• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2008년도 제39회 하계학술대회
• /
• pp.468-469
• /
• 2008

In this paper, the effects of earth continuity conductor are deeply analyzed for reducing the level of induced sheath voltage at the single point bonded sections. The various installation conditions of an earth continuity conductor are considered including conductor dimensions, its spacing from the three phase cables, and utilization of two earth continuity conductors when the grounding fault occurs on real power cable systems. Finally, the transient characteristics including reduction effects of induced sheath voltage are proved by EMTP simulations. The optimal installation condition of earth continuity conductor is also proposed based on those results.

• 한국지구과학회지
• /
• 제28권6호
• /
• pp.707-719
• /
• 2007

교육활동에서 교사는 핵심적인 역할을 수행하고 있으며, 교육활동에 대한 교사들의 인식과 지향은 교육의 실천적인 맥락에서 핵심적인 요소로 작동한다. 따라서 과학교사의 지구계 수업에 대한 인식과 지향을 분석하는 것은, 지구계 교육의 목표가 현실에서 어떠한 모습으로 구현될지 가늠할 수 있게끔 한다. 이러한 생각을 바탕으로 이 연구에서는 두 명의 과학교사가 작성한 교수 학습계획안과 심층면담을 통하여 이들이 지구계 교육에 대한 인식을 알아보고, 교사의 지향을 수업에 대한 일반적 관점과 통합의 관점에서 분석하였다. 연구 결과 지구계 교육의 궁극적 겨냥점인 '전지구적 과학소양'에 대한 교사의 충분한 이해가 선행될 때 그 취지가 충분히 반영된 지구계 수업이 실천될 수 있는 것으로 나타났다. 또한 교사가 전 지구적 과학 소양을 함양하기 위해서는 네트워크 통합을 포함한 다양한 통합의 상(像)이 교사에게 구체적으로 제시될 것이 요구되었다. 아울러 현장에서 지구계 수업을 활성화하기 위해서는 지구계 교육 커리큘럼 구성에 대한 제도적인 뒷받침이 필요한 것으로 보인다.

• 한국과학교육학회지
• /
• 제29권8호
• /
• pp.963-977
• /
• 2009

이 연구의 목적은 지구계 교육의 학습자로서 대학생들의 지구계 순환에 대한 인식을 밝혀 교육에의 시사점을 찾는 것이다. 지구과학 교양 수업을 수강하는 62명의 비과학 전공 대학생들을 대상으로 8주 동안 창의적 이야기 쓰기 활동을 실시하였다. 창의적 이야기는 스토리맵 그리기 방법으로 순환의 구성 개념과 유형을 분석하여 범주화 하였다. 지구계의 순환 구성 개념은 32가지로 매우 다양하게 표출되었고, 순환 유형은 원형과 복합형이 다수였으나 일부 사례는 순환 고리를 완성하지 못한 가지형과 선형으로 표현되었다. 지구계 순환에 대한 대학생들의 인식은 자연-생물계에 편향되어 있으며, 자연-생물계와 인간계의 3 범주를 모두 인식한 사례는 30% 미만으로 나타났다. 지구계 교육을 통해 인간 활동에 의한 피드백의 영향을 인지할 수 있도록 순환을 소재로 교수 내용을 다양화 하고, 학습자의 시스템 사고를 지원해야 하겠다.

• 전기학회논문지
• /
• 제65권1호
• /
• pp.232-238
• /
• 2016

This paper presents protection techniques against electric shock in low voltage DC(direct current) grounding systems depending on the analysis of earth fault current paths. Firstly, the comparison between alternating current and direct current on human was conducted, and current threshold values for each current path and for long duration were analyzed. Secondly, the analyses of the earth fault current flows were performed depending on the grounding types and earth fault conditions. Lastly, based on these analyses, adequate protection measures of electric shock depending on low voltage DC grounding types were provided.

• 제어로봇시스템학회논문지
• /
• 제13권1호
• /
• pp.72-78
• /
• 2007

Determination of the local vertical is not trivial for a moving vehicle and in general will require corrections for the Earth geophysical deflection. The vehicle's local vertical can be estimated by INS integration with initial alignment in SDINS(Strap Down INS) system. In general, the INS has drift error and it cause the performance degradation. In order to compensate the drift error, GPS/INS augmented system is widely used. And in the event that GPS is denied or unavailable, celestial navigation using star tracker can be a backup navigation system especially for the military purpose. In this celestial navigation system, the vehicle's position determination can be achieved using more than two star trackers, and the accuracy of position highly depends on accuracy of local vertical direction. Modern tilt sensors or accelerometers are sensitive to the direction of gravity to arc second(or better) precision. The local gravity provides the direction orthogonal to the geoid and, appropriately corrected, toward the center of the Earth. In this paper the relationship between direction of center of the Earth and actual gravity direction caused by geophysical deflection was analyzed by using precision orbit simulation program embedded the JGM-3 geoid model. And the result was verified and evaluated with mathematical gravity vector model derived from gravitational potential of the Earth. And also for application purpose, the performance variation of pure INS navigation system was analyzed by applying precise gravity model.

• 한국지구과학회지
• /
• 제43권4호
• /
• pp.532-538
• /
• 2022

Under anoxic conditions, this study investigated removal of dissolved As(III) by Si and Al oxides including natural sand, chemically washed sand (silica), alumina, and activated alumina. Despite the similar surface area, natural sand showed greater extents of As(III) sorption than chemically washed sand. This was likely due to the high reactivity of Fe(oxyhydr)oxide impurities on the surface of natural sand. For both sands, As(III) sorption was the greatest at pH 7.1, in agreement with the weakly dissociating tendency of arsenous acid. Also, the least sorption was observed at pH 9.6. At basic pH, elevated silicate, which originated from the dissolution of silica in sands, would compete with As(III) for sorption. Due to the highest surface area, activated alumina was found to quantitatively immobilize the initially added As(III) (6.0×10^-7-2.0×10^-5 M). Alumina showed As(III) sorption compared to or greater than chemically washed sand, although the former had less than 6% of the surface of area the latter. The greater reactivity of alumina than chemically washed sand can be explained by using the shared charge of oxygen.

• 한국철도학회논문집
• /
• 제9권4호
• /
• pp.394-400
• /
• 2006

Since Seoulmetro built the first line of electric railway at seoul 1974, the passengers of railway have been increased rapidly, and electric railway requires more electric power for the greater capacity of transport. It is important that we prevent the accidents related with the subway, because all systems of subway are constructed in artificial underground structure. Since the previous versions of the earth system were built to meet the old standards of the electric facility for the lightning, some accidents related with the DC earth fault are causing secondary damages to the electric equipments. So, the old grounding system must be improved, and new standards of grounding system are required. We compare the grounding systems of the domestic railway corporations and the accidents that are related with the grounding systems. And we give ideas to improve the grounding systems and present standards which are suitable to electric railway.

• 한국지구과학회지
• /
• 제38권5호
• /
• pp.357-366
• /
• 2017

Urban planning and engineering undergraduate students need to understand the earth physical systems and that how human beings interact with the earth systems to planning and engineering urban area. The eco-friendly or geo-friendly design and planning of an urban area is a critical issue not only for economic benefits but more importantly for the sustainable future of urban life. However, little study has been done dealing with the urban engineering students' understanding of the earth as a system and what pedagogical approach is appropriate to improve their understanding of the earth as a system. This study is to investigate the impact of a purposely designed ESS course on urban engineering students' understanding of the earth as a system and their perceptions about the instructional approaches of the course on their learning competency. This study utilized a mixed-methodology with three main data sources: concept maps, student's perception survey about their learning competency, and course contents. Both the survey and concept maps were analyzed quantitatively as well as qualitatively. The result of this study showed that the urban engineering students' experience of team-based research about the topic they chose based on their own interest had a positive impact on their understanding of the earth as a system and their learning competency. The results of this study suggest that structuring and presenting the earth system contents in the context of engineering students' understanding and their future career be effective not only for the improvement of students' content knowledge but also for the enhancement of their learning competency such as creativity and problem-solving skills in everyday life situation.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2005년도 ICCAS
• /
• pp.1867-1870
• /
• 2005

The celestial navigation is one of alternatives to GPS system and can be used as a backup of GPS. In the celestial navigation system using more than two star trackers, the vehicle's ground position can be solved based on the star trackers' attitude information if the vehicle's local vertical or horizontal angle is given. In order to determine accurate ground position of flight vehicle, the high accurate local vertical angle measurement is one of the most important factors for navigation performance. In this paper, the Earth geophysical deflection was analyzed in the assumption of using the modern electrolyte tilt sensor as a local vertical sensor for celestial navigation system. According to the tilt sensor principle, the sensor measures the tilt angle from gravity direction which depends on the Earth geoid surface at a given position. In order to determine the local vertical angle from tilt sensor measurement, the relationship between the direction of gravity and the direction of the Earth center should be analyzed. Using a precision orbit determination software which includes the JGM-3 Earth geoid model, the direction of the Earth center and the direction of gravity are extracted and analyzed. Appling vector inner product and cross product to the both extracted vectors, the magnitude and phase of deflection angle between the direction of gravity and the direction of the Earth center are achieved successfully. And the result shows that the angle differences vary as a function of latitude and altitude. The maximum 0.094$^{circ}$angle difference occurs at 45$^{circ}$latitude in case of 1000 Km altitude condition.

• 한국암석학회:학술대회논문집
• /
• 한국암석학회 1998년도 추계학술대회
• /
• pp.25-25
• /
• 1998