• 전력전자학회:학술대회논문집
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• 전력전자학회 2007년도 추계학술대회 논문집
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• pp.115-117
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• 2007

This paper is analyzed for DC-DC chopper performance of high efficiency added in electric isolation. The general converters of high efficiency are made that the power loss of the used switching devices is minimized. To achieve high efficiency system, the proposed chopper is constructed by using a partial resonant circuit. The control switches using in the chopper are operated with soft switching for a partial resonant method. The control switches are operated without increasing their voltage and current stresses by the soft switching technology. The result is that the switching loss is very low and the efficiency of chopper is high. And the proposed chopper is added in a electric isolation. When the power conversion system is required to electric isolation, the proposed chopper is adopted with system development of high efficiency. The soft switching operation and the system efficiency of the proposed chopper is verified by digital simulation and experimental results.

• 전기학회논문지
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• 제63권3호
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• pp.395-403
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• 2014

This paper presents a new approach to improve the signal to noise ratio (SNR) for local seismic disaster preventing system in densely populated area. The seismic data measured in the local site includes various sensing noises (offset or measurement noise) and man-made/natural noises (road and rail traffic noise, rotating or hammering machinery noise, human activity noise such as walking and running, wind/atmospheric pressure-generated noise, etc.). These additive noises are different in time and frequency characters. The proposed method uses 3-stages processing to reduce these different additive noises. In the first stage, misalignment offset noise are diminished by time average processing, and then the second and third stages, coherent/incoherent noises such as man-made/natural noises are suppressed by array stacking. In addition, we derived the theoretical equation of the SNR gain improved by the proposed method. To evaluate the performance of the proposed method, computer simulations were performed with real seismic data and test equipment generated data as the input.

• 전기학회논문지
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• 제66권8호
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• pp.1187-1194
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• 2017

After North American wide area black out on August 14, 2003, various studies have been conducted to find out the reason of the disaster. One of main reasons was misoperation of generator protection system. Since then, protective coordination between generator protection system and excitation system controls has been hot issue among electrical engineers. Among various generator protection relays, in this paper, we focused on generator overvoltage and overexcitation relay, which protect the over-flux condition of the generator. Thus, at first, we modeled the generator overvoltage, overexcitation relay and detailed power system including excitation system, governor and etc., based on actual field data. And then, we reviewed the protective coordination of generator overvoltage and overexcitation relay using electromagnetic transient program. In addition, we discussed the protective coordination method for redundant protection relays in both automatic voltage regulator and generator side.

• 대한안전경영과학회지
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• 제17권4호
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• pp.113-121
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• 2015

This study aims to examine the risk of electrical fire in places where electric heat wires are used. In general, the use of electric heating wires is becoming more common and prevalent in a bid to prevent increasing damage caused by freezing and bursting in residential water pipes, factory pipes and irrigation pipes in vinyl greenhouse and a variety of heat wire products are available in market with legal safety requirements imposed on them. However, the widespread use of anti-freezing burst heat wire products has caused increasing incidents of fire, which often fail to be incorporated into statistics due to quick onsite extinguishing and insignificant damage although damage is gradually on the rise. Against this backdrop, this study aims to look into the possibility of ignition caused by electric heat wires and the mechanism of how it turns into catching fire through overheat and short circuit tests for anti-freezing burst electrical heat wires (hereinafter called the 'heat wire') and expects to serve as the basis for further observations and analyses on the cause of fire and the process of ignition in a scientific manner.

• Smart Structures and Systems
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• 제1권2호
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• pp.141-158
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• 2005

A new design of distributed crack sensors based on the topological change of transmission line cables is presented for the condition assessment of reinforced concrete (RC) structures during and immediately after an earthquake event. This study is primarily focused on the performance of cable sensors under dynamic loading, particularly a feature that allows for some "memory" of the crack history of an RC member. This feature enables the post-earthquake condition assessment of structural members such as RC columns, in which the earthquake-induced cracks are closed immediately after an earthquake event due to gravity loads, and are visually undetectable. Factors affecting the onset of the feature were investigated experimentally with small-scale RC beams under cyclic loading. Test results indicated that both crack width and the number of loading cycles were instrumental in the onset of the memory feature of cable sensors. Practical issues related to dynamic acquisition with the sensors are discussed. The sensors were proven to be fatigue resistant from shake table tests of RC columns. The sensors continued to show useful performance after the columns can no longer support additional loads.

• 한국통신학회논문지
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• 제40권2호
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• pp.366-368
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• 2015

이 논문은 재난감지 시스템과 같이 비주기적 패킷이 발생하는 센서 네트워크를 위한 MAC 프로토콜을 제안한다. 기존 무선 센서 네트워크에 사용되던 B-MAC은 짧은 지연시간을 가지지만 과도한 프리엠블과 오버히어링으로 인한 전력손실이 발생하며, S-MAC은 동기화로 인한 전력소모가 많은 단점을 가진다. 따라서 이 논문에서는 S-MAC의 전력 소모를 개선하고 B-MAC의 오버헤드와 오버히어링을 개선한 H-MAC을 제안하고 성능을 분석한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.917-918
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• 2007

The former earth leakage breaker is operating by total leakage current which is the vector-sum of resistive leakage current and capacitive leakage current. However, the electric disaster like the electric shock and fire is caused mainly by resistive leakage current. Therefore, the earth leakage breaker is ideal when it is operating by resistive leakage current. In this paper, the theory for finding the component of resistive leakage current from total leakage current is suggested and it is embodied to actual circuit. The resistive leakage current can be found by integrating the total leakage current during half cycle of line voltage. Thus, we can simply find resistive leakage current by using OP-AMP integrators, and we can confirm that the resistive leakage current is computed exactly from total leakage current obtained by resistive leakage current and capacitive leakage current. The results that the earth leakage breaker is operating within regular interrupt time are verified when the former earth leakage breaker's controller circuit is replaced by the proposed controller circuit.

• 로봇학회논문지
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• 제19권2호
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• pp.149-158
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• 2024

This paper presents a robust autonomous navigation and reconnaissance system for tracked robots, designed to handle complex multi-floor indoor environments with stairs. We introduce a localization algorithm that adjusts scan matching parameters to robustly estimate positions and create maps in environments with scarce features, such as narrow rooms and staircases. Our system also features a path planning algorithm that calculates distance costs from surrounding obstacles, integrated with a specialized PID controller tuned to the robot's differential kinematics for collision-free navigation in confined spaces. The perception module leverages multi-image fusion and camera-LiDAR fusion to accurately detect and map the 3D positions of objects around the robot in real time. Through practical tests in real settings, we have verified that our system performs reliably. Based on this reliability, we expect that our research team's autonomous reconnaissance system will be practically utilized in actual disaster situations and environments that are difficult for humans to access, thereby making a significant contribution.

• 한국안전학회지
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• 제38권5호
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• pp.8-14
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• 2023

Lithium ions can induce the thermal runaway phenomenon and lead to reignition due to electrical, mechanical, and environmental factors such as high temperature, smoke generation, explosions, or flames, which is extremely likely to create safety concerns. Therefore, one of the ways to improve the flame retardancy of the electrolyte is to use a flame-retardant additive. Comparing the associated characteristic value of existing substances with the required experimental value, it was found that these values were either considerably different or were not documented. It is vital to know a substance's combustion characteristic values, flash point, explosion limit, and autoignition temperature (AIT) as well as its combustion characteristics before using it. In this research, the flash point and AIT of materials were measured by mixing a highly volatile and flammable substance, diethyl carbonate (DEC), with flame-retardant dimethyl methylphosphonate (DMMP). The flash point of DEC, which is a pure substance, was 29℃, and that for DMMP was 65℃. Further, the lower explosion limit calculated using the measured flash point of DEC was 1.79 Vol.%, while that for DMMP was 0.79 Vol.%. The AIT was 410℃ and 390℃ for DEC and DMMP, respectively. In particular, since the AIT of DMMP has not been discussed in any previous study, it is necessary to ensure safety through experimental values. In this study, the experimental and regression analysis revealed that the average absolute deviation (ADD) for the flash point of the DEC+DMMP DEC+DMMP system is 0.58 sec and that the flash point tends to increase according to changes in the composition employed. It also revealed that the AAD for the AIT of the mixture was 3.17 sec and that the AIT tended to decrease and then increase based on changes in the composition.

• 지질공학
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• 제28권2호
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• pp.313-324
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• 2018

한반도 지진에 대한 전조인자 연구를 위해 대전, 청원지역 지하수 관측정에서 심도별(-60 m, -100 m)로 화학성분과 라돈, 수위변화를 주기적으로 측정하였다. 관측정 특정심도 지하수의 pH와 전기전도도 값이 포항지진 발생에 따라 큰 폭으로 증가하는 등 비교적 뚜렷한 상관성을 보였다. 주요화학 성분 중에는 대전관측정에서는 ${HCO_3}^-$, $Cl^-$의 농도가 지진과의 연관성 있는 변동을 보이며, 청원지역 관측정에서는 $Mg^{2+}$, $Cl^-$, ${NO_3}^-$의 농도가 변화를 보였다. 그러나 지하수의 주요 화학성분의 변화는 지진발생과의 상관성이 명확하지는 않다. 대전관측정 지하수내 라돈 함량은 지진 발생 전 최저 162 Bq/L에서 지진발생 직후 573 Bq/L로 크게 증가하는 경향을 보여 지진과의 뚜렷한 상관성을 보여주었다. 지하수위의 경우에는 지진발생과의 상관성은 확인되지 않고 갈수기로 인한 지속적인 하강의 양상을 보여주었다. 그러나 포항 진앙지 10 km 이내 국가 지하수 관측정에서는 지진발생 직전 뚜렷한 지하수위의 하강 현상을 보여주었다. 결론적으로 포항지진 진앙지와 약 180 km 이상 떨어진 지역이지만 대전 관측정에서 라돈가스는 지진과 가장 뚜렷한 상관성을 보여 지진전조인자로서의 신뢰성할 수 있는 후보로서 가능성을 확인하였다. pH, 전기전도도, ${HCO_3}^-$, $Cl^-$성분은 지진과 일정 부분 상관성을 보여주었지만 보다 더 장기적인 모니터링을 통하여 지진전조로서 가능성을 확인할 수 있을 것으로 보인다.