• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.401-406
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• 2016

When measuring live cable faults and their location based on reflectometry, a coupler is placed between the cable and the test system. This coupler prevents damage to the test circuits by indirectly measuring the live voltage of the cable using reflectometry. It also provides a coupling path that allows the transmission and receive signal to pass into the cable. In this study, we design and construct a contact coupler to locate faults in both dead and live cables using reflectometry. The proposed coupler is of the inductive coupling type and is constructed after the calculation of the signal transmission loss by simulation. The performance of the developed coupler is tested by measuring the transmission loss and frequency flatness. The results showed that the transmission signal loss is less than -1.98dB in the frequency bandwidth above 1 Mhz. The reflectometry system was designed based on sequence time domain reflectometry (STDR) and spread spectrum time domain reflectometry (SSTDR) in order to apply it to the detection of faults and their location in live cables and tests on live cables were performed. The test results showed that the proposed coupler can be used in a reflectometry system for live cable fault detection.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1870-1871
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• 2011

본 논문에서는 전력케이블에서의 시간-주파수 영역 반사파 계측법을 기반으로 한 기준신호를 설계한다. 사용된 기준신호는 시간과 주파수 영역에서 동시에 분석할 수 있는 가우시안 포락선을 가지는 첩 신호이다. 10m 전력케이블의 특성에 적합하게 설계된 기준신호를 케이블에 직접 인가하여 반사파를 측정하고 정규화된 시간-주파수 영역 상호상관함수로 비교 분석하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.6
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• pp.367-372
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• 2018

Defects in aging infrastructures such as pre-stressed concrete bridges and cable bridges can cause a collapse of the entire structure. Defects, however, are often located inside of the structures that they are not visible from the outside. For example, in PSC bridges, because reinforcement steels are encased by exterior covers, corrosion and void on the reinforcement steel cannot be detected with a visual inspection. Therefore, in this paper, a new non-destructive evaluation(NDE) method that can detect defects inside of structures is presented. The new method utilizes sending of electrical signals, a method often utilized in electrical engineering to detect any discontinuities on power cables. In order to confirm the applicability and accuracy of the method, some experiments were conducted in the laboratory. And to overcome the hardship of conducting experiments on real structures due to their enormous size, simualtions were conudcted using a commercial program, COMSOL. The results of the experiments were analyzed and compared to confirm the accuracy of the simualtions.

• The Journal of the Acoustical Society of Korea
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• v.38 no.1
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• pp.73-81
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• 2019

This paper proposes an acoustical inversion method using cepstrum analysis of underwater ship noise. Through the cepstrum analysis, multipath structure can be extracted from the recorded ship noise. The multipath structure comes from interferences between a direct arrival and multiple reflections from the sea surface and the bottom. The acoustic inversion is the optimization process to find the best parameters which show good correlation between cepstrums of the measured signal and the replica. The inversion method was applied to the underwater ship radiated noise data measured at Straits of Korea in order to estimate the acoustic center of the ship and the hydrophone position. The inversion results showed good agreement with the measured information.

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.19-21
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• 2009

The reflectometry for locating the fault at a cable is the same as a problem estimating the time delay between the incident and the reflected signals. In this paper, we propose a method for estimating the time delay between the two signals. The proposed method is based on the modeling of the Gaussian enveloped linear chirp signal in the Gaussian noise environment. The phase and the instantaneous frequency of the received signal are estimated by linear Kalman filtering. From the estimated instantaneous frequency, we can measure the time interval between the center frequencies of the incident and the reflected signals. The time interval is the same as the time delay between the incident and the reflected signals. In a simulation assuming that the cable has open fault at the end of the cable, the proposed method showed a good result in estimating the time delay.

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.36-42
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• 1997

This paper purposes the measurement method of vibration intensity in building structure which is a method of measuring the intensity and the flow of vibration energy. We derived basic theory and measuring theory for a simple beam, and comparison of the experimental results with calculated results. As a result, according to the calculated value from acceleration distribution and the measurement result from the method of vibration intensity under the condition except near field of measurement zone. The measured results, show that this method is useful for measuring the vibration energy flow in building structure.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.12
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• pp.2333-2338
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• 2011

In this paper, we develope a wavelet transform based time-frequency domain reflectometry (WTFDR) for the fault localization of underground power cable. The conventional TFDR (CTFDR) is more accurate than other reflectometries to localize the cable fault. However, the CTFDR has some weak points such as long computation time and hard implementation because of the nonlinearity of the Wigner-Ville distribution used in the CTFDR. To solve the problem, we use the complex wavelet transform (CWT) because the CWT has the linearity and the reference signal in the TFDR has a complex form. To confirm the effectiveness and accuracy of the proposed method, the actual experiments are carried out for various fault types of the underground power cable.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1790-1791
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• 2011

In this paper, the diagnosis system for detecting and localizing the neutral wire defect in an energized XLPE power cable is proposed. The neutral wire defect is detectd and localized by the time-frequency domain reflectometry. To extract the reflected signal from the neutral wire defect, the adaptive RLS filtering is introduced. To verify the proposed method, the experiments for detecting and localizing neutral wire defect in active XLPE power cable is conducted.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.2
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• pp.268-275
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• 2008

In this paper, we introduce a new method for detecting and estimating faults on a power line using the time-frequency domain reflectometry system. The system rests upon time-frequency signal analysis and uses a chirp signal which is multiplied by Gaussian envelope. The chirp signal is used as a reference signal, and we can get the reflected signal from a fault on a wire. To detect and estimate faults, we analyze the reflected signal by Wigner time-frequency distribution function and normalized time-frequency cross correlation function. In this paper we design an optimal reference signal for power line and implement a system for estimating fault distance on a power line with the TFDR implemented by PXI equipments. This approach is verified by some experiments with HIV 2.25mm power lines.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.667-672
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• 2013

In this paper, we propose a multi-impedance changes localization method of on-voltage underground power cable using the wavelet transform based time-frequency domain reflectometry (WTFDR). To localize the impedance change in on-voltage power cable, the TFDR is the most suitable among reflectometries because the inductive coupler is used to inject the reference signal to the live cable. At this time, the actual on-voltage power cable has multi-impedance changes such as the automatic section switches and the auto load transfer switches. However, when the multi-impedance changes are generated in the close range, the conventional TFDR has the cross term interference problem because of the nonlinear characteristics of the Wigner-Ville distribution. To solve the problem, the wavelet transform (WT) is used because it has the linearity. That is, using WTFDR, the cross term interference is not generated in multi-impedance changes due to the linearity of the WT. To confirm the effectiveness and accuracy of the proposed method, the actual experiments are carried out for the on-voltage underground power cable.