• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 A
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• pp.440-442
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• 2000

This paper describes the digital distance algorithm in case of combined transmission line connected with overhead line and underground cable. Actually as fault is occurred in cable, it results in the complicated phenomena due to the several kind of grounding method in the sheath of cable. Accordingly the impedance. Therefore the correct impedance calculation algorithm is requested in combined transmission line to avoid the wrong trip of relay. This paper presents the development result of impedance calculation algorithm In such transmission line.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제51권7호
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• pp.316-321
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• 2002

In this Paper, the channel characteristics of the medium voltage(22.9kV) power line to analysis the broadband power line communication in the frequency range up to 30MHz was measured. With the sideband electrical coupler in the operating frequency range from DC to 30MHz, we measured characteristic impedance, noise and attenuation of the medium voltage power line, and then characteristic impedance was measured at the state of unloaded medium voltage power line by Scattering parameter method of Vector Network Analyzer. As a measurement result, Channel impedance shows 100~380$\Omega$ at the less than 15MHz and 70~230$\Omega$ at the more than 15 MHz. Noise characteristics of power line shows -75dBm at 20MHz and Narrowband interference noise was from 3 MHz to 7MHz.

• 공학기술논문지
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• 제7권3호
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• pp.131-135
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• 2014

In this paper was proposed a flux offset-type fault current limiter as means of reducing fault currents. To secure the operation reliability of a flux offset-type fault current limiter, constructed a simulation system to analyze its operation characteristics by generating a double line-to-line fault. According to the test results, the system performed stably without any impedance. However, when an accident occurred, the flux-offset of magnetic was not occurred. Because of this, any impedance occurred at circuit. It was confirmed that the impedance was low and fast to limit the fault current. At this time, the fault current limited rate was about 95%.

• Journal of Power Electronics
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• 제19권6호
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• pp.1575-1581
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• 2019

Due to the mismatched line impedance among distributed generation units (DGs) and uncontrolled harmonic current, the droop controller has a number of problems such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To solve these problems, this paper proposes a resistive-capacitive virtual impedance control method. The proposed control method modifies the DG output impedance at the fundamental and harmonic frequencies to compensate the mismatched line impedance among DGs and to regulate the harmonic current. Finally, reactive power sharing is accurately achieved, and the PCC voltage distortion is compensated. In addition, adaptively controlling the virtual impedance guarantees compensation performance in spite of load changes. The effectiveness of the proposed control method was verified by experimental results.

• 한국전자통신학회논문지
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• 제7권2호
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• pp.213-219
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• 2012

본 논문은 외부 영향에 의하여 고속 정보시스템의 모듈사이에서 발생되는 전송잡음과 왜곡신호에 대한 신호 보전의 방법에 대하여 제안하였다. 고속 전송선로의 왜곡효과를 제거하기 위하여 전송선로 임피던스 정합에 의한 신호보전(signal integrity)은 고속 동작에 따른 전송선로효과 발생조건을 ADS로 모델링한 후 최적의 임피던스 정합을 단선 및 차동인터페이스 방식으로 구분하였다. 실험한 결과, 고속 정보통신시스템에 따르는 신호지연을 고려하여 최적의 단자 임피던스 값을 정합시켜 고속 신호의 최적 보전이 가능함을 보여 주었다.

• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.533-540
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• 2017

Distance relay identifies the type and location of fault by measuring the transmission line impedance. However any other factors that cause miss calculating the measured impedance, makes the relay detect the fault in incorrect location or do not detect the fault at all. One of the important factors which directly changes the measured impedance by the relay is series capacitive compensation (SCC). Another factor that changes the calculated impedance by distance relay is fault resistance. This paper provides a method based on the combination of distance and differential protection. At first, faulty transmission line is detected according to the current data of buses. After that the fault location is calculated using the proposed algorithm on the transmission line. This algorithm is based on active power calculation of the buses. Fault resistance is calculated from the active powers and its effect will be deducted from calculated impedance by the algorithm. This method measures the voltage across SCC by phasor measurement units (PMUs) and transmits them to the relay location via communication channels. The transmitted signals are utilized to modify the voltage signal which is measured by the relay. Different operating modes of SCC and as well as different faults such as phase-to-phase and phase-to-ground faults are examined by simulations.

• Journal of Power Electronics
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• 제16권1호
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• pp.38-47
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• 2016

This paper presents DG based droop controlled parallel inverter systems with virtual impedance considering the unequal resistive-inductive combined line impedance condition. This causes a reactive power sharing error and dynamic performance degradation. Each of these drawbacks can be solved by adding the feedforward term of each line impedance voltage drop or injecting the virtual inductor. However, if the line impedances are high enough because of the long distance between the DG and the PCC or if the capacity of the system is large so that the output current is very large, this leads to a high virtual inductor voltage drop which causes reductions of the output voltage and power. Therefore, the line impedance voltage drops and the virtual inductor and resistor voltage drop compensation methods have been considered to solve these problems. The proposed method has been verified in comparison with the conventional droop method through PSIM simulation and low-scale experimental results.

• 한국전자통신학회논문지
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• 제18권4호
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• pp.595-600
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• 2023

본 논문에서는 λ/4 전송선로의 T형 등가회로를 응용하여 임의의 길이를 갖는 전송선로에 대한 T형 등가회로를 제안하였다. 또한, 동일한 선로 길이라는 제한 없이 등가회로의 스터브의 위치를 조정할 수 있도록 수식을 만들어 등가회로의 활용도를 높이고자 하였다. 또한, 제안된 T형 등가회로는 λ/4 전송선로 뿐만 아니라 임의의 선로 길이 및 임피던스를 갖는 경우에도 적용할 수 있다. 제안된 T형 등가회로의 활용 예로 4 분할된 T형 등가회로를 갖도록 구성하여 λ/4 임피던스 변환기에 적용하였다. 변형된 임피던스 변환기는 0.15λ로 설계되어 39.4%의 크기 감소율을 보였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 A
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• pp.317-319
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• 2003

This paper describes an adaptive distance relay for double-circuit line protection with mutual impedance and fault resistance. Double-circuit lines have two operating condition; both lines of a double-circuit line are in operation and one line is switched-off and both ends of the line are grounded. For optimal distance protection, the trip region is calculated, which have respect to mutual impedance and fault resistance.

• 한국안전학회지
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• 제30권4호
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• pp.46-50
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• 2015

This paper describes the measurement and analysis of ground impedance according to arrangement of auxiliary probe around ground grid using the fall-of-potential method and the testing techniques to minimize the measuring errors are proposed. The fall-of-potential method involves passing a current between a ground electrode and a current probe, and then measuring the voltage between a ground electrode and a potential probe. To minimize interelectrode influences due to mutual resistances, the current probe is a generally placed at a substantial distance from the ground electrode under test. In order to analyze the effects of ground impedance due to the arrangement of auxiliary probe and frequency, ground impedances were measured in case that the arrangements of auxiliary probe were straight line, perpendicular line, and horizontal line. The distance of current probe was located from 10[m] to 200[m] and the measuring frequency was ranged from 55[Hz] to 513[Hz]. As a consequence, the ground impedance increases with increasing the distance from the ground electrode to the point to be tested, but the ground impedance decreases with increasing the frequency.