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The mixed surfactants were successfully applied to fabricate the highly porous Si3N4 ceramic foams by the direct foaming method. The oppositely charged surfactants mixed in slurries could combined into catanionic surfactant by the electrostatic attraction and facilitate the formation of ultra‐stable foams. The microstructure of the Si3N4 ceramic foams, including pore structure, mean pore size, pore size distribution and porosity were tailored by varying the mixing ratio of surfactant, mixed surfactants concentration and solid content of the initial slurries. Si3N4 ceramic foams with porosity of 92%‐97%, mean pore size of 140‐240 µm and compressive strength of 0.85‐5.38 MPa were obtained by adjusting mixed surfactants between 0.1 and 0.4 wt% and solid content between 22 and 30 vol%. The compressive strength of Si3N4 ceramic foams in current work was much higher than most reported results.

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Accurate acquisition for the transient traveling wave at the fault point on overhead transmission lines (OTLs) provides powerful technical supports on the fault diagnosis and insulation design of OTLs. In the study, a novel inversion method is proposed to obtain the transient traveling wave at the fault point. First, the inversion model is created by using the frequency-domain propagation characteristics and the inversion theory. The optimization object function of the distributed parameters is constructed in combination with the wavelet packet transform. The current traveling wave at the fault point is inverted based on the obtained distribution parameters and the waveform of the detection point. Finally, practical measured data of 500-kV OTLs are analyzed by the proposed method in which different factors are considered.The results indicate that the inversion method aids in obtaining the traveling wave at the fault point with high accuracy. Therefore, the effectiveness and feasibility of the proposed inversion method are verified.