Chun Ku Lee

Cable Fault Localization Using Instantaneous Frequency Estimation in Gaussian-Enveloped Linear Chirp Reflectometry

This paper presents an application of a cable fault localization using an instantaneous frequency (IF) estimation in the Gaussian-enveloped linear chirp (GELC) reflectometry. The GELC reflectometry sends a GELC signal into a cable and measures the reflected signals from the faults. A fault distance is calculated by the estimated time delay between the incident and reflected signals. The cross-correlation method for estimating time delay can be affected by the propagation characteristics of the cable and this results in the time offset in the time delay estimation. To reduce the time offset, we propose an IF-estimation-based fault-localization method. The proposed method uses the statistical-model-based detection with the hidden Markov model and the constrained Kalman filtering for estimating the IF of the GELC. We can obtain the time delay between the incident and reflected signals by calculating the time delay between the center frequencies corresponding to the incident and reflected signals, respectively. Experimental results show that the proposed method estimates the accurate fault distance without the compensation term for the time offset. Therefore, the proposed method is an appropriate method for estimating the fault localization in a cable.

Reduction of the blind spot in the time-frequency domain reflectometry

In this paper, we propose a method to reduce the blind spot based on signal processing that indicates the minimum length of a cable under test in the time-frequency domain reflectometry without using an extension cable or adding a new high-speed hardware component. The time-frequency domain reflectometry adopted the proposed method can be achieved with not only a simple modification of the previous system but also a simple technique based on signal processing. The experimental results show that the proposed method allows us to estimate fault distance on the cable with high spatial resolution.

Impedance change localization for live underground cable using time-frequency domain reflectometry

In this paper, an impedance change localization method for a live underground XLPE cable with a straight joint using the time-frequency domain reflectometry (TFDR) is proposed. To inject the reference signal to the live cable, an inductive coupler is used. Thus, the characteristics of the cable and the coupler are analyzed and the reference signal is designed to fit for the characteristics of the coupler and the cable. The on-voltage experiment using the TFDR is performed to localize the impedance change of cable. As a result, the accuracy of the TFDR for the on-voltage cables is proved.

Localization of Concentric Neutrals Corrosion on Live Underground Power Cable Based on Time-frequency Domain Reflectometry

In this paper, we propose a time-frequency domain reflectometry (TFDR) based measurement method for localizing concentric neutrals corrosion on live underground power cable. It consists of two inductive couplers which can transmit the reference signal into live underground power cable and measure the reflected signals from the impedance discontinuities of concentric neutrals corrosion. In order to compensate the dispersion of the measured reflected signal via inductive coupler, an equalizer based on Wiener filtering is designed. To improve the localizing performance of concentric neutrals corrosion in the vicinity of the measurement point, the reference signal is removed from the measured reflected signals. The localization performance of the proposed method is verified by the concentric neutrals corrosion localization experiment.

Condition Monitoring of Instrumentation Cable Splices Using Kalman Filtering

A linear chirp reflectometry with chirp stretching processing is used to detect and to locate low-voltage control and instrumentation cable splices and fault. Time delay information in the reflected signal is transformed to the instantaneous beat angular frequency by stretching process and the instantaneous beat angular frequency is estimated by Kalman smoother in order to obtain the high resolution time-frequency spectrum of the nonstationary signal. Based on the estimated instantaneous beat angular frequency, the magnitude and phase difference of the reflection coefficient are estimated by Kalman filtering. To verify the performance of the proposed method, comparative experiments are conducted to detect and to locate the splice under different conditions in comparison with traditional time-domain reflectometry method and the proposed method. In addition, to demonstrate the efficacy of the proposed method, the experiments are carried out for the assessment of state of the shunt and serial faults on cable under test. The location and reflection coefficient of a nominal, water submerged, an opened splice, shunt fault and serial fault (10 Ω, 30 Ω, 50 Ω, 70 Ω, 90 Ω, 1 kΩ) are estimated by the proposed method. The proposed method exhibits advantages in that it uses the pulse compression to improve the range resolution and SNR of reflectometer simultaneously, and the proposed technique can accurately assess the state of the fault, which is closed to short fault or open fault.

High resolution LFMCW radar system using model-based beat frequency estimation in cable fault localization

A linear frequency modulated continuous wave (LFMCW) radar is introduced to localize the impedance discontinuities on the instrument cable used in nuclear plants. The LFMCW reflectometry uses a phenomenon that electromagnetic pulses are reflected at the impedance discontinuities to localize impedance discontinuity points on the cable. For localizing impedance discontinuities, time delays between the incident signal and the reflected signals from the impedance discontinuities have to be measured. The LFMCW is modeled by timevarying auto-regressive (AR) model. From the coefficients of the AR model, instantaneous frequency is estimated by the Kalman filtering to calculate the time delays. The performance of the proposed method is verified by experiments.

Multiple resolution chirp reflectometry for fault localization and diagnosis in a high voltage cable in automotive electronics

A multiple chirp reflectometry system with a fault estimation process is proposed to obtain multiple resolution and to measure the degree of fault in a target cable. A multiple resolution algorithm has the ability to localize faults, regardless of fault location. The time delay information, which is derived from the normalized cross-correlation between the incident signal and bandpass filtered reflected signals, is converted to a fault location and cable length. The in-phase and quadrature components are obtained by lowpass filtering of the mixed signal of the incident signal and the reflected signal. Based on in-phase and quadrature components, the reflection coefficient is estimated by the proposed fault estimation process including the mixing and filtering procedure. Also, the measurement uncertainty for this experiment is analyzed according to the Guide to the Expression of Uncertainty in Measurement. To verify the performance of the proposed method, we conduct comparative experiments to detect and measure faults under different conditions. Considering the installation environment of the high voltage cable used in an actual vehicle, target cable length and fault position are designed. To simulate the degree of fault, the variety of termination impedance (10 , 30 , 50 , and 1 ) are used and estimated by the proposed method in this experiment. The proposed method demonstrates advantages in that it has multiple resolution to overcome the blind spot problem, and can assess the state of the fault.

Non-invasive monitoring of underground power cables using Gaussian-enveloped chirp reflectometry

In this paper, we introduce non-invasive Gaussian-enveloped linear chirp (GELC) reflectometry for the diagnosis of live underground power cables. The GELC reflectometry system transmits the incident signal to live underground power cables via an inductive coupler. To improve the spatial resolution of the GELC reflectometry, we used the multiple signal classification method, which is a super-resolution method. An equalizer, which is based on Wiener filtering, is used to compensate for the signal distortion due to the propagation characteristics of underground power cables and inductive couplers. The proposed method makes it possible to detect impedance discontinuities in live underground power cables with high spatial resolution. Experiments to find the impedance discontinuity in a live underground power cable were conducted to verify the performance of the proposed method.

Concentric neutrals corrosion localization and its impedance analysis in the underground power cable system based on the reflectometry

In this paper, we adopt a Gaussian enveloped linear chirp as the incident signal of the reflectometry for localizing and analyzing concentric neutrals corrosion in the underground power cable. We model the concentric neutrals corrosion as the cutting of the concentric neutrals. In order to find the concentric neutrals corrosion in the underground power cable, we use the adaptive recursive least squares filtering to extract the reflected signal which is from the concentric neutrals corrosion. We also estimate the resistive impedance of the concentric neutral corrosion. The experiments are conducted to verify the proposed method.

Detection of the impedance variation for nuclear control cable using time frequency domain reflectometry

In this paper, an impedance change localization for the nuclear control cable using the time-frequency domain reflectometry (TFDR) is proposed. The reference signal is designed by analyzing characteristics of the target cable and capacitive coupler. To be prepared for on-voltage experiment, the reference signal is injected into the target cable via capacitive coupler. The experiment using the TFDR and TDR is carried out to localize the impedance variation spot (0, 30, 50, 70, 90 Ω) in the target cable. Through the experiment, the accuracy of the proposed TFDR system is proved.