Seung Jin Chang

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.

Offline Fault Localization Technique on HVDC Submarine Cable via Time–Frequency Domain Reflectometry

Fault localization is one of the most significant aspects in the maintenance of high-voltage direct current (HVdc) submarine cables that have unconventional installation characteristics, such as long cable lengths and underwater installation locations. In order to protect and diagnose the cable, an improved fault localization technique, that is, time–frequency domain reflectometry (TFDR) and tangent distance pattern recognition are proposed in this paper. The fault location information of the HVdc submarine cables can be obtained from the tangent distance, to support the results of TFDR. To verify the performance of the proposed method, a commercial HVdc submarine cable is used in the experiments. A test bed is constructed for creating a similar environment with that of the submarine cable and filled with sea water. Both low- and high-impedance faults are emulated in this experiment by local insulation faults with iron, sea water, and air. The theoretical concepts and experimental results of the proposed method are presented. It is expected that the proposed method can improve the reliability of real-world HVdc power systems.

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.

Time–Frequency-Based Insulation Diagnostic Technique of High-Temperature Superconducting Cable Systems

For the electrical insulation of a high-temperature superconducting (HTS) cable, wrapped polypropylene laminated paper (PPLP) tape is typically used. Unfortunately, it is possible that unexpected faults at insulation layers will be present in the cables as a result of either a problematic manufacturing process or an incomplete installation procedure. In order to protect against operational failures of grid-connected HTS cable systems, this paper proposes a nondestructive diagnostic technique, i.e., time-frequency domain reflectometry (TFDR), and focuses on the characteristic of HTS cable that caused the local insulation defects . To verify the performance of the proposed method, detection and localization of local insulation failure via TFDR are compared with traditional time-domain reflectometry. The experiments are conducted at room temperature and under liquid nitrogen in order to check the efficacy of the proposed method in varieties of HTS cables conditions. In addition, to improve the accuracy of detection and localization, a methodology to analyze incident signals, which are composed of upchirp and downchirp signals, is presented.

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.

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.

Diagnosis of Cables in Nuclear Power Plants Using Joint Time-Frequency Domain Reflectometry

Abstract In this paper, a new methodology which is referred as joint time-frequency domain reflectometry (JTFDR) is proposed to detect and to locate faults of control and instrumental cables in nuclear power plants. Since this method considers information both in time and frequency domain at the same time, we use a linearly increasing Gaussian envelope chirp reference signal as an incident signal which has a adjustable time duration and frequency bandwidth together. After calculating the time-frequency cross-correlation function with two distribution signals, we can determine the fault distance using time delay between the peak of the incident and reflected signals in the cross-correlation. The usefulness of the proposed method in nuclear power plants is verified by the experiments. Experimental results show that JTFDR can be the reliable method for diagnosis of control and instrumentation cables in the nuclear power plants.

Air gap measurement in cable of automotive electronics based on electromagnetic wave

Time-frequency domain reflectometry (TFDR) based on electromagnetic theory is first introduced to measure air gap in cables. By using the relationship between propagation velocity and permittivity in electromagnetic theory, the new relationship between the air gap and the propagation velocity in cables can be obtained. The proposed method adopts a chirp signal as an incident signal and uses a normalized cross-correlation function for deriving propagation velocity. To reduce signal distortion caused by cable attenuation characteristics, a modified overcomplete wavelet transform is applied. The air gap volume, which can be measured by the proposed method, can be used as an indicator of poor contact between the cable and connector. The performance of the proposed method is verified through experiments.

Multiple Chirp Reflectometry for Determination of Fault Direction and Localization in Live Branched Network Cables

This paper proposes a multiple inductive coupler chirp reflectometry system with multiple resolutions that can determine fault direction, and localize fault is proposed to apply the live target cable. The multiple resolution method enables us to detect and localize the faults, regardless of their location. Time delay information from multiple couplers, which is derived from the time-frequency cross correlation, indicates the fault direction and fault distance, even in cable branched network. The multiple inductive couplers system is proposed to obtain the velocity of propagation and fault direction in cable branch. Using the overcomplete wavelet transform, the signal restoration process can be carried out under signal distortion due to the propagation characteristics of the inductive coupler and target cable. In addition, combining notch filtering techniques and chirp reflectometry method is proposed to cancel 60-Hz harmonic noise, which is acquired from the actual substation. Through the experiments, impedance discontinuity localization and direction determination performance of the proposed method and the adaptability of the proposed method in live cable under harmonic noise by comparing with the existing method were verified.

Real-Time Condition Monitoring of LOCA via Time–Frequency Domain Reflectometry

The maintenance of control and instrumentation (C&I) cables is crucial to safety of operating nuclear power plants. Therefore, when an accident occurs, there is a need for an accurate assessment of the impact on the cables integrity. Unfortunately, most cable diagnostic methods are destructive and real-time assessment of the effect of accidents is not possible. Thus, in this paper, we present an analysis of a specific type of accident, a loss of coolant accident (LOCA), on C&I cables in real-time, based on time–frequency domain reflectometry (TFDR). Because the TFDR is sensitive to the signal-to-noise ratio and distortion of a reflected signal, we apply postprocessing techniques that compensate the dispersion based on the estimated propagation constant and a denoising method using singular value decomposition. The approach is verified by experimentally monitoring condition changes of localized LOCA hot spot in different C&I cables. The results are also validated by comparing with elongation at break test results.