The marine environment in which offshore wind turbines are located is very complex and subjected to a variety of random loads that vary with time and space. As an important component of offshore wind power, the cable also bears the impact of the environment in which most of the turbines are located. Under the long-term action of mechanical stresses such as tension, torsion, and vibration, the cable insulation will crack due to stress fatigue leading to partial discharge, which seriously affects its electrical performance. The study of the mechanism of the change of electrical properties of cable insulation due to mechanical behavior is of great theoretical guidance to improve the reliable operation of cables. This paper first introduces the basic characteristics and operating conditions of torsion-resistant cables and submarine cables. Then the mechanical behavior of the cables is summarized, and the deterioration mechanism and deterioration effect of wind power cable insulation under the influence of multiple factors such as heat, oxygen, and mechanical stress are sorted out. Then, the basic principles of wind power cable operation condition monitoring methods and their characteristics are described. Finally, the relevant methods for the detection of hidden defects inside the insulation are summarized.

The detection and selection of fault lines in resonant grounding distribution networks pose challenges due to the lack of sufficient state parameters and data. This paper proposes an approach to overcome these limitations by reconstructing the initial criterion for fault occurrence and fault line selection. Firstly, a combination of 15% of the traditional phase voltage and the sum of the zero-sequence voltage gradient is suggested as the initial criterion for fault occurrence. This improves the speed of the line selection device. Additionally, the transient process of high-resistance grounding in a resonant grounding system is analyzed based on the impedance characteristics of high- and low-frequency lines. The line selection criterion is then established by comparing the current and voltage derivative waveforms on high- and low-frequency lines. To verify the effectiveness of the proposed method, simulations are conducted. The results demonstrate that this method can effectively handle high-resistance grounding faults under complex conditions while meeting the required speed for line selection.

The fatigue characteristics and condition assessment of ethylene propylene rubber (EPR) power cables used in wind turbines, which operate in complex environments characterized by electrical, thermal, and torsional stresses, have not received sufficient attention. This study investigates the aging characteristics of wind power cables under the combined effects of thermal stress, electrical stress, and torsional stress, using extracted characteristic parameters to evaluate the insulation’s operational condition. Initially, cable samples underwent artificial accelerated aging under thermal, electrothermal, and electrothermal-torsional conditions. The partial discharge (PD) characteristics of the aged samples were then measured. The results demonstrated a significant increase in PD activity over the aging period, with Q_IEC values rising from 331 pC, 393.7 pC, and 437.1 pC at 168 hours to 706 pC, 776.5 pC, and 792.1 pC at 840 hours, respectively. In parallel, the mechanical properties of the cables were evaluated during the aging process, revealing elongation at break loss rates (λ_EAB) of 22.92, 23.86, and 29.73 after 840 hours, compared to initial values of 0.38, 0.57, and 1.52 at 168 hours. Additionally, Fourier transform infrared spectroscopy was utilized to assess the transmittance coefficient and calculate the carbonyl index, with growth rates reaching 32.8%, 60.7%, and 91.7% after 840 hours of aging. Scanning electron microscopy was used to inspect the microstructural features on the surface of the cable samples, offering deeper insights into the aging process and explaining the observed PD trends. Finally, Q_IEC, λ_EAB, and the carbonyl index were identified as aging parameters, and a method was proposed for comprehensively assessing the operational condition of wind power cables by integrating electrical, mechanical, and microscopic properties.

Wind turbine generator output cables are subjected to alternating torsional loads during long-term operation, combined with electrothermal stress, which may lead to insulation failure and other serious issues. Currently, the electrothermal aging mechanism under torsional stress is not fully understood. This study explores the synergistic degradation mechanism of electrothermal aging and nonlinear torsion by constructing a multi-stress aging test platform in the laboratory environment. This study involved accelerated aging tests with thermal, electrothermal, and electrothermal–torsional alternating stresses. The aged cable samples were analyzed for their physical and chemical properties using differential scanning calorimetry and Fourier transform infrared spectroscopy, while dielectric spectroscopy and mechanical tests were employed to evaluate their dielectric and mechanical performance. The results indicate that torsional stress induces physical changes at the molecular level in the ethylene–propylene rubber (EPR), leading to reduced strength, hardening, and increased brittleness, resulting in decreased mechanical strength. In addition, torsional stress promotes oxidation reactions and chain scission processes in the insulation layer, reducing crystallinity and causing a decline in mechanical performance. Increased oxidation and chain scission reactions result in an increase in polar groups, leading to an increase in the dielectric loss factor of the EPR. The findings of this study provide valuable insights for the design, manufacturing, and operational monitoring of wind turbine generator output cables.