Due to the coefficients of thermal expansion (CTE) mismatch between various materials, the bond wire of insulated gate bipolar transistor (IGBT) module is prone to heel-cracking or lift-off failure under power cycling, which will affect the performance of the module. In this article, an electro-thermal–mechanical multiphysics coupling model was constructed for IGBT module, and the accuracy of the model was validated by steady-state conduction experiment. Based on the simulation model, the characteristics of IGBT module were further simulated under the normal state conduction operation, and the results showed that the stress of the middle bond position on a single bond wire is higher. Then, the research on the influence of heel-cracking and lift-off failure of the bond wire was carried out. The simulation results showed that the heel-cracking failure of the bond wire will cause obvious effect, in which the increase stress can be as high as 77.4 MPa. When the bond wires are detached one by one until five bond wires were lifted off, the temperature in the remaining bond wires increases by 48.7 $^{\circ}$ C, which has a significant impact on the module. The research in this article can provide the basis for improving the reliability of IGBT module and the optimization of module package design.

In order to predict the spatial magnetic field distribution (SMFD) of dry-type air-core reactors (DARs), the optimal structure of the three-loop simplified scaling model with adjustable ring position and turn number for DARs was investigated. First, the formulas for calculating the SMFD of the original model and the three-loop simplified model were derived according to Biot-Savart law and superposition theorem. Then, the optimal structure of the three-loop simplified model which is the closest to the original model was obtained based on the least squares method after calculating the magnetic induction intensity in six typical directions. In the typical directions, the prediction error of the optimal simplified model was less than 5.5%. Furthermore, the corresponding laws of the optimal simplified model structure in accordance with the original model structures were obtained. The results based on the magnetic field measurement platform indicate that the optimal structure of the three-loop simplified model with frequency 50 Hz is 37.5% relative height, which is very close to the structure, calculated by the corresponding law with 36.15% relative height.

Nanocrystalline (NC) alloy may confront saturation problems with different high-frequency operation circumstances, which are summarized as two typical situations in this paper. One case is “dynamic saturation (DS)” where the alternating magnetic field contains the weak dc biasing field. Another situation is “static saturation (SS)” where the hybrid field comprises not only the weak time-varying field but also the strong dc biasing field. The external and internal factors that affect the saturation magnetization process for the NC alloys were analyzed, under two types of saturation magnetic fields. Two parameters including the saturation time and the rotational velocity of magnetic moment were employed. The external factors, which determine the working condition of the NC alloys, are the dc biasing field and the frequency of the alternating field. The effects of the above two factors are related to the type of saturated magnetic field. In the DS field, the promoting effect of frequency increase on the magnetization process is greater than that of the biasing field, while in the SS field, the opposite is true. The internal factor, which is the grain size, is essential to the soft magnetic properties of the NC alloys. The effects of this factor are independent of the type of saturation field. Increasing the grain size of the NC alloys will delay the magnetization process.

When the outer sheath of submarine cables is damaged, the degradation of cross-linked polyethylene (XLPE) insulation by anions in seawater becomes a critical factor affecting cable service life. This study investigates 500 kV three-core XLPE insulation and systematically reveals the differential and synergistic degradation mechanisms of major seawater anions (Cl⁻, SO₄²⁻, HCO₃⁻). Accelerated aging tests at 90 °C were conducted using solution systems simulating both single-ion and composite environments, combined with electrical performance evaluation, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Results show that seawater causes significantly greater deterioration of resistivity, breakdown strength, and molecular structure than any single-ion solution. Mechanistic analysis demonstrates that Cl⁻ induces nucleophilic substitution, SO₄²⁻ promotes oxidative chain scission, and HCO₃⁻ facilitates hydrolysis via pH regulation, while their coexistence produces nonlinear synergistic effects through oxidative reactions, electrochemical coupling, and ion transport. This work provides the first systematic comparison of individual and combined anion effects on XLPE, offering new mechanistic insights and quantitative evidence for understanding multi-ion degradation, with implications for insulation material design, protective strategies, and service life prediction of submarine cables.

Cu-W alloys are widely used in high-voltage circuit breaker contacts due to their high resistance to arc ablation, but few studies have analyzed the microstructure of Cu-W alloys under arc ablation. This study applied a phase-field model based on the phase-field model developed by Karma and co-workers to the evolution of dendrite growth in the solidification process of Cu-W alloy under arc ablation. The process of columnar dendrite evolution during solidification was simulated, and the effect of the supercooling degree and anisotropic strength on the morphology of the dendrites during solidification was analyzed. The results show that the solid–liquid interface becomes unstable with the release of latent heat, and competitive growth between dendrites occurs with a large amount of solute discharge. In addition, when the supercooling degree is 289 K, the interface is located at a lower height of only 15 μm, and the growth rate is slow. At high anisotropy, the side branches of the dendrites are more fully developed and tertiary dendritic arms appear, leading to a decrease in the alloy’s relative density and poorer ablation resistance. In contrast, the main dendrites are more developed under high supercooling, which improves the density and ablation resistance of the material. The results in this paper may provide a novel way to study the microstructure evolution and material property changes in Cu-W alloys under the high temperature of the arc for high-voltage circuit breaker contacts.

The OLTC (on-load tap changer) transformer is an effective means to solve the voltage quality problem dynamically. There are many problems for conventional mechanical OLTC transformers, such as small regulating amplitude, low precision, slow speed and circulating current. In this paper, a voltage regulation topology and method based on power electronic transition branch is proposed. By controlling the zero-crossing switch of power electronic switch and the state transformation of the switch, smooth switching of the regulating windings is realized, so as to adjust the equivalent turns on the high voltage side. The simulation analysis and prototype experiment show that the scheme can realize the wide range arcless automatic voltage regulation and has practical application value.