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Dielectric Properties Analysis of Gas Turbine Synchronous Generator by Polarization and Depolarization Current Measuremen
(2018-11-14)
Phloymuk, N.
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Nimsanong, P.
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Phumipunepon, N.
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Kittiratsatcha, S.
;
Pattanadech, N.
Insulation of stator winding in large electric rotating machines mostly consists of mica and epoxy resins with a number of junctions inside the insulation. The diagnostic test method for monitoring the insulation condition of these machines every specified period of operation is very important. The polarization and depolarization current (PDC) test method is one of the potential test techniques that can be used to evaluate the polarization process of the insulation by measuring the charging and the discharge currents of the insulation under the DC high voltage test. The PDC test experiments was done with the stator winding insulations of four identical gas turbine synchronous generators rated at 58,824 kVA 11 kV and 3,000 rpm (manufactured in 1997). From the results, it was found that increase in ambient relative humidity and operation winding temperatures increased the polarization and depolarization currents of the stator winding insulation. Besides, the in-serviced operation hour of the investigated machine had an effect on the tan δ. The tan δ increased with increase in the degree of insulating deterioration and the in-service operation hour also. Increasing of tan δ is associated with increasing of imaginary capacitance of the tested insulation. The analyzed parameters can be taken into account for evaluating the aging and deterioration conditions of the insulating material of the synchronous machine which are useful for a maintenance strategy of the rotating machines.
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Computation program for breakdown voltages of a gas insulation under different pressures and slightly nonuniform electric fields
(2018-07-02)
Chamnong, C.
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Chuayin, C.
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Nganpitak, T.
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Sontayananon, N.
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Kittiratsatcha, S.
This paper proposes a program for computing the breakdown voltage of a gas insulation under slightly nonuniform electric field. The development of the program is based on the knowledge of gas ionization and streamer breakdown theories, so it can compute the breakdown voltage of an ideally-simulated gas-insulated system, under a certain gas pressure level that the streamer constant is known. To verify this program, several simulations of sphere-sphere electrode systems were made using COMSOL Multiphysics with differences in sphere dimensions and gap spacings referred from IEC-60052 standard. Then the AC breakdown voltage of each simulation was computed using the breakdown voltage computation function under the pressure of 101.3 kPa according to the standard. Next, the computed AC breakdown voltages were compared with the AC breakdown data from the standard. The differences between the computed and the standard AC breakdown voltages were less than 3% in all simulated cases. Then the program was developed further by creating a new function that could estimate the streamer constant of a practical gas-insulated system under various gas pressure levels and slightly nonuniform electric field. Since the streamer constant of a practical gas-insulated system with any gas pressure level could be estimated using the streamer constant estimation function, the breakdown voltage of any practical gas-insulated system should be able to be computed pragmatically. To verify the ability to compute the breakdown voltage of a practical gas-insulated system, several practical gas-insulated systems with slightly nonuniform electric field were set up under certain gas pressure levels. Then several simulations were made to represent the practical gas-insulated system those were set up. Next, the streamer constant of each simulation was estimated using the developed streamer constant estimation function. After that, the gap spacings of both practical and simulated systems were changed. Then AC breakdown test was conducted on each practical system, while AC breakdown voltage of each simulated system was computed using the breakdown voltage computation function. Finally, the computed breakdown voltages were compared with the breakdown voltages those were practically tested. The comparison was satisfactory with less than 3% differences between the computed and the tested AC breakdown voltages in all cases.
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Analysis and experimental setup of a switched reluctance generator for maximum output power
(2014-01-01)
Thongprasri, P.
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Kittiratsatcha, S.
Output power of a switched reluctance generator (SRG) in single pulse mode operation depends on control variables which consist of dc bus voltage, shaft speed, and excitation angles (turn-on and turn-off angles). This paper presents a model using equations to express maximum output power in terms of the control variables. The proposed analytical model is applied from a nonlinear magnetization curve that is used to mathematically demonstrate relationship of the control variables and to find the optimal control variables of the SRG for maximum output power. The validity of the analytical model has been confirmed by experimental results. © 2014 Praise Worthy Prize S.r.l. - All rights reserved.
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A novel output power control for variable-speed switched reluctance generators using artificial neural network
(2014-01-01)
Kerdtuad, P.
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Kittiratsatcha, S.
This paper presents a novel output power control method for variable-speed switched reluctance generators (SRG). In the single pulse mode, the conduction angles dictate the waveform of phase current which directly influences the output power. With the proposed method, the conduction angles can be estimated from the output power profiles at several speeds using an artificial neural network (ANN). The output power profiles are simulated from a dynamic model of an 8/6 SRG and used as the training data of the network. The inputs of the network are the output power and rotor speed, and its outputs are the turn-on and turn-off angles. The proposed control scheme was developed by incorporating the trained network into the dynamic model before the simulation in MATLAB/Simulink. The experiments with the 8/6 SRG were carried out using TMS320F2812 DSP to control the SRG drive system. In addition, the optimal trained weights and biases of the network are utilized in the DSP program. The comparisons of the simulation and experimental results are made to verify the proposed method.
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Study of maximum power conversion of a switched-reluctance generator
(2011-08-12)
Kerdtuad, P.
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Kittiratsatcha, S.
This paper presents the study of maximum power conversion of a Switched Reluctance Generator (SRG). The SRG is operated in single pulse mode where the rotor speed is above base speed. The turn-on and turn-off angle are varied to study the shape of the phase current which is directly related to the power conversion. A 4 Phase, 2kW, 8/6 SRG is used to collect the experimental results. The converter is the conventional 2-switched per phase and a TMS320F2812 Digital Signal Processing (DSP) is a main controller. © 2011 IEEE.
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Analysis of a switched-reluctance generator for maximum energy conversion
(2008-12-01)
Wongguokoon, S.
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Kittiratsatcha, S.
A successful analytical expression for maximum energy conversion in terms of DC-bus voltage and turn on/off angles of a Switched Reluctance Generator (SRG) based on self-excitation mode, single pulse operation is presented. The proposed analytical model, which can describe nonlinear of the magnetic characteristics of a SRG with sufficient accuracy, is the key used to derive the relation of maximum energy conversion with those control variables. Simulation and experimental results are provided to validate the analysis. © 2008 IEEE.
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Design of a Single-Stage Single-Switch Power-Factor-Corrected (S 4-PFC) AC/DC converter
(2007-12-01)
Kongthawornwattana, P.
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Bunlaksananusorn, C.
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Kittiratsatcha, S.
This paper presents the design of a Single-Stage Single-Switch Power-Factor-Corrected (S<sup>4</sup>PFC) AC/DC converter. The converter under study is an integration of boost and flyback converters. The converter operation is equivalent to its two-stage counterpart with switches in the PFC and DC/DC converter stages turned on and off at the same time. Based on this observation, power circuit and control loop design of the converter can be carried out using standard design equations and methods, after the bulk capacitor voltage has been determined. This design concept is applied to design a 120W (12V, 10A) S <sup>4</sup>PFC AC/DC converter. Fxperimental results are given to confirm validity of the proposed design method. © 2007 IEEE.
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Switching frequency control based on phase-locked loop for a current-fed parallel resonant inverter
(2007-10-01)
Ponwiangkum, N.
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Kittiratsatcha, S.
This paper proposes a computer simulation in PSCAD program of a current-fed parallel resonant inverter. Even though the circuit parameters such as permeability and conductivity have changed regarding to the changing temperature during the heating period. The proposed idea is able to control the phase difference Δθ between the output voltage and output current to be constant at desired value. The principle of the proposed controller utilizes the phaselocked loop with a phase frequency detector. If the Δθ is constant without any effect from the temperature change, then the output power will be controlled precisely by adjusting only the dc-link current. The proposed idea is verified by the experimental results. © 2007 IEEE.
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Position estimation technique of a switched reluctance motor at standstill
(2007-10-01)
Trakrancharoungsook, K.
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Kittiratsatcha, S.
This paper proposes the rotor-position estimation technique for a switched reluctance machine (SRM). This technique can be implemented with the system with an incremental encoder or sensorless system. The results are the proper starting phase and exact starting rotor position. The phase winding is energized by the narrow voltage pulse then phase currents are detected and calculated to find the rotor position by using the cubic spline interpolation technique. The proper phase is chosen for a starting phase. This proposed idea is done in the MATLAB/Simulink program. © 2007 IEEE.
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A magnetic model of a three-phase switched-reluctance machine using cubic spline interpolation technique
(2005-12-01)
Khotpanya, S.
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Kittiratsatcha, S.
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Kazuhisa, Ishibashi
This paper presents a simple model of three phase switched reluctance machine by using polynomial flux linkage equation. The nonlinear function of flux linkage depends on phase current and the rotor position. The model requires pre-calculated or measured input data therefore Finite Element Analysis (FEA) has been used for data collection. Curve fitting method is implemented to model the magnetizing curves. Since the magnetizing curves are smooth and continuous then flux linkage at particular position and phase current can be estimated by using cubic spline interpolation technique. Moreover, this technique can be used to model torque of the SRM. The comparison between proposed model and FEA reveals the model accuracy. © 2005 IEEE.

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