• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.74_76
• /
• 2009

This paper presents a discrete wavelet analysis based algorithm to address the fault impedance calculation under transient state in radial power distribution networks. The fault impedances have been derived under different fault conditions. Furthermore, a recursive fault distance estimation method is proposed utilizing the measured fault impedance and power line parameters. The proposed scheme can resolve the errors caused by the non-homogeneous power lines, the presence of lateral loads since, the fault impedance will always be updated with the recursive form. For the verification of the proposed scheme, a filed test has been peformed with varying fault resistances in the 22.9(kV) radial system. Power meters and fault locators were installed at the substation. It was figured out that the performance of the discrete wavelet and the recursive scheme are very good even for high fault resistance condition.

• Earthquakes and Structures
• /
• v.16 no.2
• /
• pp.221-234
• /
• 2019

Today, many important concrete face rockfill dams (CFRDs) have been built on the world, and some of these important structures are located on the strong seismic regions. In this reason, examination and monitoring of these water construction's seismic behaviour is very important for the safety and future of these dams. In this study, the nonlinear seismic behaviour of Ilısu CFR dam which was built in Turkey in 2017, is investigated for various reservoir water heights taking into account 1995 Kobe near-fault and far-fault ground motions. Three dimensional (3D) finite difference model of the dam is created using the FLAC3D software that is based on the finite difference method. The most suitable mesh range for the 3D model is chosen to achieve the realistic numerical results. Mohr-Coulomb nonlinear material model is used for the rockfill materials and foundation in the seismic analyses. Moreover, Drucker-Prager nonlinear material model is considered for the concrete slab to represent the nonlinearity of the concrete. The dam body, foundation and concrete slab constantly interact during the lifetime of the CFRDs. Therefore, the special interface elements are defined between the dam body-concrete slab and dam body-foundation due to represent the interaction condition in the 3D model. Free field boundary condition that was used rarely for the nonlinear seismic analyses, is considered for the lateral boundaries of the model. In addition, quiet artificial boundary condition that is special boundary condition for the rigid foundation in the earthquake analyses, is used for the bottom of the foundation. The hysteric damping coefficients are separately calculated for all of the materials. These special damping values is defined to the FLAC3D software using the special fish functions to capture the effects of the variation of the modulus and damping ratio with the dynamic shear-strain magnitude. Total 4 different reservoir water heights are taken into account in the seismic analyses. These water heights are empty reservoir, 50 m, 100 m and 130 m (full reservoir), respectively. In the nonlinear seismic analyses, near-fault and far-fault ground motions of 1995 Kobe earthquake are used. According to the numerical analyses, horizontal displacements, vertical displacements and principal stresses for 4 various reservoir water heights are evaluated in detail. Moreover, these results are compared for the near-fault and far-faults earthquakes. The nonlinear seismic analysis results indicate that as the reservoir height increases, the nonlinear seismic behaviour of the dam clearly changes. Each water height has different seismic effects on the earthquake behaviour of Ilısu CFR dam. In addition, it is obviously seen that near-fault earthquakes and far field earthquakes create different nonlinear seismic damages on the nonlinear earthquake behaviour of the dam.

• Proceedings of the KSR Conference
• /
• 2004.06a
• /
• pp.1297-1302
• /
• 2004

In DC power distribution system for urban rail transits potential relay, 64P, is used to detect the ground faults. The problem with this 64P is that though it detects the ground fault it cannot identify the faulted region. Therefore the faulted region cannot be isolated properly. It could results in power loss of the trains on the healthy regions and the safety of the passengers in the trains could be affected adversely. A new ground fault protective relaying scheme that can identify the faulted region is presented in this paper. The new concept uses the current differential scheme and the permissive scheme to identify the faulted region correctly. A device with similar characteristic to the arrestor is adapted to use the current relay for the ground fault detection. The role of the device is to block the ground leakage current in normal operating condition and enable the ground fault current to flow in ground fault condition. The algorithm of the new relay and the effect of the newly adapted device in the new relaying scheme are discussed.

• Proceedings of the KIEE Conference
• /
• 2007.07a
• /
• pp.969-970
• /
• 2007

In this thesis, an algorithm of fault detection and diagnosis during operation for induction motors under the condition of various loads and rates is investigated. For this purpose, the spectrum pattern of input cutterrents was used to monitor the state of induction motors, and by clustering the spectrum pattern of input currents, the newly occurrence of spectrums pattern caused by faults were detected. For diagnosis of the fault detected, the fuzzy fault tree was designed, and the fuzzy relation equation representing the relation between an induction motor fault and each fault type, was solved. The solution of the fuzzy relation equation shows the possibility of each fault's occurring.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.21 no.3
• /
• pp.199-205
• /
• 2011

This paper proposes a framework to predict the mechanical fault of hot rolling mill system (HRMS). The optimum process of HRMS is usually identified by the rotating velocity of working roll. Therefore, observing the velocity of working roll is relevant to early know the HRMS condition. In this paper, we propose the framework which consists of two methods namely spectrum matrix which related to case-based fast Fourier transform(FFT) analysis, and three dimensional condition monitoring based on novel visualization. Validation of the proposed method has been conducted using vibration data acquired from HRMS by accelerometer sensors. The acquired data was also tested by developed software referred as hot rolling mill facility analysis module. The result is plausible and promising, and the developed software will be enhanced to be capable in prediction of remaining useful life of HRMS.

• Tribology and Lubricants
• /
• v.3 no.1
• /
• pp.52-60
• /
• 1987

Many kinds of condition monitoring technique as the preventive maintenance technique have been studied, so this study has investigated the possibility of chbcking the trend in the fault diagnosis of ball bearing, one of the important elements of rotating machine, by applying the cepstral analysis method. And computer simulation is conducted in order to identify obviously the physical meaning of cepstral analysis. It is identified that cepstral analysis is effective method to distinguish between the basic and reflected wave by computer simulation, and we know that it is possible to apply the cepstral analysis to the arbitrary elements of rotating machine which are different in fundamental frequency. It is verified that cepstral analysis method is more effective than the other conventional method in bearing fault diganosis.

• Proceedings of the KSME Conference
• /
• 2001.11a
• /
• pp.590-595
• /
• 2001

We must maintain the maximum operation capacity for production facilities and find properly out the fault diagnosis of the possessing equipments rapidly so as to decrease a loss caused by its failure. In this paper, we performed the fundamental study which develops a system of fault for a individually using pump widely or a pump as parts of the other machines. For each normal products, artificially transformed products, and working products under critical condition, we experimented in vibration, compared and analysed. Some faults showed into characteristic vibrations and other faults did not show consistent characters.

• Journal of the Korean Society for Precision Engineering
• /
• v.26 no.11
• /
• pp.47-54
• /
• 2009

Spin coaters are the essential instruments in micro-fabrication processes, which apply uniform thin films to flat substrates. In this research, a spin coater diagnosis system is developed to detect the abnormal operation of TFT-LCD process in real time. To facilitate the real-time data acquisition and analysis, the circular-buffered continuous data transfer and the short-time Fourier transform are applied to the fault diagnosis system. To determine whether the system condition is normal or not, a steady-state detection algorithm and a frequency spectrum comparison algorithm using confidence interval are newly devised. Since abnormal condition of a spin coater is rarely encountered, algorithm is tested on a CD-ROM drive and the developed program is verified by a function generator. Actual threshold values for the fault detection are tuned in a spin coater in process.

• Journal of Power System Engineering
• /
• v.14 no.2
• /
• pp.40-47
• /
• 2010

This paper proposes a fault detection system to detect the strip rupture in six-high stand Cold Rolling Mills based on transient current signal of an electrical motor. For this work, signal smoothing technique is used to highlight precise feature between normal and fault condition. Subtracting the smoothed signal from the original signal gives the residuals that contains the information related to the normal or faulty condition. Using residual signal, discrete wavelet transform is performed and acquire the signal presenting fault feature well. Also, feature extraction and classification are executed by using PCA, KPCA and SVM. The actual data is acquired from POSCO for validating the proposed method.

• Proceedings of the KIEE Conference
• /
• 2005.10c
• /
• pp.291-295
• /
• 2005

This paper presents the modeling of grounding system on Korean electric railway system. The system model is composed of the catenary system, the grounding-system, the sub-sectioning post, the fault point, the sectioning post, the autotransformer in the substation, and the electric vehicle. The increment of rail-ground voltage may be thought as an amplifier of danger on human body of equipment insulation. The rail-ground voltage on steady state and on fault condition should be under standard limit voltage. To analyze grounding system for steady state and fault condition on Korean railway, modeling for each railway system is performed by 10-port network model. Modeling and analysis of present grounding-system are important to protect human and electronic equipments. The examinations for systematic grounding-system are investigated.