The burgeoning demand for enhanced power-system safety means that there is increased attention on technologies for the detection and location of cable faults. The double-terminal fault location method, which senses a fault current using a current transformer (CT), is the most effective and widely applied method in industrial practice. However, CT sensors may suffer from magnetic saturation when exposed to a high fault current, resulting in significant location errors, and their sensitivity cannot be adjusted. To address this problem, this paper describes an improved method for the acquisition of fault signal and the identification of fault-wave arrival time in power cables. First, a novel noncontact sensor (NCS) is developed for the detection of electric fields, and its sensitivity-adjustment curves are obtained by theoretical calculation and simulation. Then, based on feedback variational mode decomposition (FVMD) and the Wigner-Ville distribution (WVD), an improved method (the FVMD + WVD method) for the identification of fault-wave arrival time is devised, and its efficacy and accuracy are verified by simulations in Power Systems Computer-Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC) software. Finally, the fault-wave arrival-time detection performance of the NCS is examined in a series of on-site DC and AC experiments based on damped AC technology. The results show that the NCS exhibits feasible and effective performance, and that its response can be appropriately tuned based on its sensitivity-adjustment curves. The FVMD + WVD method is more accurate than several other current methods, as its error is only 0.48%, and thus this method enables the practical location of cable faults. In sum, these findings demonstrate that the NCS and the FVMD + WVD method comprise an improved system for the detection and location of cable faults, which will enhance cable safety in power systems.

Partial discharge (PD) diagnosis is a crucial technique for assessing the insulation condition of high-voltage (HV) cables. The double-sided travelling wave method is effective for online PD localization on HV cables. However, the PD localization accuracy is limited by three main factors: inaccurate time synchronization among sensors, imprecise pulse propagation velocity, and noise interference. To address these issues, a bidirectional pulse-injected time synchronization method is proposed to correct the timing bases of detectors and assess the pulse propagation velocity along cables independently of cable parameters. Furthermore, a denoising method combining the short-time Fourier transform (STFT) and variational mode decomposition (VMD) is designed to enhance the robustness of the system to high-intensity noise. Finally, an integrated PD detector with pulse injection and signal detection functions and switchable measurement ranges is designed to improve detection sensitivity. To validate the effectiveness of the proposed method, a portable system is developed, and experiments are conducted on both a 10 kV cable in the laboratory and a 110 kV cable in the field. The experimental results confirm that the proposed method enhances the accuracy of PD localization.

A method of reconstructing the original partial discharge (PD) signal to improve the accuracy of PD localization in cross‐linked polyethylene (XLPE) cables is presented here. XLPE cables, extremely sensitive to PDs, are the most popular underground cables in urban grids. The conventional PD localization methods, based on evaluation of the arrival times of PD pulses in the time domain, are negatively affected by the dispersion and attenuation of PD signals propagating in the power cable. A method for the accurate localization of PDs realized through inverse frequency domain modelling (IFDM) is presented here. The method, eliminating the systematic localization error caused by the dispersion and attenuation, significantly improves the localization accuracy. The locations of the PD are identified by comparing peak values of the initial PD signals reconstructed from different extracted pulses. A method for evaluating the propagation constant of the cable is also presented. The efficiency of the accurate localization method was verified by laboratory experiments. Besides, the inherent limitations of the conventional PD localization method for longer cable tests are discussed. The inevitable location error in the conventional methods does not exist in the new method.

As an important part of asset maintenance strategy, power utilities carry out insulation testing of power cables to diagnose and assure their health condition. Among various testing methods, very low frequency cosine-rectangular voltage (VLF-CRV) testing is a relatively new approach that has been recently proposed because of its significant advantages of high efficiency, multi-functionality and easy transportability. This study shows the design, implementation and confirmation of the topology of a novel VLF-CRV generator based on voltage multiplier that avoids separately using HVDC sources and high voltage switches, thus accordingly strengthening its scalability. Note that the mathematical modes of the generator are presented for comprehensive analysis and optimization of the VLF-CRV generator. Simulation in MATLAB/Simulink is performed to validate the generator's feasibility and implementation of a laboratory prototype is also detailed. Moreover, experiments on a capacitor and a medium voltage power cable were performed to confirm the effectiveness of our implementation. 1

In this letter, a novel damped AC (DAC) generator is proposed and implemented, whose working principle is based on the seamless combination of the high voltage (HV) DC source and the HV solid switch by replacing the diodes in the voltage multiplier (VM) with controllable insulated gate bipolar translators (IGBTs). Both laboratory tests on a lumped capacitor and field tests on a 10kV MV cable were performed to prove the feasibility of the proposed techniques.

Damped ac (DAC) test is widely used in the insulation diagnosis of capacitive power equipment due to its flexibility and multifunctionality. The dissipation factor (DF) is one of the crucial functions in the DAC test system. However, the resolution of the existing DF measuring method under DAC is too low (i.e., $1\times 10^{-3}$ ) to accurately measure the DF value of some power equipment, such as power cables. Accordingly, this article proposes an improved DF estimation method based on the combined analysis of voltage and current waveforms of the DAC stress. Two improvements are involved in the developed method: one is that DAC voltage and current are measured simultaneously and a measurement approach is developed to minimize theoretical phase errors and avoid any increase in the ground voltage owing to the breakdown of the test object; the other one is that a DF value estimation algorithm via the joint application of all-phase fast Fourier transform and a nonlinear least squares approach is developed, and its superior accuracy and robustness are verified through simulation. Finally, the strength and feasibility of the proposed method are validated via a laboratory experiment on a 10-kV variable DF standard capacitor, along with a comparison with the conventional solution. The result shows that the proposed method can accurately measure DF with an order of $1\times 10^{-4}$ .