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[en] It is discovered that the sealing performance of the sulfur hexafluoride electrical equipment worsens under low temperature, but research in the aspect is reported rarely when corresponding measures are adopted for improving the sealing performance of electrical equipment. Therefore, sealing and leakage test of sulfur hexafluoride electrical equipment was implemented under low-temperature environment according to the analysis on gas sealing methods of sulfur hexafluoride electrical equipment. Causes of gas leakage of sulfur hexafluoride electrical equipment under low temperature environment were analyzed according to test results. Effective measures were proposed for improving the gas sealing performance of the equipment, thereby providing valuable reference for gas sealing design, installation, operation maintenance and failure analysis of sulfur hexafluoride electrical equipment under low - temperature environment. (paper)

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[en] We propose a method to find the effective pinning potential from magnetization hysteresis loops at different temperature directly. As an example, the pinning characteristics of MgB₂ are studied. The form of the effective pinning potential U_eff dependence on temperature, applied magnetic field and current density is also obtained

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[en] The effects of MgB_4 addition on the superconducting properties and the microstructure of in situ processed MgB_2 bulk superconductors were studied. MgB_4 powder of 1-20 wt.% was mixed with (Mg + 2B) powder and then pressed into pellets. The pellets of (Mg + 2B + xMgB_4) were heat-treated at 650 ℃ for 1 h in flowing argon. The powder X-ray diffraction (XRD) analysis for the heat-treated samples showed that the major formed phase in all samples was MgB_2 and the minor phases were MgB_4 and MgO. The full width at half maximum (FWHM) values showed that the grain size of MgB_2 decreased as the amount of MgB_4 addition increased. MgB_4 particles included in a MgB_2 matrix is considered to suppress the grain growth of MgB_2. The onset temperatures (T_c,onset) of MgB_2 with MgB_4 addition (0-10 wt.%) was between 37-38 K. The 20 wt.% MgB_4 addition slightly reduced the T_c,onset of MgB_2 to 36.5 K. This result indicates that MgB_4 addition did not influence the superconducting transition temperature (T_c) of MgB_2 significantly. On the other hand, the small additions of 1-5 wt.% MgB_4 increased the critical current density (J_c) of MgB_2. The Jc enhancement by MgB_4 addition is attributed not only to the grain size refinement but also to the possible flux pinning of MgB_4 particles dispersed in a MgB_2 matrix