• The Journal of the Acoustical Society of Korea
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• v.19 no.7
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• pp.28-33
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• 2000

For efficient quantization of speech representation, it is common to incorporate Perceptual characteristics of human hearing. However, the focus has been confined only to the magnitude information of speech, and little attention has been paid to phase information. This paper presents a novel approach, termed perceptually irrelevant phase elimination (PIPE), to find out irrelevant phase information of acoustic signals in terms of perception. The proposed method, which is based on the observation that the relative phase relationship within a critical band is perceptually important, is derived not only for stationary Fourier signal but also for harmonic signal. The proposed method is incorporated into the analysis/synthesis system based on harmonic representation of speech, and subjective test results demonstrate the effectiveness of proposed method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.12
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• pp.1673-1678
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• 2015

This paper describes magnetic field on power cable in underground transmission systems. Based on specification which is being used in domestic power utility, magnetic field was analyzed in accordance with line arrangement, line burial depth and phase spacing. Magnetic field magnitude and its trend were understood in each circuit type such as double circuits, triple circuits and quadruple circuits of underground transmission systems. In addition, magnetic field was analyzed according to phase arrangement changing in each circuit. Finally, the proper phase arrangement configuration type was suggested by the evaluation of analysis result. Magnetic field was calculated by using Biot-Savart's law. According to the evaluated magnetic fields based on phase layout configuration in each circuit, it figured out that each of magnetic fields was different. As a result, this paper proposes a proper phase layout configuration for generating minimum magnetic field. It is evaluated that the phase layout configuration in each circuit proposed in this paper can be used at actual underground transmission systems.

• Journal of Electrical Engineering and Technology
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• v.1 no.4
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• pp.528-533
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• 2006

Electrical discharges may occur in gas, liquid as well as solid insulating materials. This paper describes the investigation results on the discharges in air, silicone oil and low density polyethylene (LDPE) using needle plane electrode system under AC voltage of 50 Hz. The experimental results showed that for discharge in air (corona), discharge pulses were concentrated around the peak of applied voltage at negative half cycle. For silicone oil positive as well as negative discharges were observed which concentrated around the peak of applied voltage. The positive pulse number was smaller but the magnitude was higher than that of negative discharge. Discharges in void took place at wider range of phase of applied voltage. The unbalance in pulse number and magnitude similar to that of oil discharges were observed. For electrical treeing in LDPE, the discharges were spread before the zero cross of the applied voltage up to the peak at both positive and negative half cycles. The discharge pulse sequence analysis indicated that the PD occurrence in air, oil and void were strongly affected by the magnitude of applied voltage. However, for electrical treeing it was observed that the discharge occurrence was strongly affected by the time derivative of the applied voltage (dv/dt).

• KSBB Journal
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• v.9 no.3
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• pp.239-245
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• 1994

The effects of reaction temperature and the level of hydration(water activity) were studied for gas phase reactions of alcohol oxidase and alcohol dehydrogenase immobilized on DEAE-cellulose and controlled pore glass(CPG). Optimum reaction temperature zone of gas phase reaction was similar to that of aqueous phase reaction. The activity of alcohol oxidase increased dramatically and the stability decreased when the water activity was increased from 0.3 to 0.8. The apparent activation energies of the gas phase reaction decreased approaching the values obtained in the aqueous phase reaction as the water activity increased. In the both cases of alcohol oxidase and alcohol dehydrogenase, the rate constants of the gas phase reaction were lower than those of aqueous phase reaction by two orders of magnitude and these results could be correlated to the vapor-liquid equilibrium data of the substrate, ethanol.

• Journal of Power Electronics
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• v.10 no.4
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• pp.412-418
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• 2010

This paper proposes a new algorithm to generate a reference signal for an active power filter using a sliding-window FFT operation to improve the steady-state performance of the active power filter. In the proposed algorithm the sliding-window FFT operation is applied to the load current to generate the reference value for the compensating current. The magnitude and phase-angle for each order of harmonics are respectively averaged for 14 periods. Furthermore, the phase-angle delay for each order of harmonics passing through the controller is corrected in advance to improve the compensation performance. The steady-state and transient performance of the proposed algorithm was verified through computer simulations and experimental work with a hardware prototype. A single-phase active power filter with the proposed algorithm can offer a reduction in THD from 75% to 4% when it is applied to a non-linear load composed of a diode bridge and a RC circuit. The active power filter with the proposed reference generation method shows accurate harmonic compensation performance compared with previously developed methods, in which the THD of source current is higher than 5%.

• International Journal of Control, Automation, and Systems
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• v.3 no.spc2
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• pp.346-354
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• 2005

This paper presents a new approach to Thyristor Controlled Phase Shifter (TCPS) control. In this paper we have proposed a nonlinear coordinated generator excitation and TCPS controller to enhance the transient stability of a power system. The proposed controller is able to control three main parameters affecting a.c. power transmission: namely excitation voltage, phase angle and reactance in a coordinated manner. The TCPS is located at the midpoint of the transmission line. A nonlinear feedback control law is proposed to linearize and decouple the power system. The design of the proposed controller is based on the local measurements only. Simulation results have been shown to demonstrate the effectiveness of the proposed controller for the enhancement of transient stability of the power system under a large sudden fault.

• Journal of Power Electronics
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• v.5 no.2
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• pp.160-165
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• 2005

In a parallel operation of UPS, there are two types of circulating currents between UPS. One is the low order circulating current with a fundamental frequency caused by the amplitude and phase differences of UPS output voltages, and the other is the harmonic circulating current with PWM switching frequency caused by non-synchronized PWM waveforms among UPS. The elimination of the low order circulating current is essential for optimal load sharing in parallel operations of UPS, which can be accomplished by the phase and magnitude control at each UPS. The harmonic circulating current may cause troubles and deteriorate in performance of the controller for optimal load sharing in parallel operation of UPS. This paper presents a PWM synchronizing method to eliminate the harmonic circulation current in parallel operation of UPS. The effectiveness of the proposed scheme has been investigated and verified through experiments by a 50kVA UPS.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.8
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• pp.1423-1428
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• 2010

The results of off-line and on-line diagnostic tests performed on the stator winding of an air-cooled gas turbine(G/T) generator are reported in this paper. Off-line diagnostic tests included measurements of the ac current, dissipation factor(tan${\delta}$), and partial discharge(PD). Six epoxy-mica capacitors were installed in the three phases of G/T generator for performing on-line diagnostic testing with the turbine generator analyzer(TGA). The TGA showed that the normalized quantity number(NQN) and the PD magnitude($Q_m$) were high in phase A of the stator winding. Internal discharges were generated in phases B and C, and slot discharge occurred in phase A. According to the trend analyses of the NQN and $Q_m$ values available for insulation condition assessment for G/T generator stator windings, it was concluded that phases B and C were in good condition, whereas phase A has been significantly deteriorated.

• Proceedings of the KSRS Conference
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• v.2
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• pp.668-671
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• 2006

Radiative transfer modeling of ice clouds is developed. Ice clouds located near tropopause reflect most of sunlight, thus atmospheric and surface effects can be minimized. Cloud properties such as cloud optical thickness (COT) and effective radius are important parameters to determine the magnitude of reflectance, while atmospheric and surface parameters rarely affect reflectance value. For selected homogeneous cloud pixels of MODerate Resolution Imaging Spectroradiometer (MODIS) observation, reflectances are calculated using MODIS cloud products as inputs of radiative transfer model (RTM). For three types of phase function (Henyey-Greenstein, Garcia-Siewert, Baum) calculated reflectances are compared with observations for validation. All cases show linear relationship between simulated values and measured values, however each represent different bias and slope. The result shows that phase function determine angular distribution of reflectance.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.2078-2086
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• 2003

As technology advances with development of new materials, it is important to measure the thermal diffusivity of material and to predict the heat transfer in the solid subject to thermal processes. The measurement of thermal properties can be done in a non-contact way using photothermal displacement spectroscopy. In this work, the thermal diffusivity was measured by analyzing the magnitude and phase of deformation gradient. We proposed a new data analysis method based on the real part of deformation gradient as the pump-probe offset value. As the result, compared with the literature value, the measured thermal diffusivities of materials showed about 3 % error.