• Proceedings of the KSR Conference
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• 2006.11b
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• pp.631-635
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• 2006

DC traction power system is operated ungrounded to minimize the stray current. This causes rail potential increase and makes hazardous condition to the person in touch with running rails. To prevent the hazardous condition, maximum allowable limits on rail potential rise are set by regulations in advanced foreign countries. In this paper, the simplified calculation methods for the rail potential rise and the stray currents are discussed.

• 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 Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1111-1116
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• 2011

Power distribution systems onboard vessels are typically configured without any live line connected to hulls for earthing purpose, where the line to hull voltages are affected and deformed depending on the impedances consisting of insulation resistances and distributed capacitances between power lines and hull. An insulation fault at power lines causes the line to hull voltages to increase to a higher level which brings more possibilities to electric shock and deterioration of insulation material. This study focuses on how to configure a module which enables to continuously monitor the voltages between power line and hull based on the vector diagram by analyzing the neutral point of 3 phase voltages and the algorithm for plotting method on the PC monitors.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1117-1123
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• 2011

Ungrounded power systems are adopted onboard vessels which enable more stabilized power supply even in case of electric leakage to hull. If earthing faults happen at these systems, they make grounding impedances of power lines unbalanced each other on the three phases, resulting in high voltages to hull which can bring more possibilities of electric shocks and electric fires. This study focuses on how to configure a calculation module for transferring a grounded condition by lowered insulation resistance into a vector diagram of the voltages to hull. By using the module, the loci of neutral points were acquired to analyze how voltages to hull are affected by earthing faults and the distributed capacitances between power lines and hull. The suggested module was simulated and compared to the measured values from a test power system in good results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.10
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• pp.73-77
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• 2010

Most accidents occurred in power receiving & transforming facility are ground fault. The quality of power supply is deteriorated since the ground fault is not detected promptly. This paper analyzes the problems about system-grounding type of 2 step power receiving & transforming facility, arrangement of protection relaying scheme and ground-fault protection system of ungrounded system. Then, this paper presents the arranging scheme of system-grounding type to improve power supply reliability.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1948_1949
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• 2009

All the power generating station require dc auxiliary power systems to operate those dc components that must be available if a loss of ac power occur. Some examples of such components are auxiliary motors, circuit breakers, relays and solenoids. The dc source may be one common battery for both power and control or two separate batteries; one for power and another for control. Typically, a dc auxiliary power system is designed as an ungrounded system, instead of grounded system, so that a low-resistance ground fault on one of its two polarities will not affect the operation of the system, thus increasing system reliability and continuity of service. A ground detector should provide a high polarity-to-ground resistance so that a single ground fault occurring on the system will not affect the operation of that system. Sensitive relays have been known to energize momentarily while the cable and capacitive charge to ground shifts[1]. A power station had experienced this kind of incident and performed root cause analysis based on PC based simulation program known as PSpice. This simulation showed adapted relays on the system energize momentarily and design criteria on this relay should be corrected.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.96-102
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• 2001

In construction sites, portable generators and electrical equipments cause frequently electrical accidents due to the poor condition of their usage. However, there are very few technical guidelines on these equipments even though they have serious accident causing potentiality. In order to reduce such accidents in practical and economical, grounding methods are studied in this paper as the countermeasure of electrical accidents. Several Korean national standards and international standards regarding three grounding types are compared each other, and some prevention means of electrical accidents are reviewed in this study. This paper presents the most effective grounding methods by assuming the WCS with the isolated power systems.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.9
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• pp.427-433
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• 2005

In DC tracking power supply system, ground faults are currently detected by the potential relay, 64P. Though 64P relay detects ground fault, it cannot Identify the faulted region which causes long traffic delays and safety problem to passengers. Two new ground fault protective relay schemes that can identify the faulted region are presented in this paper. One is bus differential protective relay and the other is ground overcurrent protective relay. Both type of relays is similar in principle to the ordinary bus differential protective relay and the ground overcurrent relay used in other power system. In DC traction power supply system, since it is ungrounded, ground fault current is not big enough to operate those relays. To solve the problem, a current control device, called device 'X', is newly introduced in both system, which enables large amount of ground fault current flow upon the positive line to ground fault. Algorithms for these relays are developed and their validity are verified by EMTP simulation.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.486-487
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• 2006

The authors have studied on the application of IEC 60364-4-44 to Korean electrical installations of buildings from 2004 sponsored by Korean ministry of commerce, industry and energy and the test field is established in K.E.R.I. (Korea Electrotechnology Research Institute). This paper presents the summary results of establishment of test field and analysis for the application of IEC 60364 in Korea. IEC 60364-4-44 provides rules for the protection against the effects of conducted and radiated disturbances on electrical installations. Especially this standard deals with the protection of low voltage facility against the ground fault in the high voltage side of power distribution system. Many countries define the regulations on the use and production of electrical facilities based on their own power system and technical references which are considered to be suitable for them. The background of circuit of IEC 60364-4-44 is based on the ungrounded system as most of European countries. However, since Korean electric power distribution system is based on multi-grounding system different from European system, it is necessary to evaluate or prove the effect of the IEC 60364-4-44 for introducing and applying it to the domestic grounding system as a Korean standard. This paper presents the establishment of test field to get background data to introduce the IEC 60364-4-44 and to evaluate the standard is applicable to domestic rule for the protection against ground fault through the related test

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.6
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• pp.1025-1033
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• 2010

This paper proposes a method to improve and analysis error cause of FI(Fault Indicator) information to be used for detecting fault section in distribution automation system. FI error cause is made by consideration fault current magnitude and time. So, a new method to prevent FI error is proposed to include fault current magnitude, time and direction. Therefore, it's considered network environments that grounded and ungrounded network in distribution automation system. The proposed method is proved by Matlap Simulink. By the result in this research, it's possible to quickly restoration, supplying stability and reliability power to customer.