• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1600-1609
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• 2016

As the penetration of different types of renewable energy sources (RES) and energy storage systems (ESS) increases, the importance of stability in AC microgrid is being emphasized. Especially, RES and ESS which are operated using power electronics have difference in output characteristics according to control structures. When faults like single-line-to-ground fault or islanding operation occur, this means that a fault should be interpreted in different way. Therefore, it is necessary to analyze fault characteristics in AC microgrid in case of grid-connected mode and standalone mode. In this paper, the fault analysis for AC microgrid is carried out using PSCAD/EMTDC and an overvoltage problem and the countermeasures were proposed.

• 대한전기학회논문지:전력기술부문A
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• 제55권11호
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• pp.468-475
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• 2006

This paper reviews the energy characteristics of oil filled cables in transient state such as grounding fault and lightning surge. Artificial grounding fault test was firstly performed in 2003 for the analysis of arc voltage and breakdown energy according to the fault current. In this paper, energy of OF cable is variously analysed at joint box based on the actual test. Then more various conditions such as installation types, section lengths and CCPU(Cable Covering Protection Unit) connection types are applied for the simulation using EMTP when the single line to ground fault and direct lightning stroke are occurred on actual underground power cable systems and combined power cable systems, respectively. Finally, the energy by the length of crossbonded lead and grounding lead as well as fault lasting time is also calculated using EMTP simulation.

• 조명전기설비학회논문지
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• 제16권1호
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• pp.76-84
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• 2002

송전선과 배전선의 고장에 의한 voltage sag는 산업 수용가와 전력회사에 당면한 가장 중요한 전력품질(power quality) 문제들 중 하나가 되었다. voltage sag는 일반적으로 진폭과 지속시간 특성으로 기술되지만 voltage sag 현상을 규명하여 그 대책을 찾는데는 위상변위 특성을 반드시 고려해야 한다. 이 논문에서는 3상지락, 단선지락, 및 선간단락 사고가 발생하였을 경우에, 고장임피던스의 변화에 의한 voltage sag를 symmetrical components 해석을 이용하여 특성해석을 하였다. 이 때, voltage sag와 이들이 진폭과 위상에 미치는 효과를 고찰하였다. 3상지락과 같은 평형 고장은 모든 상에서 전압과 전류가 동일한 값으로 변화되고 또한 영상성분들은 영이 되었다. 그렇지만, 단선지락과 선간단락 고장과 같은 불평형 고장으로 인한 voltage sag는 진폭과 위상이 각 상마다 다르게 변화되었다. 해석결과를 확인하기 위하여 전력회로 모델들을 토대로 시뮬레이션을 수행하고 그 결과들도 검토되었다.

• 전력전자학회논문지
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• 제26권2호
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• pp.150-157
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• 2021

Nowadays, a DC microgrid that can link various distributed power sources is gaining much attention. Accordingly, research on fault situations, such as line-to-line and line-to-ground faults of the DC microgrid, has been conducted to improve grid reliability. However, the blackout of an AC system and the oscillation of a DC bus voltage have not been reported or have not been sufficiently verified by previous research. In this study, a 20 kW DC microgrid testbed using a power HIL simulation technique is proposed. This testbed can simulate various fault conditions without any additional grid facilities and dangerous experiments. It includes the blackout of the DC microgrid caused by the AC utility grid's blackout, a drastic load increment, and the DC bus voltage oscillation caused by the LCL filter of the voltage source converter. The effectiveness of the proposed testbed is verified by using Opal-RT's OP5707 real-time simulator with a 3 kW prototype three-port dual-active-bridge converter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전기설비전문위원
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• pp.83-88
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• 2004

As the electric system is getting larger to meet the increasing demand for electric power, the rating of power apparatus is becoming inevitably higher in its working voltage and larger in its capacity. According to KEPCO reports, power transformers in the KEPCO system have undergone troubles such as winding short insulation breakdowns every year since 1981. the cause of this troubles were high one line grounding fault currents in KEPCO systems that had direct grounding systems. KEPCO has installed the NGR(neutral grounding reactor) to lower this fault current and reduced winding short insulation breakdowns in power transformers. But when a circuit breaker opened a no load bus, some trips of circuit breakers for protecting transformer have occurred by mal-operation of 59GT(overvoltage ground relay) that detect disconnection of NGR. Therefore, in this paper, we analyzed the cause and examined the effect of time delav circuit to prevent wrong operation of 59GT.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 C
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• pp.946-948
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• 1998

The distance relay is very important for transmission line protection. A quadrilateral zone shape is used mainly for a modern digital distance relay. The shape of quadrilateral is vendor specific. At the stage of design, the shape is determined considering all possible types of faults and diverse configurations of system. Also this type relay must be designed to avoid the operation by a sound phase at single-Phase-to-ground fault, by a sound phase at two-phase-to-ground fault. The effect of a source impedance and a load impedance is another important factor to design. In this paper, a reliable zone shape which is appropriate for the KEPCO's transmission system is provided.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.774-775
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• 2011

Recently, by increasing of devices which are sensitive to power quality, microprocessor and power electronics, the deterioration of power quality is accelerated. Accordingly, various methods for analysis, detection, compensation and countermeasure on power quality are proposed. For this, the study of distinction of various disturbances and fault which is occurred in power system is necessary to prior. Therefore, in this paper, the classification algorithm among steady state and single line to ground fault which is commonly occurred fault is proposed using S-Transform.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.31-32
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• 2007

In this paper, a fault section detection method is proposed for ungrounded system in the case of a single line-to-ground fault. A conventional method is used for faulted feeder selection according to the angular relationship between zero-sequence currents of the feeders and zero-sequence voltage of the system. Fault section detection is based on the comparison of phase angle of zero-sequence current. Proposed method has been testified in a demo system by Matlab/Simulink simulations. Based on Distribution Automation System(DAS), Feeder Remote Terminal Unit(FRTU) is used to collect those necessary data, at present a demo system is under developing using Manufacturing Message Specification (MMS) in IEC61850 standard.

• 전기학회논문지
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• 제60권5호
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• pp.1073-1077
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• 2011

The breaking capacity of circuit breakers could be no more increased in the electric power system. This is because the fault current increases due to continuous increases in electric power demand and facilities. To solve the problem, it is necessary to come up with an alternative. The superconducting fault current limiter (SFCL) has received an attention among various alternatives. The SFCL effectively reduce a fault current in cooperation with a power circuit breaker. A various types of the SFCL are suggested and a study on them have been progressed. As a result of it, the SFCL can be applyed to the electric power system in the near future. But, a study on recovery behaviors of the SFCL is not enough for applying to the electric power system. If the superconducting elements do not completely recover to the superconducting state after fault operation, it might be a breakdown of the superconducting elements due to heavy power burden and it gives an bad influence on the working of other electric devices. Additionally, the distribution power system has reclosing operation such as open-0.3sec-closed/open-3min-closed/open procedure. So we need to study more about improvement of the recovery behaviors of the SFCL. In this paper, we analyzed the recovery behaviors of a flux-coupling type SFCL according to reclosing operation when a single line-to-ground fault occurred and we compared recovery behaviors of the SFCL with and without a neutral line between secondary reactors and superconducting elements. Also, the flux-coupling type SFCL has advantageous for increases of capacity by controlling the variation in turn ratios between two reactors. Consequently, when the number of turns of the secondary reactors increased, the power burden of the superconducting elements was bigger due to the increase of impedances of the secondary reactors. To distribute the power burden, two superconducting elements connected in series and the balanced quenching of the superconducting elements was induced by connecting a neutral line.

• Journal of Electrical Engineering and Technology
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• 제1권3호
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• pp.279-286
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• 2006

A method for estimating the instantaneous phasor of a fault current signal is proposed for high-speed distance protection that is immune to a DC-offset. The method uses a modified notch filter in order to eliminate the power frequency component from the fault current signal. Since the output of the modified notch filter is the delayed DC-offset, delay compensation results in the same waveform as the original DC-offset. Subtracting the obtained DC-offset from the fault current signal yields a sinusoidal waveform, which becomes the real part of the instantaneous phasor. The imaginary part of the instantaneous phasor is based on the first difference of the fault current signal. Since a DC-offset also appears in the first difference, the DC-offset is removed trom the first difference using the results of the delay compensation. The performance of the proposed method was evaluated for a-phase to ground faults on a 345kV 100km overhead transmission line. The Electromagnetic Transient Program was utilized to generate fault current signals for different fault locations and fault inception angles. The performance evaluation showed that the proposed method can estimate the instantaneous phasor of a fault current signal with high speed and high accuracy.