• 전기학회논문지
• /
• 제65권5호
• /
• pp.745-752
• /
• 2016

The parameters of Debye's equation were applied to analyze the frequency-dependent ground impedance of horizontally-buried wires. We present a new method, based on Debye's equation, of analyzing the effect of polarization on frequency-dependent ground impedance. The frequency-dependent ground impedances of a horizontally-buried wire are directly measured and calculated by applying sinusoidal current in the frequency range of 100 Hz to 10 MHz. Also, the results obtained in this work were compared with the data calculated from empirical equations and commercial programs. A new methodology using the delta-gap source model is proposed in order to calculate frequency-dependent ground impedance when the ground current is injected at the middle-point of the horizontal ground electrode. The high frequency ground impedance of horizontal electrodes longer than 30 m is larger or equal to its low frequency ground resistance. Consequently, the frequency-dependent ground impedance simulated with the proposed method is in agreement with the experimental data, and the validity of the computational simulation approach is confirmed.

• Journal of the Korean Wood Science and Technology
• /
• 제22권2호
• /
• pp.25-29
• /
• 1994

The effect of moisture content on acoustic absorption coefficient and impedance of the woods of Pinus densiflora, Chamaecyparis pisifela, Cryptomeria japonica, Abies koreana, Melia azedarch var. japonica, Shorea bracteolata and Shorea acuminata was investigated by standing wave method. The results obtained are summarized as follows: The acoustic absorption coefficient increased with increasing moisture content, but acoustic impedance decreased with increasing moisture content.

• 한국지능시스템학회논문지
• /
• 제9권4호
• /
• pp.426-435
• /
• 1999

A high impedance fault(HIF) is one of the serious problems facing the electric utility industry today. Because of the high impedance of a downed conductor under some conditions these faults are not easily detected by over-current based protection devices and can cause fires and personal hazard. In this paper a new method for detection of HIF which uses adaptive neuro-fuzzy inference system (ANFIS) is proposed. Since arcing fault current shows different changes during high and low voltage portion of conductor voltage waveform we firstly divided one cycle of fault current into equal spanned four data windows according to the mangnitude of conductor voltage. Fast fourier transform(FFT) is applied to each data window and the frequency spectrum of current waveform are chosen asinputs of ANFIS after input selection method is preprocessed. Using staged fault and normal data ANFIS is trained to discriminate between normal and HIF status by hybrid learning algorithm. This algorithm adapted gradient descent and least square method and shows rapid convergence speed and improved convergence error. The proposed method represent good performance when applied to staged fault data and HIFLL(high impedance like load)such as arc-welder.

• 한국전자파학회논문지
• /
• 제14권4호
• /
• pp.377-383
• /
• 2003

동(copper) 케이블을 이용한 xDSL 초고속서비스가 널리 보급됨에 따라 외부 전자파에 의한 통신케이블의 전자파 결합특성을 해hi하기 위해 케이블 쉴드층의 전달임피던스가 중요하게 되었다. 본 논문에서는 xDSL 서비스를 제공하기 위해 사용되는 대표적인 형태의 통신케이블에 대해 IEC 96-1의 line injection method를 이용하여 전달임피던스를 측정하였다. 또한 injection line의 위치, 내부 도체의 위치가 전달임피던스에 어떻게 영향을 주는지를 분석하였으며, 이를 근거로 통신케이블의 전달임피던스 특성 모델을 제시하였다.

• 전기학회논문지
• /
• 제66권1호
• /
• pp.144-152
• /
• 2017

A motor model and off-line diagnosis method of the induction motor having an interturn fault(ITF) is studied. The proposed method is based on the magnitude comparison of the six impedance in the d-q plane. To prove the impedance unbalance, the induction motor model is presented with an ITF circuit loop with a fault resistance. Then, six impedance components in the stationary d-q plane are defined depending on the connected phase windings. Finding the maximum and minimum magnitude of the six impedance, the ITF and the faulty phase can be founded. To verify the proposed method, the experimental results with an induction motor having an ITF are shown.

• Journal of Power Electronics
• /
• 제17권3호
• /
• pp.756-765
• /
• 2017

The control of the power conversion system (PCS) in a battery energy storage system has a challenge due to the existence of grid impedance. This paper studies an impedance model of an LCL-based PCS in the d-q domain. The feature of a PCS connected to a weak grid is unveiled by use of an impedance model and a generalized Nyquist criterion. It is shown that the interaction between grid impedance and the PCS destabilizes the cascaded system in certain cases. Therefore, this paper proposes a novel control method that adopts virtual resistors to overcome this issue. The improvement in the control loop leads the PCS to a more stable condition than the conventional method. Impedance measurement is implemented to verify the correctness of the theoretical analysis. Experimental results obtained from a down-scaled prototype indicate that the proposed control method can improve the performance of the PCS under a weak grid.

• 융복합기술연구소 논문집
• /
• 제3권2호
• /
• pp.23-29
• /
• 2013

When a human operator interacts with a virtual wall that is modeled as a virtual spring model, the lager the stiffness of the virtual spring is, the more realistic the operator feels that the virtual wall is. In the previous studies, it is shown that the maximum available stiffness of a virtual spring to guarantee the stability can be increased when the first-order-hold method is applied, however the effects of a human impedance on the stability are not considered. This paper presents the effects of a human impedance on stability of haptic system with a virtual spring and a first-order-hold (FOH) method. The human impedance model is modeled as a linear second-order system model. The relations between the maximum available stiffness of a virtual spring and the human impedance such as a mass, a damping and a stiffness are analyzed through the MATLAB simulation. It is shown that the maximum available stiffness is proportional to the square root of the human mass or damping respectively.

• 한국전자파학회논문지
• /
• 제25권12호
• /
• pp.1228-1235
• /
• 2014

UHF RFID 태그를 설계하기 위해서는 태그 칩의 입력 임피던스 값이 필요하다. 입력 임피던스 산출에는 직접측정 방법이 보편적으로 사용되고 있다. 본 연구에서는 이 방법을 사용할 경우, 칩을 측정장치에 연결하기 위해 도입되는 픽스쳐에서 발생되는 문제점을 분석하고, 그 결과를 확인하였다. 이 문제를 근본적으로 피해갈 수 있는 대안으로 모델링 방법을 제안하고, 실험을 통해 타당성과 정확도를 확인하였다.

• Journal of Power Electronics
• /
• 제18권4호
• /
• pp.1140-1153
• /
• 2018

The harmonic impedance characteristic of a traction power supply system (TPSS) is necessary for taking actions to suppress the high-order harmonic resonances caused by AC electric locomotives. This paper proposes a controllable harmonic generating method (CHGM) for measuring the TPSS harmonic impedance by injecting harmonic disturbances of different frequencies and amplitudes into the TPSS. This method applies phase shifted pulse-width modulation (PSPWM) and ensures that the undesired sideband harmonics can be negligible while the desired harmonic is both controllable and adjustable. Multiple harmonics can be emitted at the same time. The implementation of the method is also presented. Simulations are carried out to validate the performance of the proposed method. Finally, experimental results on a 5 H-bridge converters platform verified the effectiveness and feasibility of the proposed method.

• Restorative Dentistry and Endodontics
• /
• 제40권2호
• /
• pp.113-122
• /
• 2015

Objectives: The aim of this paper was evaluating the ratios of electrical impedance measurements reported in previous studies through a correlation analysis in order to explicit it as the contributing factor to the accuracy of electronic apex locator (EAL). Materials and Methods: The literature regarding electrical property measurements of EALs was screened using Medline and Embase. All data acquired were plotted to identify correlations between impedance and log-scaled frequency. The accuracy of the impedance ratio method used to detect the apical constriction (APC) in most EALs was evaluated using linear ramp function fitting. Changes of impedance ratios for various frequencies were evaluated for a variety of file positions. Results: Among the ten papers selected in the search process, the first-order equations between log-scaled frequency and impedance were in the negative direction. When the model for the ratios was assumed to be a linear ramp function, the ratio values decreased if the file went deeper and the average ratio values of the left and right horizontal zones were significantly different in 8 out of 9 studies. The APC was located within the interval of linear relation between the left and right horizontal zones of the linear ramp model. Conclusions: Using the ratio method, the APC was located within a linear interval. Therefore, using the impedance ratio between electrical impedance measurements at different frequencies was a robust method for detection of the APC.