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Partial discharge in oil paper insulation is an important reason for insulation breakdown. The study of partial discharge in transformer oil is of great significance for ensuring the reliability of transformers. In this paper, a comprehensive observation platform of partial discharge with needle plate electrode and oil-paper insulation is built, and the original shape image set of partial discharge is collected and established. Through multi-channel convolution processing of the true color image, gray level equivalent distribution of 3D section, segmentation stretching of threshold interval and binary neighborhood search, a general technical method suitable for processing a series of low brightness discharge images with background interference is finally obtained. [ABSTRACT FROM AUTHOR]

The DC bias may affect the transient transfer characteristics of the current transformer (CT), threatening the correct action of the relay protection and the safe operation of the power system. Compared with the high voltage direct current (HVDC) transmission in the unipolar-earth loop operation mode and geomagnetically induced current (GIC), the amplitude of the stray current is smaller, and the randomness and fluctuation are larger and accompanied by sudden changes. Combining the characteristics of stray current and the CT equivalent model considering the eddy current loss of the iron core, the mechanism of local transient saturation under the influence of bias magnetization is explained, and the CT saturation phenomenon caused by stray current and its effect on line distance protection are simulated and analyzed. The research shows that the influence of low amplitude and high duration of stray current will make the magnetic flux of CT grow and affect the transmission of steady-state and transient-state so that the measurement impedance appears amplitude-phase shift, which leads to under-range rejection of distance protection. [ABSTRACT FROM AUTHOR]

The pulse trigger generator exerts a significant impact on the Marx generator's output pulse (OP). In this paper, a pulse transformer (PT)-type trigger device is intended to give a pulse of front steepness below 30 ns, a half-width of more than 300 ns, and a magnitude of 50 kV to a 4 MV Marx generator. A steepening circuit is modeled on the output side of the PT equivalent circuit to reduce the OP front steepness, establishing the model of a closed-core PT-type trigger generator. The influence of distributed capacitance and leakage inductance (parasitic parameters) of the PT winding on the OP magnitude, triggering delay time, and front steepness are analyzed, and the design scheme of the PT is decided accordingly. Then, the pulse trigger generator model is simulated, and the trigger pulses are obtained in accordance with the design index. The OP waveforms are tested using a newly developed pulse trigger device prototype. [ABSTRACT FROM AUTHOR]

To reveal the key factors influencing vegetation productivity in sandy lands, we conducted a comprehensive analysis of vegetation productivity on regional scale, pixel scale, and plot scale of the sandy lands in northwestern Liaoning Province, based on soil physicochemical data, topographical data, climate data, and the intrinsic characteristics of vegetation. On the regional scale, we established a random forest model to explore the impact of topographical factors, climate factors, and vegetation characteristics on vegetation productivity. On the pixel scale, we performed a correlation analysis between vegetation cover and climate factors. On the plot scale, we combined the physicochemical properties of 234 soil samples with topographical factors and vegetation characteristics, and utilized the random forest model to calculate the importance values of each factor. The results showed that soil nutrients could explain 24.8% of the spatial variation in net primary productivity when other factors were excluded. When introducing topographical factors into the model, the model could explain 40% variation of net primary productivity. When further incorporating fractional vegetation coverage and leaf area index into the model, the model could explain 72.8% variation of net primary productivity. Our findings suggested that fractional vegetation coverage and leaf area index were the most influential factors affecting vegetation productivity in this area. Topographical factors ranked second, followed by climate factors, which had a relatively small impact. [ABSTRACT FROM AUTHOR]