Search

Ferroresonance is a non-linear vibrational phenomenon that is generated by the electrical interaction of the inductance compon ent with the capacitor component of a certain capacitance as the device of the inductance component such as a transformer is saturated due to the degradation, the wavef orm distortion of current and voltage, and the oscillation of overcurrent and overvoltage in a system. Recently, ferroresonance was generated from the waveform distortion of current and voltage, or the overvoltage or undervoltage phenomenon caused by the nature of an electrical power system and design technology of the transformer in the three phase transformer system. Hence, in general, ferroresonance analyzed by converting to the LC equivalent circuit. However, in general, the aforementioned analytical method only applies to the resonance phenomenon that is generated by the interaction of the capacita nce of bussbar and grounding, and switching as the capacitor component with PT and the transformer as the inductance component in a system. Subsequently, the condition where ferroresonance was generated since overvoltage was supplied as line voltage to the phase voltage and thus the iron core is saturated due to the interconnection between grounded and ungrounded systems could not be analyzed when single phase PT was connected in a △/Y connection system. In this st udy, voltage swell in the confi guration of grounded circuit of a step-up transformer with the △-△ connection linked to PT for control power and the ferroresonance generated by overvoltage when the line voltage of the △-△ connection was connected to the phase voltage of the grounded Y-Y connection were analyzed using PSCAD / EMTDC through the failure case of the transformer caused by ferroresonance in the system with the △-△ /Y-Y connection, and subsequently, the preventive measure of ferroresonance was proposed.

When the ground fault on the power side occurs on distribution system interconnected with distributed generations, the abnormal current is generated in the neutral conductor by the connection type and the iron core structure of transformers for the interconnection of distributed power supplies due to the unbalanced voltage of the system, and subsequently the false operation of the protective relay on the load side occurs. Herein, this paper proposes the method to correct errors in the phase current to prevent the false operation of the protective relay by applying p-q theory and presents the simulation result of the error correction algorithm using PSCAD/EMTDC.

A portable electronic nose system has been fabricated and characterized using an oxide semiconductor gas sensor array and artificial neural network. The sensor array consists of such thick-film oxide semiconductor sensing materials as Pd-doped WO3, Pt-doped SnO2, TiO2–Sb2O5–Pd-doped SnO2, TiO2–Sb2O5–Pd-doped SnO2+Pd-coated layer, Al2O3-doped ZnO and PdCl2-doped SnO2. The portable electronic nose system consists of an Intel 80c196kc as CPU, an EEPROM and an LCD for displaying gas concentrations, etc. As an application, the system has been used to identify 26 CO/HC car exhausting gases and the identification has been successfully demonstrated.

Ozone sensing properties of In2O3-based semiconductor thick films have been investigated. The In2O3 sensing layer is quite sensitive to ozone, but the rapid saturation in sensitivity cannot be obtained. The addition of Fe2O3 (3 wt.%) into In2O3 and the high temperature firing of the mixed powder give rise to a remarkable improvement in response and recovery, although the sensitivity decreases. The sensing layer fired at 1300°C and operated at 550°C shows excellent properties such as fast response, stable sensitivity, and rapid recovery. In addition to it, the sensor shows a good linearity with ozone concentration and a good reproducibility. The preliminary results clearly demonstrated that the sensor was successfully applied for the ozone detection of parts per billion range.

We have investigated abnormal current-voltage characteristics of an oxide semiconductor and have developed a novel method of detecting reducing gases utilizing the self-heating mechanism of the sensing layer without an additional heater. Planar-type sensors based on WO 3 -doped SnO 2 were fabricated using a screen-printing technique. The applied voltage across the sensing layer caused heating of the sensing layer and the current abruptly varied upon exposure to a gas, mainly as a result of surface reactions. A fascinating aspect of the gas sensing scheme is that no additional heater is necessary for detection. The new sensing method has been applied to C 2 H 5 OH gas in this preliminary work.

In order to identify CH3SH, (CH3)3H, C2H5OH and CO gases in the concentration range of 0.1 to 100 ppm, a gas recognition system using a gas sensor array and neural-network pattern recognition has been fabricated. The sensor array consists of such thin film oxide semiconductor sensing materials as 1 wt% Pd-doped SnO2, 6 wt% Al2O3-doped ZnO, WO3 and ZnO. The principal component analysis and the neural-network pattern recognition analysis were used for the discrimination of gas species and concentrations. Good separation among gases and concentrations was obtained using the principal component analysis. The recognition probability of the neural-network was 100% for each 5 trials of 12 gas samples.

Highly sensitive and mechanically stable micro gas sensors have been made using microfabrication and micromachining techniques. The sensing material used to detect offensive CH 3 SH gas is 1 wt.% Pd-doped, 2000A˚thick SnO 2 deposited by r.f. magnetron sputtering. The optimum operating temperature of the sensor is 250°C, and the corresponding heater power is about 55 mW. Excellent thermal insulation of the membrane is achieved by the use of a double-layer structure of 0.2 μm thick silicon nitride and 1.4 μm thick phosphosilicate glass (PSG) prepared by low-pressure chemical-vapour deposition (LPCVD) and atmospheric-pressure chemical-vapour deposition (APCVD), respectively. The sensors are mechanically stable enough to endure at least 43 200 heat cycles between room temperature and 350°C.

The Korea Atomic Energy Research Institute (KAERI) began to construct the 1 kJ Nd:glass laser facility. The KAERI laser facility (KLF) is designed to deliver 1 kJ at n-sec and 50 TW at p-sec to target chamber for high energy density plasma physics.

In order to identify CH/sub 3/SH, (CH/sub 3/)/sub 3/, C/sub 2/H/sub 5/OH and CO gases in the concentration range of 0.1 to 100 ppm, a gas recognition system using a gas sensor array and neural network pattern recognition has been fabricated. The sensor array consists of such thin film oxide semiconductor sensing materials as 1 wt.% Pd-doped SnO/sub 2/, 6 wt.% AI/sub 2/O/sub 3/-doped ZnO, WO/sub 3/ and ZnO. The principal component analysis and the neural-network pattern recognition analysis were used for the discrimination of gas species and concentrations. Good separation among gases and concentrations was obtained using the principal component analysis. The recognition probability of the neural-network was 100% for each five-trial of twelve gas samples.