• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.1
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• pp.19-25
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• 2010

Most faults are single-phase-to-ground fault in ungrounded system. The fault currents of single-phase-to-ground are much smaller than detection thresholds of measurement devices, so detecting single-phase-to-ground faults is difficult and important in ungrounded system. The protection coordination method using SGR(Selective Ground Relay) and OVGR(Overvoltage Ground Relay) is generally used in ungrounded system. But this method only detects fault line and it has the possibility of malfunction. This paper proposed to advanced protection coordination method in ungrounded system. The method just using zero-sequence current can detect fault line, fault phase, fault section at terminal device. The general protection method is used to back up protection. In the case study, the proposed method has been testified in demo system by Matlab/Simulink simulations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1141-1149
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• 2008

Most faults are single-phase-to-ground fault in ungrounded system. The fault currents of single-phase-to-ground are much smaller than detection thresholds of measurement devices, so detecting single-phase-to-ground faults is difficult and important in ungrounded system. This paper proposed to a FI(Fault Indicator) generation algorithm in ungrounded system. The algorithm just using line-to-line voltage and zero-sequence current detects fault line, fault phase, fault section and FI(Fault Indicator) at terminal device, This paper also proposed to application plan for this algorithm. In the case study, the proposed algorithm has been testified in demo system by Matlab/Simulink simulations.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.736-741
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• 2005

This paper presents electric characteristics analysis and safe configuration for extension power supply between existent 6.6kV ungrounded distribution system and establishment and improvement 22.9kV direct grounding distribution system. For this, we model 6.6kV ungrounded and 22.9kV direct grounding distribution system of urban underground, ground region. and rural electrical, unelectrical region using PSCAD/EMTDC and analyze voltage drop, charging current, ground and short fault through simulation. To analyze electric characteristics of extension power supply, we simulate extension power supply of overhead line of 6.6kV ungrounded system and underground line of 22.9kV direct grounding system of rural electrical region and propose operation condition for safe extension power supply through result of analysis. Characteristics of voltage drop, charging current, ground and short fault appear almost similarly with electrical characteristic of direct power supply. However, because unbalance of phases may cause relay's malfunction of ungrounded system and ground fault current of direct grounding system may demage facilities of ungrounded system, we propose safe system configuration such as impedance grounding system of neutral point.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.2
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• pp.114-120
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• 2003

According to the use of distribution automation systems, the function to find or to search a fault phase is necessary for automatic switches in a distribution substation. In this paper, two algorithms are developed to fine the fault circuit and the fault phase for the automatic switches in substation with ungrounded power system. One is the fault circuit searching method using the zero sequence voltage at the bus and zero sequence current of circuit current and the other is to find the fault phase using the line voltage and zero sequence current. The developed algorithms are tested in the case study simulations. An ungrounded power system is modeled by EMTP as a case study system. The developed algorithms are tested in the case study simulations and each shows correct results.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.67 no.3
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• pp.119-124
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• 2018

Recently, LVDC distribution network and DC microgrid with many advantages are being built. However, this LVDC distribution is an IT grounded or ungrounded system, and it is difficult to detect a ground fault because the fault current is small. In this paper, we propose a signal injection method for unipolar LVDC distribution network to detect ground fault in ungrounded LVDC distribution, and various analyzes were performed for ground fault detection.

• Journal of Electrical Engineering and Technology
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• v.1 no.1
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• pp.16-22
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• 2006

Selective ground relays (SGRs) are useful fur distinguishing a faulted feeder from the sound feeders in ungrounded systems. However, they sometimes mis-operate due to human or device errors. Particularly, the reversed polarity of zero-sequence current transducers (ZCTs) is the most frequent cause of mis-operation. This paper presents a modified SGR for reducing the probability of mis-operations caused by the reversed polarity of ZCTs. The modification is achieved by introducing an adaptive time delay, which depends on the magnitude of the zero-sequence current and the phase angle deviation from the reference. The modified SGR was successfully demonstrated on a sample ungrounded system without mis-operation.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.10
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• pp.550-555
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• 2004

Fault section isolation and service restoration are very important for function of DAS. In Japan, a progressive protection method is used for the line to ground fault section isolation and service restoration. But the progressive protection method has a drawback that the customer will experience outage time and that the rate in use of the feeder is not over 50%. This paper presents a new Service Restoration Algorithm which is for the line to ground fault section isolation and service restoration method for a ungrounded distribution system. If the proposed algorithm is used, the rate in use of the feeder can improve than before because a distribution system can change multi connection of feeder and the customer's outage time can be reduced. The proposed algorithm has been successfully tested in a distribution system.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.3
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• pp.296-301
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• 2008

This paper presents a study on the ground fault protection in 6.6KV ungrounded power system relay(SGR) malfunction or non-tripping. Ground test had made on 6.6KV HV(high voltage) system, Some of domestic and oversea's SGR products are different from their own specific characteristics. This study on the ground protection relay 6.6KV power supply system is focused to protect human.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.6
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• pp.899-904
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• 2012

In recent years, a lot of research was done for earth fault protection in ungrounded dc power supply system. As a result, selective-breaking integrated protective relaying system is developed in progress and is currently field-testing are planned. Algorithm on a PC using PSCAD done a lot of testing before performing field tests, but in this study developed algorithms and functions needed to determine whether they were operating normally. Therefore, simulated system is similar to the actual situation was required and made. selective-breaking algorithm verification and validation was performed with simulator.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.5
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• pp.67-72
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• 2011

In this study we investigate the background of UPS output transformer(${\Delta}-Y$) operation on neutral ungrounded system, and perform field experiment of neutral floating-phenomenon for the inter-locked securing of electric facilities and improvement of neutral floating-phenomenon. Experiment results show that a floating-phenomenon occurs when four-pole input-breaker trip and the neutral to earth voltage occurring concurrently is identified as phantom voltage. And the measures for the transient overvoltage that can occur in floating-state also are investigated. As a result, the risk elements of neutral ungrounded method as well as neutral floating-phenomenon are removed by installation of separate solidly-grounded transformer and switching four-pole input-breaker to three-pole input breaker.