• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.53-66
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• 1990

Rainfall is a phenomenon that shows a high variability both in space and time, Hy drologists are usually interested in the description of spatial distribution of rainfall over watershed. The theory of Kriging, generalized covariance technique using nonstationary mean in the regions under orographic effect, was chosen to construct random surface of total storm depth. For the constructed random surface, the double Fourier analysis of the total storm depths was performed, and the principal harmonics of storm were determined. The local component, or storm residuals was obtained by subtracting the periodic component of the storm from total storm depths. It is assumed that the residuals are a sample function of a homogeneous random field. This random field can be characterized by an isotropic one dimensional autocorrelation function or its corresponding spectral density function. Under this assumption, this study proposed a theorectical model for spectral density function adapted to two watersheds.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.186-188
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• 2003

The ZnO surge arrester is the protective device for limiting surge voltages on equipment by diverting surge current and returning the device to its original status. The occurrence of overvoltage appears in any phase to AC power supply system and it appears in mixing AC and impulse voltages, moreover because HVDC power supply system uses converter in semiconductor, it makes mixed DC and high harmonics voltages. In this study, the various mixed AC and DC voltages was made for investigating the degradation effect of ZnO arrester according to mixed voltage. As a result, the increase of DC component to mixed voltages causes the increase of resistive component of total leakage current to ZnO block. In changing V-I curve for mixed voltages, the cross-over point acts a factor as making the proper capacitor size of an equivalent circuit for ZnO block.

• Proceedings of the KIEE Conference
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• 1997.07c
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• pp.1006-1008
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• 1997

This paper presents the logic based High Impedance Fault(HIF) detection rules for distribution lines. Due to the characteristics of HIF, which shows low current on relaying points, it is difficult to detect the fault occurred in distribution line by the conventional overcurrent relay(OCR) and/or harmonics relay. The HIF data were generated by using TACS in EMTP. In this paper, The harmonic index is defined as the ratio of harmonic component to fundamental component. The proposed HIF detection rules are obtained by analysing the difference between normal condition and HIF condition.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.2
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• pp.94-100
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• 2018

Generally, in a single-phase energy storage system (ESS) for households, AC ripple component with twice the fundamental frequency exists inevitably in the DC link voltage of single-phase PCS. In the grid-connected mode of a single-phase inverter, the AC ripple component in the DC link voltage causes low-order harmonics on grid-side current that deteriorates power quality on an AC grid. In this work, a control system adopting a feedforward controller is established to eliminate the AC ripple interference on the DC link side. Optimal battery nominal voltage design method is also proposed by considering the voltage loss and AC ripple voltage on DC link side in a single-phase ESS. Finally, the control system and battery nominal voltage design method are verified through simulations and experiments.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.6
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• pp.568-575
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• 2022

This paper is a study on frequency analysis and electronic noise reduction of energy storage system (ESS). We acquired 4 necessary data for about 2 minutes and 4 seconds using a sampling frequency of 10,000 Hz in ESS. Fast Fourier transform (FFT) was used for electronic noise analysis from the acquired data. As a result, it was confirmed that DC component, fundamental wave, second and higher harmonic component exist. For the attenuation of harmonics, low-pass filter (LPF) was applied. We confirmed that an attenuation of approximately 59.3% appears from the second harmonic. The presence of many harmonic components in the data of the ESS was expected to occur due to the insufficiency of optimization among the modules inside the ESS. Therefore, we propose that a national certification system for ESS should be introduced to settle down the issue properly.

• Economic and Environmental Geology
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• v.12 no.2
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• pp.95-104
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• 1979

The position of any point on the earth's surface can be. represented in the spherical coordinates by surface spherical harmonics. Since geomagnetic field is a function of position on the earth, it can be also expressed by spherical harmonic analysis as spherical harmonics of trigonometric series of $a_m({\theta})$ cos $m{\phi}$ and $b_m({\theta})$ sin $m{\phi}$. Coefficients of surface spherical harmonics, $a_m({\theta})$ and $b_m({\theta})$, can be drawn from the components of the geomagnetic field, declination and inclination, and vice versa. In this paper, components of geomagnetic field, declination and inclination in the Korean peninsula are obtained by spherical harmonic analysis using the Gauss coefficients calculated from the world-wide magnetic charts of 1960. These components correspond to the values of normal geomagnetic field having no disturbances of subsurface mass, structure, and so on. The vertical and total components offer the zero level for the interpretation of geomagnetic data obtained by magnetic measurement in the Korean peninsula. Using this zero level, magnetic anomaly map is obtained from the data of airborne magnetic. prospecting carried out during 1958 to 1960. The conclusions of this study are as follows; (1) The intensity of horizontal component of normal geomagnetic field in Korean peninsula ranges from $2{\times}10^4$ gammas to $2.45{\times}10^4$ gammas. It decreases about 500 with the increment of $1^{\circ}$ in latitude. Along the same. latitude, it increases 250 gammas with the increment of $1^{\circ}$ in longitude. (2) Intensity of vertical component ranges from $3.85{\times}10^4$ gammas to $5.15{\times}10^4$ gammas. It increases. about 1000 gammas with the increment of $1^{\circ}$ in latitude. Along the same latitude, it decreases. 150~240 gammas with the increment of $1^{\circ}$ in longitude. Decreasing rate is considerably larger in higher latitude than in lower latitude. (3) Total intensity ranges from $4.55{\times}10^4$ gammas to $5.15{\times}10^4$ gammas. It increases 600~700 gammas with the increament of $1^{\circ}$ in latitude. Along the same latitude, it decreases 10~90 gammas. with the increment of $1^{\circ}$ in longitude. Decreasing rate is considerably larger in higher latitude as the case of vertical component. (4) The declination ranges from $-3.8^{\circ}$ to $-11.5^{\circ}$. It increases $0.6^{\circ}$ with the increment of $1^{\circ}$ in latitude. Along the same latutude, it increases $0.6^{\circ}$ with the increment of l O in longitude. Unlike the cases of vertical and total component, the rate of change is considerably larger in lower latitude than in higher latitude. (5) The inclination ranges from $57.8^{\circ}$ to $66.8^{\circ}$. It increases about $1^{\circ}$ with 'the increment of $1^{\circ}$ in latitude Along the same latitude, it dereases $0.4^{\circ}$ with the increment of $1^{\circ}$ in longitude. (6) The Boundaries of 5 anomaly zones classified on the basis of the trend and shape of anomaly curves correspond to the geologic boundaries. (7) The trend of anomaly curves in each anomaly zone is closely related to the geologic structure developed in the corresponding zone. That is, it relates to the fault in the 3rd zone, the intrusion. of granite in the 1st and 5th zones, and mountains in the 2nd and 4th zones.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.556-560
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• 2001

In this paper, a soft-switching discontinuous mode (DCM) power factor corrected (PFC) converter is analyzed by applying the double Fourier series expansion. It is found that the fundamental component and higher-order harmonics included in the input current waveform are obtained by the Fourier series expansion of the mean value of the inductor current. From the theoretical analysis, a new method removing the distortion of the input current waveform is proposed. In spite of an open loop system, the proposed method makes a great improvement of the total harmonic distortion even if the ratio of output voltage to input voltage is very low.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.822-828
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• 2001

Three-phase four-wire electrical distribution systems are widely employed in manufacturing plants, commercial and residential buildings. Due to the nonlinear loads connected to the distribution system, the neutral conductor carries excessive harmonic currents even under balanced loading since the triplen harmonics in phase currents do not cancel each other. This may result in wiring failure of the neutral conductor and overloading of the distribution transformer. In response to these concerns, a cost-effective neutral current harmonic suppressor system has been proposed [6]. This paper proposes an improved control method for the harmonic suppressor system under unbalanced load conditions. The proposed control method compensates for only the harmonic components in the neutral conductor, and the zero-sequence fundamental component due to unbalanced loading is prevented from flowing through the harmonic suppressor system. This remedies overloading and power loss of the system. The experimental results on a prototype validate the proposed control approach.

• Journal of electromagnetic engineering and science
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• v.16 no.4
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• pp.225-228
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• 2016

KRISS-V, a V-band millimeter-wave source module for a primary RF power standard and calibration system developed by the Korea Research Institute of Standards and Science is here presented. The output power of KRISS-V is several times higher than that of commercial amplifier/multiplier chains and is highly stable (the standard deviations of output power are less than 0.01% in the worst case). The spectral purity of KRISS-V is high enough to consider it a single-tone signal generator. We also added programmable attenuation capability to KRISS-V for remote power control. Moreover, the in-house source module is cost-effective and adaptable to various measurement schemes. The structure of the model as well as detailed component information are introduced so that it can be reproduced.

• Journal of Electrical Engineering and Technology
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• v.7 no.5
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• pp.730-735
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• 2012

This paper presents a method to design the waveform of a back electromotive force (back EMF) of an axial flux permanent magnet (AFPM) motor using printed circuit board (PCB) windings. When the magnetization distribution of permanent magnet (PM) is given, the magnetic field in the air gap region is calculated by the quasi three dimensional (3D) space harmonic analysis (SHA) method. Once the flux density distribution in the winding region is determined, the required shape of the back EMF can be obtained by adjusting the winding distribution. This can be done by modifying the distance between patterns of PCB to control the harmonics in the winding distribution. The proposed method is verified by finite element analysis (FEA) results and it shows the usefulness of the method in eliminating a specific harmonic component in the back EMF waveform of a motor.