• 한국전기전자재료학회논문지
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• 제20권7호
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• pp.645-649
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• 2007

Partial discharge(PD) test for simulated insulation defects of used hydro generator stator winding was conducted to analyze the PD Parameters. Simulated insulation defects are classified by 5 types corona, slot, internal, multi and aging defect. Phase resolved partial discharge, statistical parameter (skewness, kurtosis), PD magnitude as a function of the test voltage(Q-V curve) and PD magnitude change under test voltage for 2 minutes are used as PD parameters. The analysis of PD parameters by 4 types are proved to be useful methods. In particular, PD parameter characteristics of aging defect could help to assess the aging condition of stator winding because aging defect has more weak insulation strength than other insulation defects : PD distribution is wide and flat, PD rises rapidly near $0^{\circ}\;and\;180^{\circ}$ and Q-V curve rises sharply and then gently drops.

• 한국전기전자재료학회논문지
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• 제24권10호
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• pp.803-806
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• 2011

1 mol% $Li_2O$ excess $0.9(Na_{0.52}K_{0.48})NbO_3-0.1LiTaO_3$ lead-free piezoelectric multilayer ceramic actuators were investigated to determine their aging properties. To reduce the thermal aging behavior, we applied a rectified unipolar electric field of 5 kV/mm to the specimen to accelerate the electric aging behavior. By employing a rectified unipolar electric field for the piezoelectric actuators, we could remove undesirable heating from the relaxation current in the motion of the ferroelectric domain. To accelerate the aging test, the applied electric fields had a frequency of 900 Hz. To have enough time for charging and discharging, we employed an accurate time constant to design the equivalent circuit model for the aging tester. To extract exact aging behavior, we measured the pseudo-piezoelectric coefficient before and after the aging process. We also measured the electro-mechanical coupling coefficient, the frequency-dependent dielectric permittivity, and the impedance to compare with fresh and aged specimen.

• International Journal of Computer Science & Network Security
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• 제22권2호
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• pp.232-240
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• 2022

To fulfill user expectations, the rapid evolution of software techniques and approaches has necessitated reliable and flawless software operations. Aging prediction in the software under operation is becoming a basic and unavoidable requirement for ensuring the systems' availability, reliability, and operations. In this paper, an improved evolutionary computing-driven extreme learning scheme (ECD-ELM) has been suggested for object-oriented software aging prediction. To perform aging prediction, we employed a variety of metrics, including program size, McCube complexity metrics, Halstead metrics, runtime failure event metrics, and some unique aging-related metrics (ARM). In our suggested paradigm, extracting OOP software metrics is done after pre-processing, which includes outlier detection and normalization. This technique improved our proposed system's ability to deal with instances with unbalanced biases and metrics. Further, different dimensional reduction and feature selection algorithms such as principal component analysis (PCA), linear discriminant analysis (LDA), and T-Test analysis have been applied. We have suggested a single hidden layer multi-feed forward neural network (SL-MFNN) based ELM, where an adaptive genetic algorithm (AGA) has been applied to estimate the weight and bias parameters for ELM learning. Unlike the traditional neural networks model, the implementation of GA-based ELM with LDA feature selection has outperformed other aging prediction approaches in terms of prediction accuracy, precision, recall, and F-measure. The results affirm that the implementation of outlier detection, normalization of imbalanced metrics, LDA-based feature selection, and GA-based ELM can be the reliable solution for object-oriented software aging prediction.

• 한국전기전자재료학회논문지
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• 제14권1호
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• pp.84-92
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• 2001

In this papers, we proposed the new method in order to diagnosis aging state of transformers. For wavelet transform, Daubechies filter is used, we can obtain wavelet coefficients which is used to extract feature of statistical parameters (maximum value, average value, dispersion skewness, kurtosis) about each acoustic emission signal. Also, these coefficients are used to identify normal and fault signal of internal partial discharge in transformer. As improved method for classification use neural network. Extracted statistical parameters are input into an back-propagation neural network. The number of neurons of hidden layer are obtained through Result of Cross-Validation. The network, after training, can decide whether the test signal is early aging state, alst aging state or normal state. In quantity analysis, capability of proposed method is superior to compared that of classical method.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.645-650
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• 2000

The discrete wavelet transform is utilized as processing of neural network(NN) to identifying aging state of internal partial discharge in transformer. The discrete wavelet transform is used to produce wavelet coefficients which are used for classification. The mean values of the wavelet coefficients are input into an back-propagation neural network. The networks, after training, can decide if the test signals is aging early state or aging last state, or normal state.

• 대한전기학회논문지:전력기술부문A
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• 제53권4호
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• pp.234-237
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• 2004

Measuring ground resistance has been a popular method of evaluation of the grounding electrode performance. If some portions of grounding electrodes are lost by corrosion, aging or other reasons, consequent deteriotation of the grounding performance would be resulted. It is one of the reasons why it is required to evaluate the performance of grounding systems regularly. However, in case of the electric facilities with multi-grounded system such as power substations with multi-grounded overhead ground wires and/or distribution line neutrals, it is practically difficult to disconnect neutrals or skywires from the substation grounding mesh for the ground resistance measurement. In this paper, a method for the grounding performance measurement of multi-grounded systems, which is based on the measuring ground current distributions, has been proposed. A field test results has shown the validity of the proposed test method.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권4호
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• pp.234-234
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• 2004

Measuring ground resistance has been a popular method of evaluation of the grounding electrode performance. If some portions of grounding electrodes are lost by corrosion, aging or other reasons, consequent deteriotation of the grounding performance would be resulted. It is one of the reasons why it is required to evaluate the performance of grounding systems regularly. However, in case of the electric facilities with multi-grounded system such as power substations with multi-grounded overhead ground wires and/or distribution line neutrals, it is practically difficult to disconnect neutrals or skywires from the substation grounding mesh for the ground resistance measurement. In this paper, a method for the grounding performance measurement of multi-grounded systems, which is based on the measuring ground current distributions, has been proposed. A field test results has shown the validity of the proposed test method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 전기설비
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• pp.23-24
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• 2006

Stator winding of hydro generator is gradually deteriorated by multi-stress and steady degradation of insulation results in insulation breakdown. The region where insulation breakdown occurs in stator winding is part where the multi-stress causes the defect of insulation material and electrical stress has been concentrated. Therefore, we judged locations of insulation breakdown to be varied according to various stress factors in service. In this paper, we drew the stator winding of hydro generators which has run for a long time and separated it into 3 parts(central part, end winding part, drawing part) according to the positions laid on the core. We performed electrical and thermal stress on these specimens for 1000 hrs under the same condition, measured the condition regularlyand analyzed the insulation status of each winding by performing partial discharge test. In addition, we analyzed the trend of partial discharge concerning specimens that caused the insulation breakdown during aging.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1710-1712
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• 1996

This paper was practiced insulation failure test forcing to accelerate on frequency of 420 HZ. There was manufactured generator stator windings for 500MVA thermal plants and selected accelerating deterioration voltage of 5.5kV/mm for electrical aging. Moreover, so as to verification of this experiments, we carried out modeling analysis due to finite element method using to ANSYS5.0 program for common package and imitated multi-stress aging for analyzing electrical and mechanical stress distribution.

• 말소리와 음성과학
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• 제10권2호
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• pp.69-76
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• 2018

The elderly are at increased risk of developing dysphagia due to aging and illnesses. The aim of the current study was to analyze, via an acoustic study, the change in the voice quality of normal elderly people after a 3oz water-swallow test. Subjects included a group of 60 normal elderly people (age: $mean{\pm}SD=76.9{\pm}6.66$) and 60 healthy young adults (age: $mean{\pm}SD=25.1{\pm}2.36$). Every participant produced a five-second /a/ phonation pre- and post-swallowing, and the fractioned two-second sections were analyzed using the MDVP (multi dimensional voice program) analysis. The elderly group demonstrated a post-swallowing increase in the following related acoustic parameters: fundamental frequency, fundamental frequency variation, amplitude-variation, and noise in both two-second sections. However, the younger group showed an increase only in frequency related acoustic parameters (i.e., STD ) in the first two-second section. The significant changes in values in the post-swallowing parameters might indicate temporary irregularities in pitch and amplitude along with higher amounts of noise in the voice. The results could be attributed to water residues in the vocal fold and vocal tract, as well as a deterioration of the motor and sensory functions caused by anatomical and physiological changes that result from aging.