• Journal of the Korean Society of Safety
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• v.33 no.2
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• pp.14-20
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• 2018

In this study, we analyze the current status of major disasters in distribution works and propose safety measures through the distribution live-line work method and electric shock risk assessment. The result of analyzing the ratio of electric shocks to the occurrence of industrial accidents in the recent 13 years shows that the death rate is higher than other industries, especially the construction industry occupying most of the disaster, and it is higher than the collapse disaster. We analyze statistic data of 101 victims selected as core words of live work, distribution line, pole and 22.9 kV in the investigation report of major accident of electric shock fatal from 2001 to 2014. The safety measure was established through the risk assessment of the distribution method using the standard model of the risk assessment based on the results of electric shock analysis on the distribution line. In order to prevent the electric shock accident which is recently being discussed, the risk assessment procedure were carried out in the above-mentioned 22.9kV special high voltage live-line operation method. We derived the risk reduction plan for the distribution line from the results of the major accidents statistic and demonstration of the line works.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.10
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• pp.895-900
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• 2007

Partial discharge(PD) test can be performed either when the rotating machine is not operating(off-line) or during normal machine operation(on-line). This paper presents an on-line and off-line PD test on a large hydro-generator and induction motor using the same PD acquisition system(PDAS) and ceramic coupler(CC) sensor. PD signal characteristics of CC sensor proved similar with that of epoxy mica coupler(EMC) sensor as a results of PD test for simulated defect winding and frequency response test. A comparison of on-line and off-line PD test for PD characteristic parameters-phase resolved PD(PRPD), maximum PD value(Qmax) and PD occurrence energy(POE)-indicated that on-line PD test could reliably and effectively diagnose insulation conditions which were verified by off-line PD test.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.4
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• pp.35-40
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• 2012

In this study, the ultraviolet (UV) intensity of polymer insulator was measured using the Anti-Reflective (AR) coating lens on the occurrence of corona discharge. The UV intensity was compared before and after the AR coating. Under the 200-260[nm] of UV lens, the reflection rate before AR coating was 7.5~5.5[%] with 85-89[%] of transmission rate. After AR coating, however, the reflection rate decreased to 1.3~1.22[%] with improved transmission (97.4~97.6[%]). Then, the UV intensity by distance was measured in the polymer insulator. According to the measurement, the UV intensity increased 6.5 times at 37.5[%] of Vm/Vbd with 5[m] of distance. As distance increased, the growth rate declined. As high voltage increased, in addition, AR coating was less effective due to the count error caused by the UV sensor pulse signal overlap. Therefore, it appears that it would be more effective to detect corona discharge with 5[m] or less of distance at diagnosis of power facilities by AR coating and UV sensor sensitivity.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.54-60
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• 2014

This paper describes electric shock accidents on a 4.16 kV class circuit breaker for power plant. Electric shock accidents mostly involve damage of human life, in comparison with electrical fire, rate of human death tend to be higher in electric shock accidents. Specially, in a high voltage facilities rate of human death comprised about 43.7% by electric shock accidents. If electric shock accidents happen in a 4.16 kV class circuit breaker for power plant, then the power plant discontinue power production. Electric shock accidents in a power plant have a great ripple effect such as an electric power shortage. In this paper, we analyzed electric shock accidents on a 4.16 kV class circuit breaker for power plant. From the analysis results, we confirmed a cause of electric shock accidents on a 4.16 kV class circuit breaker, it happened by defect of interlock equipment or occurrence of breakdown between first feeder contactor and shielding plate. In order to reduce electric shock accidents on a 4.16 kV class circuit breaker, the power plant should consider improvement of interlock equipment and insulation of feeder contactor in circuit breaker.

• Proceedings of the KIEE Conference
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• summer
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• pp.48-50
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• 2004

The energization of high voltage transmission lines and transformers, that is an inevitable process in most countries as the first restorative action for wide-area blackout, may induce overvoltages such as sustained overvoltage, transient overvoltage and harmonic resonant overvoltage. And these may cause damages to power system equipments or failure of surge arresters. The harmonic resonant overvoltage originates in switching operations and nonlinear characteristics of equipments. Actually it is difficult to predict the occurrence of harmonic overvoltage, since they result from nonlinear characteristics of transformers and other equipments. This paper describes the analysis of domestic primary restorative transmission system using PSCAD/EMTDC. The harmonic resonance is verified and the solution to prevent harmonic resonance is proposed in this paper. As a result, the PSCAD/EMTBC simulation showed slightly conflictive results that had been presented by IEEE Power System Restoration Working Group report.

• Journal of Advanced Marine Engineering and Technology
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• v.10 no.2
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• pp.156-164
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• 1986

In the case of boiling on high temperature wall, vapor film covers fully or parcially the surface. This phenomenon, film boiling or transition boiling, is very important in the surface heat treatment of metal, design of cryogenic heat exchanger and emergency cooling of nuclear reactor. Mainly supposed hydraulic-thermal accidents in nuclear reactor are LCCA (Loss of Coolant Accident) and PCM (Power-Cooling Mismatch). Recently, world-wide studies on reflooding of high temperature rod bundles after the occurrence of the above accidents focus attention on wall temperature history and required time in transient cooling process, wall superheat at rewet point, heat flux-wall superheat relationship beyond the transition boiling region, and two-phase flow state near the surface. It is considered that the further systematical study in this field will be in need in spite of the previous results in ref. (2), (3), (4). The paper is the study about the fast transient cooling process following the wall temperature excursion under the CHF (Critical Heat Flux) condition in a forced convective subcooled boiling system. The test section is a vertically arranged concentric annulus of 800 mm long and 10 mm hydraulic diameter. The inner tube, SUS 304 of 400 mm long, 8 mm I.D, and 7 mm O.D., is heated uniformly by the low voltage AC power. The wall temperature measurements were performed at the axial distance from the inlet of the heating tube, z=390 mm. 6 chromel- alumel thermocouples of 76 .mu.m were press fitted to the inner surface of the heating tube periphery. To investigate the heat transfer characteristics during the fast transient cooling process, the outer surface (fluid side) temperature and the surface heat flux are computed from the measured inner surface temperature history by means of a numerical method for inverse problems of transient heat conduction. Present cooling (boiling) curve is sufficiently compared with the previous results.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.8 no.6
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• pp.853-861
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• 2018

This paper proposes the application of harmonic constraints to address the problems caused by abnormal voltage increases when electric railway vehicles are running. The AC line that supplies the train with power during operation is used to provide electricity of 25kV/60 Hz, but gradually the size and frequency of harmonics involved in the line are varied with the technological evolution of the railroad vehicle electrical equipment. An increase in heat losses due to the failure of the instrument transformer (PT), the main circuit device, which is a serious problem with the recent train safety operation, or to the main displacement voltage. When high frequency components are introduced through low frequency Transformers of the main circuit device, the high intensity of the components is caused by the high intensity of the core and the current flow of the parasitic core is increased, thus generating heat. To solve this problem, the recent adjustment of the sequence has applied artificial NOTCH OFF of the power converter. However, the method of receiving and controlling the OFF signal operates by interaction between the ground and the vehicle's devices, thus it is invalid in the event of failure, and an actual accident is occurring. Therefore, the harmonic currents were required to prevent possible flow of harmonics, and conducted a study to prevent accidental occurrence of train accidents and to verify feasibility of the device through the simulations of the train's experimental analysis and the simulations of the train for safe operation.

• Journal of Electrochemical Science and Technology
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• v.13 no.1
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• pp.128-137
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• 2022

For this study, the sol gel method was used to synthesize the spinel LiNi_0.5Mn_1.5O₄ (LNMO) electrode material. Structural, morphological, electrochemical, and kinetic aspects of the LNMO have been characterized. The synthesized LNMO was indexed with the Fd3m cubic space group. The excellent capacity retention indicates that the spinel framework of LNMO has the ability to withstand high rate charge-discharge throughout long cycle tests. The Li diffusion coefficient (D_Li) changes non-monotonically across three orders of magnitude, from 10^-9 to 10^-12 cm² s^-1 determined from GITT method. The variation of D_Li seemed to be related to three oxidation reactions that happened throughout the charging process. A small dip in D_Li at the beginning stage of Li deintercalation is correlated with the oxidation of Mn³⁺ to Mn⁴⁺. While two pronounced D_Li minima at 4.7 V and 4.75 V are due to the oxidation of Ni²⁺/Ni³⁺ and Ni³⁺/Ni⁴⁺ respectively. The depletion of D_Li at the high voltage region is attributed to the occurrence of two successive phase transformation phenomena.

• International Journal of Highway Engineering
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• v.19 no.6
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• pp.105-115
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• 2017

PURPOSES : The occurrence of unexpected disasters, including fire events, increases as the road network becomes complicated and traffic volume increases. When a fire event occurs on and under bridges, the damage extensively influences direct damage to structures, vehicles, and human life and secondary socioeconomic issues owing to traffic blockage. This study investigated potential fire-hazard risks on bridges of the Korean national route road. METHODS : The investigation was conducted using field investigation and analysis with satellite pictures and road views from commercial websites and the Bridge Management System (BMS). From the filed investigation, various potential fire resources were identified. The satellite pictures and road views were helpful in measuring and recognizing conditions underneath bridges, stowage areas, etc. RESULTS : There are various potential fire resources underneath bridges such as piled agricultural products, parked petroleum tanks, construction equipment, and attached high-voltage cables. A total of 94.6% of bridges have underneath clearances of less than 15 m. A bridge underneath volume that can stow a potential fire hazard resource was $7,332m^3$ on average, and most bridges have about $4,000m^3$ of space. Based on the BMS data, the amounts of PSC and steel girders were 29% and 25%, respectively. CONCLUSIONS : It was found that the amount of stowed potential fire hazard resources was proportional to the underneath space of bridges. Most bridges have less than 15 m of vertical clearance that can be considered as a critical value for a bridge fire. The fire risk investigation results should be helpful for developing bridge fire-protection tools.

• Safety and Health at Work
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• v.4 no.3
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• pp.156-159
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• 2013

Background: Cardiac pacemakers are known to be susceptible to strong electromagnetic fields (EMFs). This in vivo study investigated occurrence of electromagnetic interference with pacemakers caused by common environmental sources of EMFs. Methods: Eleven volunteers with a pacemaker were exposed to EMFs produced by two mobile phone base stations, an electrically powered commuter train, and an overhead high voltage transmission lines. All the pacemakers were programmed in normal clinically selected settings with bipolar sensing and pacing configurations. Results: None of the pacemakers experienced interference in any of these exposure situations. However, often it is not clear whether or not strong EMFs exist in various work environments, and hence an individual risk assessment is needed. Conclusions: Modern pacemakers are well shielded against external EMFs, and workers with a pacemaker can most often return to their previous work after having a pacemaker implanted. However, an appropriate risk assessment is still necessary after the implantation of a pacemaker, a change of its generator, or major modification of its programming settings.