• 대한전기학회논문지:전력기술부문A
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• 제48권1호
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• pp.16-21
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• 1999

The analysis of distribution line faults is essential to the proper protections of the power system. A high impedance fault test, which was carried in Korean electric power systems, it was found that a arcing phenomenon occurred during the high level portion of conductor voltage in each cycle. In this paper, we propose a new method for detection of high impedance faults, which uses the arcing fault current difference during high voltage and low voltage portion of conductor voltage waveform. To extract this difference, we diveded one cycle fault current into equal spanned four data windows according to the magnitude of voltage waveform and applied fast fourier transform(FFT) to each data window. The frequency spectrum of current wavefrom in each portion are used as the inputs of neural network and is trained to detect high impedance faults. The proposed method shows improved accuracy when applied to staged fault data and fault-like load.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2007년도 하계학술대회 논문집
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• pp.479-481
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• 2007

This paper presented a actual conditions on a false-tripping of ELB(Earth Leakage Breakers) and an assessment of the harmonics due to non-linear electronic equipment such as personal computers, rectifier, electric furnace and test equipments in plant installations. Actual conditions on a failure of ELB were surveyed and analyzed by making up a question to safety managers of plant installations. Also, power quality measurements such as harmonic currents, voltage and current waveform and current imbalance were made at various plant installations where nuisance tripping of ELB is often occurred. The results of this study can be used in making decisions regarding cause of ELB trip and operating and tripping characteristics test of ELB when subjected to distorted current waveform.

• 전기학회논문지
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• 제62권2호
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• pp.190-195
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• 2013

Vacuum circuit breaker(VCB) has been widely used for interruption of load current and fault current for high voltage motor in the industrial field. Its arc extinguishing capability is excellent compared to other breakers. But it has the potential to cause multi reignition surge by high extinguishing capability. Surge voltage is generated by the opening and closing of VCB. Multi reignition surge of VCB is steep-fronted waveform. It may have a detrimental effect on the motor winding insulation. So, most of users install a protection device to limit steep-front waveform at the motor terminal or breaker side. So, most of users install a protection device at the motor terminal or breaker side. This protective device is surge absorber(SA) such as ZnO and RC type. In this study, we analyzed whether there is any effect when two type SA is applied to the VCB multi reignition surge. We confirmed that ZnO SA is slightly more effective than RC SA for reduction of multi reignition surge.

• 터널과지하공간
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• 제14권2호
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• pp.108-120
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• 2004

발파작업으로 인해 발생하는 발파진동이 암반 및 주위 구조물에 미치는 영향을 분석하기 위한 동하중해석이 최근 급격히 증가하고 있다. 하지만 일반적인 동하중 해석은 발파압력이력곡선을 통하여 얻어진 발파하중을 입력 자료로 사용하고 있으므로 복잡한 지질 구조를 갖는 암반에 대해서는 그 신뢰도가 떨어지고 있다. 이에 본 연구에서는 해석 대상 지역에서의 발파작업을 통해 직접 획득된 발파진동파형을 그대로 입력 자료로 활용하였으며, 인도네시아 Pasir 노천 채광장에 대한 현장 적용을 통해 사면의 현재 상황을 수치 해석적으로 정확히 모사함으로써 발파진동파형을 입력 자료로 활용하는 기법에 대한 검증이 가능하였다.

• 한국안전학회지
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• 제20권1호
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• pp.87-93
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• 2005

In this paper, we analyzed ignition characteristics of combustible material and the waveform of power dissipation, voltage and current by poor contact. And the surface structure of plug by poor contact was analyzed. In the results of experiment, the heat generated by poor contact and ignited the combustible material on power cord sets. The insulation material was molten and carbonized by the heat conduction though plug pit and voids were formed inside of insulation material. The waveform of voltage and power dissipation distorted because of a growth of oxidation by poor contact. In particular, in case that load was big load, the waveform of voltage and power dissipation severely distorted as with the passage of time. The surface of plug pin was changed from erosion mark to welding mark according to big load. The results will be applied to the cause analysis of electrical disaster.

• 전기학회논문지
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• 제67권9호
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• pp.1159-1164
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• 2018

Vacuum circuit breakers(VCB) are widely used for current interruption of high-voltage inductive loads such as induction motors. This VCB can be chopped off before the current zero due to its high arc-extinguishing capability. One of the outstanding features of VCB is that it can cut off high frequency re-ignition current more than other circuit breakers. If the transient recovery voltage generated in the arc extinguishing is higher than the dielectric strength of the circuit breaker, a re-ignition phenomenon occurs. The surge voltage of the re-ignition is very high in magnitude and the steepness of the waveform is so severe that it can act as a high electrical stress on the winding. If the high frequency current of one phase affects the other two phases when the re-ignition occurs, it may cause a high surge voltage due to the virtual current chopping. If the magnitude of the voltage allowed in the motor winding is high or the waveform level is too severe, it may lead to insulation breakdown. Therefore, it is necessary to reduce the voltage to within a certain range. In this study, we briefly explain the various phenomena at the time of interruption, analyzed the magnitude of the dielectric strength and the transient recovery voltage at the simultaneous three-phase interruption that can give the greatest influence to the inductive load, proposed a method to reduce the impact.

• 한국생산제조학회지
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• 제23권6호
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• pp.618-623
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• 2014

This study, analyzed the waveform and mechanical properties of flux cored arc Welding on SM45C. $CO_2$ 10% + Ar 90% shows the lowest standard deviation and shunt ratio at which the arc was most stable. $CO_2$ 10% + Ar 90% is equal to $CO_2$ 20% + Ar 80%. therefore, $CO_2$ 20% + Ar 80% is the best of mixture gases. The hardness test result for the gas mixture ratio of $CO_2$ 10% + Ar 90% was HV 249.7 which is the highest measured value. According to tensile test results, the tensile strength increased with increasing Ar in the mixture gas. This was because of the inertness of the argon, which does not combine with other elements, causing $CO_2$ to combine with pearlite and ferrite and decreasing the maximum tensile strength. Microstructural examination results show that with increasing Ar, ferrite generation decreases while the mild microstructure increases which influences the hardness.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 춘계종합학술대회
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• pp.500-504
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• 2004

본 연구에서는 EPDM 고분자애자의 염무량 변화(salt:l0g, 25g, 50g, deionized water: 1000g)에 따른 표면방전과 환경적인 변화(salt fog 및 clean fog 그리고 raim)에 대한 누설전류 파형의 결과를 알아보았다. 기본파 및 3고조파 그리고 5고조파의 변화양상을 과전초기로부터 섬락시에 이르기까지 나타내었다. 표면열화의 진단기법을 개발하기위해서 누설전류파형의 주파수 스펙트럼을 이용하였고, 고분자애자의 표면열화에대한 환경적인 영향(clean fog, salt fog, rain)을 연구 하였다. 염분량의 변화시 기본파에 대한 저주파 고조파인 3고조파 및 5고조파에 대한 백분율(왜곡도)의 변화를 이용하여 표면 열화상태 및 정도를 정량화(a standard capacity)하여 나타내었다. 기본파에 대한 고조파 백분율인 왜곡율은 고분자 애자의 표면조건을 평가하는데 필요한 지시자라는 사실을 알 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.553-555
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• 1996

This paper concerns with a method to improve the current and power waveforms of the variable speed $3{\Phi}$ AC motor system driven by the single-pulse PWM, and the current waveforms and $3{\Phi}$ power waveforms are analyzed by FFT under various running conditions. By the performance analysis through the experiments, the following results have been obtained. AC source of pseudo sine waveform can be obtained from the modulated alternating square voltage by means of the well designed LC filter. It is confirmed that current waveforms and $3{\Phi}$ power waveforms can be improved by utilizing the high order low pass LC filter than that of lower order. Especially, current waveforms and $3{\Phi}$ power waveforms tan be much improved at low frequency domain. $3{\Phi}$ power waveforms have a smatter ripple and bigger power by utilizing the high order low pass LC filter than that of lower order. Also, the running condition of $3{\Phi}$ AC motor is good at low frequency domain.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 하계학술대회 논문집
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• pp.34-36
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• 2008

This paper is given a full detail of mathematical analyses of input current for novel active type power factor correction(PFC) AC-DC converter of step up-down added electric isolation. These are compared with harmonics components of input current for a conventional PFC converter of electric isolation type. The proposed PFC converter is constructed in using a new loss-less snubber circuit to achieve a soft switching of control device. Also the proposed converter for discontinuous conduction mode(DCM) eliminates the complicated circuit control requirement and reduces the size of components. The input current waveform in the proposed converter is got to be a sinusoidal form of discontinuous pulse in proportion to magnitude of ac input voltage under the constant duty cycle switching. Therefore, input power factor is nearly unity and the control method is simple. Particularly, the stored energy of loss-less snubber capacitor is recovered with input side and increases input current from resonant operation. The result is that input power factor of the proposed converter is higher than that of a conventional PFC converter. Some simulative results on computer and experimental results are included to confirm the validity of the analytical results.