This article proposes a cable defect location method based on the power spectral density (PSD) to improve the accuracy of the existing frequency-domain reflection (FDR) method. The principle of the proposed method is that empirical mode decomposition (EMD) is used to decompose the envelope of the reflection coefficient into the intrinsic mode function (IMF) of each insulation defect point and the real part of each IMF signal is windowed. Then, according to the characteristics of a random signal with a definite auto-correlation function, PSD analysis is performed on the IMF signal with limited power. In theory, the power spectrum of a stationary random process is a deterministic function, which transforms the analysis of uncertain signals into the analysis of deterministic functions from the mathematical principle. And combined with the FDR method, localizes the cable insulation defects. Finally, the feasibility and effectiveness of the proposed method are verified by simulation and experiment.

Partial discharge (PD) measurements under repetitive impulse voltages are critical for the qualification of inverter-fed motor insulation systems. Severe electromagnetic interference due to high frequency switching from power electronic devices can cause the traditional PD detection techniques of sinusoidal voltage unfeasible. This article presents the design of an Archimedes spiral antenna that can work effectively for PD detection under fast rise time repetitive impulse voltages. The antenna structure is optimized by a media superstrate with a high dielectric constant over the radiant surface. Through the optimized design, both the gains of the antenna in the 0.5–1.5 GHz frequency range and the signal-to-noise ratio for PD detection are increased substantially. Modeling and experimental results prove that the gain of the antenna can reach 2.5 dB in the frequency range of 500–900 MHz and become higher than 7.0 dB in the frequency range of 900–2.0 GHz, with a voltage standing–wave ratio smaller than 1.4. This seems to be a significant achievement for PD detection under fast rise time impulse voltages.

Due to the spurious peaks caused by multi-reflection and the randomness of the cable transfer function, the frequency domain reflection (FDR) method based on Fourier transform (FT) is inaccurate, even resulting in misjudging the soft faults of the cable. Thus, in this paper, a frequency sweep location method based on multiple signal classification (MUSIC) pseudospectrum is proposed to accurately diagnose and locate the soft faults. The idea of the method is to extend the cable transfer function into an array signal and estimate the MUSIC-pseudospectrum of the transfer function, which can transform the analysis of uncertain signals into the analysis of deterministic functions. Thus, the impact of the spurious peaks and the randomness of the cable transfer function can be eliminated. First, the transfer function of the cable is obtained by frequency sweep. Then the soft fault information in the transfer function is extracted and reconstructed by variational mode decomposition (VMD), which has a good ability to divide the harmonic frequency band. The MUSIC-pseudospectrum of the reconstructed signal is estimated to locate the cable soft faults. At last, the feasibility and effectiveness of the proposed method were verified by testing on a laboratory cable and field underground cable.

Silicone grease (SG) is used for lubrication during cable accessory installation and can penetrate into the silicone rubber (SiR), leading to properties deterioration of the SiR. In this study, the effects of SG on the breakdown characteristics of the cross‐linked polyethylene (XLPE)–SiR interface are investigated. First, the variation of the XLPE–SiR interface breakdown voltage with SG coating time is experimentally explored. The interface breakdown voltage significantly increases after SG is applied, remains stable for coating times of up to approximately 144 h and then rapidly decreases; the minimum interface breakdown voltage is lower than that without the SG coating. Next, the effects of SG on the chemical composition and surface topography of the SiR are examined by infrared spectroscopy and optical profilometry, respectively. The SG penetration does not change the functional groups of the SiR but significantly increases its surface roughness. Finally, the interface electric‐field distribution after coating with SG is analysed by finite‐element simulation, revealing that the residual SG at the interface distorts the interface electric field after a long coating time. The increase in the SiR surface roughness caused by SG diffusion and the interface electric‐field distortion caused by the residual SG together lead to the decrease of the interface breakdown voltage.

Microvaristor ceramics blended with insulation polymers can function as nonlinear dielectrics, which possess self-adaptive electrical parameters varying with the applied field. Broadening the switching (electric) field of the nonlinear dielectrics for their applications in various apparatus and voltage class is an important issue. This paper prepared ZnO microvaristor ceramics with different grain size through controlling the sintering temperature, as well as the microvaristor ceramic/polymer composites (MCPC) with different filler concentration, filler diameter, and filler grain size. The nonlinear V-I characteristics of both the single ZnO microvaristor filler and the MCPC were measured. The switching field of the MCPC is found to be adjusted in a wider range by controlling the filler grain size. The relationship between the nonlinear conducting behavior of single filler and the composite are analyzed. Suggestions were proposed for the preparation of ZnO microvaristor fillers to meet specific field grading requirement for MCPCs.

A frequency domain reflection (FDR) method has been widely used to locate cable defects. Generally, the performance of the FDR method can be enhanced by extending the sweeping frequency range of the signal. However, with the increase in the signal frequency, misdiagnosis can easily occur owing to the attenuation of the signal and noise. Thus, this paper’s authors propose the upper sweeping frequency (UF) selection method of FDR to improve the accuracy of cable defect location. First, the cable’s three-dimensional location spectrum, including the frequency and spatial information, is obtained at a wide frequency range based on short-time Fourier transform with excellent time-frequency aggregation characteristics. Second, the reasonable UF is selected through the energy change characteristics of the cable end. Then, the optimal localization result of the cable defect is calculated by interpolating the sum of energy among the effective frequency bands. Finally, two single-and multi-defect cases are used for the YJV-8.7/10kV XLPE power cable in the experiment to demonstrate the performance of the proposed method. The experimental results show that with the UF selection method, the impact of high-frequency signal attenuation on defect location is eliminated, and cable defect can be localized with more accuracy.