• Corrosion Science and Technology
• /
• 제11권6호
• /
• pp.247-256
• /
• 2012

Harmonic current was measured for a dummy cell with various values of resistance, and the procedure developed through the measurements was applied to the investigation of effects of the amplitude of applied frequency and applied potential on the harmonic current of a stainless steel and a carbon steel in chloride containing solutions. From the measurements of harmonic current in the dummy cell, the optimum values of applied frequency and applied potential in harmonic current measurements were found to be 1 mHz and 20 mV (or lower), respectively. Increase in harmonic current with applied frequency was observed in the case where the level of harmonic current is low as in a stainless steel. Decrease in polarization resistance was also noted in this corrosion system with either increasing applied frequency or decreasing applied potential. However, no obvious effects of applied frequency was observed on harmonic current and polarization resistance in a carbon steel in which the level of harmonic current is high.

• Transactions on Electrical and Electronic Materials
• /
• 제15권4호
• /
• pp.182-188
• /
• 2014

When the windowed DFT algorithm is applied in harmonic measurements, the problem of initial-phase sensitivity will be encountered, this has an effect on harmonic amplitude accuracy. In this paper, the origin of initial-phase sensitivity is analyzed and the main factors that influence the level of initial-phase sensitivity are demonstrated. A method of reducing initial-phase sensitivity is proposed to increase the stability of harmonic measurements. We found that initial-phase sensitivity is determined by the side lobe peak level of the window functions when synchronous deviation is fixed. In addition, increasing the length of the time recorded can be used to remove initial-phase sensitivity. The correctness and validity of our conclusions have been confirmed through numerical results and field tests.

• 비파괴검사학회지
• /
• 제34권3호
• /
• pp.211-219
• /
• 2014

Closed cracks are difficult to detect using conventional ultrasonic testing because most incident ultrasound passes completely through these cracks. Nonlinear ultrasound inspection using sub-harmonic frequencies a promising method for detecting closed cracks. To implement this method, a sub-harmonic phased array (PA) is proposed to visualize the length of closed cracks in solids. A sub-harmonic PA generally consists of a single transmitter and an array receiver, which detects sub-harmonic waves generated from closed cracks. The PA images are obtained using the total focusing method (TFM), which (with a transmitter and receiving array) employs a full matrix in the observation region to achieve fine image resolution. In particular, the receiving signals are measured using a laser Doppler vibrometer (LDV) to collect PA images for both fundamental and sub-harmonic frequencies. Oblique incidence, which is used to boost sub-harmonic generation, inevitably produces various surface waves that contaminate the signals measured in the receiving transducer. Surface wave interference often degrades PA images severely, and it becomes difficult to read the closed crack's position from the images. Various methods to prevent or eliminate this interference are possible. In particular, enhancing images with signal processing could be a highly cost-effective method. Because periodic patterns distributed in a PA image are the most frequent interference induced by surface waves, spatial frequency filtering is applicable for removing these waves. Experiments clearly demonstrate that the spatial frequency filter improves PA images.

• 한국조명전기설비학회:학술대회논문집
• /
• 한국조명전기설비학회 2002년도 학술대회논문집
• /
• pp.111-116
• /
• 2002

With the proliferation of nonlinear loads such as personal computers in an educational office building, high neutral harmonic currents have been observed. High neutral currents in three-phase four-wire distribution power systems can cause overloaded neutral conductors, overloaded transformers, voltage distortion, common mode noise, and malfuntion of protective equipment. On-site measurements of harmonic currents and voltages were made and the corresponding equivalent circuits was developed. The circuit model under study was simulated numerically and graphically through the use of the software MATLAB.

• 비파괴검사학회지
• /
• 제31권1호
• /
• pp.1-10
• /
• 2011

Nonlinear harmonic waves generated at cracked interfaces are investigated both experimentally and theoretically. A compact tension specimen is fabricated and the amplitude of transmitted wave is analyzed as a function of position along the fatigued crack surface. In order to measure as many nonlinear harmonic components as possible a broadband Lithium Niobate ($LiNbO_3$) transducers are employed together with a calibration technique for making absolute amplitude measurements with fluid-coupled receiving transducers. Cracked interfaces are shown to generate high acoustic nonlinearities which are manifested as harmonies in the power spectrum of the received signal. The first subharmonic (f/2) and the second harmonic (2f) waves are found to be dominant nonlinear components for an incident toneburst signal of frequency f. To explain the observed nonlinear behavior a partially closed crack is modeled by planar half interfaces that can account for crack parameters such as crack opening displacement and crack surface conditions. The simulation results show reasonable agreements with the experimental results.

• 조명전기설비학회논문지
• /
• 제26권5호
• /
• pp.48-57
• /
• 2012

This paper analyzes the characteristic of gird connected photovoltaic power generation system which is available to connect the utility. Renewable energy photovoltaic power system has been linked to the system to analyze the impact of photovoltaic system. It is measured that power data for the Grid connected photovoltaic power plant with instantaneous measuring and 3-sec measuring for 7 days. Harmonic field measurements have shown that the harmonic contents of a waveform varies with time. A cumulative probability approach is the most commonly used method to solve time varying harmonics. So, it is used 50[%] cumulative probability approach. This paper provides an in depth analysis on power quality field measurement of the Grid connected photovoltaic power plant.

• 한국조명전기설비학회:학술대회논문집
• /
• 한국조명전기설비학회 2006년도 춘계학술대회 논문집
• /
• pp.272-277
• /
• 2006

High speed electric trains have nonlinear loads including converters and inverters for the contol synchronous motors. Harmonic field measurements have shown that the harmonic contents of a waveform varies with time. Direct application of the harmonic assessment to the snapshot measurements would result in ambiguous conclusions depending on which instant is sampled. A cumulative probablistic approach is the most commonly used method to solve time varying harmonics. This paper provides an in depth analysis on harmonics field measurement of the high speed electric train loads, harmonics assessment by the international harmonic standards IEC 61000-3-6 and IEEE std. 519-1992, and harmonics simulation using EDSA program for the case study.

• 조명전기설비학회논문지
• /
• 제17권1호
• /
• pp.103-111
• /
• 2003

교육용 건물에는 개인용 컴퓨터와 같은 비선형 부하가 증가하여, 중성선에는 많은 고조파 전류가 흐른다. 3상 4선식 배전 계통을 채용하는 중성선에 과다한 고조파 전류가 흐르면 중성선 도체 과열과 보호 시스템의 오동작등 많은 고조파 장해를 일으킨다. 본 논문에서는 현장에서 실측한 고조파 전류와 전압으로 고조파 해석용 3상 등가회로를 구성하였다. 실측한 값과 MATLAB으로 시뮬레이션한 값을 수치와 그래프로 비교 검토 하였다. 또한 중성선 고조파 전류 저감 대책으로 동조 수동 필터를 사례연구 시스템에 적용하여 고조파 저감 효과도 알아 보았다.

• 조명전기설비학회논문지
• /
• 제20권5호
• /
• pp.9-17
• /
• 2006

규모가 큰 제철소는 전기로와 같은 비선형 부하를 가지고 있다. 고조파 측정 결과로 고조파는 시간에 따라 변하는 특성이 관측되었다. 순시치 측정에 의한 고조파 평가는 측정 순간에 따라 고조파가 다를 수 있으므로 모호한 결과를 초래할 수 있다. 시간에 따라 변하는 고조파를 해결하기 위해 쓰이는 가장 보편적인 방법은 누적확률을 사용하는 것이다. 고조파 시뮬레이션은 사례연구 시스템의 전압 및 전류 왜곡을 평가하기 위해 이용되었다. 본 논문에서는 전기로 부하의 고조파 현장 측정, 국제 고조파 관리 기준인 IEC 61000-3-6과 IEEE Std. 519에 의한 고조파 평가, 시간에 따라 변하는 고조파의 시뮬레이션을 심도 있게 다루고자 한다. 고조파 해석 프로그램인 EDSA는 사례 연구에 시뮬레이션 도구로 사용되었다.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2003년도 춘계학술대회 논문집
• /
• pp.493-498
• /
• 2003

Harmonic current originating from electric locomotives can be magnified due to the impedance characteristics of power supply circuit and bring about various problems. That is, electromagnetic interference with communication lines, operational trouble in signaling, overheat and/or vibration in power capacitor, mis-operation in protection relay and so on. Therefore, the exact assessment of the harmonic current flow must be undertaken at design and planning stage for the electric traction systems. For these reasons, this study propose a new approach to model and to analyse traction power feeding system focused on system response to current and voltage harmonic(PART I ). Measurements of harmonics are also performed for railway power supply systems under normal operation. Spectrum and distortion analyses in measurement data are variously described in PART II