High voltage circuit-breakers with superior performance are demanded as the transmission distance extends and voltage rises, which are often subject to high current and voltage surges. Commercial circuit-breaker contacts are conventionally manufactured with CuW alloy by infiltration method, limiting their performance improvement in withstanding current (or voltage) and lifespan. In this paper, we optimize the microstructure and component of Al₂O₃ reinforced Cu@W80 composites (Al₂O₃/Cu@W80), which fabricates the Cu@W powder first by chemical coating and the composites by spark plasma sintering (SPS) method. The composites exhibit enhanced hardness (maximum value up to 273 HV) due to the addition of Al₂O₃ powder and a more homogeneous and refined tungsten phase compared to the CuW counterpart. Moreover, the dispersed Al₂O₃ particles with low work function become the preferred ablation phase and guide the electrical arcs, further improving the anti-arc erosion performance of Al₂O₃/Cu@W80. Our findings suggest that the Al₂O₃/Cu@W80 composite with optimized components could be potentially used as a candidate for high-voltage circuit-breaker contacts.

In order to solve the noise reduction problem of acoustic emission signals with cracks, a method combining Complementary Ensemble Empirical Mode Decomposition (CEEMD) and wavelet packet (WPT) is proposed and named CEEMD-WPT. Firstly, the single Empirical Mode Decomposition (EMD) used in the traditional CEEMD is improved into the WPT-EMD with a more stable noise reduction effect. Secondly, after decomposition, the threshold value of the correlation coefficient is determined for the Intrinsic Mode Function (IMF), and the low correlation component is further processed by WPT. In addition, in order to solve the problem that it is difficult to quantify the real signal noise reduction effect, a new quantization index “principal interval coefficient (PIC)” is designed in this paper, and its reliability is verified through simulation experiments. Finally, noise reduction experiments are carried out on the real crack acoustic emission dataset consisting of tensile, shear, and mixed signals. The results show that CEEMD-WPT has the highest number of signals with a principal interval coefficient of 0–0.2, which has a better noise reduction effect compared with traditional CEEMD and Complementary Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN). Moreover, the statistical variance of CEEMD-WPT is evidently one order of magnitude smaller than that of CEEMD, so it has stronger stability.

The conductor connection structure in gas-insulated transmission lines (GIL) is vital for power grid stability. Traditional inspections require power outages or fault signal detection post-failure, lacking real-time internal structure assessment. This paper introduces an in situ computed Tomography (CT) inspection technology for ultra-high voltage GIL conductors, aiming for non-destructive, high-precision, real-time monitoring. It analyzes Yuyang line GIL’s inspection needs and designs a system with a ring-clamping mechanism and adaptable scanning path. A specialized algorithm tackles incomplete data and imaging accuracy issues unique to GIL. Experiments show the technology’s ability to image GIL conductor connections in three-dimensional (3D), detect defects, and deformations, crucial for GIL’s safe operation and maintenance by identifying and preventing potential failures.

In the present work, the modification effect of Te and the corresponding growth process of Mg₂Si were clarified. With 0.5 wt% Te addition, the dendritic primary Mg₂Si transformed to polygons, accompanied by a reduction in size from over ∼165 μm–∼18 μm. However, 2.0 wt% Te addition resulted in degradation of modification effect, and the morphology of Mg₂Si changed to dendrite. Three-dimensional morphology of primary Mg₂Si indicated that Te altered the morphology of primary Mg₂Si from dendrites to polyhedrons surrounded by {111} and {100}. The modification mechanism of Te can be attributed to the heterogeneous nucleation and the doping of Te during the growth process of primary Mg₂Si, which greatly contributed to dimension decrease and morphology evolution of primary Mg₂Si respectively. With Te corporation, the relative surface energy between the {100} and {111} (r) drops, contributing to the exposure of {100}. Our work shows that the solute concentration under non-equilibrium solidification plays an important role in determining the final morphology of Mg₂Si. The local segregation of Mg and Si solutes results in the degradation of dendrite arms along certain directions during the initial stage of crystal growth. Combined with the modifying effect of Te, which alters the surface energy of the crystal, the final crystal morphology deviates from its equilibrium state. Our study demonstrates that ultimate morphology and dimensions of primary Mg₂Si can be determined simultaneously with the addition of certain modifiers, which can be achieved by regulating the growth and nucleation of Mg₂Si at the same time.

Cracking occurred on the aluminum alloy sealing cover of a transformer in a 220kV substation after three years of operation. To investigate the cause, a systematic analysis was conducted on its chemical composition, macroscopic appearance, and microscopic morphology. The results revealed that the sealing cover was made of a 7xxx series aluminum alloy with a composition of Al-6Zn-2Cu-1Mg, which does not comply with the requirements of Q/GDW11717-2023, “Technical Supervision Guidelines for Metal Equipment in Power Grids” (Section 4.4.1 states that “Series 2 and Series 7 aluminum alloys should not be used”), indicating that the material was unqualified. The Al-6Zn-2Cu-1Mg aluminum alloy contains a large number of second-phase particles at the grain boundaries, which have a significant potential difference with the matrix aluminum alloy, leading to a susceptibility to intergranular corrosion. The sealing cover underwent stress corrosion cracking in a stressful and corrosive environment.

To accurately detect the position of the paper insulating component inside the UHV (ultra-high voltage) transformers and prevent the discharge fault, the research on ultrasonic phased array three-dimensional imaging detection technology of the insulating cardboard position was carried out. Firstly, a large-size multi-medium (steel-oil-paper-steel) simulation detection component was fabricated, and a multilayer medium accurate positioning method based on sound velocity error compensation was established. Based on Snell’s theorem, the focused delay rule of the ultrasonic phased array in a multilayer medium is established, and the effectiveness of the focus delay rule is verified in the finite element simulation model of acoustic propagation in a multilayer medium. According to the characteristics of the data collected by phased array ultrasonic testing, combined with the structure of the transformer bushing, the point cloud data with three-dimensional spatial coordinates and characteristic values is generated to realize the three-dimensional visual imaging of the detection results. The results show that the established ultrasonic phased array three-dimensional imaging detection method can effectively realize the positioning detection and three-dimensional imaging of the position of the insulating cardboard in the bushing, providing advanced nondestructive testing technology for ensuring the safe operation of the UHV/EHV transformer.