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The problem of vibration and noise in the iron core of power transformers remains quite topical. Insofar as the state-of-the-art iron core and binding production adopt the lamination method and weft-free adhesive tape, respectively, the transformer core vibration is mainly attributed to the silicon steel sheet (SSS) magnetostriction. In this paper, based on the magnetostriction of grain-oriented SSS, an in-depth analysis of the vibration generation mechanism in the transformer core was performed. The SSS microstructure was observed, its magnetostrictive properties at different magnetic flux densities were tested, and a core-simulating four-corner iron core model was constructed to analyze the vibration characteristics. Modal, vibration, and noise tests were performed on an actual 110 kV transformer core under no-load conditions. The results show that the core vibration is related to SSS's deformation mechanism. The vibration magnitude in different core parts varies due to the magnetostriction anisotropy. The vibration in vertical to the core plane is the largest, and its magnitude in the core center is lower than those at the seams in the same plane. The core vibration and noise exhibit a significant correlation, while modal characteristics strongly influence the core vibration and noise intensity. [ABSTRACT FROM AUTHOR]

Buried depth of grounding grids is one of the important factors to determine the grounding performance in substations, however, the real buried depth of grounding grids is changed and unknown due to the drawing loss and backfill during the reconstruction of the grounding grids. This paper proposes a derivative-based method to detect the buried depth of different metal conductors. First, the theoretical basis for the derivative-based method to detect the buried depth is described, and an example calculation on buried depth detection according to the magnetic derivation characteristic is carried out for a single conductor case. The results indicate that the main-side-peaks characteristic of the derivative method can determine the buried depth of metal conductor effectively. Then, the analysis of grounding grids is carried out to verify its validation in grounding grid buried depth detection, and results indicate that the method is effective in the cases of magnetic field superimposing, different buried depths of grounding grid, and nonuniform distribution of current in grounding grid. Finally, the experimental results prove that the derivative method works well with low error. [ABSTRACT FROM AUTHOR]

The topology and breakpoints of the grounding grid will directly affect its working performance. This paper proposed a resistivity reconstruction method based on magnetic detection electrical impedance tomography (MDEIT) to measure the topology and breakpoints of the grounding grid. First, this paper describes the forward problem of grounding grid detection in MDEIT, and calculates the magnetic-field distribution above the grounding grid. Then, the resistivity reconstruction method based on the least squares method is proposed. Finally, this paper verifies the feasibility of the proposed method by a numerical example, which shows that the proposed method can be applied to measure the topology and breakpoints of the grounding grid. [ABSTRACT FROM AUTHOR]

The charged haze particles will affect the electric field of a high-voltage direct current (HVDC) transmission line and insulator contamination, and even result in pollution flashover. Based on the meshless local Petrov–Galerkin method, the influence of ionized electric field on haze particles’ motion is investigated using numerical calculation and experiments. Example of a coaxial electrode model is studied to verify the validation of the proposed method at first. It is proven that the proposed method agrees well with the measurements. Then, the motion principle of haze particles around an actual HVDC insulator is calculated under different ionized field levels. The result shows that the path of the charged haze particles will deflect along the electric field line driven by the electric field force, accelerating the precipitation of the haze particles on the dc insulators. Also, the contamination accumulation gets worse under severe pollution weather and high-voltage side of insulator. [ABSTRACT FROM AUTHOR]