• 전기학회논문지
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• 제57권9호
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• pp.1485-1490
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• 2008

This paper proposes a new Fourier transform-based phasor estimation method to eliminate the adverse influence of the exponentially decaying dc offsets when Discrete Fourier Transform (DFT) is used to calculate the phasor of the fundamental frequency component in a relaying signal. By subtracting the result of odd-sample-set DFT from the result of even-sample-set DFT, the information of dc offsets can be obtained. Two dc offsets in a relaying signal are treated as one dc offset which is piecewise approximated in one cycle data window. The effect of the dc offsets can be eliminated by the approximated dc offset. The performance of the proposed algorithm is evaluated by using computer-simulated signals and EMTP-generated signals. The algorithm is also tested on a hardware board with TMS320C32 microprocessor. The evaluation results indicate that the proposed algorithm has the stable and accurate eliminating performance even if the input signal contains two decaying dc components having different time constants.

• 한국지능시스템학회논문지
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• 제8권5호
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• pp.72-82
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• 1998

Power transformer protective relay should block the tripping during magnetizing imrush and rapidly operate the tripping during internal faults. But traditional approaches maloperate in the case of magnetizing inrush with low second harmonic component and internal faults with high second harmounic component. To enhance the fault detection sensitivities of conventional technuques, flux-differential current derivative curve by fuzzy theory approaches is used. This paper deals with fuzzy logic based protective relaying for power transformer. The proposed fuzzy based relaying algorithm consisits of flux-differential current derivative curve, harmonics restraint, and precentage differential characteristic curv. The proposed relaying was tested with relaying signals obtained from Salford EMTP simulation package and showed a fast and accurate trip operation.

• 대한전기학회논문지:전력기술부문A
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• 제48권10호
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• pp.1215-1221
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• 1999

A high speed digital distance relaying algorithm based on a Wavelet Transformation is proposed. To obtain stable phasor values very quickly, first, a lowpass filter which has low cutoff frequency is used. Secondly, db2(Daubechies 2) Wavelet which has the data window of 4 samples is used. A FIR filter which removes the DC-offset component in current relaying signals is applied. In accordance with a series of tests, the operation time of the relaying algorithm is less than 3/4 cycles after faults in a 80 [km], 154[kV], 60[Hz] over-head transmission line system.

• 대한전기학회논문지:전력기술부문A
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• 제48권7호
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• pp.855-862
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• 1999

A high speed digital distance relaying algorithm based on a least square error method is proposed. To obtain stable phasor values very quickly, first, a lowpass filter which has very short transient period and no overshoot is presented. Secondly, the least square error method having the data window of 3 samples is used by applying a FIR filter which removes the DC-offset component in current relaying signals. Test results show that the proposed distance relaying algorithm detects most of internal faults within a half cycle after faults in a 154[kV] overhead transmission line system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 D
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• pp.871-874
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• 1997

A new typed distance relaying scheme is proposed. Artificial neural networks are applied to the distance relaying system composed of pattern recognition based. The proposed distance relaying scheme have the two block of pattern recognition stages to estimate the fundamental frequency and to classify the fault types. The advantage of this approach is demonstrated by the random waves and the fault transient wave signals of EMTP(electromagnetic transients program) in power systems fault conditions. The proposed method is compared with the conventional method and the simulation results show the efficiency of the neural networks.

• 전기학회논문지
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• 제59권8호
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• pp.1360-1365
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• 2010

In this paper, we propose a distance relaying algorithm using a Discrete Fourier Transform (DFT)-based modified phasor estimation method to eliminate the adverse influence of exponentially decaying DC offsets. Most distance relays are based on estimating phasors of the voltage and current signals. A DFT is generally used to calculate the phasor of the fundamental frequency component in digital protective relays. However, the output of the DFT contains an error due to exponentially decaying DC offsets. For this reason, distance relays have a tendency to over-reach or under-reach in the presence of DC offset components in a fault current. Therefore, the decaying DC components should be taken into consideration when calculating the phasor of the fundamental frequency component of a relaying signal. The error due to DC offsets in a DFT is calculated and eliminated using the outputs of an even-sample-set DFT and an odd-sample-set DFT, so that the phasor of the fundamental component can be accurately estimated. The performance of the proposed algorithm is evaluated for a-phase to ground faults on a 345 kV, 50 km, simple overhead transmission line. The Electromagnetic Transient Program (EMTP) is used to generate fault signals. The evaluation results indicate that adopting the proposed algorithm in distance relays can effectively suppress the adverse influence of DC offsets.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.193-196
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• 1997

This paper presents the Fault Pattern Estimator(FPE) using the neural network for the protection of the T/L. The proposed FPE has two neural network parts of the fault-types classification and the fault-location estimation. It can detect the fault signals more Quickly and accurately. To prove the performance of the FPE, we have tested using a relaying signals obtained from the EMTP simulations.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 추계학술대회 논문집 학회본부
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• pp.375-379
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• 1990

A microprocessor-based multi-function switchgear for the protection, measurement and control of the power system is presented. For the extraction of the RMS values of the fundamental components of current and voltage signals, a simple digital filter based on cross-correlation of the distorted signal with even and odd heptagonal waves is used. The frequency response of this filter is almost identical to that of the filter based on the discrete fourier transform, while its computational requirement is far less. For the time delay element relaying, a new log-table based relaying algorithm is suggested. The suggested use of the heptagonal wave cross-correlation digital filter algorithm and a new relaying algorithm reduce the computational needs so drastically that all functions of the switchgear can be implemented on the microprocessor system. Real time testing of the implemented daboratory prototype show good practical response under different operating conditions.

• 전기학회논문지P
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• 제62권1호
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• pp.12-17
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• 2013

Fault currents are expressed as a combination of harmonic components and exponentially decaying DC offset components, during the occurrence of fault in power system. The DC offset components are included, when the voltage phase angle of fault inception is closer to $0^{\circ}$ or $180^{\circ}$. The digital protection relay should be detected quickly and accurately during the faults, despite of the distortions of relaying signal by these components. It is very important to implement the robust protection algorithm, that is not affected by DC offset and harmonic components, because most relaying algorithms extract the fundamental frequency component from distorted relaying signal. So, In order to high performance in relaying, advanced DC offset removal filter is required. In this paper, a new DC offset removal filter, which is no need to preset a time constant of power system and accurately estimate the DC offset components with one cycle of data, is proposed, and compared with the other filter. In order to verify performance of the filter, we used collecting the current signals after synchronous machine modeling by ATPDraw5.7p4 software. The results of simulation, the proposed DC offset removal filter do not need any prior information, the phase delay and gain error were not occurred.

• 한국전자통신학회논문지
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• 제11권3호
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• pp.271-276
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• 2016

협력 네트워크는 여러 중계기를 통해서 수신되는 신호 및 직접파 신호를 결합하여 복조함으로써 전체 통신성능을 향상시킨다. 본 논문에서는 철도환경에서 혼합 중계 프로토콜을 이용하는 협력통신 시스템의 성능을 분석한다. 송신기와 수신기 사이에 여러 개의 중계기 사용을 가정하고, 각 중계기들은 하나의 정해진 중계 프로토콜이 아닌 복조 후 전송 혹은 증폭 후 전송 프로토콜을 이용하는 경우를 고려한다. 두 가지 중계 프로토콜이 존재하는 경우 각 중계 프로토콜이 전체 시스템의 성능에 미치는 영향을 분석하고 중계기 위치에 따른 성능에 대해서도 고려한다. 변조방식은 철도환경과 같은 빠른 채널변화에서도 채널상태정보의 이용 없이 신호의 복조가 가능한 차등변조 방식을 적용한다.