• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.1-10
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• 2018

Wide-area monitoring of tree-related high impedance fault (THIF) efficiently contributes to increase reliability of large-scaled network, since the failure to early location of them may results in critical lines tripping and consequently large blackouts. In the first place, this wide-area monitoring of THIF requires managing the placement of sensors across large power grid network according to THIF detection objective. For this purpose, current paper presents a framework in which sensors are distributed according to a predetermined risk map. The proposed risk map determines the possibility of THIF occurrence on every branch in a power network, based on electrical conductivity of trees and their positions to power lines which extracted from spectral data. The obtained possibility value can be considered as a weight coefficient assigned to each branch in sensor placement problem. The next step after sensors deployment is to on-line monitor based on moving data window. In this on-line process, the received data window is evaluated for obtaining a correlation between low frequency and high frequency components of signal. If obtained correlation follows a specified pattern, received signal is considered as a THIF. Thereafter, if several faulted section candidates are found by deployed sensors, the most likely location is chosen from the list of candidates based on predetermined THIF risk map.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1491_1492
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• 2009

The impedance of a vertical grounding electrode is not lowered by expanding the dimension of the grounding electrode, and the length of thr vertical grounding electrode which shows the minimum value of the grounding impedance for each condition of frequency and soil characteristics is existent, and it is defined as Critical length. In this paper, the critical lengths for the vertical grounding electrodes are calculated by using the distributed parameter circuit model. The adequacy of the simulations has been confirmed by comparing the simulated results with the measured results.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.260-264
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• 2003

In this paper, a $\lambda/4$ hairpin resonator is proposed to reduce the size of planar resonators for a LTCC MLC bandpass filter. The $\lambda/4$ hairpin resonator operates as stepped impedance resonator (SIR) without changing the width of the planar resonator. It is composed of two sections those are parallel coupled line and transmission line. The characteristic impedance of two sections is different each other. The design formulas of the bandpass filter using the coupling element at the arbitrary position are derived from even and odd-mode analysis. The formulas can take account of the arbitrary coupling of lumped ana/or distributed resonators. The advantage of this filter is its abilities to change freely the coupling structure between two resonators. Experimental bandpass filters for 2.4GHz Band are implemented and their performances are shown.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.10
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• pp.780-787
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• 2014

This paper experimentally deals with the vibration characteristics of flat ring transducers used for ultrasonic sensors and actuators. Radial vibration mode, which is the fundamental mode of a thin piezoelectric transducer, was measured by a laser in-plane vibrometer. An impedance analyzer was used to measure natural frequencies. The results measured by experiments verified theoretical predictions. The vibration characteristics of ring transducers were identified according to the outer diameter size. The shape of the fundamental mode is almost uniform but slightly decreases from the inner to the outer circumferential surfaces. The natural frequency of the fundamental mode decreases as the outer diameter increases. It appears that the ring type transducer is suitable to excite uniformly distributed vibration on a flat surface.

• Journal of Power Electronics
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• v.16 no.3
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• pp.1046-1055
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• 2016

A controller to mitigate the destabilizing effect of constant power load (CPL) is proposed for a DC/DC buck-boost converter. The load profile has been considered to be predominantly of CPL type. The negative incremental resistance of the CPL tends to destabilize the feeder system, which may be an input filter or another DC/DC converter. The proposed sliding mode controller aims to ensure system stability under the dominance of CPL. The effectiveness of the controller has been validated through real-time simulation studies and experiments under various operating conditions. The controller has been demonstrated to be robust with respect to variations in supply voltage and load and capable of mitigating instabilities induced by CPL. Furthermore, the controller has been validated using all possible load profiles, which may arise in modern-day DC-distributed power systems.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.283-287
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• 2003

A new method to miniaturize ${\lambda}/4$ transmission line of power divider is proposed. The method utilizes simple combination of the shorted coupled-line pair instead of the transmission line with very high impedance and shunt lumped capacitors. The length of ${\lambda}/4$ transmission line of power divider is about 16% over the conventional power divider at 1 GHz.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1896-1899
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• 1997

In this paper, New radiation system is presented to improve efficiency and distribution of MWO. And it has one input for two excitatied lines with located on them radiation elements(slots). Radiation elements are distributed along the lines the way that the same electrical distances from the magnetron. New radiation system recompences change of impedance at wide b and frequency.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.7
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• pp.966-973
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• 2011

Power distribution onboard vessel is typically configured as ungrounded system due to the ability to continuously supply electric power even when an earth fault occurs. The impedance connections between 3 phase power lines and hull cause the line-to-hull voltages to become unstable and increased in case the impedances are unbalanced, bringing the situation susceptible to electric shock and deterioration of insulation material. Also the line-to-hull voltage can reach to a certain maximum value in the steady state depending on the distributed capacitances and grounding resistances between lines and hull. This study suggests how to find and calculate the maximum line-to-hull voltage in view of magnitude and phase angle based on the vector diagram.

• Journal of KSNVE
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• v.8 no.6
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• pp.1113-1120
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• 1998

For an analysis of some Helmholtz resonators, it is likely to be more appropriate to consider acoustic field within cavity than just the 1-DOF analogous model. However, a design method that considers increased parameters than the lumped model. is not a trivial process due to the trade-off effect among the parameters. In this paper. the genetic algorithm. one of the optimization technique that rapidly converges to global fittest solution and robust convergence. is applied to the design process of Helmholtz resonators. Results show that the genetic algorithm can be successfully and efficiently used to find the resonant frequencies for both lumped model and distributed model.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.7
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• pp.1263-1269
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• 2009

Stable and sustainable power supply means maintaining a certain level of power quality and service while securing energy resource and resolving environmental issues. Distributed generation (DG) has become an essential and indispensable element from environmental and energy security perspectives. It is known that voltage violation is the most important constraint for load variation and the maximum allowable DG. In distribution system, sending voltage from distribution substation is regulated by ULTC (Under Load Tap Changer) designed to maintain a predetermined voltage level. ULTC is controlled by LDC (Line Drop Compensation) method compensating line voltage drop for a varying load, and the sending voltage of ULTC calls for LDC parameters. The consequence is that the feasible LDC parameters considering variation of load and DG output are necessary. In this paper, we design each LDC parameters determining the sending voltage that can satisfy voltage level, decrease ULTC tap movement numbers, or increase DG introduction. Moreover, the maximum installable DG capacity based on each LDC parameters is estimated.