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With the increasing demand for power supply reliability, online monitoring techniques for cable health condition assessments are gaining more attention. Most prevailing techniques lack the sensitivity needed to detect minor insulation defects. A new monitoring technique based on the harmonic anomaly feature analysis of the shield-to-ground current is introduced in this paper. The sensor installation and data acquisition are convenient and intrinsically safe, which makes it a preferred online monitoring technique. This study focuses on the single-core 10 kV distribution cable type. The research work includes the theoretical analysis of the cable defect's impact on the current harmonic features, which are then demonstrated by simulation and lab experiments. It has been found that cable insulation defects cause magnetic field distortion, which introduces various harmonic current components, principally, the third-, fifth-, and seventh-order harmonic. The harmonic anomaly features are load current-, defect type-, and aging time-dependent. The K-means algorithm was selected as the data analysis algorithm and was used to achieve insulation defect prediction. The research outcome establishes a solid basis for the field application of the shield-to-ground harmonic current monitoring technique. [ABSTRACT FROM AUTHOR]

Due to the limitations imposed by urban power grid outages for maintenance, on‐line harmonic current detection technology for distribution network cables is expected to become an effective supplement to traditional offline diagnostic methods, enhancing the real‐time diagnosis of distribution network cable insulation conditions. This study established a 10 kV distribution network cable test platform and prepared typical defective cables subjected to moisture and long‐term thermal aging. Using COMSOL finite element electromagnetic simulation, the magnetic flux evolution laws of the cable insulation under typical defects were obtained. Experimental tests provided the harmonic current characteristics and statistical features of cables with typical defects. Based on these data, a method for analysing the degradation degree of distribution network cables was constructed using least absolute shrinkage and selection operator (LASSO) regression analysis. Furthermore, a defect‐type identification method based on cluster analysis was proposed. Results indicate that the odd harmonics and the 4th harmonic of the distribution network cable's harmonic current are closely related to the cable's degradation state. A model integrating principal component analysis (PCA) data dimensionality reduction and expectation‐maximization clustering analysis achieved a recognition accuracy of up to 75.64% in distinguishing between moisture‐affected and normal cable states. The proposed on‐line detection and evaluation methods can effectively identify high‐risk cables with latent defects. [ABSTRACT FROM AUTHOR]

SF6 gas insulated transformers (GITs) are extensively utilized in underground substations within densely populated areas of large- and medium-sized cities, praised for their excellent non-flammability and operational reliability. However, the aging characteristics of gas–solid composite insulation (SF6–PET) within GITs remain unclear, complicating the effective evaluation of their aging condition. In this study, we performed accelerated thermal aging experiments on type 6020 polyethylene terephthalate (PET) films under an SF6 gas environment at 150 °C. We investigated the aging characteristics of PET materials at various stages using differential scanning calorimetry, tensile tests, near-infrared spectroscopy (NIRS), and frequency domain dielectric spectroscopy. Our findings indicate that the crystallinity and fracture elongation of PET materials initially increased before decreasing as aging progressed, while tensile strength steadily declined. In addition, the absorption rate observed in NIRS diminished with aging. Utilizing linear discriminant analysis, we achieved dimension reduction of characteristic parameters across different wavelengths, facilitating the classification of PET materials at diverse aging times. The tan δ–f curves of PET films initially decreased and subsequently rose with aging. By applying the Havriliak–Negami (H–N) dielectric relaxation model across three distinct frequency bands of the dielectric spectrum, a significant correlation was discerned between the aging state of PET materials and the characteristic relaxation peaks, τ1 and τ2. Fitting the H–N relaxation model and Arrhenius equation allowed us to negate the impact of "temperature drift," yielding an interface polarization activation energy of Ea = 0.69 eV. This research on the aging performance of PET materials in an SF6 gas atmosphere provides a vital foundation for assessing the aging state of SF6-insulated GITs. [ABSTRACT FROM AUTHOR]