• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.10
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• pp.82-88
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• 2014

This paper presents the results of model tests for the attachment process of lightning leader to ground which is one of poorly understood processes of cloud-to-ground lightning discharges. In order to simulate the attachment process of lightning leader to ground, we investigated the discharge characteristics of air gap between the tip of needle-shaped electrode and the soil surface as a parameter of moisture content in soils when the positive and negative $1.2/50{\mu}s$ lightning impulse voltages are applied. The breakdown voltage and the discharge light were observed. As a result, the attachment processes of lightning leader to ground are strongly dependent on the grain size and the moisture content of soils. The time to breakdown was shortened with increasing the magnitude of incident impulse voltages. The delay time from application of the highest voltage to breakdown in sand is shortened with increasing the moisture content. The delay time from application of the voltage to breakdown in gravel varied from about $0.5{\mu}s$ to several ${\mu}s$. As the moisture content in soil increases, the breakdown voltages are decreased and the breakdown voltage versus time to breakdown curves are shifted toward the lower side. The results obtained in this work are similar to those for non-uniform air gap stressed by lightning impulse voltages.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1807-1809
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• 1996

The axial discharge at switching operations of EHV $SF_6$ disconnector can lead to the breakdown to the enclosure. Precursor in periphery zone leads to formation of leader over some time delay. Injected charge value depends on electric field and gap geometry. The calculation method for parameters of $SF_6$ insulation for DS in EHV-GIS is suggested by using the new criterion of leader inception in connection with periphery field nearby the boundary of streamer zone.

• Journal of Astronomy and Space Sciences
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• v.35 no.2
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• pp.93-103
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• 2018

Non-specular, vertically upward transit, fast-moving radar echoes are observed in the summer polar upper mesosphere near 90 km using 52 MHz VHF radar at Esrange, Sweden. By resolving maximum echo power movement, the unusual meteor trails propagate vertically upward with taking horizontal displacements at an initial speed of 10 km/s exponentially decreasing with increasing height from 85-89 km, lasting for 3.5 sec. Another upward transit is observed as following a downward transit echo target in about ~1 sec, lasting over 5 sec. The upward motion cannot be explained with the dynamics of penetrating meteors or by atmospheric dynamics. The observation proposes that secondary produced plasma jets occurring from meteor trail are possibly responsible for upward fast moving echoes. The long-lasting (3-5 sec), ascending meteor trails at speeds of a few $10^4m/s$ are distinctive from any previous occurrences of meteors or upper atmospheric electrical discharges in the aspect of long-lasting upward/downward motions. This result possibly suggests a new type of meteor-trail leader discharge occurring in the summer polar upper mesosphere and lower thermosphere.

• International Journal of Safety
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• v.5 no.2
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• pp.18-23
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• 2006

Studies have claimed that ESE (Early Streamer Emission) air terminals offer a vastly increased zone of protection over that of traditional lightning rods (Franklin rods) by causing the emission of an upward streamer/leader: The upward streamer/leader will propagate towards the tip of the downward leader at an early stage in the attachment process.. This paper shows the results of a performance evaluation test of a particular type of the ESE air terminal (called "ElecHippo") with a simple rod tested at the Korea Electrotechnology Research Institute (KERI). The corona emission current of the ElecHippo made by Yong-Jin Enterprise Corp. has also been measured at the Occupational Safety & Health Research Institute (OSHRI). The results show that the ElecHippo meets the French standard of NFC 17-102-1995. The results also verify the ESE performance by measuring the ion emission current generated in the discharge electrode gap as a function of the capacitance and inductance of the equipped devices. Finally, we propose a new method for grounding the system to reduce the lightning damage by combining the ESE air terminal, the early discharge earth plate, the lightning strike recorder and the surge protection device.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.2002-2004
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• 2000

The discharge processes in electro-negative gases with non-uniform field gape are composed of the formation of pulsed streamer corona, the transition of the streamers into leader step, the temporal development of the leader channel, and the stepped propagation of leader through the gap. In this paper, the first corona inception characteristics in $SF_6$ gas and $SF_{6}-N_{2}$ mixtures, related to the propagation of loader and the space charge effect, were experimentally investigated with positive and negative transient impulse voltages.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2140-2142
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• 2005

This paper presents the experimental results on the preliminary breakdown characteristics under a highly non-uniform electric field in $SF_6/CO_2$ gas mixtures. The impulse preliminary breakdown developments are investigated by the measurements of corona current and light emission images. As a result, the preliminary breakdown development mechanisms for both positive and negative polarities are same. The first streamer corona is initiated at the tip of needle electrode, and the leaders develop with a stepwise propagation and bridge the test gap. The pause time of leader pulses in the positive polarity is significantly shorter than that in the negative polarity. Also, the time interval between the first streamer corona onset and breakdown in the negative polarity was much longer than that in the positive polarity The discharge channel paths in the positive polarity were zigzag. On the other hands, the leader channel in the negative polarity was thicker than that in the positive polarity.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.12
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• pp.1290-1295
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• 1991

The paper presents the measurement results on the parameters affecting the breakdown mechanism of a large air spacing under switching impulse voltages. Measured parameters are the velocities of leader channels, predischarge currents, electric charges injected into the rod-plane air gap and electric field intensities on the plane. For the 3m air gap under switching impulse voltages, the velocities of leader channel have been measured to be of 1cm/x10S0-6Ts - 5cm/x10S0-6Ts, electric field intensity of 2kv/cm, predischarge current of 1.2-1.6A, the charges injected into the air gap of 11-40x10S0-6TC for 400-887kV impulse voltages.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.1
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• pp.85-90
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• 2006

This paper presents experimental results relating to the preliminary breakdown characteristics in $SF_6/CO_2$ gas mixtures under a highly non-uniform electric field. The impulse pre-breakdown developments are investigated by the measurements of corona current and light emission images. As a result, the preliminary breakdown development mechanisms for both the positive and negative polarities were fundamentally same. The first streamer corona was initiated at the tip of needle electrode, and the leaders developed with a stepwise propagation and bridged the test gap. The pause time of leader pulses in the positive polarity was significantly shorter than that in the negative polarity. Also, the time interval between the first streamer corona onset and breakdown in the negative polarity was much longer than that in the positive polarity. The discharge channel path in the positive polarity was zigzag, and the leader channel in the negative polarity was thicker and brighter than that in the positive polarity.

• Transactions of the Korean hydrogen and new energy society
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• v.17 no.3
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• pp.317-323
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• 2006

Electric conductive material should be homogeneously mixed with sulfur in sulfur electrode fabrication of lithium/sulfur battery, because sulfur is electric insulator. In this paper electrochemical properties of Li/S battery was studied with various compositions of sulfur electrodes. When content of sulfur changed from 40 wt.% to 80 wt.%, the 60 wt.% sulfur electrode showed the maximum capacity of 1489 mAh/g-sulfur. Electrochemical properties of Li/S battery using 60 wt.% sulfur was also investigated with various carbon contents. The discharge capacity changed as a function of carbon contents. The optimum composition was 25 wt.% carbon for 60 wt.% sulfur electrode.

• Journal of Korean Neurosurgical Society
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• v.29 no.12
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• pp.1620-1627
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• 2000

Objectives : DAMA cases were analyzed to examine what the main casual factors of DAMA were and how to deal with these cases effectively in hospital with the DAMA interdisciplinary team including medical social worker whose role is to perform psycho-social assessment, family counsel, to evaluate family's DAMA need. Patients and Methods : The content analysis of medical record and social work record were reviewed in 37 cases referred by medical doctor to DAMA team. These cases were reported by patients' self discharge request or family's request for discharge from September 1998 to February 2000. The DAMA team consists of Assistant Director of Hospital as team leader, medical staff in-charge, social worker, QI nurse, other staff members who are not involved in direct treatment for patient, and administrative clerk. Results : The results of content analysis are as follows : 1) The most causal factors of DAMA consist of combination of more than 2 factors. 2) The major decision-maker is revealed to be son and daughter of patient. 3) In 59.4% of cases, family was not informed of patients' prognosis, alternatives, the consequence of DAMA at all. 4) In cases of DAMA report, the rapid intervention of social worker is carried out. Conclusion : In this study, we propose the interdisciplinary team approach to make decision legitimately and ethically for DAMA. The suggestions from this study are as follows : 1) To deal with DAMA case properly, the interdisciplinary team approach should be considered. 2) The criteria for DAMA case should be formed carefully. For the explicit selection of DAMA case, preliminary system for high-risk patient screening is recommended. 3) The medical social worker is available for the psycho-social problems of the patient once family members. For the effective family counselling, discharge planning and nursing home placement, the participation of medical social worker should be mandatory.