 2 parallel electrode plates that are coated by Nylon with 0.4 mm thick and mounted together by Resin with 2.5 mm of gap (0.09 times greater than electrode width). Any capacity changes will be compared with the electric circuit that is obtained from the Good Will R-L-C standard instrument, model CTR, at the frequency extending from 100Hz to 2 kHz. From the experiments, it was found that the sensor designed for Ethyl Alcohol solution within concentration of 5% to 95% and 10% concentration interval, at room temperature of 23°C and frequency of 100 Hz, can provide the results with high linearity as well as high resolution of capacity change which is 2 pF per 1% of concentration. © 2006 ICASE.
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2-V 3.36-mW 2.5-GHz fourth-order inductorless CMOS RF bandpass filter
(2002-01-01)
Thanachayanont, A.
Using a low-voltage VHF CMOS active inductor, based on the exploitation of the intrinsic device capacitance, a compact tuneable 2nd-order RF bandpass filter is realised by adding a series capacitor to the input port of the inductor. This approach renders a simple realisation of a high-order RF bandpass filter, required for its enhanced image rejection ability, by coupling the 2nd-order stages. Second- and fourth-order fully differential filters are realised in a 0.35 μm CMOS process, and HSPICE simulations show that the filters can operate at the 2.4 GHz ISM frequency band under a 2 V power supply voltage with power dissipation less than 0.9 mW/pole.

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